Signalling and Operational Telecommunications Design: Technical Guidance

Transcription

1 ailway Group Guidance Note Signalling and Operational Telecommunications Design: Technical Guidance Synopsis Guidance on the technical details to enable the design of railway signalling systems to meet the requirements of GK/T0206 Submitted by Nick Howland Standards Project Manager Authorised by ichard Spoors Controller, ailway Group Standards This document is the property of ailtrack PLC. It shall not be reproduced in whole or in part without the written permission of the Controller, ailway Group Standards, ailtrack PLC. Published by Safety & Standards Directorate, ailtrack PLC, Floor DP01, ailtrack House, Euston Square, London NW1 2EE Copyright 1999 ailtrack PLC

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3 ailway Group Guidance Note Page A1 of 4 Contents Section Description Page Part A Issue record Distribution Health and Safety esponsibilities Supply A4 A4 A4 A4 Part B 1 Purpose B1 2 Scope B1 3 Definitions B1 4 Use of this Guidance Note B27 5 Signalling System B28 6 Alterations to Existing Installations B28 Appendix B1 Conflicting Standards B29 Appendix B2 Safety Hazards equiring etrospective Work B31 Appendix B3 Temporary Work B35 Part C not used Part D Electrical Circuits 1 Introduction D1 2 Design Principles D1 3 Circuit Design for Occupational Safety D5 4 Circuits (General) D9 5 Circuit Conductors D13 6 Circuit Components D13 7 elay Logic Circuit Techniques D18 8 Time Delays D20 9 Proving D24 10 epeat elays D30 Appendix D1 Fusing and Looping of Signalling Circuits D34 Appendix D2 Electromagnetic Compatibility of Electronic Equipment D36 Part E not used Part F Interlockings 1 Introduction F1 2 Design Principles F2 3 Interlocking equirements F7 4 Application to Mechanical Signalling Systems F92 5 Application to Electro-Mechanical Signalling Systems F96 6 Application to All-Electric Non-oute Setting Interlocking Systems F102 7 Application to oute Setting Interlocking Systems F106 8 Hybrid Systems F111 Appendix F1 Lever Frame Interlocking Guidelines F113 Appendix F2 Free-Wired elay oute Setting Interlocking Guidelines F145 Appendix F3 Geographical elay Interlocking Guidelines F165 Appendix F4 Electronic Interlocking Guidelines F183 Appendix F5 Layout and Control Tables to Illustrate Examples F197 Part G not used A1

4 ailway Group Guidance Note Page A2 of 4 Withdrawn Document Part H Part I not used not used Part J Transmission Systems (including Cables, Terminations and Cable outes) 1 Introduction J1 2 Design Principles J2 3 equirements J3 4 Application J6 5 ailway Signalling Cable J9 6 Terminations J11 7 Cable outes J14 8 Special Arrangements J14 9 Earthing and Equipotential Bonding Conductors J15 Appendix J1 Typical Loop esistance and Current Carrying Capacities J17 Part K Part L Part M Part N Part O not used not used not used not used not used Part P Points 1 Introduction P1 2 Design Principles P1 3 Point Operation P4 4 Point Detection P8 5 Point Switch Heaters P11 Appendix P1 Supplementary Mechanical Information for Point Fittings P12 Appendix P2 elay Circuits for Points P15 Appendix P3 SSI Application for Points P16 Part Q Part not used not used A2 Part S Signals 1 Introduction S1 2 Design Principles S1 3 Main Signals S1 4 Permissive or Shunting Signals S1 5 Junction Signals and oute Indicators S1 6 Miscellaneous Indicators S1 7 Electrical equirements S2 8 Signal and Lamp Proving S5 9 Signal Post eplacement Switch S11 10 Signal Structures and Physical Arrangements S11 11 Supplementary Train Interactive Systems S11 12 Speed estrictions S11 13 Positioning of unning Signals S11 Appendix S1 Supplementary Information for Semaphore Signals S12

5 ailway Group Guidance Note Page A3 of 4 Appendix S2 elay Circuits for Signals S13 Appendix S3 SSI Application for Signals S18 Part T Part U Part V Part W Part X Part Y not used not used not used not used not used not used eferences ef1 A3

6 ailway Group Guidance Note Page A4 of 4 Withdrawn Document Issue ecord Part A This Guidance Note will be updated when necessary by distribution of a replacement Part A and such other parts as are amended. Amended or additional parts of revised pages will be marked by a vertical black line in the adjacent margin. Issue Date Comments One April 1999 New Document superseding GK/C0706 & STDGs 017 and 021. Health and Safety esponsibilities In issuing this Guidance Note, ailtrack PLC makes no warranties, express or implied, that compliance with all or any ailway Group Standards and Approved Codes of Practice is sufficient on its own to ensure safe systems of work or operation. Each user is reminded of its own responsibilities to ensure health and safety at work and its individual duties under health and safety legislation. Supply Controlled and uncontrolled copies of this Guidance Note may be obtained from the Industry Safety Liaison Dept, Safety and Standards Directorate, ailtrack PLC, ailtrack House DP01, Euston Square, London, NW1 2EE. A4

7 ailway Group Guidance Note Page B1 of 36 1 Purpose 2 Scope Part B This Guidance Note, in support of GK/T0206, gives guidance on meeting the minimum technical requirements to ensure that the design of railway signalling and operational telecommunications systems is safe and dependable. This Guidance Note applies to all types of signalling and operational telecommunications works and systems defined in GK/T0206. This Guidance Note covers both hardware and software, including software development, software tools and data used in programmable signalling systems. This Guidance Note does not cover the general duties of design authorities, including: qualifications and competence requirements (see GM/T2450 and GK/T0101); presentation and production processes for design details (see GK/T0201); documentary requirements for the different types of design detail drawing and their inter-relationship (see GK/T0201). eference to particular items of equipment in this Guidance Note does not imply product acceptance or type approval. 3 Definitions In the remainder of this Guidance Note, the term signalling includes operational telecommunications. A glossary of general signalling terms is given in GK/T0002. Those terms are not repeated here except where they have been given a more technical definition for use within this Guidance Note. Safety terms are defined in GH/ZC0002. Symbols to be used on plans and sketches are defined in GK/T0004, on signaller s display systems in GK/T0025 and on circuit diagrams in GK/T0205. In the definitions that follow, a word or group of words in bold type refers to another entry providing further information. Any reference to source indicates that the definition has been taken from an external document. B1

8 ailway Group Guidance Note Page B2 of 36 Withdrawn Document TEM DEFINITION 930 Series (relay) A miniature plug-in relay in one of the following styles (see GK/T0330 and GK/GN0630): 930, 931, 932, 933, 934, 935, 936, 937, 938, 939, 940, 941, 942, 943, 945, 946, 947, 949, 960, 961, 962, 963, 964, 966 (all variants) or 968. A.C. Electrified Area A.C. Immune elay Abnormal (conditions) Acceptable (risk) An Electrified area equipped for a.c. electric traction; including a buffer zone, where the track circuit equipment is immunised against the a.c. traction frequency, extending generally for at least 3000m along any lines equipped solely for d.c. traction. A d.c. relay which is immune to operation by a.c. of specified voltage and frequency. Extreme loading on a part of the railway system (e.g. as a result of extended delays on one part of the service impinging on another). [source: SPG] Associated with a risk that is either: Tolerable AND as low as reasonably practicable; or Negligible as defined in ailtrack s ailway Safety Case. Acceptance (product or engineering details) Accident Anti-Preselection Apparatus Apparatus Case Apparatus Cupboard Apparatus Housing Application Criteria The status given by ailtrack before use is permitted. Unplanned, uncontrolled event giving rise to death, injury, ill-health, damage or other loss. The prevention of Preselection of a Signalling Function, thus maintaining the protection of the Signalling System should a wrong side failure occur. A product with an intrinsic function intended for the end-user and supplied or taken into service as a single commercial unit. [source: EMC egs - modified] An Apparatus Housing which is intended for unprotected outdoor use, is smaller than a building or EB and is usually capable of being transported as a made-up unit. It is usually of metallic construction. The wooden equivalent is commonly known as an Apparatus Cupboard. An Apparatus Housing which is intended for unprotected outdoor use, is smaller than a building or EB and is usually capable of being transported as a made-up unit. It is usually of wooden construction. The metal equivalent is commonly known as an Apparatus Case. This is provided to house relays and/or other equipment at lineside Locations or Interlockings, and may consist of an apparatus case, Apparatus Cupboard, Disconnection Box, equipment room, EB, signal box, control centre, or other equipment building. Document(s) specifying the constraints applied to the installation and maintenance of a system or an item of equipment in order that it can be guaranteed to deliver the performance attributes stated in the system or equipment specification. B2

9 ailway Group Guidance Note Page B3 of 36 TEM Apportionment Approval Approval In Principal Approved For Construction Assessment Authorisation Automatic Function DEFINITION A process whereby the dependability elements for a system are sub-divided between various items which comprise the system to provide individual targets. [source pr EN50126] The status given by the requisite authority when the product or works complies in all respects with the specification and addresses all identified risks. The status given to a signalling scheme when the Scheme Plan is approved. The status given to engineering details by the esponsible Design Engineer following Acceptance by ailtrack. The undertaking of an investigation in order to arrive at a judgement, based on evidence, of the suitability of a product, competence of a person or acceptability of a risk. [source: pr EN50126 expanded] The formal permission to use a product within specified application constraints. [source: pr EN50126] A Signalling Function that, under ordinary operation, is operated automatically by the passage of trains and is not interlocked with any other Signalling Function. The function is generally associated with a particular signal box from which its operation is supervised, unless some form of local monitoring is provided. The state of the function when there are no trains present is designated normal. Auxiliary (optical system) Availability Available Back (B) Contact Back Feed Basic Event Bearer Biased elay Duplicate lamp or filament on hot or cold stand-by. The probability that a system will be able to perform its required functions under given conditions at a stated instant of time or over a given time interval, assuming the required external resources are provided. [source ENV50129] The state of an item when it is capable of performing its required functions in the defined condition of use. [source: BS 4778] A contact of a relay which is made when the relay is released and broken when it is operated. An inadvertent feed which has arisen at an intermediate point within a circuit due to the uncontrolled combination of positions of several pieces of control equipment. See Fundamental Cause. An item of steel or concrete of non standard dimensions used to support the track in Switch And Crossing (S & C) areas. (See also Sleeper and Timber.) A d.c. relay which only operates when a d.c. supply of the correct polarity and voltage is applied to the coil. Otherwise referred to as a 2-position polarised relay. Bonding Plan A detailed plan of the track layout showing individual rails and position of IJs, together with track circuit feed and relay connections with polarities, cross Bonds, Structure Bonds, Impedance Bonds, etc., as applicable. This term may also include track plans and negative bonding plans in D.C. Electrified Areas. B3

10 ailway Group Guidance Note Page B4 of 36 Withdrawn Document TEM Cab Secure adio (CS) Cable Core Plan Cable oute Plan DEFINITION A form of radio telephone system provided as an alternative to a signal post telephone system. Facilities include secrecy of call under normal operations, emergency override calls and system wide broadcasts. A plan showing the allocation of Signalling Functions or systems to specific cores in multicore and data link cables. A layout plan showing the position of principal cable routes relative to signal boxes or Interlockings and Locations. This plan is generally combined with the Location Area Plan. Cable Schematic Plan Catch Point Central Processing Unit (CPU) Certificate Of Completion Certificate Of Compliance Certificate Of Conformity (plant or equipment) Change Control Change-Over Contact Check ail Circuit Controller Circuit Diagrams Class I Equipment Class II Equipment Closure Panel (track) Closure ail A plan showing all signalling and power distribution cables required, together with sizes, to be installed between signal boxes or Interlockings and Locations. A point (switch and tiebar only), on running line gradients to de rail wagons etc., running away in the wrong direction. The central part of an electronic system or sub-system that manipulates data. It receives inputs from various interfaces, processes them in accordance with the control program and geographical data in the memory and returns the resulting outputs to the interfaces. Advice that works are ready for inspection. A statement of conformity to requirements and standards. A statement of compliance with Type Approval. See Configuration Control. See Dependent Contact. See figure under Switches And Crossing. A circuit switching device containing a number of contact bands, each of which may be individually cut to length and adjusted to make and break separate circuits at appropriate points in the cycle. The bands are operated by a mechanical device, such as a lever or signal. A collection of individual drawings showing the equipment layout and circuit arrangement associated with a location, an interlocking or signal box. Electrical equipment that requires the connection of the Exposed-Conductive- Parts to a Protective Conductor connected to earth, to ensure personal safety. See also BS7671. Electrical equipment with double or reinforced insulation, either to prevent contact with Exposed-Conductive-Parts, or to ensure no contact between such parts and live parts. The insulation is not therefore to be pierced by screws. Such equipment is never connected to earth. See also BS7671. See figure under Switches And Crossings. See figure under Switches And Crossings. B4

11 ailway Group Guidance Note Page B5 of 36 TEM Common Cause Failure (CCF) Common AIL DEFINITION A failure which is the result of an event(s) which, because of dependencies, causes a coincidence of failure states of components in two or more separate channels of a redundancy system, leading to the defined system failing to perform its intended function. [source: IEC 61508] The rail of a single rail track circuit that is electrically common to one or more adjacent track circuits or forms the traction return path where an isolated single rail track circuit is provided. In non-electrified areas the common rail is bonded with track circuit bonding. In electrified areas the common rail is known as the traction return rail and carries the traction return current. It is therefore bonded with traction return bonding. Also referred to as single rail or traction rail. Common ail Bonding (C) Competent Person Comprehensive Approach Locking Concentrator Configuration (system) Construction A track circuit arrangement where only one rail (the Insulated ail) is used with IJs to separate the track circuits. The other rail (the Common ail) is electrically continuous but is not used for traction return purposes. A person who has the qualifications or certification, experience and ability necessary to perform a particular task. (See GK/T0101.) A form of approach locking on a signal, by which the approach locking is only effective when a train is approaching in order to afford maximum train operating flexibility. It uses look-back circuitry or logic to ascertain the line occupancy between a given signal at danger and the sighting point of the signal displaying the first caution aspect for the signal under consideration. A facility to connect several telephone circuits to one terminal and thus avoid the need for a telephone instrument for each circuit. The structuring and interconnection of the hardware and software of a system. The carrying out of any building, civil engineering or other engineering work, particularly that which falls within the scope of the Construction (Design and Management) egulations Also known as installation. Contactor Continuity Bonding A relay with heavy duty contacts. Fishplate bonding specifically provided for traction return purposes, i.e. on nontrack circuited lines in electrified areas, including non-electrified sidings, etc. ail to rail bonding is required and Cross Bonding may also be provided. It is denoted by the addition of a 'c c c' symbol on the bonding plan. Control Area The area of railway controlled or supervised by a particular signal box or control centre, as defined by the Signalling Plan. Also known as signal box control area. Control Point Controlled Function A signal box (including control centre), gate box or ground frame (including ground switch panel or shunting frame). A Signalling Function that, under ordinary operation, is controlled from the signal box (or other control point) to which the function is allocated and may be interlocked with other Signalling Functions. B5

12 ailway Group Guidance Note Page B6 of 36 Withdrawn Document TEM Corrective Maintenance Correlation Cross Bond Crossing Angle Crossing Back Crossing Nose Cut-Section (location) Cut-Section (track circuit) DEFINITION The maintenance carried out after fault recognition and intended to put a product into a state in which it can perform a required function. [pren50126] The comparison of the configuration and version status of a system with the design records to ensure that the two are in agreement. A Jumper Cable cross connecting the Common ails or centre points of impedance bonds of parallel tracks to form a mesh of alternative paths, e.g. for traction return current. See figure under Switches And Crossings. See figure under Switches And Crossings. See figure under Switches And Crossings. Non-preferred term; see epeater Location. A method of reducing the continuous length of a track circuit by the use of individual track circuits, each one controlling a common final track repeat relay, or equivalent. These are indicated as one track circuit on the signaller s panel. This is also known as a multi-section track circuit. Cut-Off Contact (elay) D.C. Electrified Area Data (signalling) Data Collection Area Data Link A Front Contact of a Latched elay, internally wired in series with the elease Coil such that the coil cannot be energised unless the relay is in the Operated position. Also known as economising contact. An Electrified Area equipped for d.c. electric traction; including a buffer zone where the track circuit equipment is immunised against the d.c. traction voltage, extending generally for at least 3000m along any lines equipped solely for a.c. traction. (The distance is subject to specialist assessment and verification.) Site specific geographical and control information in an electronic form, which may be of a safety-critical nature or otherwise. In order to be used in an electronic system or sub-system, data from master data files is usually permanently stored in an EPOM (erasable programmable read only memory). The area of railway over which the train describer or IECC gathers information about train movements. It extends beyond the Control Area of the signal box. A Serial data transmission system. In SSI systems, this refers to the link between the interlocking and the lineside location and may take the form of a baseband unmodulated trackside data link cable, or a long line link using standard telecommunications PCM equipment. Internal data link cables are also provided between the modules in an SSI cubicle and, where applicable, between modules in adjacent interlocking cubicles. De-Energised (relay) Defect Degraded Conditions Demodulator See eleased. See Fault, Defect, Error, Failure, Mistake. The state of the part of the railway system when it continues to operate in a restricted manner due to the failure of one or more components. [source: SPG] See Modem. B6

13 ailway Group Guidance Note Page B7 of 36 TEM Dependability Dependent Contact DEFINITION The ability of a product to perform one or several required functions under given conditions. See also AMS. [source: pr EN50126] A contact set which consists of a front contact, a back contact and one arm shared between them, with not more than one contact path made at any one time. Also referred to as change-over contact. Design Disconnection Box Disproved Wrong Side Failure Diversity Double-Coil A.C. Vane elay Double-Cut (circuit) Double-Junction Double-Pole (lamp) Double-ail Track Circuit Double-ail Track Circuit Bonding (D) Double-Wound Down Time DACAS Driver Only Operation (DOO) adio Drop Away Time (Track Circuit) A wide term including specification and the production of drawings, design details and bills of quantity (including specification of systems or equipment). [source: CDM egulations - modified] An Apparatus Housing for unprotected outdoor use, which is intended to contain mainly terminations and is commonly smaller than an Apparatus Case. A Failure which was reported as wrong side but where the Failure was conclusively shown not to have occurred or to have been a ight Side Failure. A means of achieving all or part of the specified requirements in more than one independent and dissimilar manner. [source: ENV50129] A double element relay with separate local and control (or track) coils which are required to attain a particular phase relationship for the relay to operate. The inclusion of controls in both feed and return legs in order to mitigate the risk associated with a false feed. The point of junction of two double track routes. It comprises two turnouts and a crossing. A double-filament lamp in which both filaments are connected permanently in parallel. [source BS 469] A track circuit, either jointless, or defined by IJs in both rails at all its extremities. On electrified lines, both rails carry traction return current. A track circuit arrangement where both rails are fitted with IJs, or tuned zones are used to completely isolate a track circuit. A relay fitted with two electrically independent operating coils. Application of rated voltage across either coil causes the relay to operate. The time interval during which a product is in a down state. [source: pr EN50126] An acronym meaning Data ecording and Corrective Action System A form of Cab Secure adio especially provided to facilitate driver only operation. The time between the application of a shunt to the rails and the front contacts of track relay (T) fully opening. The converse is Pick Up Time. Drop Away (DA) Voltage (elay) The maximum voltage applied to an operated relay coil at which the last front contact breaks. B7

14 ailway Group Guidance Note Page B8 of 36 Withdrawn Document TEM Drop Shunt Dual Electrified Area Earth Fault Detector DEFINITION The maximum value of non inductive resistance which, when placed across the rails, causes the track relay to fully open its front contacts. An Electrified Area meeting the criteria of both an A.C. Electrified Area and a D.C. Electrified Area. A permanent device, wired to the busbars, that will detect an earth fault on the power supply and give an alarm that will alert the maintainer. Also known as earth leakage detector. Earth Fault Loop Impedance Earth Leakage Detector Economising Contact (Lever Lock) Economising Contact (elay) Electric Traction Engineer Electrical System The impedance of the earth fault current loop starting and ending at the point of earth fault. [source: BS7671 extract] See Earth Fault Detector. A contact internally wired in series with the coil such that the lock coil is not energised when the lever is in the full travel position. Alternatively the function may be controlled externally (which is the only available method where cut-off is required at other than a full travel position). See Cut-Off Contact. Engineer responsible for the electric traction fixed equipment. An installation, identified by the relationship that the source and the exposedconductive-parts of the installation have to earth: TN System: where one or more points of the energy source are directly earthed, the Exposed-Conductive-Parts of the installation being connected to that point by Protective Conductors, either completely separate from the neutral or return conductors (TN-S), with the neutral and protective functions combined in a single conductor throughout the system (TN-C), or with the neutral and protective functions combined in a single conductor in part of the system (TN-C-S). TT System: where one point of the energy source is directly earthed, the Exposed-Conductive-Parts of the installation being locally earthed, independent of the source earth electrodes. IT System: where there is no connection between the live parts and earth, the Exposed-Conductive-Parts of the installation being locally earthed, e.g. an unearthed signalling power supply. [source BS7671 adapted] Electrified Area An area of railway encompassing all lines equipped for electric traction, extended to include any non-electrified lines or sidings. The area also includes a buffer zone where track circuit equipment is immunised against traction interference, extending generally for at least 800m, or the length of two track circuits with double IJs, whichever is the further, beyond the end of the electrified line. See also A.C. Electrified Area, D.C. Electrified Area and Dual Electrified Area. Emergency Situation Energised B8 A current unforeseen or unplanned event which has life threatening or extreme loss implications and requires immediate attention (e.g. a fire). [source: SPG] See Operated.

15 ailway Group Guidance Note Page B9 of 36 TEM Equipotential Bonding Exposed-Conductive-Part External (circuit or power supply) Extra Low Voltage Extraneous-Conductive-Part Fail-Safe Failure DEFINITION Electrical connection maintaining various Exposed-Conductive-Parts and Extraneous-Conductive-Parts at substantially the same potential. It need not include a direct connection to earth. [source: BS7671 augmented] A conductive part of equipment that can be touched and which is not a live part but which may become live under fault conditions. [source: BS7671] Failing to wholly meet the Internal criteria. See Voltage, Nominal. A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation, e.g. structural metalwork. [source: BS7671 augmented] A concept which is incorporated into the design of a product such that in the event of failure, it enters or remains in a safe state. [source: ENV50129] The termination of an item to perform a required function. [source: BS4778] See also Fault, Defect, Error, Failure, Mistake, Common Cause Failure, andom Hardware Failure, and Systematic Failure. Failure Classification Fault Tolerance Fault, Defect, Error, Failure, Mistake Faulting Feed Classification of a failure as ight Side, Wrong Side, protected, etc. The attribute of an item that makes it able to perform a required function in the presence of certain given sub-item faults. [source: IEC 61508] The cause of an error is a fault (for example a hardware defect) which resides temporarily or permanently in the product. An error is that part of the product state which is liable to lead to a failure. A failure occurs when the delivered service deviates from the intended service. A failure is the effect of an error on the intended service. A mistake occurs when human action (at any phase of the life- cycle) may result in unintended product behaviour. [source: pr EN50126 modified] See Corrective Maintenance. Power Supply phase (BX) or positive (B) connection. In some cases may be used as a composite term to incorporate both feed and eturn (e.g. track circuit feed). Fishplate Bond Provided to ensure electrical continuity between two rails mechanically connected, e.g. by a steel fishplate, common chairs, or other bolted connection. Also referred to as fishplate type bond, or rail joint bond. Fishplate Type Bond Fixed Data Free-Wired Interlocking Frequency Division Multiplex (Fdm) See Fishplate Bond. See System Program. A relay interlocking that comprises individually wired relays rather than pre-wired sets of relays. A data transmission system that uses unique frequencies to separate channels over a single pair of conductors. B9

16 ailway Group Guidance Note Page B10 of 36 Withdrawn Document TEM Frequency otation Front (F) Contact Functional Earthing Functional Safety Analysis Functional Unit Fundamental Cause (failure) DEFINITION The sequential application of specified frequencies. A contact which is made when the relay is operated and broken when it is released. The connection to earth necessary for the proper functioning of electrical equipment, i.e. an earth return. This may be used for telecommunications purposes, but is no longer permitted for new signalling circuits. Conductors for functional earthing are identified by the colour cream. [source: BS7671 augmented] Assessment of elements within a safety system to demonstrate that it attains the required safety integrity. An entity of hardware or software, or both, capable of accomplishing a specified purpose. [source: ENV50129] A primary deficiency or prevailing condition which permitted the Immediate Cause to lead to a Wrong Side Failure. Also known as basic event. Geographical Data Geographical Interlocking Graceful Degradation Guaranteed Power Supply Fixed information stored in EPOMs that configures an electronic system or sub-system to the requirements of a particular site. A route relay interlocking in which standard pre-wired sets of relays are provided for each Signalling Function, arranged and electrically interconnected in a geographical manner. A means by which a more complex control sub-system has the facility to switch into some other (more restricted) mode of operation if a particular input fails, or if availability is otherwise reduced by some means. See Secure Power Supply. Hazard A physical situation with a potential for human injury. [source: IEC 61508] Headway Chart Heavy (H) Duty Contact (relay) Heel (of switch) High Current D.C. Electrified Area Immediate Cause (failure) Impedance Bond Incident (Near Miss) Infrastructure Controller A time/distance graph based on standard braking and acceleration curves that may be used to determine optimum signal positions. A relay contact that is rated to make and break a current of up to 30A. These generally have magnetic blow out to suppress the arc, but are not guaranteed to be non-weld and so the relay must be down proved. See figure under Switches And Crossings. A D.C. Electrified Area capable of supplying trains with a peak total traction current in excess of 6.5kA. A direct act, omission or equipment fault which triggered the Failure. Special device which presents a low impedance to traction current and a higher impedance to track circuit current. An unplanned, uncontrolled event, which under different circumstances could have resulted in an Accident. A railway business which is responsible for the control and operation of the railway lines, including the track, structures, plant and control equipment. An Infrastructure Controller may either own or lease the infrastructure concerned. B10

17 ailway Group Guidance Note Page B11 of 36 TEM Installation (activity) Installation (infrastructure) Insulated Block Joint (IBJ) Insulated ail DEFINITION See Construction. That part of the Signalling System associated with the infrastructure at a particular place. Non-preferred term; see Insulated ail Joint. The rail of a single rail track circuit that is fitted with IJs to separate adjacent track circuits. The insulated rail is always bonded with track circuit bonding, as it does not carry traction return current. Also known as signal rail. Insulated ail Joint (IJ) A method of joining rail ends together whilst maintaining electrical insulation between them. An alternative non-preferred term is insulated block joint (IBJ) Interlocking (building) Interlocking (equipment) The (generally dedicated) building housing the Interlocking System, where separate from the signal box (or other control point). The equipment that performs the role required of the Interlocking System. Interlocking (system) The safety-critical locking provided between Signalling Functions in accordance with control tables. Interlocking Area Internal (Circuit) The area of railway controlled by a particular interlocking, extended up to a boundary with each other adjacent interlocking controlled by the same or another signal box. A circuit that does not leave the Apparatus Housing in which it originates and which is fed from a busbar which feeds only internal circuits. This includes the feed to an isolating transformer supplying an External Circuit. Circuits that extend between adjacent Apparatus Housings may be considered to be internal if they are run in a protective non-conducting duct and are judged to be away from any environment that might be susceptible to earth faults. Internal (Power Supply) A power supply feeding only Internal Circuits. Also known as local power supply. Intolerable (isk) Joint Hopping Jointed Track Circuit Jointless Track Circuit Jumper Jumper Cable (Track Circuit/Traction) Associated with a risk that is greater than the upper limit of tolerability, as defined in ailtrack s ailway Safety Case. Where fast moving short vehicles pass from one track circuit to the next, the difference between the Pick Up and Drop Away Times can cause the vehicle to momentarily be undetected. A track circuit whose extremities are defined by the use of IJs. A track circuit whose extremities are defined by the use of tuned circuit techniques. The extreme limits of a jointless track circuit area are either defined by the use of IJs or by the use of a tuned circuit between the rails. An interconnecting cable (commonly single core) between two termination points within an apparatus housing. An interconnecting cable (commonly single core) between two pieces of rail that are not adjacent, for track circuit or traction purposes. This includes midpoint connections to Impedance Bonds. B11

18 ailway Group Guidance Note Page B12 of 36 Withdrawn Document TEM Junction Indicator (JI) Keyboard Lamp Proving elay Latch Latched elay Left Hand elay Level Crossing Ground Plan Level Crossing Order Lever (Or Switch) Nomenclature Plate Life-Cycle Cost DEFINITION A route indicator that has category one (long range) performance and displays the route at a signal by means of a line of white lights. An interface between an operator and a system facilitating the input of commands or data. A neutral d.c. relay designed to operate from the current supplied to signal lamps and to release when lamp or lamps burn out. Some relays incorporate a bridge rectifier to operate from a.c. lamp currents. A memory location that switches between two states, representing a particular Signalling Function. The states are commonly known as set and unset. A relay that switches between two states, representing a particular Signalling Function, and stays in the last set position when the operating feed is removed. The states are known as Operated and eleased. The left hand half of a twin relay as viewed from the front. In a 930 Series twin relay this controls the Contacts in banks C and D. A scaled and dimensioned drawing showing the position of all equipment, utilities and associated features in the vicinity of the level crossing, and the detail necessary for engineering, operating and statutory requirements. A statutory instrument describing the application of the SPG to a specific level crossing. Formerly known as section order. A plate fixed to a lever or adjacent to a switch, describing the lever/switch function, together with 'order of pulling' details. The total cost of ownership of an item taking into account all the costs of acquisition, personnel training, operation, maintenance, modification and disposal. [source: BS 4778] Also known as whole-life cost. Like-For-Like Work Line Circuit Lineside Location Local Panel Local Power Supply Location The removal and restoration of an item of equipment (including a cable renewals), where the work does not require any update to signalling Design Details. An external relay circuit, which is not an On-Track Circuit. See Location. A panel (sometimes simplified) provided at the interlocking and capable of being used to take over control from the main panel at the signal box. It may also be used as a maintainer's monitoring panel, when the operating function is not in use. See Internal Power Supply. A group of all signalling lineside Apparatus Housings (including buildings) at a particular site and the equipment contained therein. (This excludes Apparatus Housings that perform a main Interlocking function, although some Interlocking local to ground frames or level crossings may be included.) Alternatively known as lineside location. B12

19 ailway Group Guidance Note Page B13 of 36 TEM Location Area Plan DEFINITION A scale layout plan showing every signalling Location, together with their identities, position and type of cases, Interlocking boundaries, certain equipment identities (e.g. TFMs) and the area of signalling equipment that is controlled by each Location. This plan is generally a sub-version of the Scheme Plan or Signalling Plan. Low Voltage Low Voltage Alarm Main (Optical System) Main Cable Main Earthing Terminal (Met) Maintainability Maintained Locking Maintainer's Monitoring Panel Maintainer's Terminal See Voltage, Nominal. See under voltage detector. Primary lamp or filament of a duplicated pair. A twin or multicore lineside cable carrying Signalling Functions or power supplies between Apparatus Housings. The terminal or bar provided for the connection of Protective Conductors, including Equipotential Bonding conductors, and conductors for functional earthing if any, to the means of earthing. [source: BS7671] The ability of a product under given conditions, to be retained in, or restored to, a state in which it can perform it s required function. [source: ENV50129] An alternative to the term route locking. (see GK/T0002) An indication panel situated at the interlocking that repeats the indications sent to the signaller and allows the maintainer to observe the state of the interlocking. It also indicates various fault conditions. This may be combined with a Test Panel. This consists of a VDU, keyboard and printer connected to a solid state interlocking, or an IECC system monitor sub-system. It is used to obtain essential fault diagnostic information and also acts as an interface with the system to enable restrictive controls on the equipment to be set. Also known as technician s terminal. Maintenance Major Works Make-Before-Break Contacts Mechanical Locking Chart Mechanical Locking Control Tables Medium (M) Duty Contact Meshed Circuit The combination of all technical and administrative actions, including supervision actions, intended to retain a product in, or restore it to, a state in which it can perform a required function. [source: pr EN50126] Any infrastructure alterations which are outside the scope for Minor Works. A pair of relay contacts, where at each state of the relay only one of the pair is made, but which during transit momentarily have both contacts made. A plan showing the arrangement of mechanical locking components to achieve the mechanical locking control tables. A tabulation of the locking between Signalling Functions associated with a mechanical lever frame. A relay contact that is rated to make and break a non-inductive current of 3A to 6A. Complex circuitry feeding more than one relay, where the same could be achieved by independent circuits, thereby requiring duplication of contacts. Not all paths in a meshed circuit are applicable to all relays. B13

20 ailway Group Guidance Note Page B14 of 36 Withdrawn Document TEM Microcore Miniature oute Indicator (MI) Minor Works Mistake Mod State Modem Modulator Monitored (level crossing) Movement Authority Multi-Processor Module (MPM) National adio Network (NN) Multi-Section (track circuit) Negligible (risk) Neutral elay Non-Safety Contact Non-Safety-elated DEFINITION A Parallel data transmission system using a multicore cable having a large number of small diameter conductors. Interface buffer relays may be provided at each end. An alphanumeric route indicator having category three (short range) performance (equivalent to the former stencil route indicator). Infrastructure alterations which are listed as such in HSE/HMI Guide to the Approval of ailway Works, Plant and Equipment. See Fault, Defect, Error, Failure, Mistake. See Modification Status. An electronic device that converts a signal to make it suitable for transmission (modulator) or reception (demodulator) of information over a particular medium. See Modem. Checked by the observation of indications which provide the signaller with the status of equipment. Permission for a train to run to a specific location. The part of an SSI system that performs the Interlocking. Each SSI cubicle contains three MPMs that control the signalling using a majority voting technique to ensure safety and availability. A radio telephone system provided specially to facilitate railway operations. See Cut-Section. Associated with a risk that is less than the lower (broadly acceptable) limit of tolerability, as defined in ailtrack s ailway Safety Case. A d.c. relay which operates with either polarity of supply to the coil. A relay contact that is not a safety contact. This includes metal to metal contacts for medium duty use, where both elements are made of silver, silver cadmium oxide, or 60/40 silver palladium. A Signalling Function or sub-system where operational safety and the integrity of the interlocking are not directly affected. Manual intervention, where a failure would be noticed, may be part of the process. Formerly known also as non-vital. Non-Vital Normal (function) See Non-Safety-elated. Position of a lever when it is fully back in the lever frame. The un-operated or quiescent state of a two-state system. The converse is everse. Normal Contact Normal (Conditions) B14 A contact in a Polar elay, which is closed when the relay is operated to the Normal position. The operating conditions which a part of a railway is designed to accommodate. This would include peaks, e.g. rush hours, and troughs in demand experienced during the day. [source: SPG]

21 ailway Group Guidance Note Page B15 of 36 TEM On-Track Circuit Operate Coil Operate Time (elay) DEFINITION An External circuit run to, or via, an item of on-track signalling equipment in a Tail Cable. A winding which when energised at the rated voltage and frequency, causes the armature of a relay to move to the operate position. The time interval between the energisation of the relay coil and the first front contact making. The converse is elease Time. Operate Voltage (elay) The minimum voltage applied to a released relay coil at which the last front contact makes. Also known as pick-up (pu) voltage. Operated (elay) The state of a relay when the armature is energised, picked up (PU), or latched, all Front Contacts are made and all Back Contacts are broken. Also known as energised, and colloquially as picked or up. The converse is eleased. Optical Fibre Ordinary Acting (elay) Out Of Use An optically transparent fibre consisting of a central core surrounded by a cladding of lower refractive index and used to transmit light by means of multiple internal reflections. A relay without a particular stated specialised operating characteristic. Non-operational equipment that is still connected to the infrastructure. See also Spare. Overlay Track Circuit Parallel (Bonding) Parallel (Data Link) Pick Up (PU) Shunt Pick-Up (PU) VOLTAGE (elay) Pick-Up TIME (Track Circuit) A track circuit which can be superimposed over another, neither having any effect on the other and both operating independently. The method of bonding ail Sections with diverse parallel electrical paths for Availability. Track circuit bonding in this mode is non-fail-safe, since failure of a single Jumper Cable, Fishplate Bond, or IJ will not necessarily release the track circuit relay, and hence could result in loss of vehicle detection. A means of data transmission by which many discrete bits of information are sent at the same time along a Microcore link. The minimum value of resistance between the two running rails at which the track relay just closes its front contacts. See Operate Voltage. The time between the removal of a shunt to the rails and the first front contact of the track relay (T) making. The converse is Drop Away Time. Pin-Code Plug-In Plugboard See egistration Pin-Code The attribute of an item of electrical equipment which can be replaced without disconnecting any wiring. The permanent mounting block and termination for external wiring, for use with plug-in equipment. B15

22 ailway Group Guidance Note Page B16 of 36 Withdrawn Document TEM Polar (elay) DEFINITION A relay with two Operated positions (Normal and everse) and a central, eleased state. The Operated position depends upon the direction of the current or phase of the current in the operating circuit. A polar relay may not have contacts in the eleased position. See also Biased elay (sometimes referred to as a 2-position polar relay). Polarised Circuit Preselection Preventative Maintenance Primary Function elay Product Acceptance Programmable Logic Controller (PLC) Protective Conductor A circuit where the resulting operation is dependent on the polarity or phase angle of the feed. The selection of a Signalling Function prior to the conditions becoming available, so that it is automatically set when some other function is restored. This could result in a protected Wrong Side Failure becoming unprotected. The maintenance carried out at predetermined intervals or according to prescribed criteria and intended to reduce the probability of failure or the degradation of the functioning of an item. [source: pr EN50126] The relay by which the logic required to control a Signalling Function is brought together. It is the first relay in a chain that directly controls all safetycritical Signalling Functions. It is the only function relay which has Back Contacts valid for use in safety-critical functions. Authorisation of a product type for use. See GI/T7002. A self-contained electronic sub-system that manipulates data. It receives inputs from an interface, processes them in accordance with the System Program and Geographical Data in its memory and returns the resulting outputs to the interface. A conductor used for some measures of protection against electric shock and intended for connecting together any of the following parts: Exposed-Conductive-Parts, Extraneous-Conductive-Parts, the Main Earthing Terminal, earth electrode(s), the earthed point of the source or an artificial neutral. Protective conductors are identified by the colours green and yellow. [source: BS7671 augmented] Public Emergency Telephone System (PETS) Pulse Code Modulation (PCM) Quartz Halogen Lamp ail Joint Bond ail Section (track circuit) A special telephone system for use at level crossings, which includes provision for proving that handset connections are intact and also for the transmission of level crossing status indications. The speech path has priority over other facilities. A Serial data transmission system by which many channels of information are passed over a data link, by use of a multiplexer. See Tungsten Halogen Lamp. See Fishplate Bond. A section of one running rail continuously electrically bonded with its extremities defined by IJs, and within which all continuity connections are by Fishplate Bonds. It may extend over several track circuits (as the Common ail) or only part of a track circuit. B16

23 ailway Group Guidance Note Page B17 of 36 TEM AMS andom Hardware Failure DEFINITION An acronym meaning a combination of eliability, Availability, Maintainability and Safety. See also Dependability. [source: pr EN50126] Failures occurring at random times, which result from a variety of degraded mechanism in the hardware. Note 1) There are many degradation mechanisms occurring at different rates in different components and since manufacturing tolerances cause components to fail due to these mechanisms after different times in operation, failures of a total equipment comprising many components occur at predictable rates but at unpredictable (i.e. random) times. Note 2) A major distinguishing feature between random hardware failures and Systematic Failures is that system failure rates (or other appropriate measure), arising from random hardware failures, can be predicted with reasonable accuracy but systematic failures, by their very nature cannot be accurately predicted. That is, system failure rates arising from random hardware failures can be quantified with reasonable accuracy but those arising from systematic failures cannot be accurately quantified. [source IEC 61508] eceiver (X) ed Bond edundancy egistration Pin-Code An electronic device that converts, filters or decodes into a discrete output, information that has been received from another site. A traction bond that has been designated as being dangerous to staff if disconnected. It is marked red to draw attention to its importance and to aid inspection. Special procedures are in place for the reporting of damage to a red bond. The provision of one or more additional elements, usually identical, to achieve or maintain Availability under failure of one or more of those elements. [source: ENV50129] A series of locating pins assembled in a unique pattern to prevent equipment being incorrectly used. The unique pattern also acts as a means of identification for a specific style and variant of a relay. The term registration pin-code is commonly abbreviated to pin-code. elease Coil elease Time (relay) A winding which, when energised at the rated voltage, disengages the latching mechanism and causes the relay to release. The time interval between the removal of the supply (at rated voltage) to the relay coil and the last front contact breaking. The converse is Operate Time. eleased (relay) The state of a relay when the armature is de-energised, dropped away (DA), or unlatched, all back contacts are made and all front contacts are broken. Also known as de-energised and colloquially as dropped or down. The converse is Operated. eliability elocatable Equipment Building (EB) The ability of an item to perform a required function under stated conditions for a stated period of time. [source: ENV50129] Apparatus housing to specification B 1615 or equivalent. B17

24 ailway Group Guidance Note Page B18 of 36 Withdrawn Document TEM epeater Location DEFINITION A Lineside Location where all Line Circuits are interrupted by the provision of repeat relays for the purpose of limiting interference voltage. Also known as Cut-Section location. esidual Voltage The voltage remaining across the rails or relay of a track circuit after the feed has been disconnected. It may be caused by mutual interference between adjacent Single ail Track Circuits, the battery effect of the track formation, cathodic protection measures, or d.c. traction return or other stray currents. esolved (failure) eturn At the time of closure of the investigation, the engineer is satisfied that a fault occurred and the cause has been established. Power supply neutral (NX) or negative (N) connection. The converse is Feed. everse (function) Position of a lever when it is pulled fully forward in the lever frame. The operated state of a two-state system. The converse is Normal. everse Contact ight Hand elay ight Side Failure oute Holding Safe State A contact, in a Polar elay, which is closed when the relay is operated to the reverse position. The right hand half of a twin relay as viewed from the front. In a 930 Series twin relay this controls the Contacts in banks A and B. A Failure which does not result in the protection normally provided by the Signalling System being reduced. An alternative to the term route locking (see GK/T0002). Any one of the following: the state of the last valid request at the Interlocking, correspondence with the state of the trackside equipment, or the most restrictive state. Safety Contact Safety Integrity (SI) Safety Integrity Level (SIL) Safety-Critical Safety-Critical Failure A relay contact that is specified for safety purposes in the 930 Series specifications. These are non-weld contacts, generally silver to carbon for ordinary use. For medium duty use, the contact elements may be of silver impregnated graphite (SIG) and silver. The probability of a safety-related system satisfactorily performing the required functions under all the stated conditions within a stated period of time. [source: IEC 61508) One of four possible discrete levels for specifying the safety integrity requirements of the safety functions to be allocated to the safety-related systems. Safety Integrity Level 4 has the highest level of safety integrity; Safety Integrity Level 1 has the lowest. Safety Integrity Level 0 is non-safety-related. [source: IEC augmented] Carries direct responsibility for safety. [source: ENV50129] See Wrong Side Failure. B18

25 ailway Group Guidance Note Page B19 of 36 TEM Safety-elated Scheme Plan Section Order Secure Power Supply DEFINITION Carries responsibility for safety (direct or indirect). [source: ENV50129] A longitudinally scaled layout plan, based on the record Signalling Plan, that is produced to depict proposed new or altered signalling systems. An obsolete term, see Level Crossing Order. A power supply system that can be relied upon to keep certain Safety-Critical Signalling Functions operating for a predetermined minimum time, in the event of a total failure of the main incoming supply. Also known as Guaranteed Power Supply. Selective (telephone system) Sensitive elay Serial (data link) Series Bonding Sheath (cable) Short Circuit Bond Signal Box Control Area Signal Box Notes Signal ail Signal Sighting Form Signal Spacing Parameters Signaller s Area A system with many telephones on one circuit, where one telephone may call another chosen telephone without all the other telephones receiving the call. Generally a Neutral elay with a high coil resistance and low power consumption. It may be used to give accurate timings in conjunction with a capacitor/resistor unit. A means of data transmission by which many discrete bits of information are encoded and sent in turn along a Data Link. The fail-safe method of bonding track circuits with ail Sections connected in series, such that the failure of a single Jumper Cable, Fishplate Bond, or IJ results in de-energisation of the track circuit. An outer protective layer of a cable containing the insulated conductor(s). A Jumper Cable between the rails immediately beyond the final track circuit IJs, in order to detect double joint failure. This is the only bonding required on non-track circuited lines in non-electrified areas. See Control Area. A list of the key features of a signal box, or control centre, including any functions that are not clear from the Signalling/Scheme Plan. Non-preferred term; see Insulated ail. A form that depicts the profile, location and other details of each signal as agreed by the signal sighting committee. A tabular representation of the parameters (such as braking distances and average gradients) that may influence the relative positioning of signals. The area of railway controlled or supervised by any one signaller, as defined by the boundaries between control panel sections or Signalling Workstations. Formerly known as signalman's area. Signalling Function Final discrete component of a Signalling System listed on control tables with a unique identity (such as signals, points, train detection devices, releases and level crossing barriers) and the circuitry or logic by which it is controlled and/or proved. Signalling Functions are allocated (as defined by the control tables) to a specific interlocking controlled by a particular signal box (or other control point) and are given a unique identity within a particular signaller s area. B19

26 ailway Group Guidance Note Page B20 of 36 Withdrawn Document TEM Signalling System DEFINITION Equipment, circuitry and software associated with: lineside signals; point operatio; level crossings; train detection; trainborne equipment conveying information about the state of the line; operational telecommunications (excluding electrification control systems and electrification telephones); and fixed trackside safety systems. Signalling Workstation Signalman's Area Significant Failure Single ail Single ail (S) Bonding Configuration Single ail Track Circuit Sleeper Slow Acting elay Slow To Operate elay Slow To elease elay Spare Spur (track circuit) Stagger (electrical) Stagger (physical) Standard oute Indicator (SI) Standby A workstation controlled by a signalling display sub-system with facilities for signalling control by trackerball and keyboard together with signalling display monitors and a general purpose VDU. Obsolete term, see Signaller s Area. A Wrong Side Failure which by its seriousness or because of its volume introduces a risk requiring attention. Non-preferred term; see Common ail. A track circuit arrangement where only one rail (the Insulated ail) is used with IJs to separate the track circuits. The other rail (the Common ail) is electrically continuous and is used for traction return purposes. A jointed track circuit with IJs in only one rail (the insulated rail) that is series bonded (except for the presence of spurs of limited length at switches and crossings). The other rail, known as the common rail, is electrically common to one or more adjacent track circuits. An item of wood, steel or concrete of standard dimensions, used to support and gauge the track. (See Bearer and Timber.) A relay in which both Operation and elease are intentionally delayed. A relay in which the Operation is intentionally delayed and the operate time is significantly longer than the elease Time. A relay in which the elease is intentionally delayed and the elease Time is significantly longer than the Operate Time. Equipment not connected to any part of the infrastructure. See also Out Of Use. A section of running rail required to be electrically common to a series bonded rail, but which is not itself in series. The phase or polarity difference between one track circuit and the next, or between the rails on either side of an IJ within one track circuit. Occurs where two IJs in a pair of rails are not exactly opposite each other, thus creating a dead section between track circuits or within a track circuit. An alphanumeric route indicator having category two (medium range) performance (equivalent to the former theatre type route indicator). The state of an item when it is available but not required to be operating. [source: BS 4778] B20

27 ailway Group Guidance Note Page B21 of 36 TEM State (of a function) DEFINITION Position or action of the equipment. Examples of complementary states are: Operated/eleased, Normal/everse, on/off, raised/lowered, locked/free, enabled/inhibited, energised/de-energised. In data driven systems this is stored as Variable Data. State (of the infrastructure) Stock ail Structure Bond Supervised (level crossing) Supervisory (circuit) Switch Nomenclature Plate Switch ail Switch einforcing Bond Switch Toe Switches And Crossings (S&C) Configuration of an Installation. See figure under Switches And Crossings. A bond required in a.c. electrified areas, that connects adjacent lineside metal structures to the traction return rail system, where required to ensure staff safety through equipotential zoning. Checked by visual observation, either directly or by use of CCTV. Control or indication circuit, particularly in respect of electric traction power supplies. See Lever (Or Switch) Nomenclature Plate. See figure under Switches And Crossings. A jumper cable installed around the switch in S&C, in order to strengthen the fishplate bonds between the switch and crossing components and also to link two spur ends together, so improving the integrity of a parallel bonded rail section. See figure under Switches And Crossings. Sections of track other than plain line. See the figure for constituent parts. Closure Panels Heel Of Switch ail Wing ails Crossing Angle Switch Toes Switch ails Stock ails Closure ails Crossing Nose Check ail Crossing Back System Program The software necessary to drive a programmable electronic system. Also known as fixed data. B21

28 ailway Group Guidance Note Page B22 of 36 Withdrawn Document TEM Systematic Failures DEFINITION Failures due to errors (including mistakes or acts of omission) in any safety lifecycle activity which cause it to fail under some particular combination of inputs or under some particular environmental condition. Systematic failures could arise in any safety life-cycle phase. Examples of systematic failure include: Systematic failures due to errors in the safety requirements specification; Systematic failures due to errors in the design, manufacture, installation, operation of the hardware; Systematic failures due to errors in the design, implementation etc. of the software. [source: IEC 61508] Systems Approval Tail Cable Approval granted to systems. A cable between trackside or on-track signalling equipment and other such equipment or a lineside Apparatus Housing. For track circuits, see also Track Cable. Technician's Terminal Terminal Line Test Panel Through Circuit Timber Time Division Multiplex (TDM) Time Element elay See Maintainer's Terminal. The length of plain line approaching buffer stops. Single rail traction return is adequate for the final 300m of such lines in d.c. electrified areas, as traction return current is low. A control panel provided at the interlocking for testing or maintenance purposes. It may be provided temporarily for a commissioning or the function may be performed by the Local Panel. An external circuit drawn in entirety from supply to destination. An item of wood of non standard dimensions, used to support the track in S & C areas. (See also Bearer and Sleeper.) A non-safety-critical serial data transmission system that addresses each channel in turn and converts it into a unique digital code. It is generally used to transmit operating controls and indications between a signal box and Interlockings. A relay, whose timing contacts do not change state until a predetermined time after Operation or elease, as appropriate. Commonly known as timer. Timer Tolerable (risk) Touch Potential Track Cable Track Circuit Actuator (TCA) See Time Element elay. Associated with a risk that is within the limits of upper & lower tolerability, as defined in ailtrack s ailway Safety Case. The potential difference between a person's hand which is touching an Exposed-Conductive-Part and any other part of the body which is touching another Exposed-Conductive-Part at a different potential. A track circuit tail cable which connects directly to the rails. Non-preferred term, see track circuit assister. B22

29 ailway Group Guidance Note Page B23 of 36 TEM Track Circuit Actuator Interference Detector (TCAID) Track Circuit Assister (TCA) Track Circuit Assister Interference Detector (TCAID) Track Circuit Bonding Track Circuit Interrupter Track Jumping Track elay (T) Trackside Functional Module (TFM) Traction Bond Traction ail Traction eturn Bonding Transmitter (Tx) Transposition Bond Transposition Joint Trap Point Triple-Pole (Lamp) Tungsten Halogen Lamp Twin elay Type Approval DEFINITION Non-preferred term, see Track Circuit Assister Interference Detector. A device fitted to a vehicle which causes a 165kHz signal to pass between the wheels of the vehicle and assists in the breakdown of the insulation at the wheel to rail interface due to leaf-fall, rust etc. A device fitted to the track which, when it detects the presence of a 165kHz signal in the rail, causes the track circuit to show occupied. The connection of one rail or component of a track circuit to another rail or component, so as to ensure electrical continuity. On rails carrying traction return current its function is performed by the Traction eturn Bonding. A device that records the passage of a vehicle by causing a permanent disconnection within the track circuit until the device has been renewed. Occurs when a fast moving vehicle passes over a very short track circuit (or a short arm of a longer track circuit) and fails to de energise the track relay. Generally a neutral relay with a low coil resistance and low power consumption, which acts as part of a track circuit. It is either connected directly to the rails, or via a capacitor or tuner unit. SSI signal or points modules situated in lineside locations to operate and prove trackside equipment and interface with the Data Link from the interlocking via the data link module. A cable specifically provided for continuity of traction return current, although it may additionally carry track circuit current. See Common ail. The bonding required to carry the traction return current on both ac and dc electrified lines. Traction return bonding is generally parallel bonded. An electronic device that converts, modulates or encodes a discrete input, into a form that is suitable for sending to another site. A jumper cable provided where track circuit polarities and/or traction return rails change sides across a pair of IJs, or transposition joints. Purposes include the correction of track circuit polarity stagger or traction current imbalance, or to facilitate Series bonding in S&C. An IJ where transposition bonds are used to transpose the traction and/or track circuit rails. A point (usually switch and tiebar only), inserted in sidings etc., to unauthorised movements away from a running line. A double-filament lamp in which one end of each filament is connected to the cap shell and the other ends of the filaments are connected one to each contact plate. [source BS 469] A lamp in which the tungsten filament is enclosed in a gas filled quartz bulb containing a quantity of a halogen. A unit which contains two electrically and mechanically independent relays. See Product Acceptance B23

30 ailway Group Guidance Note Page B24 of 36 Withdrawn Document TEM Under Voltage Detector DEFINITION A permanent device, wired to the busbars, to inhibit operation and/or give an alarm to alert the maintainer, when the voltage falls below an acceptable level. Also known as low voltage alarm. Uninterruptible Power Supply (UPS) Unresolved (Failure) Variable Data Visual Display Unit (VDU) Map Layout Voltage, Nominal A power supply with a secondary source which is capable of providing an uninterrupted changeover in the event of a failure of the incoming supply. It generally consists of low maintenance cells, a charger, voltage regulator, and monitoring, changeover and bypass devices. At the time of closure, exhaustive testing has failed to reveal the fault but the possibility of a fault has not been totally eliminated. Information associated with a data-driven system which records the real-time State of Signalling Functions. A full size layout plan that details the information to be displayed for each screen overview or detailed view on a VDU. Voltage by which an installation (or part of an installation) is designated. The following ranges of nominal voltage (r.m.s. values for a.c.) are defined: Extra-low. Generally not exceeding 50V a.c. or 120V ripple-free d.c., whether between conductors or to earth, Low. Generally exceeding extra-low voltage but not exceeding 1,000V a.c. or 1,500V d.c. between conductors, or 600V a.c. or 900V d.c. between conductors and earth. [source: BS7671 amended] Wing ail Wrong Side Failure See figure under Switches and Crossings. A Failure which results in the protection normally provided by the Signalling System being reduced. Also known as Safety-Critical Failure. Yellow Bond A jumper cable that is necessary to ensure the electrical integrity of a track circuit that is fully or partially Parallel bonded. It is marked yellow to draw attention to its importance and to aid inspection. B24

31 ailway Group Guidance Note Page B25 of 36 4 Use of This Guidance Note The subsequent Parts of this Guidance Note set out means by which an acceptable level of dependability can be achieved for each type of equipment or sub-system, in the form of Codes of Practice. Where they entirely address the situation under consideration, their use is an alternative to the risk-based approach illustrated in GK/T0206. However, where the particular application or intended environment for the system introduces additional risks, these should be subject to separate assessment. The Design Principles in each Part give guidance on the minimum requirements that need to be addressed, even when a risk-based approach is used. Supplementary material is provided in the form of appendices to each Part of the Guidance Note. 5 Signalling System It is convenient to divide the signalling system into the following sub-systems. The examples and exceptions are quoted for illustrative purposes only in order to define the scope, and are not intended to be exhaustive: a) signal box to signal box interface, including block instruments, emergency alarms and radio electronic token block (ETB) sub-systems; b) signalling control and display system, including any train describer (TD), automatic route setting (AS) and level crossing CCTV supervision subsystems, but excluding signaller s information sub-systems, such as automatic train reporting (AT), automatic train supervision (ATS) and timetable processor (TTP); c) signaller s voice communication systems used in the protection of trains, public, or staff, e.g. signal post telephone (SPTs), cab secure radio (CS), level crossing emergency telephones and point zone telephones (PZT), but not national radio network (NN) or electrification telephones; d) transmission systems for controls and indications between the signal box and its interlockings; e) interlocking systems; f) transmission systems for functional controls and proving between each interlocking and its lineside locations; g) operating equipment for signalling functions contained within lineside locations; h) lineside location to trackside equipment feeds; i) functional trackside signalling equipment; j) train detection system; and k) track to train transmission systems and train-borne equipment using signalling data to control some function of the train or to provide safetyrelated information to the driver, including the automatic warning system (AWS), automatic train control (ATC), automatic train protection (ATP), train protection and warning system (TPWS), and track circuit assister interference detectors (TCAID), but not track to train information systems that are not safety-related. B25

32 ailway Group Guidance Note Page B26 of 36 Withdrawn Document 6 Alterations to Existing Installations Examples of conflicting standards whose perpetuation is generally acceptable are given in Appendix B1. Examples of certain safety hazards within an existing installation, which may have no bearing on proposed alterations, but may justify the retrospective upgrading of the whole installation to certain new standards, are given in Appendix B2. Examples of relaxations that are generally acceptable for temporary work, are given in Appendix B3. B26

33 ailway Group Guidance Note Page B27 of 36 Conflicting Standards Appendix B1: Examples of situations where the perpetuation of existing arrangements is generally acceptable when alterations are undertaken, are as follows: B1:1 Identification Existing signalling functions should not be renumbered or lettered to the current practice given in GK/T0009 unless the alterations are of such magnitude that all functions of a particular type in the locality concerned can be identified in the new manner. More than three point ends on the same number may be tolerated, for power operated points, where it is particularly expedient, e.g. for the addition of switch diamonds. B1:2 Line Circuits and On-Track Circuits A.C. line circuits may be perpetuated for alterations to existing installations in non-a.c. electrified areas and may extend up to 5,000m in length, subject to voltage drop considerations, the use of converters giving sufficient capacitive immunity and any other relevant factors, such as electromagnetic compatibility with rolling stock. It is recommended that common returns are not perpetuated for safety-critical line circuits and that earth returns are not perpetuated for any line circuit. Any down proving of line relays that is not a current requirement should not be removed unless the line circuit is double cut and does not use a common return. It is recommended that single cutting of circuits is not perpetuated where the current requirement calls for double cutting. On-track circuits feeding trackside equipment extending up to 1,375m in length, rather than limited to 200m, may be perpetuated for alterations to existing installations in non-a.c. electrified areas, subject to voltage drop considerations and any other relevant factors, such as electromagnetic compatibility with rolling stock. See Part D. B1:3 elays The use of predecessors of the 930 series, shelf type relays, a.c. line relays, double element vane relays, moving iron relays, WBS type 'P', larger plug-in type relays and other types may be perpetuated, subject to availability and any conditions imposed in GK/T0129, for alterations to existing installations. This includes the perpetuation of local batteries as a power source for moving iron relays. Any down proving of older style relays that is not a current requirement should not be removed until relays are replaced by those meeting current standards. Any standard convention may be perpetuated for the orientation of relay contacts with respect to the supply polarity, for alterations to existing installations. The use of non-safety relays in safety-related applications, such as signalling control and display systems, may be perpetuated for alterations to existing systems, provided that a satisfactory safety history can be demonstrated. The use of 12V circuits to feed indication lamps, instead of a minimum of 24V, may also be perpetuated, unless the whole diagram structure is being replaced. B27

34 ailway Group Guidance Note Page B28 of 36 Withdrawn Document See also Part D. B1:4 Meshed Circuits Care should be taken when altering meshed circuits or removing back proving contacts that are no longer a requirement, in case the original designer intended them to prove sequence of operation or to prevent certain right side failures causing a wrong side failure. See Part D. B1:5 Negative Fusing The fusing of the negative leg of circuits instead of the positive may be perpetuated for alterations to existing installations. See Appendix D1. B1:6 Geographical Circuitry It is important, so as not to create a hazard for the unwary, that geographical circuitry is altered in a consistent manner with the necessary straps and free wiring, in accordance with the manufacturers' design documentation. Similar occurrences of the required controls should also be studied to ensure consistency. See Part F. B1:7 Obsolescent Signals Lower quadrant semaphore signals, as described in GK/T0031, may be retained for the sake of consistency, but consideration should be given to conversion to upper quadrant. Other types of signal that are illustrated in the ule Book, but are not included in GK/T0031, may be retained for the sake of consistency, but consideration should be given to replacing them with those that meet current standards. B1:8 Point e-drive Point re-drive may be omitted for the sake of consistency, at existing interlockings that have not employed this facility. See Part P. B28

35 ailway Group Guidance Note Page B29 of 36 Safety Hazards equiring etrospective Work Appendix B2: When alterations are undertaken on existing signalling installations, the infrastructure controller should consider whether certain retrospective safety work, both on the parts of the installation being altered and on those parts of the installation not being altered, should be carried out. A fully documented process of risk assessment should be conducted if the infrastructure controller considers that the work is not merited by the reduction of risk that would be achieved. The infrastructure controller should keep a record of which safety hazards have been addressed at each installation, and those that have not been addressed. See GK/T0206. Examples of such safety hazards are as follows: B2:1 epositioning of Non-Safety Contacts Interlockings and lineside locations being altered should be checked to ensure the correct positioning of non-safety relay contacts. Any incorrect positioning found should be dealt with in accordance with Part D. B2:2 Approach Locking Interlockings being altered should be checked to ensure that approach locking circuits provide the current requirement of sequence proving (see Part D). emedial work should be undertaken to correct any discrepancies, such as the omission of down proving, which could give rise to a hazardous failure. Situations where the de-energisation of the GP is delayed by the use of several repeat relays, or vital FDM transmission are particularly vulnerable. B2:3 Checking of Back Contacts Interlockings and lineside locations being altered should be checked to ensure the correct use of relay back contacts in existing circuits (see Part D). emedial work should be undertaken to correct any discrepancies which could give rise to a hazardous failure or false indication to the signaller. Particular attention should be paid to track repeat relays which give approach releases (including temporary approach control). See Appendix F2. B2:4 Delayed Signal eplacement Interlockings being altered should be checked to ensure that signals with delayed replacement controls are in accordance with the requirements (see Part F). emedial work should be undertaken to correct any discrepancies that could give rise to a hazardous failure, particularly if the signal in rear can be cleared before a train has replaced the signal with delayed replacement. Where appropriate, this may be effected by converting the replacement to first wheel. B2:5 Swinging Overlaps Interlockings and lineside locations being altered should be checked to ensure that the design of swinging overlap circuits address all significant risks (see Appendix F2). emedial work should be undertaken to correct any discrepancies which could give rise to a hazardous failure, such as preselection of points. B29

36 ailway Group Guidance Note Page B30 of 36 Withdrawn Document B2:6 Single Post Terminations Where work is to be done in an apparatus housing, one of the following should be applied (see Part J): either separate sliding links should be provided for every incoming and outgoing cable, eliminating the use of binding posts; or all cable termination sheets should be issued, inscribed with the following note: "All Single Post Terminations to be Fitted with ed Dome Nuts", to act as a reminder in case cable fault jumpering becomes necessary. B2:7 Shrouds for Terminals Where work is to be done in an apparatus housing, equipment should be checked to ensure that any terminals located on horizontal surfaces are adequately shrouded to prevent items being dropped on them causing false circuit operation. This applies to shelf-type relays, transformers, capacitors, and terminal blocks, etc. emedial work should be undertaken as necessary. See Part D. B2:8 B 998 Detector Boxes All B 998 detectors should be wired in one of two permissible wiring configurations, i.e. right hand switch normally closed or left hand switch normally closed. An extract of the layout showing the orientation of the detectors should be provided on the circuit diagram. Because of microswitch deficiencies, B 998 detectors should either be duplicated, or used in conjunction with some other detection device, such as a point machine, unless mechanically connected to a lever frame or ground frame. See also Part P. B2:9 Level Crossing Modifications See Part X for a schedule of the modifications to be made to level crossings when any alteration is undertaken. B2:10 Transmission of Safety-elated Controls Transmission systems that are not safety-critical and do not fail safe should be checked to ensure that safety-related single function controls, where a failure could lead to a hazardous event, are not transmitted by a single channel, but by two independent channels. This applies particularly to signal and crossing clear controls. emedial work should be undertaken as necessary. See Part L. B2:11 eplacement Indications for Automatic Signals Signal boxes where alterations are being undertaken should be checked to ensure that all replacement indications for automatic signals prove the signal on (H de-energised), signal alight (EC energised) and signal box replacement control effective at the signal. Additionally, where provided, related distant and/or banner repeating signals should also be proved on and alight in the signaller s indication. emedial work should be undertaken as necessary. See Part L. B2:12 Absolute Block Controls Signal boxes where alterations are being undertaken should be checked to ensure that all absolute block sections on passenger lines are equipped with the block controls required in GK/T0042. emedial work should be undertaken as necessary. B30

37 ailway Group Guidance Note Page B31 of 36 B2:13 Overlaps Interlockings being altered should be checked to ensure that the overlaps of all signals requiring them are of adequate length in accordance with GK/T0078. emedial work should be undertaken as required by risk assessment and in particular where: the attainable speed approaching the signal has increased; the signal sighting has worsened; any warning arrangements (e.g. AWS, ATP, banner signals, or the number of cautionary aspects) have been changed; or the signal has a history of SPADs (signal passed at danger). B2:14 SPAD Mitigation Interlockings being altered should be checked to ensure that any starting signals or other signals with particular SPAD risks, requiring enhanced overrun protection in accordance with GK/T0078, are adequately protected. emedial work should be undertaken as necessary. B2:15 Track Circuit Clearances Whenever permanent way alterations are undertaken, the actual position of all affected and adjoining insulated rail joints should be correlated with their dimensioning on signalling and bonding plans, and checked to ensure compliance with GK/T0011. Minimum track circuit length should also be checked. Any discrepancies found should be remedied. This may be effected by an extension of track circuit locking, or a special sequential control on the track circuit clearance. B2:16 Track Circuit Joint Hopping Interlockings and lineside locations being altered should be checked to ensure that any necessary delay is incorporated into the operation of track circuit primary function relays. Details may be found in GK/C0752. emedial work should be undertaken to correct any discrepancies that could give rise to a hazardous failure, particularly where locking could be released because of a delay in registering the occupancy of a track circuit in the interlocking, or where intermittent incorrect aspect sequences could occur. B2:17 Track Circuit esidual Voltage Whenever track circuit alterations are undertaken, the residual voltage occurring on any altered d.c. track circuit should be checked, where a wrong side failure is likely to lead to a hazardous event. Details may be found in GK/C0755. Any discrepancies found should be remedied. This may be effected by any means permitted within GK/T0252 that do not affect adjacent track circuits not otherwise being altered. There is no requirement to extend the remedial work beyond the original track circuit being altered, unless this is shown to be necessary during the risk assessment. B2:18 Statutory equirements When alterations are undertaken at any installation, the opportunity should be taken to review its compliance to recent statutory changes, in particular the following regulations, as interpreted in this Guidance Note and in GK/T0206: the Electricity at Work egulations 1989; the Electromagnetic Compatibility egulations 1992; the Management of Health and Safety at Work egulations 1992; the Workplace (Health, Safety and Welfare) egulations 1992; the Construction (Design and Management) egulations 1994; and the Health and Safety (Safety Signs and Signals) egulations Adequate information should be provided on the design details, as described in GK/T0206. B31

38 ailway Group Guidance Note Page B32 of 36 Withdrawn Document Temporary Work Appendix B3: B3:1 General This appendix covers the following types of work as described in Section B3:2: temporary non-conceptual work; short-lived work; stagework progressing towards an approved overall scheme; and redundant assets left in situ for a limited time (see Section B3:3). Temporary work is defined as alterations which remain in use for a limited period of time. Where it is desired to use the relaxation given in Section B3:4, the protection described in Section B3:5 should also be applied. The following considerations should be addressed by a fully documented process of risk assessment: the time for which the work may remain; the likelihood of future alterations to the temporary work; the possibility of protracted timescales, requiring imposed solutions in the event of slippage; and the introduction of temporary work on life-expired equipment with no maintainability. B3:2 Specific Examples of Temporary Work The following are examples of the types of temporary work to which the relaxation given in Section B3:4 applies: Like-for-like emergency work (imposed due to genuine emergency situations such as accidents, fire and vandalism). ectification of cable faults (using red cable fault jumpers to spare conductors). See GK/T0231. Temporary speed restrictions (TSs) (involving the disconnection of AWS inductors associated with the planned application of a TS). See GK/T0038. elease of controls for engineering work or single line working, in accordance with ule Book, Section E and the instruction on giving releases in GK/T0231. Short-lived alterations to circuitry during civil engineering works after which all signalling returns to the previous arrangement (either to maintain point detection, and disconnection of affected routes, or to maintain track circuit operation following temporary removal of defective switch and crossing components).short-lived new work and alterations to circuitry during disarrangement of locking or long term civil engineering works after which all signalling returns to the previous arrangement (including the temporary provision of automatic signalling or single line operation). Stagework at installations with a very limited life. Partially commissioned work. Minimum stagework alterations where switch and crossing work is to be recovered before the final design work can be completed (in order to maintain point detection and/or track circuit operation, and hence associated signal or route operation, when redundant switch and crossing components are to be recovered). ecovery of redundant assets, but only in situations (c) and (d), defined in Section B3:3. B32

39 ailway Group Guidance Note Page B33 of 36 B3:3 edundant Assets In order to maintain the integrity of circuit principles set out in this Guidance Note, circuits and relays made redundant by the abolition or change of facilities should generally be shown to be removed in full on circuit diagrams. Spare terminals and fuses may be left in situ, providing their existence is correctly shown on circuit diagram layouts and analysis. Where cable cores become spare as a result of circuit alterations, disconnection links at intermediate locations and their associated jumpers should be left in situ (subject to circuit length limitations due to induction). See Part J. The only permitted relaxation to this rule is for certain specific temporary alterations: stagework; at installations with a very limited life; and at installations with degraded or fragile wiring. The proposed extent of recoveries should be established with the infrastructure controller, considering: the need to maintain the integrity of circuit principles; and whether it is safe to disturb the existing wiring. The recovery work should then be categorised as follows: a) retrospective work to be undertaken to recover redundant assets; b) assets made redundant by the current alteration to be recovered; c) assets to be recovered at the next major alteration; or d) no recoveries to be undertaken until the installation is renewed. Categories (a) and (b) should accord with permanent design procedures and are not subject to the relaxation given in Section B3:4, but (c) and (d) are temporary expedients that require justification within the risk assessment. B3:4 elaxation The following expedients may be used in connection with temporary work: the retention of redundant circuitry and equipment, as described in Section B3:6; the retention of temporarily out of use circuitry and equipment; the provision of not yet commissioned circuitry and equipment in working installations; the disconnection, insulation and securing of wires in accordance with Section B3:5, in lieu of complete removal; the bridging out of contacts with crimped straps; the replacement of fuses with dummy fuses; the removal of links to form single post terminals with red domed nuts and insulating battens to prevent the replacement of links; "top-nutting" single post terminals, or provision of horizontal terminals, for stagework cable connections; the use of coloured jumpers crimped at each end; the false feeding of circuits by the use of jumpers crimped at each end; the patching of signal box diagrams and panel faceplates with overlays. Note that non-commissioned latched lock relays should be removed and their bases plugged and labelled to prevent the insertion of a relay latched the wrong way. If necessary, crimped straps may be used to enable other circuits to be introduced. B33

40 ailway Group Guidance Note Page B34 of 36 Withdrawn Document B3:5 Protection Protection should be arranged in accordance with the following principles, whilst the temporary arrangements remain in force: the strategy for any stagework should be identified in the design specification for the scheme (see GK/T0201) and be subject to a fully documented process of risk assessment; the affected wiring should be correlated as far as reasonably practicable, in accordance with GK/T0115; all the relevant diagrams, including analysis, cable core plans and bonding plans, should be produced and issued for production, testing, commissioning and maintenance purposes, in accordance with GK/T0201, except for nonconceptual work (see Section B3:7); temporarily out of use, not yet commissioned and redundant circuitry should be identified on the production and record diagrams by the use of special notes with arrows, or symbols, as described in GK/T0201 (but nonconceptual temporary alterations to circuitry need only be identified on the record diagrams); trackside equipment that has temporary alterations, is temporarily out of use, not yet commissioned, or redundant and left in situ should be shown on record signalling plans, as described in GK/T0004; not yet installed trackside equipment with circuitry provided in the interlocking and recovered trackside equipment with circuitry left in the interlocking should also be shown on record signalling plans, as described in GK/T0004; temporarily out of use, not yet commissioned and redundant controls, where the circuitry (or mechanical locking) is left in the interlocking, should be shown on record control tables, as described in GK/T0201; and each end of redundant / temporarily out of use wiring should, as appropriate, be fully terminated or bomb tailed at all times; B3:6 ecovery of edundant Assets When the relaxation given in Section B3:4 is applied to the recovery of redundant assets, the following rules should be adopted: B3:6.1 General All out of use equipment, fuses and links should be permanently labelled as such. A note to that effect should be provided on the design details. B3:6.2 Trackside Equipment Generally, all equipment should be recovered, but the following special requirements apply: Points. See ule Book GO/T3000, Section B (Part ii). Point mechanisms. Track equipment and tail cables should be recovered. Operating circuits should be isolated by the removal of fuses and links in the adjacent apparatus housing. Point detection (entire abolition of a set of points). Detection circuits should be isolated by the removal of fuses and links in the adjacent apparatus housing and false fed at the interlocking. Point detection (abolition of one end of a set of multiple ended points). Detection circuit and point end lettering should be altered to the final arrangement. B34

41 ailway Group Guidance Note Page B35 of 36 Ground frames. Track equipment and tail cables should be recovered. Incoming and outgoing circuits should be isolated by the removal of fuses and links in the adjacent apparatus housing. If partially in use, the track fittings should be removed and levers fixed normal. Signals and AWS. Track equipment, tail cables and disconnection boxes should be recovered. Incoming and outgoing circuits should be isolated by the removal of fuses and links in the adjacent apparatus housing. If part of the signal remains in use, the profile on the sighting form should be altered. oute indicators. PLJIs and route indicators should be recovered. edundant feeds to partially operative route indicators should be disconnected. PLJIs should be rearranged, if necessary, for remaining routes. Track circuits. Tail cables and disconnection boxes should be recovered. Bonding should be altered. Adjacent track circuits may require adjusting. emaining track circuits should not be altered, unless they can be rationalised by abolishing Ts and combining TPs at the interlocking. B3:6.3 Lineside Locations Generally, tail cables, fuses and links should be removed, but the internal wiring and equipment may be left in situ. False feeding in locations should only be considered where no other solution is reasonably practicable. In such cases, the false feeds should be crimped, wired and labelled to permanent standards. Wherever possible, busbar fuses should be removed and dummy fuses inserted. Main cables may be left in situ, in which case they should remain terminated with the links removed and red dome nuts fitted. B3:6.4 Signal Boxes and Interlockings Work should be undertaken as follows: Lever frames. Levers and locking should be left in situ. Levers retained solely to maintain locking and which have to be pulled to release other levers should be plated Interlocking Lever or otherwise according to existing practice at the signal box. Levers that are temporarily fixed, preferably normal, to maintain locking should be plated Not in Use. (Any levers fixed reverse require the agreement of the infrastructure controller.) Levers that are free of all locking should be painted white, in accordance with GK/T0005. edundant locks should be recovered and looping restored. Locking charts should be accurately updated. Free wired interlocking. Wherever possible, busbar fuses should be removed and dummy fuses inserted. Otherwise power should be removed from redundant parts of the circuitry by disconnecting wires in accordance with Section B3:5. Out of use latched lock relays should be removed and their bases plugged and labelled to prevent the insertion of a relay latched the wrong way. Points free relays (WZ or equivalent) are thus deenergised. Other redundant relays should be treated similarly. Any false feeds or straps used to maintain working circuits, including point detection, should be crimped, wired and labelled to permanent standards. A controlled signal with only one route remaining may be converted to an automatic signal. Geographical interlocking. To be similarly treated, but by fitting dummy relays, or reconfiguring straps, generally on plug couplers. Solid State Interlocking. No relaxations are permitted. B35

42 ailway Group Guidance Note Page B36 of 36 Withdrawn Document Signal box diagram. An overlay may be used for a minor alteration, otherwise a new diagram print should be provided. edundant track circuit lamps should be removed. edundant points should be marked "C&P" qualified by HSC (right hand switch closed) or LHSC (left hand switch closed), as appropriate. Signal box block shelf. edundant repeaters, indicators and block instruments, etc., should be removed. Control panel. An overlay may be used for a minor alteration, otherwise permanent artwork should be provided. edundant track circuit lamps should be removed. edundant points should be marked "C&P" as above. edundant push buttons, switches and train describer displays should be removed, replaced with blank tiles and strapped as necessary. Train describers. These should be altered to reflect the actual situation as far as practicable. B36

43 ailway Group Guidance Note Page D1 of 39 1 Introduction Part D Electrical Circuits 1.1 This Guidance Note applies to the design of electrical circuits associated with: electro-mechanical signalling systems; electro-pneumatic signalling systems; relay based signalling systems; and electronic signalling systems. It applies to both internal and external circuits, commencing on the load side of the final busbar. 1.2 It does not apply to wiring associated with the power supply side of the final busbar or to earth bonding, which are covered in Part C, nor to circuits associated with signalman s voice communication systems, which are covered in Part N. For the presentation and use of circuit diagrams within the design process see GK/T0201. elay and circuit nomenclature, as well as symbols, are defined in GK/T Where it entirely addresses the situation under consideration, the use of this Guidance Note is an alternative to the risk-based approach illustrated in GK/T0206. However, where the particular application or intended environment for the system introduces additional risks, these should be subject to separate assessment. The Design Principles in Section 2 give guidance on the minimum requirements that need to be addressed, even when a risk-based approach is used. 1.4 Use of the following guidelines will satisfy the principles encompassed within the Guidance Note: Guidelines on fusing and looping are given in Appendix D1. Guidelines on the electromagnetic compatibility of electronic equipment are given in Appendix D2. Guidelines on the application of different types of circuit are given in the relevant parts of this Guidance Note. Typical circuits may be used. As a minimum, any typical circuits should follow the guidance of this Guidance Note. 2 Design Principles 2.1 General Circuits should be provided, as necessary: to interlock the signalling functions in accordance with the control tables; to operate the trackside and on-track signalling equipment and prove that operation; to control the signalling functions from the signalbox and to indicate their state; and to monitor the system to warn of failures or operating irregularities. D1

44 ailway Group Guidance Note Page D2 of 39 Withdrawn Document Consistency in the operating and proving circuits associated with any interlocking should be maintained, irrespective of whether the trackside and on-track equipment is directly or indirectly fed from the interlocking. Where it is necessary to house the controlling relays at the interlocking, the same type of circuitry should be used, as far as practicable, as if the relays were remote. 2.2 Safety Integrity The use of fail-safe circuits and components should be commensurate with the levels of safety and availability required, as described in GK/T0206. The following areas should be considered: safety-critical systems and components to fail safe, such that no foreseeable failure mode can introduce a hazard within the signalling system that was not present before the failure; safety-related systems and components that are not safety-critical to fail safe wherever reasonably practicable; the possible failure modes of each component of a safety-related system and the implications of a fail safe circuit component failing in its predetermined mode (such as a relay failing to energise, or overcurrent protective device operating); circuits to be designed to prevent feedback from current taking an unintended path, both under ordinary and failure conditions (care should be taken when interfacing with electronic equipment where outputs could be conductive even when nominally de-energised); circuits to be designed to take all transient conditions into account, i.e. concurrent changes in other circuits (care should be taken to consider any fleeting outputs from electronic equipment that could occur under either normal or failure conditions); circuit faults to be self-revealing and rapidly detectable, to reduce the risk of a subsequent fault, in combination with the first fault, leaving the system in an unsafe state; circuit components that do not fail safe (e.g. diodes, relays with non-safety contacts, and electronic flashers), and cannot be otherwise proved, to be used only where a hazardous failure cannot arise; secondary protection, or proving, to be provided for safety-critical functions (even at a lower safety integrity level) such that, if a wrong side failure were to occur, a hazardous event would be unlikely to follow; warnings to the signalman or train driver in the event of a failure of safetyrelated functions; and the use of a probabilistic approach with complex systems. 2.3 Proving Where necessary to reduce risks to an acceptable level, proving should be used to ensure equipment is in a safe state before another operation can be carried out. Proving should automatically disable a potentially conflicting operation. Proving is generally provided for safety-critical functions, as in the following situations, but this list is not exhaustive: to verify the state of trackside and on-track equipment, in accordance with control tables (lamp proving, point detection, etc.); to verify correspondence between outputs from systems duplicated by diversity; to verify that certain safety-critical relays, repeat relays, latched relays, contactors and timers have reverted to the de-energised or released position (down proving); to verify the removal of a bridge path in certain locking levels; to verify that two mutually exclusive safety-critical functions are not operated at the same time (cross proving); D2

45 ailway Group Guidance Note Page D3 of 39 to verify that certain safety-critical events have occurred in the correct sequence (sequence proving); and to verify that certain lever locks are effective (lock proving contacts). The application of proving is considered further in Section Fault Monitoring Where necessary to achieve the required availability level, monitoring should be provided to warn the signalman or maintainer of a failure, by means of an audible and/or visual alarm. The result of monitoring functions that directly affect train operations should be communicated to the signalman as an alarm, but other alarms need only inform the maintainer. Details of interlocking monitoring requirements are given in Part F and the signalman s display in Part L. Where circuit components or cables are duplicated to ensure continued availability in the event of a single failure, a facility should be provided to permit the independent monitoring, either manual or automatic, of both elements, for example disconnection links for duplicated tail cables. 2.5 Maintainability Circuits should be designed to facilitate preventive and corrective maintenance, minimise failure potential and the consequences of failure, and simplify testing, as required in GK/T0206. Where a risk to train operations is presented by the resetting of equipment following a failure, a means of isolation to enable out-of-service resetting and testing by the maintainer prior to restoration by the signalman should be provided, in accordance with GK/T Power Supply Considerations The voltage drop within a circuit should not be sufficient to prevent the circuit operating correctly under all permitted conditions of power supply fluctuation (as stated in GM/T1102), and should, in any case, not exceed 10%. Circuits should be designed to ensure that systems revert to a safe state in the event of a power failure. Where this is impracticable, or there is no safe state, a secure power supply should be provided. Safe state is explained in GK/T0206. Where necessary to achieve the required availability level, the state of safetycritical interlocking functions should be stored by a means that will remain secure in the event of a total failure of all power supplies. Circuits should be designed to prevent an unsafe state occurring during power supply failure or restoration, including momentary loss. Where the state of safety-critical information is not, or cannot be stored, e.g. in the case of electronic interlocking systems, processes should be provided to reset or refresh the system to correspond to the state of the railway before being restored to use. Wherever practicable, circuits should function in their usual manner following power supply loss and restoration without having to be manually reset by a maintainer, unless a safe state cannot otherwise be ensured. See also Part C for power supply requirements. 2.7 Electrical Safety Appropriate measures should be taken to comply with the Electricity at Work egulations D3

46 ailway Group Guidance Note Page D4 of 39 Withdrawn Document The main requirements are as follows: Protection from direct contact. See Section 3.1. Protection from indirect contact. See Sections 3.2 and 6.6, and Part C. Provision of a single earth. See Part C. Use of appropriate equipment. See Section 6 and GK/T0206. Overcurrent protection. See Section 3.3. Ability to disconnect the supply. See Section 3.4. Sufficient working space. See Part G. Competent staff. See GK/T0101. Accurate documentation. See GK/T Circuit Conductors The current carrying capacity of circuit conductors should be adequate for the design, considering its environment, range of ambient temperature, insulation and whether the current is continuous or intermittent. Conductors (including earth and equipotential bonding, where reasonably practicable) should be capable of carrying overload and short circuit currents to survive beyond the time necessary to operate the protective device(s). The insulation should be sufficient to withstand the operating temperature and provide adequate protection against the highest voltages present in the immediate vicinity of the conductor. Conductors are considered further in Part J. 2.9 Circuit Components The continuous and intermittent rating of circuit components should be adequate for the design. Circuit switching devices should be sufficiently robust to make and break the highest current for which the circuit is designed, within its designed life-cycle, without sustaining damage. Components should be capable of carrying overload and short circuit currents to survive beyond the time necessary to operate the protective device(s). Insulation should be effective to enable the equipment to withstand the applied voltage and any likely transient overvoltages. A circuit component that presents a hidden or unexpected danger to staff should have a warning sign affixed indicating the specific danger, e.g. hazardous substance, hot surface, moving parts, etc. Where circuit components are provided with plug-in connectors, measures should be taken to prevent a hazard being caused by a wrong component being plugged in. Components are considered further in Section Electromagnetic Compatibility (EMC) All electrical and electronic systems and equipment should be capable of demonstrating conformity to the following EMC protection requirements, in accordance with the Electromagnetic Compatibility egulations 1992: the electromagnetic disturbance (a.c., d.c. or h.f.) it generates, by conduction or radiation, should not exceed a level allowing other equipment to operate as intended, unless the electromagnetic emission is a stated necessary function of operation; and it should have a level of intrinsic immunity adequate to enable it to operate as intended. D4 It may be assumed that such equipment present in the electromagnetic environment is that which might reasonably be expected to be present. The manufacturer's declaration of conformity and associated Conformité Européene

47 ailway Group Guidance Note Page D5 of 39 (CE) marking should only be used to demonstrate compliance for the particular application and in the particular environment specified by the manufacturer in the instructions supplied with the equipment. Systems and equipment that are assembled from components that individually may, or may not, have CE markings should, nevertheless, be provided with a declaration of conformity and CE marking for the overall configuration. This also applies to existing systems that are altered to such an extent that their EMC characteristics are substantially changed, and to systems that are used in different applications or environments from those specified by the manufacturer. Conformance may be demonstrated by application of experimental European Standards ENV (for the railway system environment as a whole) and DD ENV (for signalling and telecommunications apparatus within the railway system environment). Protection of signalling equipment is required against: direct contact with traction current through rail connections; direct contact with earth or rails through insulation damage; high frequency (h.f.) contamination of power supplies; and induction from parallel a.c. or h.f. circuits; so as to ensure an appropriate level of system safety and dependability and safeguard staff from danger. The application of these requirements is considered in Section 4. 3 Circuit Design for Occupational Safety The Electricity at Work egulations 1989, made under the Health and Safety at Work Act 1974, require both employers and employees to take precautions in respect of electrical systems, equipment and conductors, and activities on or near such equipment. All electrical and electronic systems and equipment are required to comply with these regulations. They may generally be satisfied by following the IEE Wiring egulations (BS 7671). Although BS 7671 is not mandatory for railway signalling equipment, every area of protection addressed therein should be covered, either by compliance with BS 7671, or by providing an equivalent degree of protection. Note that the use of an earth-free supply alone is not recognised as an adequate form of protection from direct contact or indirect contact with live parts. Procedures and training for work on or near electrical equipment are outside the scope of this Guidance Note, but are covered in GM/T Direct Contact with Live Parts All live parts that could present danger to staff should be insulated, or enclosed with external warning signs affixed. Transient and likely fault conditions should be considered in assessing whether bare conductors may be tolerated. See Sections and 4.3. Protection from direct contact is assured by the total insulation or enclosure of all live parts able to be raised to a potential exceeding 25V a.c. or 60V ripple-free d.c., or able to be supplied with a current exceeding 25A. This may be satisfied by the provision of locked apparatus cases, or other enclosures. Where insulation is not reasonably practicable, voltages up to a nominal 110V a.c. or 120V d.c. may be tolerated on open fuses and terminals, provided they are clearly labelled and it can be demonstrated that all persons having access are trained and aware of the dangers. D5

48 ailway Group Guidance Note Page D6 of 39 Withdrawn Document Where insulation is not practicable, the use of enclosures and intermediate physical barriers should be considered in order to prevent or deter unintentional contact with live parts. Such enclosures and barriers (with the exception of portable shields) should be removable only by use of a tool and should carry a permanent warning label. They should be arranged so that the removal of a barrier to permit one work activity will leave other live parts protected. Barriers may be made of transparent material to reduce the need for removal. For further details see Part G Precautions to be Taken in Electrified Areas Danger from a.c. overhead line equipment is addressed in GO/T3087. Danger from induced voltages from parallel a.c. overhead lines should be avoided by following Section 4.3. A special exemption from insulation or enclosure exists for live conductor rails. Danger should be reduced by the provision of warning notices, special training for staff and, where appropriate, barriers. On-track equipment should be positioned such that no lid, or other movable part, can make contact with the conductor rail. Where there is danger to maintainers working on such equipment, precautions should be taken to reduce the risk to be as low as reasonably practicable. The following options are in order of effectiveness: the conductor rail should be gapped; conductor rail protective boarding fitted; or staff provided with portable shields. Further precautions are given in GO/T Danger from Track Cables in Electrified Areas In order to protect staff and signalling equipment in electrified areas from traction voltages under fault conditions, track circuit tail cables should be fully insulated, generally by terminating them on a pair of BS 88 fuse carriers and bases in the lineside apparatus housing nearest to the rail connections. The terminals of all track circuit equipment should be shrouded or enclosed, except when using the safety procedures for work on electrical equipment. Connections to impedance bonds and track circuit capacitors that are not at running rail potential could be charged at a dangerous voltage at any time. A fuse is to be provided in one fuse carrier and a link in the other, as follows. Fuses in both legs would give unpredictable results. Single rail track circuits should be fused in the insulated rail leg. Double rail track circuits should be fused in the leg connecting to the impedance bond winding. For double rail track circuits, a two electrode surge arrestor should generally be provided across the track circuit tail cable (on the external side of the fuse) in the apparatus housing nearest to the rail connections. It should not be connected to earth, unless precautions are taken to prevent a surge creating multiple earth faults. Electrical isolation between track cables and the interlocking environment is desirable. Consequently, track relays and track feeds should generally be confined to lineside locations with repeat relays provided in interlockings. D6

49 ailway Group Guidance Note Page D7 of 39 The requirements of this section (3.1.2) do not apply to track circuits which are coupled to the rails by means of isolating transformers or tuning units adjacent to the track, such as HVI and TI 21 types. Detailed arrangements for individual types of track circuit are given in the Train Detection Handbook, GK/H Danger from Back Electromotive Force (EMF) Inductive loads generate a back EMF when the current is broken, which is usually dissipated through the power supply unit. This applies particularly to AWS inductors, hydraulically powered trainstops and lever locks. Precautions should be taken to guard against dangerous voltages occurring on the cable in the event of the disconnection links being removed. These may take the form of: a reverse biased protection diode for back EMF suppression provided across the external side of the cable terminations; or fully insulated cables terminated on a pair of BS 88 fuse carriers fitted with links. Suitable diodes are as follows: 1A, 400V for standard strength AWS inductors and suppressors, or 6A, 800V for high strength. Details of the protection of electronic devices from back EMF are given in Appendix D2: Safety Equipotential Bonding The purpose of equipotential bonding is to protect against indirect contact with exposed-conductive-parts and extraneous-conductive-parts made live by an electrical fault. Earthed equipotential bonding within apparatus housings is associated with the signalling power supply system and is required where specified in Part C. Equipotential bonding of extraneous-conductive-parts that are not within apparatus housings is associated with external electrical systems, such as traction supply, and is required where specified in Part J. In a.c. electrified areas and where overhead power distribution lines cross the track in non-electrified areas, equipotential bonding provides protection from dangerous touch potentials appearing between adjacent metalwork (and rail connections) in the event of a fault on the high voltage system. The connection of equipotential bonding to the traction return system facilitates the automatic disconnection of the traction supply if damaged overhead lines should make contact with structural metalwork. However, in d.c. electrified areas, a greater danger would arise from large traction currents flowing to earth via the equipotential bonding, which consequently is not provided. 3.3 Overcurrent Protection An overcurrent protective device should be provided for each circuit or group of circuits, of sufficient rating to prevent damage from the current carrying capacity of a circuit conductor or circuit component being exceeded under failure or overload conditions and, where applicable, to make safe any exposedconductive-parts or extraneous-conductive-parts made live by an electrical fault. Indirect contact protection is considered further in Part C. Protective devices should be selected by considering the following characteristics: D7

50 ailway Group Guidance Note Page D8 of 39 Withdrawn Document nominal current of the device; speed of operation and sensitivity, depending on the type of load, e.g. highly inductive, starting or in-rush currents, or electronic equipment; voltage rating; discrimination between successive stages of protection (see Part C); suitability for the railway environment; reliability; whether fuses or circuit breakers; whether a monitoring facility is required; whether required to be enclosed to provide protection from direct contact (see Section 3.1); whether required to provide disconnection facilities, e.g. fuse switches, (see Section 3.4); and whether required to provide isolation facilities, e.g. locking off, (see Section 3.4). The nominal current of the device should be chosen to be greater than the design load of the circuit, but less than the current carrying capacity of the circuit conductors. This will ensure operation of the device before the conductors are exposed to a current greater than they can safety withstand (generally accepted as 1.45 times their current carrying capacity), or the insulation is subjected to an unacceptable rise in conductor temperature. The design load should include any foreseeable peak load of a protracted nature. Where this excludes anticipated transients, such as motor starting currents or transformer inrush currents, it may be necessary to use reduced sensitivity or slow operation devices to avoid nuisance tripping. The infrastructure controller should be informed of any measures taken to avoid nuisance tripping and an appropriate note should be made on the design details. It should also be ensured that the current rating of each circuit component is greater than the nominal current of the device. Overcurrent protective devices should generally be provided in all non-earthed legs (only) of final circuits. However, for supplies with no earth connection that do not exceed 120V, protective devices may be provided in one leg only. For non-earthed supplies, it should be recognised that there is a risk of a return circuit conductor in an unfused leg of a low current circuit being unprotected, in the event of a double earth fault allowing a fault current from an adjacent high current circuit to flow in it. All branches of a circuit (including both branches of a ring feed) should be connected to a single overcurrent protective device. Where practicable, every feed (phase BX, or positive B ) device or terminal should have a corresponding return (neutral NX, or negative N ) terminal or device. Overcurrent protective devices should be arranged so as to minimise potential disruptions to train operations in the event of a fault. Discrimination between successive stages of protection should therefore be arranged, as described in Part C. The standard arrangement for signalling circuits is given in Appendix D1. D8

51 ailway Group Guidance Note Page D9 of Isolation and Emergency Switching Where necessary to prevent danger, each circuit should be capable of emergency on-load switching and isolation (fixing off). Emergency switching is a means of de-energising a circuit to prevent danger from operating equipment or from electric shock. (Overcurrent protective devices are not generally suitable for on-load switching, unless specifically designed, e.g. fuse switches.) isk of danger with respect to emergency switching may be considered to be acceptably low if: the electrical equipment has no moving parts that could cause danger; and there are no bare conductors in the circuit over 25V a.c. or 60V ripple-free d.c., or carrying over 25A. Isolation is a means to allow work in safety, e.g. by locking off. Isolation facilities may be omitted if all the following apply: it is unreasonable for the equipment to be disconnected to allow work to take place; it is reasonable for work to be undertaken on the live conductors; and suitable precautions, such as protective equipment and/or permit to work, will be available. Emergency switching and isolation devices should be clearly labelled, and their accessibility should be appropriate to the risks involved. Emergency switching and isolation facilities may be combined, and may be common to several items of equipment where it is appropriate for them to be energised and de-energised as a group. In practice, lockable 650V fuse switches will generally satisfy both these requirements for each individual apparatus case. For further details see Part C. 4 Circuits (General) Except where stated otherwise, the following requirements should be adopted for all new installations irrespective of the type of traction present, and also apply to non-safety-related circuits: 4.1 Electromagnetic Compatibility (EMC) Measures should be taken to prevent false operation of circuits arising from interference from any source. The most common sources and preventative measures are listed in Figure D1. Note that any CE marking on manufactured equipment only demonstrates conformity to the EMC protection requirements for the particular application and in the particular environment specified by the manufacturer. 4.2 Internal Circuits Internal circuits should be designed to minimise the length of wire runs between relay contacts. Internal circuits do not require to be double cut because they are fed from a separate internal supply, thus rendering them significantly less susceptible to earth faults. Where an external supply is used to feed circuits that would otherwise be internal, they should be treated as line circuits and should comply with Sections 4.3 and 4.5. D9

52 ailway Group Guidance Note Page D10 of 39 Withdrawn Document Interference Source Preventative Measures eference Traction current the use of traction immune signalling equipment, such as see the equipment contamination point machines, track circuits and relays. parts of this Code of feeds to on-track circuits that are not susceptible to contamination by the type of traction interference likely to be present, i.e. a.c., d.c., coded or audio frequency. Practice Induction from parallel the use of d.c. feeds and a.c. immune relays for external see Section 4.3 a.c. or high frequency circuits circuits (except for circuits to trackside and on-track equipment in d.c. and dual electrified areas). limiting the length of through connected conductor parallel to the railway, such that the maximum induced current would be insufficient to operate any a.c. circuit. limiting the length of signal lamp circuits parallel to the see Section 4.4 railway, such that the maximum induced current would be insufficient to light a lamp. Earth faults double cutting of all external safety-critical circuits. see Section 4.5 separate power supplies for certain groups of circuits. see Part C earth fault monitoring on vulnerable power supply busbars. High frequency keeping leads to electronic equipment as short as see Appendix D2 contamination of practicable. electronic systems segregating systems capable of mutual interference. providing special cables, such as twisted pair or screened. using highly coded systems for safety-critical applications. prohibiting the use of radio transmitters or mobile telephones, etc., in the vicinity (with warning notices). Electrical surges, such as fast transient earths. see Appendix D2 lightning strikes, flashovers from the traction supply and switching transients, affecting solid state components Magnetic interference between low current devices surge suppressors (not connected to earth unless the system is coded to prevent multiple earth faults). moving iron relays and indicators not to be placed in close proximity where the magnetic field generated can affect an adjacent device. see Section Figure D1 Protection Against Electromagnetic Interference Circuits between adjacent buildings and/or apparatus cases and under signal box lever frames may be treated as internal, provided that measures are taken to sufficiently reduce the risk of earth faults, e.g. by use of a protective nonconducting duct. Isolating transformers, including converters, may be used in the feed to individual on-track or line circuits to reduce the need for earth fault detection and double cutting, as the circuit on the primary side of the transformer is effectively an internal circuit. Where components of non-safety-related circuits are particularly susceptible to earth faults, such circuits should not share a common power supply with safetycritical circuits. 4.3 Line Circuits and Lineside Cables All relay line circuits for new installations should be for d.c. operation to allow maximum immunity to a.c. interference. The standard arrangement should use 50V d.c. The physical length of line circuits is limited by the following considerations: D10

53 ailway Group Guidance Note Page D11 of 39 the external effect of resistive, inductive and capacitive links with other circuits; restricting induced voltages from any adjacent high voltage a.c. line, including any parallel overhead power distribution line, to ensure the safety of staff (see Section 3.1); prevention of induced voltages under traction fault conditions from exceeding 430V a.c. and thus preventing false operation of an a.c. immune relay; and keeping the line circuit voltage drop within acceptable limits, particularly where biased relays are used on polarised circuits, allowing universal use of 0.75mm 2 multicore cable. Note that an a.c. traction fault current of 5,500A for 200ms may be considered as a maximum. A length of through connected conductor parallel to the line not exceeding 2,000m will generally satisfy these constraints. Where necessary, line circuits should be terminated within the length limit and intermediate repeater circuits created. However, in special cases in a.c. and dual electrified areas, including sites where traction booster transformers and return conductors are not used, or where the cable route is elevated, calculations will be required to verify the maximum length of through connected conductor to ensure staff safety. Any proposal to exceed 2,000m should be subject to documented risk assessment. For the use of polarised circuits, see Section 7.6. Similarly, loop inputs to electronic devices, such as Solid State Interlocking (SSI) trackside functional modules (TFMs), should feed an absolute maximum distance of 2,000m (4,000m loop). Further considerations are given in Section Where a common power supply feeds line circuits in more than one direction, the maximum length should be applied to the distance between the extremities of circuits fed from the one supply. Consequently, consideration should be given to providing separate power supplies for the groups of line circuits feeding in the up and down directions. Precautions necessary with remote control systems are described in Appendix D2. When determining the degree of protection necessary from direct contact with live parts, the induced voltages from normal traction load should be considered. If such voltages are likely to exceed the values stated in Section 3.1, it may be necessary to shroud any exposed terminations. 4.4 On-Track Circuits General The maximum voltage at which on-track equipment is fed should be commensurate with the degree of protection that it is practicable to afford to ontrack tail cables. A supply not exceeding 120V nominal will satisfy this limitation. Signal and indicator lighting circuits are not required to be double cut, as partial earth faults would be insufficient to illuminate a lamp. However, two wire feeds generally are double cut, as this is easily provided. Immunisation of AWS equipment should be provided by individual isolating transformer rectifiers. Circuits to other track mounted equipment, such as point detectors, switch heaters, insulated track circuit interrupters, treadles and ground frame lever contacts and locks, are particularly susceptible to earth faults and to traction interference. This also applies to other on-track circuits, such as first filament failure proving, plungers and switches, where the tail cables cross the tracks at D11

54 ailway Group Guidance Note Page D12 of 39 Withdrawn Document ground level. Double cutting should be provided for all such circuits that are classified as safety-critical. Separate supplies may also be of benefit, unless the on-track supply is equipped with earth fault detection. For further details of circuits associated with particular equipment, see the appropriate parts of this Guidance Note. On-track relay circuits should be fed from a 50V d.c. external supply in conjunction with a.c. immune relays, except in d.c. electrified areas, where a 110V a.c. supply should be used to feed a.c./d.c. converters (adequately isolated and protected against capacitive coupling) connected to relays which may be non-immune. A dual immune system, such as reed or SSI, should be used in dual electrified areas. For line circuits see Section 4.3. The requirements of this section (4.4.1) are not mandatory for non-safety-related functions, such as switch heaters, first filament failure proving, and TTS and CD plungers, provided they are not fed from a power supply feeding safetyrelated functions Maximum Lengths of On-Track Circuits The distance between a signal and its signal control relays (or TFM), parallel to the line, is limited by the following considerations: limiting induced voltages from any adjacent high voltage a.c. lines, including any parallel overhead power distribution line, to a level that will be inadequate to illuminate the lamps; restricting induced voltages from any adjacent high voltage a.c. line, including any parallel overhead power distribution line, to ensure the safety of staff (see Section 3.1); keeping the voltage drop within acceptable limits using 0.75mm 2 cable; reducing electromagnetic interference in electronic circuits (see Appendix D2:6); and facilitating testing and maintenance. A length not exceeding 200m will generally satisfy these constraints, except for signals fed at low voltage d.c. Exceptionally, in non-a.c. electrified areas, longer circuits may be used, subject to voltage drop, to feed into tunnels or along viaducts, or in other situations that are particularly expedient. Such arrangements where on-track circuits exceed 200m should be subject to documented risk assessment. In a.c. and dual electrified areas, where a common power supply feeds more than one signal, the maximum length should be applied to the distance between the most remote signals fed from the supply. The considerations applicable to other types of on-track equipment are given in the appropriate parts of this Guidance Note. Whilst the absolute maximum lengths for relay circuits and loop inputs to electronic devices are considered in Section 4.3, when these are connected to trackside and on-track signalling equipment, the considerations of this section (4.4.2) are applicable and any circuits exceeding 200m should be subject to documented risk assessment. 4.5 Double Cutting The following should generally be double cut: all safety-critical line circuits in their entirety. D12

55 ailway Group Guidance Note Page D13 of 39 all safety-critical on-track circuits in their entirety, except for signal lighting. This includes external loop inputs to electronic devices and their external outputs. any other circuit fed from a power supply that feeds either of the above. This is because signalling circuits are susceptible to earth faults, due, for example, to mechanical damage or insulation degradation permitting contact with a relay rack, lever frame, apparatus case body or running rail. As signalling supplies are not generally earthed, two earth faults would be necessary to create a hazardous failure, e.g. by bridging out contacts, although the first fault could go undetected. By duplicating contacts in both legs of a circuit, four faults would be required to cause such a failure (and these faults would probably short circuit the supply and disable the circuit). This precludes the use of common returns for safety-critical line circuits. Earth returns should not be used for new installations, nor under any circumstances in electrified areas. Where practicable, contacts of the same relay should be used in each leg of the circuit in order to double cut. Where different relays are used in each leg, for consistency the first relay to operate and release should be placed in the feed leg. (For polarised circuits see Section ) The requirement to double cut does not apply to: contacts used solely to impose non-safety-related controls on safety-critical circuits; back contacts used solely for down proving; back contacts used solely for cross proving; contacts used solely for correspondence proving; contacts used solely to economise power consumption; contacts on the internal side of an isolating transformer, or transformer rectifier, feeding external circuits (see Section 4.2); signal lighting circuits (see Section 4.4); internal circuits on a dedicated power supply (see Section 4.2); non-safety-related circuits on a dedicated power supply; nor to systems that use alternative equivalent measures to mitigate the risk of earth faults, such as earth fault disconnection devices. 4.6 Further Measures to Address Earth Faults Further details on the requirements for separate power supplies and earth fault monitoring are given in Part C. 5 Circuit Conductors 6 Circuit Components Cables and wiring should be in accordance with Part J. 6.1 elay Types Generally, only 930 series plug-in relays (see GK/T0330 and GK/GN0630) are available for new work, but exceptions include: specialised applications where no 930 series relay provides the required facility, e.g. double element track relays, flashers and timer relays (see Section 8); or non-safety-related uses. Wherever practicable, relays should be mounted in 930 series cases and allocated a unique pin code by ailtrack S&SD. D13

56 ailway Group Guidance Note Page D14 of 39 Withdrawn Document elays for the control of signalling functions should generally be for 50V d.c. operation, except for track relays, lamp proving relays (which are current operated) and relays associated with the control of level crossings (which may operate at 24V d.c. to simplify the provision of secure power supplies). All relays fed from an external 50V d.c. supply should be a.c. immune. Nonimmune relays may be used on internal circuits where a separate supply is provided, but, in new installations, a reduction in the variety of relays in use should be considered by the use of a.c. immune relays for both internal and external circuits. The following is a complete list of standard a.c. immune relays (excluding track relays): Style Description 931 Neutral Line elay 932 Biased Neutral Line elay 933 Slow Pick-Up Neutral Line elay 934 Slow elease Neutral Line elay 943 Biased Contactor elay 961 Twin Biased Neutral Line elay Unit 966 F4 Biased Contactor elay 966 F6 Twin Neutral Line elay Unit elays manufactured to these specifications should be immune up to 1,000V a.c. Point detection circuits for new installations should generally use four wire d.c. circuits with biased relays (see Section 7.6), except in d.c. and dual electrified areas. See Part P for further details. Circuits should be designed so that the relays specified may be obtained from any manufacturer. Where certain attributes, such as coil resistance or operating times, are not given in the relay specification, care should be taken to ensure that the circuit characteristics cannot be adversely affected by changing a relay for one from a different manufacturer. See Sections 7.5, 8.3 and 8.4 for examples Shelf-Type elays Shelf-type relays are not generally available for new work, although they may be necessary in association with battery supplied block circuits. Shelf-type relays should be mounted in a stable manner to resist vibration and prevent falling. To prevent magnetic interference, low current devices, such as moving iron relays, should not be mounted back to back, nor placed within a relay space apart. The terminals of shelf-type relays should be fully shrouded to reduce their vulnerability to false circuit operation. See Section Double Element A.C. Vane elays (BS 561 or BS 1745) Local and control (or track) coils should always be fed from the same power supply point, as it is essential that their relative phases remain constant. Vane relays operating at 83 1 / 3 Hz provide immunity in a.c. and dual electrified areas. In this situation the local coil is fed from a separate supply obtained from a converter which is linked in a fixed phase relationship with the main supply. D14 Double element 50 Hz track relays for use with a.c. track circuits may be used to give immunity in d.c. electrified areas. Detailed arrangements for individual types of track circuit are given in the Train Detection Handbook, GK/H0751.

57 ailway Group Guidance Note Page D15 of 39 Three position vane relays may be found providing immunity on polarised point detection circuits, but are not generally available for new work Flasher Units The following flasher units are suitable for safety-critical applications, provided they are wired in the configuration intended by the specification: specification B 901 for level crossing road lamps; and specification B 991 for signals with flashing aspects, or signal passed at danger (SPAD) indicators. Pulsed supplies to operate ratchet impulse timers (see Section 8.2) should be provided to safety-critical integrity, e.g. by using duplicated and monitored pulse generators. Flasher units providing supplies to operate flashing panel indications should be duplicated where necessary to give the appropriate level of safety and availability. Signalman s display systems are safety-related, but maintainer s panels are generally non-safety-related. 6.2 elay Contacts Polarity For new installations, the following convention should be applied to the wiring of relay contacts, in both the feed and return legs of circuits. Other conventions can be found in some existing installations. D.C. feeds over relay contacts (except for heavy duty contacts of 943 and 966 F1, F4 & F5 style contactors) should be standardised, so that the fixed spring which carries the carbon contact is positive with respect to the moving spring carrying the silver contact. On 930 series relays the fixed spring has an odd number (A1, B1, etc.) for front contacts and an even number (A8, B8, etc.) for back contacts. A similar arrangement should be used for a.c. circuits. The 943 and 966 F1, F4 & F5 style contactors have permanent magnets fitted adjacent to the heavy duty contacts in order to suppress the arc. It is essential, therefore, that they are always wired in parallel such that the current flows in the following sequence: Positive supply - connectors C1 & C2; Connectors C3 & C4 - load - connectors C5 & C6; Connectors C7 & C8 - negative supply. Internal wiring loops are provided between each pair of connectors. In order to reduce the current flowing through the connectors, external connections should always be made to both connectors (in a ring configuration so that the current carrying capacity of the conductor is not exceeded), with a loop between them ating The 930 series metal to carbon relay contacts will make or break an unquenched current representing a load of three 930 series relay coils. They should not be used to break higher currents, such as d.c. lever lock circuits, unless a spark quenching device is in use. If such circuits can be designed to be broken under ordinary operation by higher rated devices, such as lever or economiser contacts, rather than relay contacts, it is permissible to use 930 series relay contacts up to their continuous rated value of 3A. Another situation where a 3A rating is appropriate, is where it is unlikely that the contact will break the circuit, e.g. the (PO)J contact in Figure D2. Medium duty contacts (elkonite or metal to metal) are generally designed to carry 6A continuously for lamps, subject to individual relay specifications. For example, each medium duty back contact of a 966 F3 style relay will supply a D15

58 ailway Group Guidance Note Page D16 of 39 Withdrawn Document maximum of one 50W halogen lamp unit, as used in level crossing road traffic signals. Metal to carbon contacts may be used to break such a load, but should not make the circuit, unless there is a series component, such as a EC coil, to reduce the surge current. The 943 and 966 F1, F4 & F5 style heavy duty contacts will make or break a point operating mechanism circuit passing up to 30A (for a limited number of operations during the service life of the contactor). The operating circuits should be protected by overcurrent protective devices rated at a maximum of 15A Minimum Voltage The 930 series relay contacts should not be used where the applied potential is less than a nominal 24V since high resistance contacts are likely to develop, except to feed 12V signal lamps, as in this case the current is relatively high and the load largely non-inductive Contact esistance Circuit design should generally restrict the number of relay contacts wired in series to a maximum of twenty. However, this may be increased to a maximum of thirty in certain special applications, such as push button ring proving circuits, provided that calculations are made to ensure that the voltage drop across all the series contacts leaves an adequate voltage to operate the circuit. A nominal worst case resistance of 7Ω per relay contact should be used in this calculation. Where there is no other practicable solution, e.g. in geographical relay interlocking systems, contacts of the same relay may be wired in parallel Non-Safety elay Contacts Non-safety relay contacts should not be used for safety-critical or safety-related purposes. However, they may be used in safety circuits for non-safety-related purposes, provided that no failure mode of the contact, i. e. open circuit, closed circuit, earth fault, or false feed from another circuit, would give rise to a hazardous failure of the safety circuit. This may be achieved by grouping all non-safety contacts at the power supply ends of a circuit so that no failure mode could enable a false feed to bypass safety contacts. (Application to the positive or negative end of the circuit will give equal protection.) Alternatively, the non-safety contact can be used to drive a safety relay and contacts of that relay used in the controls. 6.3 Switching Devices When a switch, plunger, or microswitch is required in a safety-critical signalling circuit then the mechanical construction and possible failure modes of the device should be considered to ensure that an acceptable level of safety is achieved. Microswitches cannot be relied upon to fail in a particular position and so require cyclical back proving and back-up duplication, as used on point detection. See Part P for details. Any switching devices that do not fail safe, and cannot be otherwise proved and/or duplicated, should be treated in accordance with Section Where untrained persons have access to switches or plungers, full protection against direct contact (see Section 3.1) and indirect contact (see Part C) with live parts should be provided. D Converters Generally available 12V/50V d.c./d.c. or 24V/50V d.c./d.c. converters will simultaneously feed a maximum of six 930 series relays, but, due to a thermal cut-out, they should not be used for safety-critical circuits requiring sequential operation, such as line clear or route releases, where an automatic restoration of supply could lead to a hazardous failure. The pin codes are pc 106 or pc 229

59 ailway Group Guidance Note Page D17 of 39 (12V) and pc 186 (24V). They are used to feed 50V relays from secondary cells. Converters used for 110V/50V a.c./d.c. or 110V/24V a.c./d.c. should give adequate isolation and immunity to inter-cable capacitance up to 1µF. 'QX1' style models, pc 6015 (50V) and pc 6011 (24V) comply and will feed one or two 930 series relays. See Section 4.4 for their use with on-track circuits. elay contacts should be positioned on the appropriate side of converters and transformer rectifiers: on the primary side: where necessary to avoid excessive wear from back EMF, or to avoid double cutting external circuits; or on the secondary side: where necessary to obtain an immediate cut-off, or to enable one unit to feed several circuits. 6.5 Other Components When some other device is required in a safety-critical signalling circuit then the possible failure modes of the device in the particular application (open circuit or closed circuit, etc.) should be considered. The consequences of such failure should be examined by a fully documented process of risk assessment to ensure that an acceptable level of safety is achieved. For example, note the restrictions placed on equipment with thermal cut-outs in Section 6.4. Any devices that do not fail safe, and cannot be otherwise proved, should be treated in accordance with Section Where practicable and where an improvement in reliability will result, the device should generally be rated higher than the working requirement. Wherever practicable, special units should be mounted on 930 series bases and allocated a unique pin code by ailtrack. 6.6 Double Insulated Equipment Where it is not reasonably practicable to achieve an earthing system that is sufficient to make safe, by automatic disconnection of the supply, any exposedconductive-parts or extraneous-conductive-parts made live by an electrical fault (see Part C), then class II, double insulated, equipment should be provided. This will ensure that a single fault cannot cause a dangerous exposed potential. Class II equipment, by definition, should not be earthed and an associated earthing terminal should not be provided. Socket outlets should not be included in class II systems and warnings should be provided on the design details to prevent the connection of any equipment other than class II. Where it is impracticable to obtain class II equipment, supplementary insulation of an equivalent standard may be applied on site, provided the degree of safety achieved can be verified by testing. Where class I and class II equipment is mixed within an electrical system, Part C should be followed with regard to the provision of an earthing system. All newly specified trackside and on-track equipment should be double insulated. Existing designs of signalling equipment should comply with this requirement from their next revision. D17

60 ailway Group Guidance Note Page D18 of 39 Withdrawn Document 6.7 Component Terminals Components should be chosen with terminals that are capable of securely terminating up to two conductors of sufficient size to carry the design load of the circuit. The terminals should be fully shrouded in the following circumstances: where they are vulnerable to items being dropped on them that could cause false operation of the circuit (especially applicable to terminals on horizontal surfaces); or where the likely exposed voltage could present a danger to staff (see Section 3.1). A suitable note should be added to design details. 7 elay Logic Circuit Techniques 7.1 Meshed Circuits Where meshed circuits feeding more than one relay are necessary, they should be kept as simple as reasonably practicable. Circuit design should ensure that the relays cannot be falsely energised by means of an unintended path, or as a result of a circuit disconnection. Measures to prevent feedback are described in Section Complex meshed circuits should not be used, because of the extra work involved in testing and corrective maintenance, unless their suitability can be demonstrated by documented risk assessment and approved by the infrastructure controller. Such circuits in geographical relay interlocking systems are risk assessed as part of the system approval. Note that each path in a meshed circuit should be fed from the same overcurrent protection device. Further considerations for changeover paths in meshed circuits are given in Section Power Supply estoration Special measures are required in certain situations to retain the stored information in the event of a power failure. A contact of a power off timer relay, (PO)J, set at 5 to 10 seconds, should be included in safety-critical stick circuits that use back contacts of track repeat relays, to allow the slow to operate relays time to operate after a total power failure. See Figure D2. Contacts should also be used where power up transients would cause a confusing display to the signalman, such as with point route lights. 7.3 Stick Circuits The stick circuit is used in relay logic where the condition(s) required to switch a relay from the de-energised state to the energised state are not the converse of those which are to switch it from energised to de-energised. It can thus be used to store information or remember a previous occurrence. Disengage Controls Pick Up Controls Hold Up Controls S S (PO)J Where Necessary (Section 7.2) Figure D2 Stick elay Circuit D18

61 ailway Group Guidance Note Page D19 of 39 The circuit consists of a relay wired with a parallel path, known as the stick path, that contains a front contact of the same relay, the stick contact. This path is capable of holding up, or sticking up, the armature, but cannot pick it. The circuit is illustrated in Figure D2. Note that both paths in a stick circuit should be fed from the same overcurrent protection device. Further considerations for changeover paths are given in Section Bridge Paths These are in some respect similar to stick paths except they operate in the opposite way, allowing a relay to energise without proving a particular function, but then de-energising to ensure the function concerned is proved before further levels of locking are considered. Where it is necessary to by-pass standard control contacts in circuits, e.g. for complex swinging overlaps, circuit design should ensure that such bridge paths are broken before the signal can clear, and that a circuit disconnection, or the failure of a relay to energise, would not cause a hazardous failure. 706 ZLP 506 NL 506 L DG(UP) US 707 OA 707 C Bridge Path DG(UP) US 506 G Figure D3 Bridge Path Used for Swinging Overlaps The situation can be protected against by ensuring that the bridge path has been removed before the next level of locking can be achieved. The most convenient way of doing this is to down prove a function in the bridge path in the next level of locking. If necessary it is perfectly acceptable to introduce a function into the bridge path purely for this purpose. This is illustrated in Figure D3. (The signalling plan for this example can be found in Appendix F5.) 7.5 Latched elays Latched relays may be used to store the state of signalling functions in a way that will remain secure in the event of a total failure of all power supplies. The relay has two coils (operate and release) and remains secure in each state until specifically driven to the other state. This security is achieved magnetically. In fact the relay will operate if both coils are energised and will only release when the operate coil is de-energised. (Magnetic stick relays serve a similar purpose, but have two polarised operating coils, so that, when they are wired in series, the armature is driven to a state that is dependent on the direction of the current.) Pairs of latched relays may be either mechanically or electrically interlocked to prevent both relays being operated at the same time. They may thus be used as lock relays to lock a signalling function in the normal or reverse state. Both relays should be released, or unlocked, to allow the function to change state. A typical electrically interlocked configuration is shown in Figure D4. Applications are given in Part F. Note that it is essential for controls (generally the signalman s request conditions) to be provided in the negative legs of the circuit to prevent a backfeed through a common return from falsely unlatching a relay (see Appendix D1:3). D19

62 ailway Group Guidance Note Page D20 of 39 Withdrawn Document Normal Controls L Unlock Controls NL Normal Controls everse Controls NL Unlock Controls L Figure D4 Typical Circuit for a Pair of Lock elays everse Controls The only relays generally available for new work are magnetically latched 935 style relays. Circuits that require latch relays to latch up over their own back contacts should not be used, because that feature is only available with certain manufacturer s relays and is additional to the requirements of the specification. Designers should ensure that maintainers are warned, when changing relays, to observe that the replacement is in the correct state before plugging in. 7.6 Polarised Circuits Pairs of biased relays (two 932 style relays or a 961 style twin relay) may be used to save cable cores on line circuits. Two wire circuits should generally be used for new work. However, in existing installations, and where the voltage drop would otherwise be excessive, particularly where the standard form of cross proving (described in Section 9.2.3) presents an energising load of two relay coils in parallel, three wire circuits (using separate feeds and a common return) may be found. Details of the relay end of the circuit are given in Section 9.2.3, intermediate repeaters in Section and the feed end in Section Time Delays 8.1 Timing Circuit equirements Time delays are required in electrical circuitry for a variety of reasons. Each application has different requirements with regard to: time delay (150ms to 24 hours); safety integrity; whether slow to operate, or slow to release (or both). Safety-related applications should distinguish between requirements for delayed operation and delayed release, so as to prevent any premature de-energisation causing a hazardous failure: If a function must not operate until after a given time has elapsed, this should be effected by the front contact of a device with delayed operation. If a function must cease to operate before the expiry of a given time, a front contact of a device with delayed release should be used. D20

63 ailway Group Guidance Note Page D21 of 39 Safety Integrity Application Category Safety-elated To release safety-critical controls in accordance with control tables, giving time for a train to reduce speed or come to a stand, such as in the timed release of approach locking, approach release of signal aspects, and release of route locking with a train at a stand, or overlap locking in front of a train. See Appendix F2 for examples. Operate after time (delayed operation) Non-Safety- elated Similarly, to provide a safety margin, e.g. when giving a manual release, slow to pick route sticks, and performing auto normalisation of points or other automatic working. To give other equipment time to operate, e.g. delaying the release of a signal protecting a level crossing. To reset functions that have not completed their operation within a due time, such as resetting an automatic level crossing. To reset functions that have not completed their operation within a due time, such as replacing signal aspects if a swinging overlap does not complete its operation, or a flashing aspect in rear has not been proved to flash. To momentarily delay the response to a change of state to give other equipment time to respond first, e.g. to avoid momentary loss of train detection when a vehicle moves from one track circuit to another, or where information is transmitted by different speed systems, or to protect circuits following a power failure. See Section 10.2 for further details. To overcome timing problems in relay logic circuits. For example, a relay may be required to hold up while its feed changes over from one path to another. See Sections 8.4 and To create a sequence of operations, as in the level crossing barrier operating sequence. See Part X. To reset functions that have not completed their operation within a due time, such as preventing panel push button circuits from locking up. To reset functions that have not completed their operation within a due time, such as preventing points from overrunning. To give the signalman time to respond, e.g. in the operation of NX push buttons, or the timing of short audible alarms. Long interval timers for non-safety-related applications, such as operating point heaters for a predetermined time. Figure D5 Typical Timing Applications operate after time (delayed operation) operate after time (delayed operation) operate after time (delayed operation) cease before time (delayed release) operate after time (delayed operation) operate after time (delayed operation) cease before time (delayed release) cease before time (delayed operation) cease before time (delayed release) cease before time (delayed release) cease after time (delayed release) Back contacts of timing devices should not be used to operate safety-related time-dependent circuits, unless no additional risk could be created by any foreseeable failure of the device. These requirements do not apply to non-safety-related uses, so, for instance, a point operation timer can use a back contact of a non-safety timing device. Some of the most common applications are given in Figure D5. Safety-critical applications of conventional (slow to operate) timers should generally be down proved as stated in Section 9.1, but see Section 8.2 for exceptions. Timers used in certain level crossing applications should always be down proved, where required to enhance the safety integrity (see Part X for details). Where timers have insufficient back contacts, a repeat relay may be used as the primary function relay (see Section 10.5) for all timing and down proving requirements. Appendix F2 describes how down proving is applied to track circuit timers. D21

64 ailway Group Guidance Note Page D22 of 39 Withdrawn Document The method of initiating the timer is another consideration, especially when there are several repeat relays (see Section 10.5). A timer relay used for track circuit occupied application (TJ) should be controlled by a back contact of the track circuit primary function relay (usually the TP) wherever practicable. If there are none available, front contacts of the T2PZ, or T3PZ, etc. may be used. (The PZ nomenclature is explained in Section ) A timer relay used for track circuit clear application (TZJ) should be controlled by a front contact of the track circuit primary function relay (usually the TP) wherever practicable. If there are none available, front contacts of the T2P, or T3P, etc. may be used. 8.2 Types of Timing Device Timing devices for use in safety-critical applications should be chosen from the following: Slow to operate or slow to release relays (neutral d.c. relays with a built in copper slug) increase the operate time by 400ms (933 style relay) or the release time by 250ms (934 style relay). The 963 style twin relay increases both times by 150ms. Slow to operate devices are not required to be proved down as timer relays, but only when required to prove the sequential operation of the interlocking in accordance with Section 9.4. atchet impulse timers (slow to operate) may be used where a pulsed supply is available (see Section 6.1.3). Thermal timers (slow to operate) are not appropriate for new work as they are susceptible to voltage fluctuation and overheating, and the timing varies with repeated operation and changes in ambient temperature. (Economising contacts should be used to prevent any operation that is not required, e.g. a timer should not operate for every passage of a train if it is only required when a particular route is set.) Synchronous motor timers (slow to operate) require a 110V supply and a secure 50V supply. Commercially available timers (either slow to operate or slow to release) may be used if there is no other practical solution, e.g. Agastat 24V timers for level crossing applications. (However, if employed in a safety-critical or safety-related circuit, the timers should be duplicated and their contacts wired in series.) Capacitor/resistor networks (slow to release) are described in Section 8.3. The 946 style relay includes a dedicated capacitor/resistor network and voltage regulator within the casing, for use in level crossing applications with a 24V battery supply. Electronic timers are available as direct replacements for many of the above types of timer. Where so determined in the approved safety case, they do not require down proving. 8.3 Capacitor/esistor Network The simplest form of slow to release device is obtained by delaying the release time of a conventional relay. The time taken for a relay to drop may be increased by providing a capacitor (C farads), in series with a resistor (r 1 Ω), in parallel with the coil. The capacitor is charged by the supply until the circuit controls are de-energised, at which point the capacitor discharges through the relay coil, holding up the relay for a further time. The time delay (t sec) is given by the formula: t = -C(r 1+r 2) log e (V/E) where E is the supply voltage; V is the relay drop away voltage; r 2 is the resistance of the relay coil in Ω; and log e means logarithm to the base e. D22

65 ailway Group Guidance Note Page D23 of 39 The tolerances associated with each element in the formula may result in the maximum time delay being up to three times the minimum. The capacitor should be electrolytic and rated at (say) 100V. If intermediate values are required, capacitance may be added by connecting capacitors in parallel. A typical circuit is shown in Figure D6. Controls β α Figure D6 r 1 Ω C δ r 2 Ω Typical Arrangement The potential across the capacitor when fully charged is dependent on the type of power supply. For instance, a ripple-free 50V d.c. supply (either smoothed or from a battery) will charge the capacitor to 50V. However, a 50V supply obtained directly from a transformer/rectifier is in the form of a rectified sine wave with a peak value of 70V (to give a root mean square value of 50V). Consequently, the capacitor will charge to 70V. A diode (δ) should therefore be provided in the capacitor feed path where the 50V busbar is fed from a transformer/rectifier, in order to prevent a back feed from the capacitor raising the busbar voltage. However, a diode should not be used where a.c. immunity is required, including any circuit fed from an external 50V supply. The resistor (r) is generally situated in both the charge path and the discharge path. It is necessary when charging because a fully discharged capacitor would otherwise effectively present a short circuit to the supply. A resistor of minimum value, say 150Ω, will limit the charging current and prevent the overcurrent protective device from operating. For a ripple-free supply, r should have a minimum value of 150Ω, whereas, for a rectified supply: (r 1+r 2)/r 2 = 70/50, i.e. r 1 = 0.4 r 2. This is because the resistor serves to divide the potential of the fully charged capacitor in the discharge path between itself and the relay coil, in the ratio of r 1 to r 2. The resistor (r 1) should be suitably rated to carry the maximum charging current (say 50W). Note that the recharge time is proportional to the value of the resistor. Where a dangerous situation would result from the capacitor discharging and momentarily picking up a de-energised relay, due to the clearing of a possible high resistance fault on the capacitor path, a precaution should be taken by adding a front contact (marked α on Figure D6) of the relay in series with the capacitor/resistor. If the relay is only re-energised for a short time before it is required to drop again, the capacitor should be recharged by connecting it to the supply with a back contact (marked β on Figure D6) of the relay, in conjunction with the front contact (α) between the capacitor/resistor and the relay coil. Care should be taken to specify the use of relays whose coil resistance does not vary from manufacturer to manufacturer. Any variation in coil resistance should not be capable of affecting the time delay (nor the discharge voltage across the relay coil) by more than the permitted tolerance for the application concerned. Examples of useful configurations for 50V operation are given in Figure D7. D23

66 ailway Group Guidance Note Page D24 of 39 Withdrawn Document elay Style or Coil esistance (r 2) Capacitor (C) esistor (r 1) H/O Unit Pin Code Nominal Time Delay Pin Code (t) Ω 470 µf 330 Ω pc s Ω 1,000 µf 330 Ω pc s Ω 2,000 µf 330 Ω pc s pc ,000 Ω 3,000 µf 400 Ω pc s pc ,000-18,000 Ω 1,000 µf * 150 Ω - 30 s pc ,000-18,000 Ω 22,000 µf * 150 Ω s * for ripple-free supply only Figure D7 Typical Values 8.4 Timing Problems In any complex circuitry the transient conditions should always be considered to avoid timing problems. The only way to identify such a problem is to carefully consider the operation of a circuit, not only in terms of the proving that is included in that circuit but also when each condition becomes applied, and the effect each relay operation has on other relays in the system, if any. For example, a relay may be required to be slow to release in order to hold up while its feed changes over from one path to another. The circuit techniques involved are described in Section Inputs to programmable electronic systems that are required to give rise to a rapid response (e.g. an instantaneous response is necessary for SPAD detection) should be examined to ensure that the maximum scanning time is not likely to exceed the required response time or give unpredictable results. If such a risk exists, precautions should be taken to prevent incorrect operation. For instance, if the condition treadle A occupied after treadle B occupied is required in SSI, it may be necessary to generate a stick circuit to prove the condition and give a single input to the SSI. Alternative action may be required where an unwanted delay is created by the transmission system, particularly where cross proving is used. For instance, because the position of the signalman s control device is cross proved in the point calling circuit by the alternative means (described in Section 9.2.2), when this is transmitted by FDM the repeater of the centre position should be held up until after the normal or reverse repeater has de-energised. See Part L and also the section on anti-bobbing in SSI design standards for further examples. Other timing problems are described in Appendix F2. 9 Proving Consideration should be given to the use of various types of proving, wherever reasonably practicable, as a diverse or secondary line of defence against the residual risk of a fail-safe item of equipment failing in an unexpected mode and thereby creating a hazardous situation. Proving may be regarded as impracticable if the added complexity or reduced availability, etc., are considered to outweigh the benefits. 9.1 Down Proving The 930 series non-latched relays can generally be relied upon to drop after the feed has been removed from the coil. This is also applicable to WBS type P miniature relays and larger plug-in type relays at existing installations. The situations where the down proving of 930 series relays, and their predecessors, is necessary may be summarised as follows: D24

67 ailway Group Guidance Note Page D25 of 39 Magnetic stick or latched relays should be proved down to ensure correct operation, unless other precautions are taken to prevent hazardous failures. Contactors should be proved down to ensure that their heavy duty contacts have not welded, unless other precautions are taken to prevent hazardous failures. The 943 and 966 F1, F4 & F5 style contactors should have both banks of contacts proved down together. Timer relays used for safety-critical controls should generally be proved down to ensure correct operation. See Section 8 for details and exceptions. Trackside and on-track equipment is vulnerable to circuit faults. As far as reasonably practicable, down proving should be used to ensure that the principal control and detection relays are appropriately de-energised. Cross proving. See Section 9.2. Sequence proving. See Section 9.4. For examples see Appendix F2. Other types of relays, such as shelf-type relays, may require more extensive proving, in addition to the above, according to application. Down proving should be accomplished by including a back contact of the relay in a second circuit, so as to cause it to fail right side should the first relay fail to drop. The second circuit should be chosen so that it will monitor every operation of the first relay. It is not required to be double cut by the back contact (see Section 4.5). 9.2 Cross Proving Cross proving is the mutual down proving of relays with complementary functions, such as normal/reverse, on/off, clear/occupied and left/centre/right. The prime purpose of cross proving is to avoid a confusing or unsafe condition arising if complementary relays are energised at the same time. Without cross proving this condition could occur as a transient during an ordinary change of state (if the relay pick-up time is less than its release time). The condition could also occur due to a relay or circuit fault, but cross proving does not automatically provide full protection against these faults and is not generally provided for this reason. Due to the transient problem, cross proving should be provided on complementary primary function relays and their subsequent repeats, unless one of the following applies: The time taken for the function to change states is inherently much greater than the release time of the de-energising relay. The provision of cross proving creates consequential problems. The provision of cross proving is particularly complicated. A secondary use of cross proving is to reduce the load on a polarised circuit when the polarity change is detected by a pair of biased relays connected in parallel. The following four sections give further details on the provision and omission of cross proving. However it is always necessary to assess the benefits and disbenefits of cross proving Standard Form of Cross Proving With this method of cross proving, the control circuit of each relay includes a back contact of its complementary relay(s) and the transient problems are avoided, as shown in Figure D8. However, if a relay fails to release, the complementary relay(s) will not energise and the incorrect state will prevail. This basic arrangement is therefore a recognised compromise and, although additional protection is not generally provided, it is not precluded. D25

68 ailway Group Guidance Note Page D26 of 39 Withdrawn Document N N50 B50 N N N50 B50 Figure D8 Standard Form of Cross Proving Alternative Form of Cross Proving With the standard form of cross proving, the complementary back contacts delay the response to a change of state as these back contacts have to make before the correct relay starts to respond. Where it is necessary to minimise the delay, an alternative form of cross proving should be used. This alternative form of cross proving does not have complementary back contacts as in the standard form but the equivalent cross proving is included in all functions controlled by the complementary relays, as shown in Figure D9. N N50 B50 N N50 B50 N Figure D9 Alternative Form of Cross Proving Another example of this arrangement is the control of point lock relays NL/WZ/L (in the typical free-wired route setting interlocking circuits described in Appendix F2) by switch relays N/C/ and for this simple arrangement there is a slight reduction in the number of back contacts required. This alternative form of cross proving has the additional merit of providing some protection against a relay failing to release, as all the controlled circuits are interrupted if more than one complementary relay is in the energised position Polarised Circuits with Biased elays When a pair of biased relays are used to detect the polarity of a polarised circuit, then as far as practicable, the load on the circuit should be minimised by confining the current flow to the coil of the appropriate relay. It is preferable to use local controls in order to select a path to the correct biased relay (shown as selection or correspondence proving in Figure D10). This will ensure that at all times the maximum load on the circuit is a single relay coil. The selection in this particular example is double cut because it also provides additional controls in the circuit. Selection or Correspondence Proving 105G/B P (1) 105 H 105G/B (ON)P 105 H 105 H 105G/B (OFF)P 105 H 105G/B P (2) Figure D10 Polarised Circuit: elay End D26

69 ailway Group Guidance Note Page D27 of 39 This preferred type of selection should not be used where both relays deenergised would be unacceptable because it is necessary to monitor the actual state of the incoming function. For example, the standard signal proving circuit (GP/HGP) should not be selected at the interlocking by the state of the corresponding G. In such cases, the biased relays should have the standard form of cross proving as described in Section Although the initial load on the polarised circuit will be two relay coils the load will reduce to a single coil when the appropriate relay responds and disconnects the complementary coil. Unless the selection or correspondence proving inherently prevents both complementary relays being energised at the same time (using either front and back contacts of the same relay or front contacts of complementary pairs of relays that are themselves cross proved), additional cross proving should be provided for primary function relays and subsequent repeats, as shown in Figure D11. Selection or Correspondence Proving 42 P (1) 99 N Additional Cross Proving 42 P 42 NP 101 N 42 NP 42 P 42 P (2) Figure D11 Polarised Circuit with Correspondence and Cross Proving For the arrangement at the feed end of polarised circuits, see Section Omission of Cross Proving Cross proving is not essential on intermediate relays that control the primary function relay and it is preferable to avoid the standard form of cross proving when circuits, other than polarised, are vulnerable to external faults. An example of inherent delay that makes cross proving unnecessary occurs with the correspondence proving of points. The relay feed for the initial state of correspondence is disconnected when the interlocking starts to change and the relay feed for the new state of correspondence is dependent on the operating time of the point mechanism. This point operating time is significantly greater than any appropriate delay in the release of the initial relay and the transient problem is not a valid consideration. An example of a consequential problem that is avoided by the omission of cross proving, occurs with the (UP)K/(DN)K circuits at manned barrier crossings. The provision of cross proving could lead to the road traffic lights cycling on/off. Therefore cross proving is deliberately omitted and due allowance made in the overall design. An example of unnecessary complications that could be created by the zealous provision of cross proving, occurs when complementary primary function relays are repeated in two or more interlockings (or lineside locations). It is generally considered unnecessary to provide complicated cross proving between the relays in different interlockings but the overall design should ensure that the omission does not lead to problems, transient or otherwise. D27

70 ailway Group Guidance Note Page D28 of 39 Withdrawn Document 9.3 Correspondence Proving Correspondence proving is a means of ensuring that a proving circuit for a function cannot give information that conflicts with the state of its respective operating circuit, as shown in Figure D10. It is generally provided for related outgoing and incoming polarised circuits (see Sections and ) and for point detection circuits (see Part P). 9.4 Sequence Proving The integrity of interlockings (and level crossings) requires relays to operate in the correct sequence. It is possible for this sequence to be interrupted, particularly if there is some delay inherent in the operation. Proving should be used to prevent this occurrence and ensure that the interlocking is effective. Sequence proving should be applied in the following situations. (The terminology relates to the typical free-wired route setting interlocking circuits described in Appendix F2.) The local signal relay(s) that control the signal off, should be proved down in the signal on proving relay (GP). A front contact of the GP should be placed in the unconditional path of the approach lock stick relay (ALS) circuit to prove the signal on in the approach locking. (When situated at the interlocking, the local signal relay may be proved down in the ALS instead of generating an GP.) A back contact of the signal control relay (G) should also be added in series with the GP contact, to set the approach lock by controls off. Finally, the ALS should be down proved in the control circuit feeding the local signal relay. The first route stick relay (US) past a signal should prove all routes from that signal normal before it can energise. Conversely, a front contact of the opposing US for the first track past the signal should always be included in the common leg of all routes from that signal and, wherever the route passes a signal reading in the opposite direction, a front contact of the opposing direction US should be included for the last track of the route leading up to the opposing signal. In the aspect level, a back contact of the last US that is released when the route is set should be included in the signal G circuit. This ensures the route locking is correctly applied before the signal clears and prevents the momentary clearance of opposing signals. The ordinary approach lock release condition is a sequential operation of tracks, usually one clear and another occupied after both occupied simultaneously. Both tracks occupied will be included in the train approach stick relay (TAS), with the one shown as becoming clear stuck out by a contact of the TAS. By including front contacts of both the TAS relay, and the track required clear, in one leg of the ALS, sequential track operation is proved. Such circuitry should be provided to prove the sequential operation of tracks in accordance with the control tables. The proving of bridge path removal in the aspect level is a form of sequence proving that should be applied as described in Section 7.4. At automatic level crossings relays should be correctly primed to ensure automatic closure of the crossing. Down proving should be used to verify the required priming. See Part X for further details. The equivalent of sequence proving on lever frames is sequential locking, whereby each running signal lever requires the lever for the signal ahead normal, so that levers have to be pulled and replaced in order, thus ensuring that each signal is replaced behind a train before it can be cleared again for a subsequent train. This should be provided wherever signals are not automatically replaced, in accordance with GK/T0039. Where it is reasonably practical to provide it, the proving of sequential operation of track sections should be considered. Other situations similar to those listed above, as required by risk assessment. D28

71 ailway Group Guidance Note Page D29 of epeat elays 10.1 General epeat relays are used for four basic purposes: To delay the response of the primary function relay. See Section To provide electrical isolation. See Section To overcome limitations on circuit length. See Section To provide additional contacts when it is impracticable to directly control all circuits by the primary function relay. See Section A single repeat relay may provide any or all of the first three functions, but a repeat relay provided to supply additional contacts will not generally perform any other purpose Delayed esponse To avoid momentary loss of train detection to the interlocking, or to the signalman, when a vehicle moves from one track circuit to another, some types of track circuit require one or more slow to operate repeat relays (see Section 8.2), unless extra delay can be incorporated into the interlocking system. A detailed Guidance Note, GK/C0752, is included in the Train Detection Handbook Electrical Isolation Electrical isolation between certain trackside equipment and the interlocking environment is desirable. The requirements for electrified areas are given in Section Limited Circuit Length The physical length of line circuits is limited by consideration of voltage drop within the circuit and also the external effect of electromagnetic interference with other circuits, necessitating line circuits to be terminated within the length limit and intermediate repeater circuits created. See Section Safeguards with Polarised Circuits elated outgoing and incoming polarised circuits should, wherever practicable, be repeated at a common lineside location. Correspondence proving should then be provided between the associated circuits in order to protect against an untoward change in the polarity of the power supply. This protection is particularly relevant to point circuits as an incorrect polarity can convert an outgoing normal control into reverse and also convert the associated reverse detection back to the expected normal. The repeater location circuits should therefore ensure that the incoming detection matches the outgoing control. All power supply arrangements should be considered in designing appropriate protection epeat elays to Provide Additional Contacts When the primary function relay has insufficient contacts to control the required circuits, repeat relays are provided. Circuits should be designed such that, if a repeat relay fails to energise when its primary relay is energised, it will not result in a hazardous situation. As repeat relays can cause various problems, care should be exercised in their use. See Appendix F2 for examples of potentially hazardous situations. (The primary function relay is defined as the relay by which the logic required to control a signalling function is brought together. With a chain of repeat relays, such as TP, T2P, etc., the primary function relay is the first one to directly control safety-critical signalling functions, rather than just operate the next repeat relay in the chain.) D29

72 ailway Group Guidance Note Page D30 of 39 Withdrawn Document If the primary device does not have a full range of safety contacts, such as a switch, a reed receiver, or a timer with only one or two contacts, then a separate primary function relay may be generated, fed over a contact of the device. Any control device for the function concerned, that precedes the primary function relay, should not be used for any other safety-related purpose and should generally have only the one contact used (two if the circuit is double cut). The contact analysis should have a note added to this effect Back Contacts of epeat elays Back contacts should not be used for control purposes except on primary function relays. Back contacts of repeat relays give no positive information. When there are insufficient contacts on a primary function relay, repeat relays may be provided fed over a front or back contact of the primary relay. To justify the provision of a repeat relay at least two of its front contacts have to be used. When repeat relays of both front and back contacts of a primary function relay are provided, they should be cross proved. No relay should be operated directly in parallel with a primary function relay. epeat relays of the back contacts of primary relays should be designated PZs. The designation C for a simple back contact repeat does not imply the repeating of the primary relay. Where both front and back contact repeats of a primary function relay are required in two or more interlockings, P and PZ relays, directly controlled by the primary relay, should be provided in each interlocking. Back contacts of front contact repeats of primary relays may only be used in the following circumstances: where the sole function is to prevent feedback in meshed circuits, when used in conjunction with a front contact of the same relay (see Section ); for cross proving (see Section ); for indication purposes, except for red signal indications (see Section 10.6); or to economise power consumption. Back contacts of back contact repeats of primary relays may only be used in the following circumstances: where the sole function is to prevent feedback in meshed circuits, when used in conjunction with a front contact of the same relay (see Section ); or for cross proving (see Section ) epeat elays in Changeover Paths A relay may be required to hold up while its feed changes over from one path to another. The relay required to hold up should be slow to release (see Section 8.2). The contacts performing the changeover should preferably be of the same relay, as shown in Figure D12. (This does not apply to changeover in meshed or polar circuits. See Section ) If the changeover is between contacts on more than one relay, it should have a minimum drop away time of 250ms, as provided on the 934 style relay. If, however, the changeover is from front to back on the same relay, 150ms will suffice, as on the 963 style. D30 An application is in the last wheel replacement circuit, where the signal relay is required to hold up whilst one of the track repeat relays breaks its front contact and makes its back contact.

73 ailway Group Guidance Note Page D31 of 39 DG TP 212 GS Changeover Contacts DG TP 212 G 212 G Figure D12 Changeover Contacts If the back contact were replaced by a contact of a repeat relay, e.g. back contact repeat T2PZ, the required hold up time would increase. Conversely, if the front contact were replaced by a contact of a repeat relay, T2P, the required hold up time would decrease. In order to minimise this problem, the use of contacts of slow acting repeat relays for changeover purposes should be avoided wherever practicable. (Note that a.c. immune relays are slightly slow acting.) If, due to lack of contacts, further repeat relays are required, so as not to introduce a further delay these should preferably be parallel repeat relays, e.g. T2P(2) or T2PZ(2), rather than T3P or T3PZ. See Section 8.4 for other timing problems Changeover Paths in Meshed Circuits The 930 series relays are constructed such that front and back contacts cannot be made at the same time. This permits their use in polarised, and other meshed circuits, without the risk of a momentary back feed. (This does not apply to heavy duty or medium duty contacts.) However, if one of the contacts in Figure D13 were to be replaced by the contact of a repeat relay, there would be the possibility of a momentary short circuit. B50 JG TP JG T2P/T2PZ (1) N50 N50 JG TP JG TP JG T2P/T2PZ (2) B50 JG TP Figure D13 Polarised Circuit: Feed End D31

74 ailway Group Guidance Note Page D32 of 39 Withdrawn Document To prevent momentary back feed, a back contact of the repeat relay should be inserted in the opposite leg of the circuit, as shown in Figure D14, or Figure D15, respectively. Note that this should be in addition to the contact of the primary function relay, as back contacts of repeat relays should not be used for controls (see Section ). B50 JG T2P JG T3P/T2PZ (1) N50 JG TP JG T2P Figure D14 B50 JG TP JG T2PZ JG T2P/T3PZ (1) N50 JG T2PZ Figure D15 Where both front and back contact repeat relays are provided, the circuit shown in Figure D16 may be used with simply a front contact of each, providing the repeat relays are cross proved (see Section ), thus preventing both contacts being made together. Otherwise, an additional back contact of each would be required in the meshing. B50 JG T2P JG T3P/T3PZ (1) N50 JG T2PZ Figure D16 Any combinations of these arrangements shown in Figures D13 to D16 may be used in the (1) and (2) legs of polarised circuits. Similar precautions are required in other meshed circuits, particularly where stick paths are present. For the arrangement at the relay end of polarised circuits, see Section Provision of Multiple Track elay epeats Where required, up to three repeat relays may be provided in parallel, so long as all the front contact repeat relays are cross proved in all the back contact repeats (if any), and vice versa (see Section ). The 930 series relay contacts are not suitable for switching more than three relays. See Section Special care should be taken when the T controls any circuit other than just one TP, because the TP is then not the primary function relay (see Section 10.5) and the back contacts of the TP should not be used for controls. The T becomes the primary function relay and its back contact repeat, if required, would be a TPZ Indication Circuits Where repeat relays are used, signalman's and maintainer's panel indications should generally be controlled by contacts of the last repeat relay, so that the failure of a repeat relay to energise would be apparent to the signalman. D32 The application to each type of indication is given in Part L.

75 ailway Group Guidance Note Page D33 of 39 Fusing and Looping of Signalling Circuits Appendix D1: D1:1 Fuse Values The preferred overcurrent protective device for final circuits in the railway environment is the BS 88 or BS 714 cartridge fuse, as appropriate, although faster acting fuses may be necessary to protect electronic equipment. The minimum conductor size for each fuse is given in Figure D17, which includes some allowance for the grouping of cables. The design process should take place as follows: assess the design load of the circuit; select the nearest fuse value higher than the design load (of a type that is suitable for any anticipated transients, as described in Section 3.3); obtain the conductor size from Figure D17; ensure the rating of each circuit component exceeds the fuse value. BS 714 Fuse ating Environment Minimum Conductor Size Protection of Cables 3A 5A 10A 15A 20A internal, external internal (SSI) internal external internal external on-track internal external on-track internal external, on-track 0.75mm 2 1mm mm mm 2 2 x 1.5mm 2 2.5mm 2 2 x1mm 2 1.5mm 2 2.5mm 2 2 x 2.5mm 2 (pink) * 1.15mm 2 or 2 x 1.15mm 2 # 1.15mm 2 Notes: * 0.75mm2 is permissible if wiring is not tightly grouped # single 1.15mm 2 (or 1mm 2 ) is permissible if wiring is not tightly grouped Figure D17 D1:2 Positive Fusing and Looping Final circuit fusing should generally be in the positive feed only. Positive final circuit looping for internal circuits should take the form of one or two radial feeds from a fuse (and not as a ring). The number of looping connections should be limited to those which may be simultaneously supplied from a 3A fuse. The voltage drop at the end of the loop should also be considered. For the convenience of maintainers, where fuses are provided on each relay rack, the positive feed for each relay should originate from the rack on which the relay is situated. The following should generally be fed from individual fuses: internal circuits rated at higher than 3A; any circuit requiring an individual point of isolation; and all circuits that are not entirely within an apparatus housing. D1:3 Negative Looping Negative final circuit looping for internal circuits should take the form of one or two radial feeds from a busbar terminal (and not as a ring). For the convenience of maintainers, the feed for each circuit should originate from the negative busbar associated with the busbar from which the positive feed came. D33

76 ailway Group Guidance Note Page D34 of 39 Withdrawn Document Negative looping should be arranged so that feedback in the event of a high resistance connection is impossible. This may be achieved either by having separate negative feeds from the busbar for each function, or by eliminating all meshing of circuits that could permit coils to be fed in series following a looping fault. In the latter case, the number of looping connections should be limited by the current carrying capacity of the conductor and the voltage drop at the end of the loop. Where meshed circuits are essential, other precautions may be necessary (see Section 7.5 for an example). D1:4 A.C. Final Circuits Sections D1:1 to D1:3 should also apply to a.c. final circuits, where, by convention, BX is treated in the same manner as positive and NX as negative. Generally, internal 110V looping has limited application. One example is for synchronous motor timers. 24V looping is used for signalman's panel indication feeds. D1:5 Grouping of Circuits Looping connections that are not crimped should be positioned at the end of the looping in order to minimise fault conditions in the event of a loose connection. Where power supply monitoring is required, power off relays and repeaters should be wired at the end of significant loops, to detect any loss of feed. Any safety-related functions that do not fail safe may need to be grouped with other functions whose failure would be apparent in the event of a blown fuse. D1:6 Fusing of Cable Terminations In d.c. electrified areas, the practice of terminating multicore cables entering interlockings on fuses instead of termination links provides a degree of protection for interlockings where conductor rails and trackside cables lie in close proximity. It should be provided: for tail cables; for main multicore cables not running entirely in a protected route; or where justified by risk assessment. Where provided, it is not necessary to discriminate and each such fuse should be rated higher than the respective circuit busbar fuse. D34

77 ailway Group Guidance Note Page D35 of 39 Electromagnetic Compatibility of Electronic Equipment Appendix D2: This appendix applies to electronic signalling equipment, such as: operational telecommunications equipment, electronic train describers, remote control systems, panel processors, electronic track circuits, SSI, IECC and CCTV equipment. In order to avoid problems, electronic equipment should have leads as short as practicable, which may be screened or consist of twisted pairs, and not be located close to known interference sources, such as HVI track circuit equipment. Where surge protectors or filters are provided, the clean side wiring should be segregated from the dirty side and from unfiltered power supplies. Equipment likely to produce electromagnetic disturbance in apparatus housings, such as base station transmitters, should have the associated cabling screened and earthed, and any aerial should be mounted externally. Where special restrictions apply to positioning or wiring of equipment, this should be clearly shown on circuit diagrams or rack/case layouts, so that if alterations are made at a later date the restrictions are readily apparent. On electrified lines with route acceptance for three phase traction, restrictions on the use of equipment operating at certain frequencies, such as reed and FDM, should be obtained from the relevant safety case. D2:1 Audio Frequencies elay coils in axle counter circuits may require suppressing to prevent electromagnetic interference to axle counter evaluators by connecting a reverse biased diode across the coil. Where axle counters and audio frequency track circuits are installed in the same vicinity, it is preferable for the track circuit receiver, rather than the transmitter, to be adjacent to the axle counter section. SEL axle counter heads should not be installed within 5m of a track circuit tuned zone, 15m of an end termination unit, 100m of a 1550 Hz or 1850 Hz transmitter (applies only to 5 khz heads), nor 200m of a 1700 Hz transmitter (applies only to 5 khz heads). To avoid intermodulation effects, the following audio frequency equipment should be separated from each other by a minimum of 150mm: reed equipment; Aster track circuit equipment; and TI 21 track circuit equipment. Their wiring should not run parallel in the same ducting. CCTV equipment and audio frequency equipment should not be housed in the same apparatus case, nor in an equipment building within 2m of each other. Only one TI 21 transmitter or receiver of a given frequency should be fed from any one TI 21 power supply unit. Only one reed transmitter or receiver of a given frequency should be fed from any one reed power supply unit. D35

78 ailway Group Guidance Note Page D36 of 39 Withdrawn Document D.C./d.c. converters should not be housed adjacent to, nor fed from a battery supplying, any audio frequency signalling equipment. Additional restrictions to prevent the mutual interference of track circuits may be found in the Train Detection Handbook, GK/H0751. Wherever non-suppressed reed or axle counting equipment is mounted, a warning notice should be affixed to equipment racks and apparatus cases (inside the door), prohibiting the use of equipment that does not conform to the requirements of the particular EMC environment, e.g. portable radio transmitters, mobile telephones, vacuum cleaners or power tools within one metre. (Type reed receivers with radio frequency suppression have a type number suffix 'B' or 'C'.) Care should be taken when locating equipment, such as TI 21 transmitter tuning units, emitting an audible frequency, so as not to cause a nuisance to local residents. If necessary, sound proofing should be specified on the design details. D2:2 eed Systems All connections to reed filters, and other reed system wiring longer than 400mm, should be run in twisted pair cable and segregated from other wiring. The positioning of equipment should be carefully designed, so as to keep the wiring as short as reasonably practicable. Non-safety a.c. relays should not be used to provide input contacts for reed transmitters as they could give rise to a.c. harmonics on the line. To avoid mains based interference, reed power supply units should not be mounted within 150mm from reed transmitters and receivers. High and low frequency type reed transmitters should not be housed in the same apparatus case, nor in an equipment building within 2m of each other; to avoid over amplifying lower frequency signals and subsequent false operation of adjacent channels. The following restrictions should be observed between reed track circuit, point detection and FDM equipment: receiver filters should not be housed in the same apparatus case, on the same equipment rack, nor on an immediately adjacent rack, as other reed equipment of the same frequency (this does not apply to two track circuits of the same frequency, which should follow the guidelines given in GK/H0751); track circuit receiver filters should not be mounted within 700mm of a track filter of the same frequency; receiver filters should not be mounted within 300mm of a track filter of a different frequency, nor a constant voltage transformer; receiver filters should not be mounted within 50mm of any power amplifier or reed follower relay; and reed track circuit, point detection and FDM systems should not share power supply units. The proximity restrictions given in this section are provisional and await up to date information from the manufacturer. For restrictions between reed and other equipment, see Section D2:1. D36

79 ailway Group Guidance Note Page D37 of 39 D2:3 Frequency Division Multiplex (FDM) Safety-critical FDM systems should be carried in an approved twisted pair signalling cable. Other FDM systems may be carried in conventional signalling cable, provided that: the direction of lay alternates for successive core layers; each system uses a pair of adjacent conductors in the same layer; and additional systems in the same cable are separated as far as practicable and do not use a conductor adjacent to another system. In a.c. and dual electrified areas, transmission lines for FDM systems should have isolating transformers (or line amplifiers incorporating transformers) installed to restrict induced voltages to a safe level. The system should be designed to operate satisfactorily in the presence of interference containing any odd harmonic of a fundamental in the range 48.5 to 50.5Hz, up to 100V per harmonic. Safety-critical systems should also make allowances for traction supply faults, e.g. including even harmonics and induced voltages up to 1,000V a.c. This will generally be satisfied by restricting the permissible frequencies and installing an isolating device every 1,000m (alternately an isolating transformer and line amplifier). For further details of transmission systems for general signalling purposes see Part J. D2:4 Time Division Multiplex (TDM) TDM systems are susceptible to electromagnetic interference and are not generally suitable for safety-critical applications, unless specifically designed to have the required integrity, in conjunction with an appropriate medium for transmission. Signalling circuits in telecomms cables should be identified at all access points with red markers and should be jumpered in accordance with Part J. See GK/T0197. In a.c. and dual electrified areas, TDM transmission circuits should use balanced pairs in telecomms cables. Earth free terminations should be used, preferably with a maximum unbalance ratio in excess of 200. The TDM system should be approved for this particular environment and designed to operate satisfactorily in the presence of 10mV induced interference. For further details of interlocking to signal box transmission systems see Part F. D2:5 Closed Circuit Television (CCTV) Transmission Systems For proximity restrictions between CCTV and other equipment, see Section D2:1 In a.c. and dual electrified areas, lengths of co-axial transmission lines for CCTV level crossings vulnerable to dangerous levels of induced voltages should be screened. A 10 MΩ resistor should be provided between each conductor and earth at each termination to prevent the build up of static charge. D2:6 Solid State Interlocking (SSI) HVI track circuit transmitters, feed transformers, or cable connecting them, should not be housed in the same apparatus case as SSI TFMs (signal and points modules), DLMs (data link modules), or LDTs (long distance terminals). SSI interlockings and HVI track circuit equipment should not be situated in the same equipment room, without a risk assessment to demonstrate that adequate separation or screening of the HVI equipment has been provided. The requirements of this paragraph only apply until all the equipment concerned is provided with EMC declarations of conformity and CE markings. D37

80 ailway Group Guidance Note Page D38 of 39 Withdrawn Document Wiring between DLMs (or LDTs) and their associated repeater DLMs and TFMs should be in twisted pair cables and limited to a length of 5m. Where SSI DLMs and TFMs are housed in the same equipment room, the TFMs connected to each pair of DLMs should be mounted in a related group, so as to avoid confusion. Wiring from tail cables should be segregated from the data and power wiring (see Part J). It is also preferable for track circuit tail cables to be routed separately from other tail cables directly connected to a TFM. Segregation between individual data link cables is not, however, necessary. To avoid electrically induced noise, SSI cabling should be kept as short as practicable. All SSI circuits should be subject to the requirements of Section 4, particularly those relating to length restrictions and double cutting. However, due to the highly coded nature of SSI, any corruption will not affect safety, but only dependability. Generally SSI systems are extremely tolerant to interference and a length of external loop input to TFMs of 2,000m (4,000m loop) is permitted, but it is preferable to limit this length to 200m (400m loop) for inputs from on-track equipment. External inputs should be double cut. TFM outputs that require double cutting should be buffered with an interface relay, isolating transformer, or transformer rectifier, as they are not double cut by the module. (Lever locks require an interface relay.) Interface relays for connection across TFM signal module outputs should be 110V a.c. 966 F7 style. Where voltage-free contacts are required from a standard TFM output feeding equipment, such as signal lighting, a lamp proving relay (941 style) may be used in series between the TFM and the load, in the supply leg (not in the return leg). In a.c. and dual electrified areas, trackside data link cables should be immunised. To prevent damage to TFMs from back EMF, relay contacts that can deenergise the output load should not be introduced into the circuit between the TFM and its load. However, contacts used for down proving or cross proving are acceptable. Wherever SSI equipment is mounted, a warning notice should be affixed to equipment racks and apparatus cases (inside the door), prohibiting the use of equipment that does not conform to the requirements of the particular EMC environment, e.g. portable radio transmitters, mobile telephones, vacuum cleaners or power tools within one metre. (Test equipment should only be connected in accordance with GK/T0221.) D2:7 Panel Multiplexers (PMUXs) Panel multiplexers are vulnerable to electromagnetic interference and the following safeguards are required: for new panels and where practicable for existing panels (subject to the last bullet point), the panel multiplexer should be located within the panel framework; or otherwise in a cubicle as close as reasonably practicable to the panel. the panel multiplexer to panel cabling should be screened cable, the screen of which should be earthed at one end only. The inputs and outputs should be in separate cables. See Part J. the proximity of adjacent equipment and cables should be considered so as to minimise possible electrical interference, especially when routing the panel multiplexer to panel cabling. D38

81 ailway Group Guidance Note Page D39 of 39 D2:8 Earthing of Equipment Fast transient earths (FTEs) minimise the effects of interference from electrical surges, such as lightning strikes, flashovers from the traction supply and switching transients. Solid state devices require that fault surges are suppressed very quickly to avoid malfunction and damage. FTEs are generally provided for telecommunication equipment, electronic train describers, remote control systems, panel processors, electronic track circuits, SSI, IECC and CCTV equipment. This equipment should be earthed as described in the system documentation. A FTE need not have a very low resistance, but should have low inductance. This can be met by ensuring as short, straight and rigid a connection as practicable, i.e. at least 16mm 2, between the equipment and the earth electrode. Spur earth connections should be used rather than ring configurations. A typical value of a FTE would be 20Ω. Long earth leads should be avoided, where practicable, by bonding equipment to the mounting rails, which, in turn, are bonded to the structure of the apparatus housing. Wherever practicable, particularly at lineside apparatus cases, a common earth rod, bonded to the structure of the apparatus housing, should be used to provide both a FTE and a safety earth. If a separate safety earth exists, this should be bonded to the FTE to avoid the need to shroud the FTE and all metalwork connected to it, and to avoid damage due to the high potential differences between the two earths in the event of a lightning strike. Electrodes joined end to end vertically should be used, rather than connected in parallel, and bonded to the main earth terminal (MET) in the apparatus housing. Where the exposedconductive-parts of equipment are earthed, the MET should always be bonded to the structure of the apparatus housing. For further details see Part C. Surge arrestors on safety-critical circuits should not be earthed, unless the equipment has been specifically designed to resist dangers from multiple earth faults, e.g. by coding. In such cases, line surge protection units (e.g. for SSI data links and TDM transmission) should be connected to the earth busbar and positioned as close as practicable to it. In a suite of apparatus cases, datalink cables should always be terminated on surge protection units situated in the same apparatus case as the MET. All cases situated within 2m of each other should be bonded together. TI 21 tuning units are not required to have the earth terminal connected to earth. The requirements for earth bonding conductors are given in Part J. D39

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83 ailway Group Guidance Note Page F1 of Introduction Part F Interlockings 1.1 This Guidance Note applies, in support of GK/T0060, to the design of interlockings (including ground frames) associated with: a) mechanical signalling systems; b) electro-mechanical signalling systems; c) electro-pneumatic signalling systems; d) all-electric non-route setting signalling systems; e) free-wired route setting signalling systems; f) geographical route setting signalling systems; g) electronic signalling systems; and h) hybrid systems. Where appropriate, reference to signals should be understood in relation to movement authorities within both lineside signalling and cab signalling systems. 1.2 This Guidance Note does not cover the presentation and production processes for design details. For the presentation and use of mechanical locking charts, interlocking circuit diagrams and central interlocking data listings within the design process, see GK/T0201 and GK/T0205. Documentary requirements for control tables are given GK/T Where it entirely addresses the situation under consideration, the use of this Guidance Note is an alternative to the risk-based approach described in GK/T0206. However, where the particular application or intended environment for the system introduces additional risks, these should be subject to separate assessment. The design principles in Section 2 give the minimum requirements, even when the risk-based approach is used. More detailed requirements for the design of interlockings are given in Section 3. Sections 4 to 8 describe the application of the design principles and requirements, as evolved through different interlocking systems, starting with the most basic. The Appendices describes in further detail arrangements for some commonly encountered types of interlockings. The examples shown in this Guidance Note are based on the signalling layout and control table illustrations given in Appendix F5. F1

84 ailway Group Guidance Note Page F2 of 191 Withdrawn Document 2 Design Principles 2.1 egulatory equirement Suitable and sufficient interlocking, in conjunction with appropriate operating and maintenance procedures, must be provided to prevent, so far as is reasonably practicable, the following occurrences: a) collision between vehicles; b) collision between a vehicle and a buffer stop; c) derailment caused by confliction with movable infrastructure; and d) derailment caused by excessive speed. This is a requirement of the ailway Safety (Miscellaneous Provisions) egulations Selection of Interlocking System The choice of interlocking system should be made to achieve an appropriate balance between manual and automatic protection, in order to control risks so far as is reasonably practicable. A risk assessment should consider such factors as: a) service frequency; b) traffic type and mix (including light railway/metro, passenger and/or freight); c) permissible speeds; d) layout complexity; e) interfacing with trains; f) interfacing with adjacent interlockings and existing systems; g) available space or housing; h) power supply availability; i) target life span; and j) skills availability (in design, installation, operating and maintenance fields). 2.3 Interlocking Integrity and Proving Interlockings and interfaces between interlockings should follow the principles for safety-critical systems given in GK/T0206. The interface with the trackside signalling equipment (or cab signalling system) should also be safety-critical. Interlocking equipment should provide for the operation of interlocked trackside signalling equipment, corresponding to the state of the appropriate function within the interlocking. Where necessary to reduce risks to an acceptable level, proving should be used to ensure interlocking and/or trackside equipment is in a safe state before another operation can be carried out, as described in the design principles in Part D. Where necessary to achieve the infrastructure controller s specified availability level (see Part P of GK/C0701), the state of safety-critical interlocking functions should be stored by a means that will remain secure in the event of a total failure of all power supplies, e.g. by locked lever, latched relay or non-volatile memory. Interlockings should be designed to prevent an unsafe state occurring during power supply failure or restoration, including momentary loss. F2

85 ailway Group Guidance Note Page F3 of 191 Where the state of safety-critical information is not stored (e.g. in the case of relay interlocking systems without latch relays, or certain electronic interlocking systems), the system should be designed to revert to a safe state, or refresh to correspond to the state of the railway, before being restored to use. Wherever practicable, circuits should function in their usual manner following power supply loss and restoration without having to be manually reset by a maintainer, unless a safe state cannot otherwise be ensured. Where necessary to re-establish the integrity of the interlocking, a delay should be incorporated into the restoration to ensure that all movements have come to a stand. Transient conditions or faults in the train detection system should not allow conflicting routes to be set, or routes to be prematurely released. 2.4 Movement Authorities and Proving of oute It should only be possible to give a movement authority when it is safe to do so, i.e. when movable infrastructure over which it is given is set and locked in the correct position. The interlocking should ensure that no conflicting authority can be given to trains or level crossing users. Wherever practicable, the interlocking should be proved effective before a movement authority can be given. The operation of the trackside signalling equipment should be proved to be in correspondence with the state of the appropriate function within the interlocking before a movement authority can be given. For example, points should be detected before a signal reading over them can be cleared and a signal should have been proved on before a conflicting signal can be cleared. A movement authority should not be given if any foul track sections on the flanks of the route are occupied. Facilities should be provided to allow for the maintenance of a safe distance between trains travelling on the same line through, or within, the interlocking area. Except where permissive working is authorised, an authority should not be given for a running movement to proceed over a line of route that is occupied. The requirements for block systems are given in GK/T0041, GK/T0042 and GK/T0051. Signals should not show a proceed aspect unless the next signal ahead is displaying a valid aspect, in accordance with GK/T0032. Wherever practicable, this should be engineered in such a way that will facilitate degraded operation with a reduced level of protection, as detailed in Section Any shunting signals in the line of route that are not associated with a main aspect should be cleared before authority for a running movement past them can be given. It should not be possible to give a movement authority for a diverging route unless the train speed has been appropriately controlled, or the driver has had sufficient warning of the divergence to be able to appropriately control the train speed. Wherever practicable, the movement authority should be automatically cancelled if any of the conditions that allowed the authority to be given are lost, except for those conditions that are required only at time of signal clearance. 2.5 Permissive Movements Where facilities for attaching and detaching operations are required, at terminal platforms, or otherwise where specially authorised in the Sectional Appendix, a subsidiary signal (PLS or semaphore) should be used to give authority for a shunting movement, or permissive movement in accordance with GK/T0044, as appropriate. F3

86 ailway Group Guidance Note Page F4 of 191 Withdrawn Document It should not be possible to select more than one class of route from a signal at any one time. 2.6 Withdrawal of Authority Once authority to proceed over a line of route has been given, the route should remain protected until that authority is withdrawn. The interlocking should prevent the release of points and conflicting signals that have been locked to give an approaching train authority to proceed until the train has passed through the route or has been proved to have come to a stand before entering the route, in accordance with GK/T0063. The route may be released progressively for operational flexibility. The route may also be released in order to authorise a permissive movement up to a stationary train. Wherever practicable, movement authorities should be withdrawn as soon as possible after the passage of a train. Where this is not practicable, other precautions should be taken to prevent more than one train being inadvertently admitted to the same signal section. The route may be released automatically once it has been confirmed that the train has passed through the route. Facilities should be provided for the signaller to withdraw movement authorities from any train under his/her control. These facilities should be maintained under degraded operating conditions. Under ordinary operating conditions, an independent facility should be available for each signal or train. 2.7 Movable Infrastructure Once authority to proceed over a set of points, controlled level crossing, movable bridge, or traverser, etc. has been given, the infrastructure should be locked until that authority is withdrawn. The locking of the infrastructure should be maintained, preventing operation: a) when the section of track over the infrastructure is occupied (track locking); and generally b) when the section of track between a protecting signal and the infrastructure concerned is occupied (route holding). 2.8 Overrun Protection and Mitigation Where the risk of a Signal Passed at Danger (SPAD) is high, and it is impracticable to reduce the risk, special precautions should be taken to warn the driver in the event of a SPAD (see Part S) and, where reasonably practicable, withdraw movement authorities on conflicting routes. isk criteria are given in GK/T0078. A minimum distance between trains (i.e. overlap) should be maintained, in accordance with GK/T0078. This requirement should be enforced in the case of running movements in track circuit block by proving the overlap clear in the signal in rear, as if it were in the line of route. Where there is a low risk of a SPAD, the overlap may be shorter than normal, or may be zero length. Examples of movements where this may apply include: a) those made under the restricted approach arrangement; b) permissive movements; and c) non-running movements. F4 Where facing points are situated in the overlap, they may be moved to give an alternative overlap without replacing the signal, providing the alternative is available and detection is re-established within a certain time. Where trailing points are situated in the selected overlap, they should be locked as if they were in the line of route. Such overlap locking may be released once the movement

87 ailway Group Guidance Note Page F5 of 191 authority has been withdrawn and the train is proved to have come to a stand at the destination signal. Trap points and other points that afford flank protection should generally be set to avoid the risk of collisions, in accordance with GK/T Control Point The interlocking equipment should be controlled from a signal box (or other control point). The state of the signalling equipment should be indicated at the signal box (or other control point). Control and display systems should be designed in accordance with GK/T0025. Where proving or detection is required in Section 2.4 for use in the interlocking (e.g. for the state of controlled functions, train detection, routes and time releases) it should also be indicated to the signaller. See Part L. The interface between the interlocking and the signalling control and display system should be safety-related Degraded Operation Wherever reasonably practicable, provision should be made for the graceful degradation of operating facilities in the event of a failure of a strategic signalling system. (See GK/T0206 for the shortcomings of graceful degradation and other means of improving availability.) It should be possible to give restricted movement authorities with a certain minimum level of protection in order to maintain safe operation under degraded conditions. Examples include: a) facilities to allow a signal to clear to single yellow with the signal ahead displaying no aspect, provided the controls of the signal ahead are off, (but, wherever reasonably practicable, a failed green aspect at the signal ahead should step down to display a cautionary aspect); b) allowing a signal to clear with the signal ahead displaying a single yellow aspect in lieu of a double yellow, (but, wherever reasonably practicable in four aspect sequences, the signal in rear should step down to display a cautionary aspect); c) use of the restricted approach arrangement; d) remote control override (an interface system with restricted facilities that can override the main signal box to interlocking transmission system); e) reconfiguration to isolate failed equipment and permit other parts of the system to be reinstated; and f) initiation of single route setting following the failure of flank protection. Where necessary, procedures should permit maintainers or signallers to release certain equipment to permit restricted movement authorities to be given System Monitoring Where necessary to achieve the infrastructure controller s specified availability level (see Part P of GK/C0701), monitoring should be provided to warn the signaller or maintainer of a failure, by means of an audible and/or visual alarm. Monitoring alarms that directly affect train operations should be communicated to the signaller, but other alarms need only inform the maintainer. F5

88 ailway Group Guidance Note Page F6 of 191 Withdrawn Document 2.12 Maintainer s Facilities The following maintainer s facilities should be provided at the interlocking, to the degree necessary to satisfy the infrastructure controller s specified maintainability requirements (see Part P of GK/C0701): a) monitoring of indications being transmitted to the signalling display; b) means of taking local control; c) failure monitoring, giving indication of faults; d) operation monitoring, including event recording equipment and data loggers; e) maintenance facilities to assist the tracing of faults; f) isolation devices to allow off-line resetting of equipment, as required by GK/T0027; and g) means to set restrictive controls, in accordance with GK/T Identity of Interlocking Functions All signalling functions should bear an identity, in accordance with GK/T0009, that is unique to the interlocking and corresponds with the identity shown on the signalling display Documentation The signalling functions controlled from each interlocking should be depicted on a signalling/scheme plan and their interlocking logic should be tabulated in the form of control tables, as described in Part N of GK/C elaxation Certain principles that it is not reasonably practicable to satisfy may be relaxed where the section of track concerned is clearly visible from the controlling point. These may include the requirements for: a) continuous train detection in non-track circuit block; b) approach control of signals; c) approach locking of signals, as permitted in GK/T0063; d) track locking and route holding of controlled level crossings, where the protecting signal is within 100m of the crossing; e) track locking and route holding of ground frame points, as permitted in GK/T0061; f) track locking and route holding of trailing points and other movable infrastructure; and g) detection or locking of facing points (non-passenger movements only). See Part P. In such cases the automatic protection generally afforded by the interlocking should be provided manually by the signaller, in accordance with instructions. Any proposed use of this relaxation should be subject to the agreement of the infrastructure controller and should demonstrate that risks are acceptably low. F6

89 ailway Group Guidance Note Page F7 of Interlocking equirements This section gives the detailed requirements to be incorporated, where appropriate, in all types of interlocking. For the application of the design principles and requirements to different types of interlockings, see the following sections: a) purely mechanical lever frames - Section 4; b) electro-mechanical lever frames - Section 5; c) all-electric non-route setting interlockings - Section 6; and d) route setting interlockings - Section 7. The following abbreviated terms are used in this section: At a stand = the track section has been occupied for such a time that it may be assumed that the movement has stopped. Block overlap (BOL) = the acceptance overlap beyond the home signal up to the clearing point in non-track circuit block. Hinge points = facing points within an overlap that are permitted to swing in order to give an alternative overlap. Independent PLS = a position light signal not associated with a main aspect. LC/TA = block indicator at line clear (absolute block)or train accepted (tokenless block). Limit of shunt (LOS) = shunting signal fixed on (PLS or semaphore), or LOS indicator. Non-colour light signal = semaphore signal or reflectorised board. Non-track circuit block = absolute block or one of the various (Non-TCB) types of single line block. F7

90 ailway Group Guidance Note Page F8 of 191 Withdrawn Document Overlap (OL) = for a stipulated distance ahead of the next signal in advance, or to the end of the overlap track section (where provided), whichever is the greater. Permissive track = the track section(s) where permissive working is authorised, e.g. where attaching and detaching operations take place. Phantom overlap (POL) = the limit of overlap locking in cases where the overlap track section extends further. Power operated signal = motorised semaphore, or colour light signal. Pre-set signal = a facing signal in the line of route that is required off by a pre-setting signal. Pre-setting signal = the signal that requires pre-set signal(s) off in the line of route. elated stop signal(s) = in relation to a distant signal, all of those signals that are required to be proved clear before the distant signal can be cleared. educed overlap = a full overlap of reduced length. estricted overlap (OL) = a short overlap used under the restricted approach arrangement (e.g. delayed yellow) where there is also a full overlap. Subsidiary PLS = a position light signal associated with a main aspect. TOL/TIS = block indicator at train on line (absolute block) or train in section (tokenless block). Track (Tk) = track section, i.e. track circuit(s) or other means of continuous train detection. Train interactive systems = train interactive systems for SPAD mitigation, such as the automatic warning system (AWS), automatic train protection (ATP), train protection and warning system (TPWS) and trainstops. The requirements of this section are summarised in tables (Figures F1 to F6 and F12 to F18) which are referred to in the text. Options which are explained in the appropriate columns of the tables are shown in [square brackets]. Controls that are required unconditionally are marked with a tick (ü). F8

91 ailway Group Guidance Note Page F9 of Signallers Interface The interlocking system should be capable of operating from a specified signalling control and display system, using an appropriate interface. It should also operate, where required, in conjunction with an automatic route setting system that simulates the signaller's controls. Full details of signalling control and display systems are given in Part L Content The interface for a lever frame is mechanical (see Appendix F1). The interface for a non-route setting interlocking operated from a control panel is generally directly wired (see Section 6). (It may also include a remote control system, where the interlocking is remote from the signal box, and/or generation of suitable track and route displays from the indication functions.) The interface system for a route setting interlocking may include: a) derivation of the interlocking control functions from the signaller s requests; b) route setting, unless provided in the interlocking system; c) automatic route setting (AS), where required (see Section 3.1.3); d) train operated route release (TO), where required (see Section 3.7.4); e) generation of track and route displays from the indication functions, to suit the display system; and f) remote control system, where the interlocking is remote from the signal box (see Section ). The operation of an interface system is described in Sections and Arrangement The infrastructure controller s future requirements should be considered when designing the signaller s interface with the interlocking, e.g. whether control of the interlocking might subsequently be transferred to a remote signal box or a VDU based system. The interface system is required to be safety-related, but not safety-critical (see Section ), so there are advantages in separating it from the safety-critical interlocking system. However, it should satisfy the infrastructure controller s availability requirements (see Part P of GK/C0701). There are disadvantages in using non-standard components, such as subminiature or non-safety relays. Note that the interface system may be located either at the interlocking or at the signal box. The location should generally be chosen to minimise the number of remote control system channels. The length of cabling susceptible to interference, the number of interfaces and the size of equipment rooms should also be minimised after considering the other factors. The following are examples of interface systems (requiring appropriate approval for each application in accordance with GK/T0201): F9

92 ailway Group Guidance Note Page F10 of 191 Withdrawn Document a) The most fundamental arrangement comprises an interlocking system without route setting that simply locks the signalling functions, together with a comprehensive interface system (as in Section 3.1.1) that inputs the signaller s requests, performs the route setting and outputs signalling functions normal or reverse. b) Panel processors are interface systems with inputs and outputs that may be configured to suit the required control and interlocking systems. Programmable logic controllers may be used. c) The BS-SW67 route relay free-wired interlocking system (see Appendix F2) incorporates a push button interlocking (PBI) interface using relays at the interlocking. (WBS systems are similar.) This is the conventional interface designed for use with entrance-exit (NX) panels, transmitting button pushed/pulled. oute setting and TO is performed within the interlocking system, using safety relays. d) With the solid state interlocking (SSI) system (see Appendix F4) the interface is a panel processor module (PPM) in the interlocking cubicle, but the route setting is performed in the safety-critical interlocking multi-processor module (MPM). e) Electronic route setting equipment (ESE) is an interface system, located at the interlocking, between a simplified relay interlocking without route setting and an NX panel. f) An electronic interface between a BS-SW67 route relay interlocking (I) and a VDU based control system is available, but route setting is performed within the interlocking system, using safety relays. TO and AS can be provided in the electronic control system at the signal box. g) The E10k free-wired interlocking uses an interface system of non-safety relays at the signal box. This may be used with turn-push panels, transmitting route set to the interlocking. Alternative circuits are provided for NX and one control switch (OCS) panels. (AEI-GS systems are similar, but with the interface at the interlocking.) h) The GEC geographical system uses a common control set as the interface. i) Other arrangements that comply with the considerations of this section (3.1.2) may also be used. See eferences for the interlocking systems quoted above Automatic oute Setting (AS) Systems These are systems, invariably electronic, for setting routes without any action of the signaller, based upon a stored timetable, train running information, defined priority selection criteria and operating algorithms. It is a requirement of AS that TO be provided (see Section 3.7.4). They are provided where necessary to reduce the workload of the signaller, and form part of the interface system with the interlocking. For automatic platform or junction working see Section (c). 3.2 Signal and oute Controls This section describes the signalling controls, interlocking and other signalling facilities which the interlocking system should be designed to provide. F10

93 ailway Group Guidance Note Page F11 of 191 Each controlled signal (except for co-acting signals) should generally be controlled by a separate signaller s request (but see Section for calling-on arrangements). Signals reading to more than one destination should generally be controlled by separate signaller s requests for each destination. For signal positioning, operation and proving, aspect sequence controls and special signal controls, see Part S Controlled Stop Signals Associated with Non-oute Setting Interlockings Non-route setting interlockings should provide the controls and facilities summarised in Figure F1. The requirements for normalisation are summarised in Figure F2. The controls for each signal should be specified in control tables, in accordance with GK/T0202. Figures F1 and F2 may be read for any type of non-route setting interlocking, as follows: a) On purely mechanical lever frames, both the interlocking and aspect (arm) controls are mechanically operated. Mechanical controls require lever reverse, mechanical point detection and mechanical slots off. Electric locks are only required where there are track circuits, electrical detection, or block controls, etc. b) On electro-mechanical lever frames, the interlocking is generally mechanical, but electrical locking is applied through an electric lock known as the selection lock (to distinguish it from the interlocking lock, where electrical interlocking is provided). Mechanically operated signals also have the controls applied through the selection lock as shown, as they have no aspect circuits. c) Non-route setting interlockings with lock relays, e.g. individual function switch (IFS), combine the interlocking and selection lock functions in the lock relay operation and release circuits. F11

94 ailway Group Guidance Note Page F12 of 191 Withdrawn Document NON-OUTE SETTING SIGNALLING SYSTEMS INTELOCKED STOP SIGNALS Main Subsidiary or Shunt Mechanical or Mech l Electric Mech l Mech l Electric Interlocking Lock, if Aspect locking Lock, if Selection Op or Inter- Selection Electro-Mechanical Interlocking - Level All-Electric (Miniature) Lever Frame - Level All-Electric elay (IFS) Interlocking Controls and Facilities - Level E Q U E S T Signal requested by operation of signal lever or switch, the class of route being selected by separate lever or switch. Signal lever reverse or reverse lock relay energised. Directly opposing signals normal, including conflicting overlaps. provided Selection Lock Controls Aspect Controls Lock elays Aspect Controls Interlocking Lock Interlocking Lock provided Selection Lock Mech l Op or Aspect Controls Aspect Controls Lock elays Aspect Controls See Section or Part ü ü Part L Confliction in route or OL ü ü 6.5 Confliction in route, [or opposing locking omitted] Other classes of route from this signal normal. ü ü Any slot from another control point given. ü ü Where required for junction signals, approach control satisfied, including special controls for signals with flashing yellows, splitting distant, or splitting banner in rear. ü Approach controlled to clear when train nearly at a stand, O main signal in rear locked normal. [May be by instruction in non-tcb.] Mech op sigs only: appr contr if signal ahead on Approach control if semaphore sig ahead on Signal in rear normal Mech ly operated sigs only: approach control Approach control When applied, temporary approach control satisfied. ü Signal clearance is delayed, where necessary, to give sufficient warning for an automatic level crossing or train activated warning system. Mech'ly operated sigs only ü Mech'ly operated sigs only ü Signal clearance is delayed until train is at a stand in platform, for an automatic level crossing with stopping selected. Permissive track occupied for calling-on at time of selection and at time of signal clearing. Mech'ly operated sigs only ü Mech'ly operated sigs only For call-on only For call-on only Where provided, Lime Street controls satisfied. For call-on only Signals required to be pre-set by this signal reverse and proved off. The line of route, foul tracks [and overlap] are clear [delayed replacement tracks clear at time of signal clearing only]. [May be by instruction in non-tcb.] All shunts in route reverse Mech ly operated signals with power op sig ahead Mech ly operated signals only Power operated signals proved off Up to end of OL Any shunt close ahead reverse Mech ly operated signals only ü In route up to permis ive track (exclusive) Part X Figure F1 Non-oute Setting Signalling System Controls continued... F12

95 ailway Group Guidance Note Page F13 of 191 INTELOCKED STOP SIGNALS Main Subsidiary or Shunt Mechanical or Electro-Mechanical Interlocking - Level Mech l Interlocking Electric Selection Lock, if Mech l Op or Aspect Mech l Interlocking Electric Selection Lock, if All-Electric (Miniature) Lever Frame - Level All-Electric elay (IFS) Interlocking Controls and Facilities - Level provided Selection Lock Controls Aspect Controls Lock elays Aspect Controls Interlocking Lock Interlocking Lock provided Selection Lock Mech l Op or Aspect Controls Aspect Controls Lock elays Aspect Controls See Section or Part Points set, locked (except where released by other points that release signal), and detected in line of route, [overlap], and flank/trap points. [Flank points detected where required only.] [Power operated facing points in OL set to acceptable position and detected only.] [FPLs provided only for mechanical facing points. Nonpassenger moves require FPL or detection.] [Trailing mechanically operated points not detected.] [BOL locking is by instruction in non-tcb.] Trailing points, switch diamonds, etc. in overlap set to prevent conflicting moves. Facing train operated points detected and pressure normal. Set and locked in route, OL, flank and trapping & FPLs in (route and OL only) Mechanically operated sigs only: electrical detection Mech'ly operated sigs only Locked and detected in route, OL, flank and trapping (and FPLs detected) ü Set and locked in route, flank and trapping & FPLs in (line of route only) Shunts only Mechanically operated sigs only: electrical detection Mech'ly operated sigs only Locked and detected in route, flank and trapping (and FPLs detected) ü Facing hand points or spring points detected normal. For shunt moves GF releases and GF points set, locked, and detected In route, Mech'ly In route, In route, Mech'ly In route, normal in line of route, [overlap] and flank/trap points. [Trailing mechanically operated points not detected.] [BOL locking is by instruction in non-tcb.] OL and flank: release normal operated sigs only: electrical detection OL and flank: detected normal and flank only: release normal operated sigs only: electrical detection and flank only: detected normal Gate box releases are normal (with gates locked across ü ü road or barriers proved down and crossing clear). Signal stick set (not applied). Or auto ü working selected Where necessary for permissive working, signal ahead ü locked normal. All authorised opposing and conflicting movements clear ü of route and overlap, or overlap swung away. (oute locking.) All authorised opposing and conflicting movements at a stand on permissive track or at destination signal, or clear of route [or opposing locking omitted]. (oute locking.) ü Interlocked gated level crossings in the route: gates proved locked across the road. [Does not generally apply to gated level crossings in the overlap.] Controlled barrier crossings, in the route [and 50m overlap]: proved barriers down and crossing clear, at time of signal clearing only. [CCTV crossings also require barriers intact and local controls locked.] Gate stops normal or gate locks in Where lock lever provided (route & OL) Mech'ly operated sigs only (route & OL) In route and overlap Gate stops normal or gate locks in Where lock lever provided (route only) Mech'ly operated sigs only (route only) In route only 3.8 Part X Any movable bridge set, locked and detected normal. Bolts in ü Bolts in ü Any lockout devices normal. ü ü ü ü Where provided, all-signals-on switch not operated. ü ü Where required for route holding or sequential locking, trailing points in rear locked both ways. ü ü Signal ahead proved on if it is not automatically replaced by the passage of a train. (Sequential locking.) Nonreciprocal mech l lock g (not new work) ü 4.5 Figure F1 Non-oute Setting Signalling System Controls continued... F13

96 ailway Group Guidance Note Page F14 of 191 Withdrawn Document INTELOCKED STOP SIGNALS Main Subsidiary or Shunt Mechanical or Mech l Electric Mech l Mech l Electric Interlocking Lock, if Aspect locking Lock, if Selection Op or Inter- Selection Electro-Mechanical Interlocking - Level All-Electric (Miniature) Lever Frame - Level All-Electric elay (IFS) Interlocking Controls and Facilities - Level Main colour light signal ahead proved alight (both distant and stop signals where applicable, including each head of a splitting distant). Any banner repeater ahead proved on and alight or controls off. (For signals leading onto single lines, controls are bypassed by lamp failed alarm acknowledged.) Independent PLS ahead proved red lamp alight or controls off, for limiting wrong road moves. LOS proved alight. Where required for colour light junction signals, route indicator proved alight. Special controls satisfied where signal ahead is for closing-up. Where provided, special controls satisfied where signal ahead is a tunnel signal, at time of signal clearing only. Where provided, special controls satisfied for signals in advance of junction signals to guard against reading through, at time of signal clearing only. Section signal for non-tcb requires: LC/TA or token release (one train only), at time of signal clearing only. provided Selection Lock Controls Aspect Controls Lock elays Aspect Controls See Section or Part Bidirectional lines only Entrance signal for direction lever working requires: This SB lever normal Mech'ly operated sigs with colour light signal ahead Mech'ly operated sigs only Mech'ly operated signals only Interlocking Lock Interlocking Lock provided Selection Lock Mech l Op or Aspect Controls Aspect Controls Lock elays Aspect Controls ü Not for call-on ü ü ü ü ü Next SB lever reverse Bidirectional lines only: by special instr ns This SB lever normal Mech'ly operated sigs only: by special instr ns Not for call-on ü Authorised by special instr ns Next SB lever reverse Where provided, released when king lever reversed. ü ü Hazard detectors (trip wire etc) proved normal. ü ü Figure F1 Non-oute Setting Signalling System Controls Normalisation Facilities Interlocking Electrical Selection Backlock Aspect eplaced 2.4 Part S Any related distant signal normal. ü Any other signal normal that requires to be preceded by this one. ü Signaller s control device not reversed. ü Part L Withdrawal of electrical aspect controls (except those marked at time of clearing only). ü Signaller s control device not reversed, signal on and free of approach locking. ü 2.6 Signaller s control device not reversed with signal approach locked. Timed or manual release Line is clear between signal and points, where separate route locking is not provided. ü Figure F2 Normalisation of Controlled Signals (Non-oute Setting Systems) Part S Part K See Section F14

97 ailway Group Guidance Note Page F15 of Controlled Stop Signals and outes, Associated with oute Setting Interlockings oute setting interlockings should provide the controls and facilities summarised in Figure F3. The requirements for normalisation are summarised in Figure F4. The controls for each signal should be specified in control tables, in accordance with GK/T0202. Figures F3 and F4 may be read for any type of route setting interlocking, as follows: Conventional route setting interlockings register a route request if the locking is free (i.e. points available), and then automatically call the points to the required position. The route request with the points correctly called sets the route, which, in turn, locks the points. With programmable electronic interlockings, the route request may control the points and set the route, if the points are free to move. There may be no separate locking. With route setting systems, signals should be controlled by the following types of route: a) main colour light or semaphore signal: main or warning route; b) subsidiary signal (PLS or semaphore): call-on or shunt route; c) shunting signal (PLS or semaphore): shunt route; d) semaphore calling-on signal: call-on route; e) semaphore shunt-ahead signal: shunt route; f) semaphore warning signal: warning route (not for new work). F15

98 ailway Group Guidance Note Page F16 of 191 Withdrawn Document OUTE SETTING SIGNALLING SYSTEMS Signal Type Main Main Subsidiary PLS Any PLS See oute Class Main (M) Warning (W) Call-On (C) Shunt (S) Sect- Level Controls and Facilities E Q U E S T oute requested by switch, push buttons, tracker ball, or keyboard. oute set (both parts of route if dual controlled). Directly opposing routes normal, [unless opposition only in overlap and able to be swung away]. Other class routes from this signal normal. Any slot from another control point given. Approach controlled to clear when train nearly at a stand. Where required for junction signalling, approach control satisfied. When applied, temporary approach control satisfied. Signal clearance is delayed, where necessary, to give sufficient warning for an automatic LC or train activated warning system. Signal clearance is delayed, for an automatic level crossing with stopping selected, until train is at a stand in platform. Where provided, Lime Street controls satisfied. outes from any signal pre-set by this route normal. outes pre-setting this signal normal. Signals pre-set by this route proved off. Aspects of routes pre-setting this signal ready to clear. (Aspect controls as pre-setting route.) The line of route and foul tracks are clear [delayed replacement tracks clear at time of signal clearing only]. The overlap and foul tracks are clear, or alternative overlap available. oute Set and Locked Normal exit [with perm sive tk clear at setting, if (C) route exists] In route and full OL Aspect Controls (M) route, or steppedup (W) route oute Set and Locked Selected by special exit device or full OL unavailable In route and OL Aspect Controls Auto stepup to (M) route if a propriate (before sig clears) (W) route, or (M) route if no locking in OL oute Set and Locked Normal exit, with permissive track occ'd at time of setting In route only Aspect Controls Permis ive track occupied at time of signal clearing oute Set and Locked Selected by shunt exit device Aspect Controls (C) route (S) route, (or pre-set - indep PLS only) In route only [or opposing locking omitted] ion or Part Part L ü ü ü ü ü ü ü ü ü ü Clears to yellow aspect only ü Only for subsidiary PLS ü ü ü ü ü ü ü ü Part X ü ü ü ü ü Indep PLS only ü ü ü ü ü ü Up to perm sive track (exclusive) Up to full OL Up to OL if separate track Independent PLS when preset Up to perm sive track (exclusive) Figure F3 oute Setting Signalling System Controls continued... F16

99 ailway Group Guidance Note Page F17 of 191 Signal Type Main Main Subsidiary PLS Any PLS See oute Class Main (M) Warning (W) Call-On (C) Shunt (S) Sect- Level Controls and Facilities Points set, locked & detected in the route, [overlap, or alternative overlap available], and flank/ trap points. [Flank points detected where required only.] [Facing points in overlap set to acceptable position and detected only.] [Trailing mechanically operated points not detected.] Trailing points, switch diamonds, etc. in overlap set and locked to prevent conflicting moves. Facing train operated points detected and pressure normal. Facing hand points or spring points detected normal. GF releases and GF points set, locked, and detected normal in the route, [overlap, or alternative overlap available] and flank/trap points. [Trailing mechanically operated points not detected.] Gate box releases are normal with gates locked across road or barriers proved down and crossing clear. oute Set and Locked Set and locked in route, full OL, flank and trapping Set and locked in route, full OL, flank and trapping Aspect Controls Locked and detected in route, full OL, flank and trapping oute Set and Locked Set and locked in route, OL, flank and trapping Aspect Controls Locked and detected in route, OL, flank and trapping oute Set and Locked Set and locked in route, flank and trapping only Aspect Controls Locked and detected in route, flank and trapping only oute Set and Locked Set and locked in route, flank and trapping only Up to independent PLS/LOS Aspect Controls Locked and detected in route, flank and trapping only ion or Part ü ü ü ü Locked and detected in route, full OL, flank and trapping Signal stick set (not applied). Or auto working selected All authorised opposing and conflicting movements clear of route and overlap, or alternative overlap available. (oute locking.) All authorised opposing and conflicting movements at a stand on permissive track or at destination signal, or clear of route [or opposing locking omitted]. (oute locking.) Controlled level crossings in the route [and overlap]: proved barriers down and crossing clear at time of signal clearing only. [CCTV crossings also require barriers intact and local controls locked.] Any movable bridge in route [and overlap]: set, locked by this route and detected normal. Set and locked in route, OL, flank and trapping Locked and detected in route, OL, flank and trapping Set and locked in route, flank and trapping only Locked and detected in route, flank and trapping only Set and locked in route, flank and trapping only ü ü ü ü oute and full OL In route, & OL if no trap points In route and overlap of 50m In route, & OL if no trap points oute and OL In route, & OL if no trap points Or auto working selected In route and OL In route, & OL if no trap points ü In route only ü Locked and detected in route, flank and trapping only ü ü In route only In route only ü In route only In route only In route only Part X Any lockout devices normal. ü ü ü ü ü ü ü ü Where provided, all-signals-on ü ü ü ü switch not operated. oute [or aspect] not disabled. oute Aspect oute Aspect oute Aspect oute Aspect Figure F3 oute Setting Signalling System Controls continued F17

100 ailway Group Guidance Note Page F18 of 191 Withdrawn Document Signal Type Main Main Subsidiary PLS Any PLS See oute Class Main (M) Warning (W) Call-On (C) Shunt (S) Sect- Level Controls and Facilities Signal ahead proved alight (both distant and stop signals where applicable, including each head of a splitting distant). Any banner repeater ahead proved on and alight or controls off. (For signals leading onto single lines, controls are bypassed by lamp failed alarm acknowledged.) Independent PLS ahead proved red lamp alight or controls off, for limiting wrong road moves. LOS proved alight. Where required for junction signalling, I proved alight. Special controls satisfied to ensure driver sees whole sequence where flashing yellows, splitting distant, or splitting banner in rear. Special controls satisfied when signal ahead is only for closingup, at time of signal clearing. Special controls satisfied when signal ahead is a tunnel signal, at time of signal clearing only. Special controls satisfied to guard against reading through, at time of signal clearing only. Section signal for non-track circuit block requires: LC/TA or token release (one train only), at time of signal clearing only. oute Set and Locked Bidirectional lines only Aspect Controls oute Set and Locked Aspect Controls oute Set and Locked Aspect Controls oute Set and Locked Aspect Controls ü ü For shunt moves up to main signal only ü ü ü ü ü Full OL (platform) clear Plat occ, next tk occ OL clear ü ü ü ü ü Bidirectional lines only: restricted accept ce estricted acceptance arrangement Perm sive working only (unidirectional) Bidirectional lines only: by special instr ns Hazard detectors (trip wire etc) proved normal. Note: For signals designated controlled solely to protect a controlled level crossing, see Figure F5. Figure F3 oute Setting Signalling System Controls Normalisation Facilities ü Authorised by special instr ns ü ü ü ü oute eleased Aspect eplaced ion or Part 2.4 Part S oute cancelling device operated. ü Part L Withdrawal of aspect controls (except those marked at time of clearing only). ü TO, or route cancelling device operated, signal on and free of approach locking. ü 2.6 oute cancelling device operated with signal approach locked. Timed release Part S Part K See Section Pre-set signals: pre-setting route cancelling device operated, unless train between pre-setting and preset signals. Figure F4 Normalisation of Controlled Signals and outes (oute Setting Systems) ü F18

101 ailway Group Guidance Note Page F19 of Stop Signals not Associated with an Interlocking a) General This section applies to signals without separate locking and aspect levels, where all the controls are provided in the signal aspect. (Signals operated from a lever frame should instead follow Section ) These signals are not centrally interlocked and should generally be provided with the controls and facilities summarised in Figure F5. The controls for each signal should be specified in control tables, in accordance with GK/T0202. A non-interlocked signal should be controlled as follows: i. by the passage of trains, for automatic and semi-automatic colour light signals in track circuit block only (see GK/T0035); ii. by a single device, for signals (including non-block signals) that are only designated controlled in order to protect a neutral section, or other hazard (together with an automatic working facility in track circuit block); iii. by an entrance/exit request in route setting interlockings, with an indication of route set, for controlled signals protecting a controlled level crossing; or iv. exceptionally, for non-block signals, by the absence of a hazard. (Where necessary to maintain consistency in existing signal boxes, signals in category iii may instead be controlled by a single device in route setting interlockings, with no indication of route set.) Certain of these signals may be controlled or locally locked by a ground frame or level crossing, as shown in Figure F5 (see GK/T0061). Signals that work automatically may be normally off. Block signals should be automatically replaced following the passage of a train wherever reasonably practicable, and under all circumstances where permissive working is authorised. Block signals that protect movable infrastructure, such as a ground frame or controlled level crossing, should not be designated automatic or intermediate block home. Stop boards, such as those instructing the driver to obtain token, should be regarded as unworked block signals. Non-block signals are not required to be controlled by train detection, but only by a particular hazard or infrastructure detection system. Non-block signals should be located close to the hazard or infrastructure that they are to protect, but overlap distance clear (see Figures F12 and F13). Where non-block signals are arranged to be normally off with automatic replacement by the presence of a hazard (e.g. if a rock fall is detected, or if detection of ground frame points is lost), special instructions should be issued to inform train crew of the action to be taken if such signals are found to be at danger. emote ground frame markers and stop boards, such as those protecting unmanned or automatic level crossings, should be regarded as unworked non-block signals. In the case of ground frame markers (and gated level crossings without a protecting stop signal), the controls should be applied to a worked distant signal (see Sections 3.4.2(h), 3.6.2(a) and 3.7.2(j)). Both block and non-block signals that protect movable infrastructure should generally be provided with approach locking and route holding, although relaxations are available. See Sections and For signals on bi-directional lines, see Section F19

102 ailway Group Guidance Note Page F20 of 191 Withdrawn Document See Aspect Controls Sect ion Automatic and semi-automatic signals: signal box replacement control not operated, O E Q Non-interlocked controlled signals (simple control, e.g. single push button): signal box control operated for signals protecting a Part L U E track sectioning cabin/ neutral section, or where train must not pass red signal with failed SPT (signal designated controlled or non-block signal), O S T Non-interlocked or locally-locked controlled signals (standard control): signal box control operated for signals protecting a controlled level crossing or ground frame (signal designated controlled or non-block signal). Where provided, hazard detectors (trip wire, etc.) proved normal Signal clearance is delayed, where necessary, to give sufficient warning for an automatic level crossing (e.g. with stopping selected, clearance delayed until train is at a stand in platform). Facing train operated points detected and pressure normal Ground frame points (facing points within 800m of signal) are set, locked, and detected normal (signal designated semi-automatic 3.6 or non-block signal). [Trailing mechanically operated points are not detected.] [Signals over 800m from facing points, including points in overlap, to be designated controlled or non-block signal]. Level crossing gates in route locked across road (signal designated semi-automatic or non-block signal). [Does not generally apply to gated level crossings in the overlap.] 3.8 Part X Controlled level crossings in route [and 50m overlap]: proved barriers down and crossing clear, at time of signal clearing only (signal designated controlled, semi-automatic or non-block signal). [CCTV crossings also require barriers intact and local controls locked.] Any lockout devices proved normal B The line of route and overlap are clear L estricted overlap, with approach control to clear only to yellow aspect when train nearly at a stand, automatically stepped up O to full overlap if available before signal clears [requires special controls satisfied when the next signal is for closing-up]. C Facing points in overlap set to acceptable position and detected K Entrance route to bi-directional lines set [or, for signals reading in predominant direction, opposing entrance route not set] Gate box or ground frame releases are normal or slots off (signal designated semi-automatic or controlled). 3.6 S Signal stick set (not applied) or auto working selected, where signaller's control provided I Where signal box control transmitted by main remote control system, all-signals-on switch not operated G Aspect not disabled [SSI signals] or signal post switch [where provided] set to auto N Where provided, special controls satisfied where signal ahead is a tunnel signal, at time of signal clearing only. Part S A L Where provided, special controls for signals in advance of junction signals to guard against reading through, at time of signal clearing only. S Block signal ahead proved alight (both distant and stop signals where applicable, including each head of a splitting distant). Any banner repeater ahead proved on and alight or controls off. Note: For signals designated semi-automatic because signal box can switch out, see Figure F1 or F3, as appropriate. Figure F5 Block and Non-Block Stop Signals Not Associated with an Interlocking (all systems) b) eplacement Devices Signaller s replacement devices should be provided for all block signals that are not controlled (i.e. automatic and semi-automatic signals). These should always be given safety-critical integrity, so that they can be used to provide the following facilities, as applicable: i. protection for personnel working under possession; ii. protection for users at unmanned or automatic level crossings, when verbally authorised by the signaller; iii. suppression of level crossing strike-in or gate box warning when shunting movements are taking place; and iv. provision of stopping/non-stopping controls where a station platform is located within the strike-in of an automatic level crossing. (Where necessary to maintain consistency in existing signal boxes, signals providing facilities ii, iii or iv may instead be controlled by a single device in route setting interlockings with an automatic working facility, but no indication of route set. Such signals should be designated automatic.) F20

103 ailway Group Guidance Note Page F21 of 191 A typical replacement arrangement would be a direct wired circuit operated by a stick relay at the signal box, de-energising a replacement relay at the signal, which in turn controls the signal aspect relay. A red replacement indication should prove that the remote replacement has been effective (replacement relay de-energised), as well as proving the signal on (aspect relay de-energised) and proving the lamp alight. Any related distant and/or banner repeating signals should also be proved on and alight. An off indication should not be provided. In the case of semi-automatic signals that are approach locked to protect ground frames, etc., (see Section 3.6.2) the red indication should flash whilst any manual approach lock release is timing. See Section for general signal replacement requirements. Wherever such a signal is equipped with a signaller s replacement facility, any signal post replacement switch should be removed, to prevent personnel placing reliance on a device which could be susceptible to hazardous failure epeating Signals and Indicators Distant and banner repeating signals should be provided with the controls and facilities summarised in Figure F6. The controls for each signal should be specified in control tables, in accordance with GK/T0202. A separately controlled distant signal should be released by the related stop signal(s). If no lever is provided for a power operated distant signal there can be no interlocking or selection lock, so any such controls should be provided in the aspect. The signal should then work automatically, its aspect dependent upon the aspects displayed by its related stop signal(s). A distant signal should be controlled as follows: a) by a different device from its related stop signal(s) for mechanically operated signals; b) by the same signaller s request as the related stop signal in route setting interlockings; or c) by either method (a) or (b) for other power operated signals. (If a common device is used, a replacement device should also be provided in circumstances where: non-track circuit block working is in force; a level crossing is situated in the route beyond any related stop signal; or otherwise as requested by the infrastructure controller.) In semaphore signalled areas, where the minimum signal spacing distance (from GK/T0034) places a distant signal within the station limits of a signal box in rear, it should be mounted on the same post as the next stop signal in rear, repeated below any intervening stop signals between the outer distant and its first related stop signal, and slotted in accordance with Section F21

104 ailway Group Guidance Note Page F22 of 191 Withdrawn Document Controls and Facilities Distant or inner distant requires all related stop signals ahead levers reverse, and aspect requires any signals proved off if power operated. (In the latter case the distant should be power operated.) Outer distant requires inner distant lever reverse, and aspect requires it proved off if power operated. (In the latter case the outer distant should be power operated.) Interlocking Levers reverse Electrical Selection Lock Aspect Controls Lever reverse Distant signal lever/switch reverse, if provided. ü See Section Proved off Proved off Distant arm is slotted to require any stop arm off, either on the same post as the distant, or between the distant and its first related stop signal. (In the latter case, a repeat distant arm is required.) ü Distant arm requires slot off from any other signal box for which it acts also as distant. ü Distant signal associated with remote ground frame marker requires ground frame points ü 3.6 detected normal. (Mechanically operated signals require mechanical detection.) Distant signal requires colour light stop signal ahead proved alight. Any banner repeater ahead proved on and alight or controls off. Mech ly op signals only ü Part S Banner repeater requires its related stop signal proved off (and alight if colour light). ü Any train detection device between a power operated distant signal or banner repeater (except in terminal platforms) and its first related stop signal is clear. ü Figure F6 Distant Signal and Banner epeating Signal Controls (all systems) A banner repeating signal should be controlled by the same signaller s request as its related stop signal. Wherever reasonably practicable, and under all circumstances where permissive working is authorised, a distant or banner repeating signal should be replaced by a train detection device situated between itself and its first related stop signal. An exception is made in the case of a banner repeating signal in a terminal platform, where it is generally more informative for it to reflect the state of the platform starting signal. Where provided (for the use of station personnel), an off indicator should be controlled simply by the platform starting signal and never be replaced by a train detection device between itself and the signal. Where permissive working is authorised, off indicators should not be positioned such that they can be read by a driver estricted Approach Arrangement (also known as Warning Arrangement) Under the restricted approach arrangement trains are brought nearly to a stand at a main signal before it is allowed to show the most restrictive proceed aspect to indicate that the next stop signal is at danger and the overlap may be unavailable. For new work, movements made under the restricted approach arrangement should be signalled with the main signal, approach controlled in accordance with Section , and should be provided with a restricted overlap. Otherwise, these controls may be imposed by instruction. (However, a slightly higher approach speed is preferable to minimise the likelihood of drivers accelerating sharply between the signals. The overlap length related to the approach speed is given in Section 3.3.3(c).) In colour light track circuit block, such movements should be authorised by a warning aspect (delayed yellow); also where colour light signals are used within station limits in non-track circuit block. In route setting interlockings they should be controlled by a separate warning route, if the overlap locking is less than that required by the main route. Otherwise the main route should suffice, controlled by a restricted approach arrangement when only the restricted overlap is available. F22

105 ailway Group Guidance Note Page F23 of 191 If the signal ahead is subsequently selected such that the full overlap becomes available (locked and clear), before the warning aspect has cleared, the interlocking (or aspect if the locking is the same) may step up to allow an unrestricted main aspect to be displayed, in accordance with GK/T0078. An automatic signal may also be provided with a warning aspect where necessary for operating purposes, e.g. as a closing-up signal. Likewise, a controlled signal may be provided with an automatic working facility. These signals may step up to a main aspect, as above, but should revert to restricted overlap conditions following the passage of each train. For non-track circuit block sections, restricted acceptance arrangements are given in the appropriate regulations in the B30062 series. Where stated in signaller s instructions, this should be enforced by manually delaying the clearance of the section signal. If the section signal is colour light, it is preferable for it to be combined with the distant signal ahead (subject to the signal spacing requirements of GK/T0034), to enable a delayed yellow, rather than a delayed green, aspect to be displayed. A signal authorising movements under the restricted approach arrangement should be controlled as follows: a) in non-route setting interlockings where the overlap locking is the same, or where the control system is subject to particular constraints (e.g. on lever frames), by a single device, but with the restricted overlap selected by a supplementary operating device (such as a plunger); b) in route setting interlockings and other non-route setting interlockings, by a different signaller s request from the main route; c) by the passage of trains, for automatic signals; or d) by a separate device from the main signal where a separate warning signal is provided (not for new work). Examples are given in Figure F1:12 for non-route setting systems and Figure F5:5 for route setting systems. For further details of restricted overlaps see Section Permissive Movements a) General The provision of permissive running movements, as distinct from shunting movements, for either passenger or freight trains, requires risks to be controlled so far as is reasonably practicable in accordance with GK/T0044. A permissive movement should be signalled with a subsidiary signal (PLS or semaphore), and should be controlled by a call-on route in route setting interlockings. A signal authorising permissive movements should be controlled as follows: i. by a different device from the main signal for mechanically operated signals; ii. by the same signaller s request as the main route in route setting interlockings; iii. by either method i) or ii) for other power operated signals (a different device should generally be used where the main signal has interlocking in the overlap). F23

106 ailway Group Guidance Note Page F24 of 191 Withdrawn Document Examples are given in Figure F1:12 for non-route setting systems and Figure F5:5 for route setting systems. In track circuit block, signals authorising permissive movements require a permissive track section occupied, both when setting the route (or selecting the signal) and at time of signal clearance, but subsequent clearance of the track section should not replace the signal. Conversely, a main signal associated with a permissive signal requires the permissive track section clear, both when setting the route (or selecting the signal) and at time of signal clearance. Stepping down of aspects is not permitted. Stepping up of aspects is not permitted where permissive passenger movements are authorised. In non-track circuit block, permissive working is permitted in accordance with GK/T0042 (absolute block), GK/T0051 (only within station limits on single lines), or GK/T0054 (ETB). (See also the B30062 series of regulations.) In absolute block sections a counting device (or special block instrument) may be used to determine when the line is clear. For new work, approach control should be provided, in accordance with Section No controls ahead of the destination signal are required. Automatic working facilities for controlled signals authorising a permissive movement are not permitted. However, on a permissive goods line, intermediate automatic signals may be provided, with selection of main or subsidiary aspect by track occupancy. Such signals should be track replaced with the subsidiary aspect approach controlled to prevent the stepping down of aspects. Stepping up may be permitted when the train ahead is clear of the route and overlap. b) Platform Space Where passenger trains of more than two vehicles are required to be signalled into an occupied terminal platform, the following controls (commonly known as Lime Street Controls) may be provided: i. a berth track section, known as the measuring track, at the signal controlling the entrance to the platform, of the same length as the outer platform track section; ii. two platform track sections, the inner one nearer the buffer stops being as short as possible to accommodate the longest train that may be in the platform when it is necessary to signal in a further train; iii. the permissive aspect controls should require the inner platform track occupied (for a permissive movement), the outer platform track clear (short space available), the measuring track occupied (for approach control) and the track section in rear of the measuring track clear (proves short train). These controls prevent a train that is longer than the available space from being signalled into a platform. If it is desired to signal one or more locomotives onto a train when both platform tracks are occupied, the measuring track may be divided to prove the length of the locomotive(s). Alternatively, a shunting facility may be provided, controlled by a different signaller s request as described in Section F24

107 ailway Group Guidance Note Page F25 of 191 Similar controls, but with only one platform track and a shorter measuring track, may be provided where it is not required to signal more than locomotive(s) into an occupied platform. Where required by the infrastructure controller, similar controls may be provided at through platforms. Where required by the infrastructure controller, more complex controls may be provided for longer platforms, perhaps using three platform tracks and two measuring tracks Shunting Movements A shunting movement should be signalled with a shunting signal or subsidiary signal (PLS or semaphore) and should be controlled by a shunt route in route setting interlockings. A signal associated with a main aspect that authorises shunting movements should be controlled by a different signaller s request from the main signal. In track circuit block, shunting signals (PLS or semaphore), that read onto or along running lines, should generally require all track sections clear up to the signal (or LOS) ahead. However, where attaching or detaching operations are necessary, the track sections where these operations occur may be omitted from the controls. In such cases, the signal ahead should have a separate overlap track section and first wheel replacement. In non-track circuit block, train detection control may be omitted from shunting signals, except for those reading into an intermediate block section. Shunting ahead into the block section should be in accordance with GK/T0042, GK/T0051 or GK/T0054, as appropriate. (See also the B30062 series of regulations.) For new work, approach control should be provided for subsidiary signals (PLS or semaphore), in accordance with Section For pre-set shunting signals see Section For shunt overlaps see Section For omission of opposing locking see Section Pre-Set Signals One or more independent shunting signals (PLS or semaphore) may be pre-set by any class of route from a signal. When such signals are pre-set, they should not clear until the aspect controls for the pre-setting route are off, awaiting only the clearance of the pre-set signal(s). Once the signals have cleared, the track sections between the pre-setting and the pre-set signals should be selected out of the pre-set aspect controls to prevent premature replacement. These aspect controls should then include any further pre-set signals in advance proved off. Approach locking and route locking should be applied to the pre-setting route, as if the pre-set signal did not exist. eplacement conditions should be as follows: a) Before the train passes the pre-setting signal, restoring the pre-setting signal control device should replace the pre-setting and pre-set signals. The signals may be recleared by re-stroking the whole route. (If the train has, by then, entered the route, only the signals ahead of the train should clear.) F25

108 ailway Group Guidance Note Page F26 of 191 Withdrawn Document b) After the train enters the route, restoring the pre-setting signal device should have no effect on the pre-set signals. (Additionally on permissive lines it should be possible to extend the replacement of the pre-set signal to include replacement only after the pre-setting route has been cancelled and the route locking release has reached the pre-set signal ). c) estoring the pre-set signal control device(s) at any time should replace the signal whose device is restored, as well as pre-set signals to the rear and the pre-setting signal. Such restoration should not initiate the approach lock release timer. The restoration may be nullified by re-stroking the whole route. d) Once the pre-setting signal has been replaced, an emergency replacement facility should be provided, whereby the restoration of any pre-set control device should replace all the pre-set signals in the route. The restoration may be nullified by simply operating the device again to reclear the pre-set signal(s). e) Track section replacement conditions should be as described in Section The pre-set signal should have the same type of replacement as the pre-setting signal when in pre-set mode, but may have another type in non-pre-set mode. Exceptionally a main signal may be required to be pre-set by another main route, in which case controls similar to those described above should be provided Slots and eleases Where signals are required to be controlled from more than one signal box or ground frame (as described in Section 3.6.1), a slot should be provided such that signal clearance requires authority from two or more control points. The withdrawal of any authority should replace the signal. It should not be possible to fully normalise a slot so as to release other locking, until the signal concerned is proved on and free of approach locking. Semaphore distant signals mounted below any stop signal for another signal box should be slotted by that stop signal. An outer distant should also be slotted by any stop signal mounted on the same post as the inner distant. The outer distant should, conversely, be back slotted by the inner distant and any stop signal mounted on the same post. The slotting should be extended in like manner where there are more than two distant signals. See also Section for distant signals. Back slotting is a means of ensuring that an outer distant arm cannot be off when either: a) the inner distant arm is on; or b) an intervening stop signal worked from another box is on. Slotting should be achieved either mechanically or electrically, as appropriate. Where any of the slot controls are electrical, the slotted signal should be made power operated, so that it is replaced immediately any of the controls are withdrawn. A combination of mechanically operated signal and electrical slot (via the lever lock) should not be provided for new work. Mechanical slotting should be achieved by balance levers on the signal post, as described in Part S. Previous alternative methods of control (such as by underbolting the signal lever with a release from the other signal box) should not be provided for new work. (In the case of underbolting, the signal is not automatically replaced when the slot is withdrawn.) F26

109 ailway Group Guidance Note Page F27 of 191 Where such slotting is not practicable, a separate electrical release may be provided to release the locking on one or more signals, e.g. for a shunter or at a gate box. Where the withdrawal of such a release does not replace the signals, it may be necessary to provide an emergency replacement facility, or alarm, at the appropriate control point. The response of the signal (aspect or arm) and slot control (disengaging relay or slot balance lever) in the on position, and of the slot control in the off position should be suitably repeated and indicated. The minimum indication requirement is to show slot off from the other control point(s) at the signal box that has primary control of the signal, i.e. the signal box whose identification plate and/or signal post telephone is provided at the signal. For ground frame releases see Section 3.6. For ground frame and slotted signal control circuits see Appendix F2: Approach Control Approach control of power operated signals should generally be provided, with automatic signal clearance, in the following situations: a) where there is insufficient spacing between a single yellow and a red aspect in a four aspect sequence, as described in GK/T0032 (the signal to be released after passing the previous signal); b) at the commencement of a four aspect sequence to avoid a signal displaying the first cautionary aspect for more than one signal, as described in GK/T0032 (the signal to be released after passing the previous signal); c) to ensure that train speed is adequately reduced to safely negotiate a turnout, as an alternative to advance warning of divergence, either by approach control from red or from yellow, in accordance with GK/T0035 (the signal to be released when the train has attained the correct speed, as shown in Figure F10); d) to prevent the driver sighting a proceed aspect before the route indicator, where no advance warning of divergence has been received and this could result in a train approaching the turnout at an excessive speed (the signal to be released at the sighting point of the route indicator, as shown in Figure F9); e) to ensure that train speed is adequately reduced to stop short of buffer stops in a bay platform (the signal to be released when the train has attained the correct speed, as shown in Figure F10); f) before displaying a delayed yellow (warning) aspect, to ensure that train speed is adequately reduced to safely approach the signal beyond with only a restricted overlap available (the signal to be released when the train has attained the correct speed, as shown in Figure F10); and g) before displaying a subsidiary aspect (permissive or shunting), where necessary to ensure that train speed passing the signal is such that the train can stop short of any obstruction (the signal to be released when the train is nearly at a stand, nominally 15mph, at approximately 50m from the signal, as shown in Figure F8). For mechanically operated signals, the above should be applied where reasonably practicable, with manual signal clearance by the signaller. Other options include providing advance warning of divergence by means of splitting distant arms and subsidiary signals that lock the signal in rear. F27

110 ailway Group Guidance Note Page F28 of 191 Withdrawn Document See Section for the use of track section timers. See Section 4.5 for approach controlled signals with sequential locking. Additionally, a temporary approach control facility (requiring berth track section occupied) should be provided to cover any such need for a reduction in speed that may arise, but a timer or additional track circuit is not required for the purpose. See also Section Automatic Working Facilities Facilities should be provided in the interlocking to allow controlled signals in track circuit block to be automatically re-cleared, as well as replaced, dependent upon track section conditions, in the following situations: a) for nominated signals, by the provision of an additional automatic working control device for each signal; b) where automatic working is in operation under remote control failure conditions (see Section 3.10); or c) for automatic terminal platform or junction working, initiated by special control device and/or a remote control override system. TO is a requirement. A first come, first served arrangement may be used for trailing junctions. outing information may be derived from a train describer system for facing junctions. See Section for other arrangements. The points should not be called until a time has elapsed after the release of all point locking, to protect against wrong side failure of track sections. The interlocking should be capable of allowing a signal to work automatically for each main route to which it applies as selected by the signaller on initiation of automatic working. This facility may also be extended to warning class routes, as described in Section Automatic working of controlled signals should otherwise be inhibited by means of a signal stick. This control should be applied by the occupation of the first track section beyond the signal when the signal is off. (The berth track is required occupied at the same time to guard against a failure of the first track.) Once applied the signal route must be cancelled and re-set to enable the signal to clear when the remainder of the controls come off again Delayed Clearance Where signal clearance requires some other function to have been operating for a time, automatic operation may be achieved by arranging for the signal aspect controls to initiate the other function and operate a timing device for the required time. Signal clearance then requires the aspect controls and the time cycle completed. Examples include signals positioned within the strike-in point of an automatic level crossing, or of a train activated warning system. See Section (a) for a manual option No Signaller oute Setting Signal route setting may be initiated by train or station personnel under certain circumstances. The following examples are illustrative: a) Where a station platform is located close to an automatic level crossing and the time for station duties is not consistent, a train ready to start (TTS) plunger may be provided for train crew to initiate the time cycle described in Section b) Where automatic terminal platform working is provided (see Section (c)) and there is more than one platform, TTS plungers may be used to select the first departure. F28

111 ailway Group Guidance Note Page F29 of 191 c) Where automatic junction working is provided (see Section (c)) and there is no train describer, TTS plungers may be used to select the appropriate route at the facing junction. At a remote token control point, the route may be selected by withdrawal of the appropriate token. 3.3 Track Sections Mandatory requirements are given in GK/T0011. For the engineering constraints that are dependent on the type of train detection system in use (such as maximum and minimum lengths and response times of track circuits), see GK/H0751. a) Track Sections to be epeated at the Interlocking or Signal Box All track sections that directly control the operation of interlocking functions should be individually repeated at the interlocking. See Section (b), below. The following track sections should be individually indicated to the signaller: i. those that directly control the operation of interlocking functions, up to the berth track of the first caution signal approaching the signal box; ii. any others that control a signalling function operated from the signal box; iii. those associated with the release of in-section ground frames, but only as required in Section 3.6.3(g); iv. those that control any non-track circuit block, but only as required in GK/T0042 and GK/T0051; v. those that control automatic and semi-automatic signals; and vi. those that indicate the position of trains relative to fixed infrastructure (such as tunnels and level crossings), but only where continuous train detection is provided. Where continuous train detection is provided, track sections that are subdivided to operate automatic level crossings, train activated warning systems, or ground frames, etc., are not required to be individually indicated to the signaller, unless they fulfil item vi), above. Subdivided track sections should generally be combined into a single indication to the signaller, and do not need to be separately repeated at the interlocking, except where they consist of more than two non-monitored subdivisions (see Section ). Where continuous train detection is not provided, isolated train detection that is provided to operate automatic level crossings, or train activated warning systems is not required to be indicated to the signaller, unless it also controls any of items i) to iv), above. All track sections (including subdivisions provided to operate automatic level crossings, train activated warning systems, or ground frames, etc.) should be individually identified in the control tables and on the signalling/scheme plan. However, track sections that are subdivided because of equipment limitations (e.g. too long to be one section, or part single rail/part double rail track circuit) need not be identified on the signalling/scheme plan, provided they are shown in the control tables and on the location area plan. For the signaller's indication requirements, see GK/T0025. b) Precautions with Track epeat elays When a track circuit is used to control any signalling function the first repeat relay within the interlocking should be of the slow to operate type, to ensure that trains cannot be lost to the interlocking due to different response and transmission times of the train detection system. Similarly, extra delay should be provided with such inputs to electronic interlockings. Full details are given in GK/C0752. F29

112 ailway Group Guidance Note Page F30 of 191 Withdrawn Document Train detection devices that fail safe (see Part T) generally fail in the occupied state. Consequently, where a less restrictive control requires a track section to be occupied (e.g. approach control), or a more restrictive control requires a track section clear (e.g. last wheel replacement), precautions should be taken to prevent a right side failure creating an unsafe situation. Track repeat relays and timers should be proved as described in Section 3.3.3(e). c) Jointless Track Circuits Certain train detection devices do not provide precise track section extremities, e.g. jointless track circuits (tuned zones and centre points). These are only suitable for applications with sufficiently wide tolerances and should not generally be used to define clearance points, nor replacement joints at 5.5m or less beyond a signal. d) Short Track Circuits Track circuits that are shorter than the maximum distance between adjacent wheel centres on any vehicle (see GK/T0011) require special controls to prevent them clearing until an adjacent track section is clear. For example in Appendix F5, considering the portion of DD track section over the diamond crossing with 713 and 714 points reverse, DD track repeat would be additionally controlled by 713 detected normal, or 714 detected normal, or CE track clear, or FA track clear Track Circuit Block Lines signalled by track circuit block (see GK/T0041) should be provided with continuous train detection compliant to GK/T0011. Each line should be divided into track sections on the following basis. An illustrative example is given in Appendix F5. a) The line should be divided into separate track sections between each stop signal. For signal replacement requirements see Section Wherever practicable, the first track section should start at between 5.5m and 20m beyond the signal. However, where trains regularly stop in advance of a signal having accepted its authority to proceed (e.g. at a station platform or when setting back to shunt), the first track section should commence 0m to 5.5m beyond the signal, so that the signaller and the interlocking are aware that the train has passed the signal. At signal gantries with signals reading in both directions, it may be necessary for the first track section to commence at the signal post. Where it is necessary for the first track to commence 0m to 5.5m beyond the signal, the required distance should be shown on the signalling/scheme plan. b) Separate overlap track sections should be provided beyond signals protecting S&C, movable bridges, or controlled level crossings; beyond signals provided with route locking for some other reason (e.g. trailing points in the destination signal overlap); beyond signals within the strike in point of an automatic level crossing; and beyond signals that have permissive movements up to them. Otherwise, berth and overlap track sections may be combined. (Where the first track section commences 0m to 5.5m beyond the signal, this track section should always be provided in the controls of the signal in rear, including warning aspects. This is to ensure that a train that has passed through the section does not overhang onto the approach side of the signal.) See also Section c) In S&C, as few track sections as practicable should be provided, whilst considering all other requirements and ensuring that parallel movements do not share common track sections. Care should be taken that points are not F30

113 ailway Group Guidance Note Page F31 of 191 track locked by one movement, when they could be legitimately moved to allow a parallel movement (see also Section 3.5.4). Wherever practicable track sections over S&C should extend to include all applicable clearance points (see Section 3.3.4). d) Track section joints should generally be provided immediately in advance of any points and level crossings, so that track locking can be released as soon as possible after a train has passed clear, to prevent other traffic being unnecessarily delayed. e) Additional track sections should be provided to control an AWS inductor and/or replace a distant or banner repeating signal on a permissive line (see GK/T0016 and GK/T0060). These signals should also be replaced by a train detection device, where reasonably practicable, on non-permissive lines. See Section f) Separate track sections should be provided to prove tunnels (and other similar environments) clear of trains, in accordance with GK/T0011. g) Additional track sections may be required where it is necessary to compare the length of a train about to enter a permissive section with the length of the unoccupied track section available (Lime Street controls). See Section 3.2.6(b). h) Additional track sections may be required where it is necessary to approach release a junction signal at the point the route indication becomes readable, or to approach release a warning aspect or a subsidiary signal (PLS or semaphore) when a train is nearly at a stand. It is preferable for these berth track sections to be within 275m of the signal. See Section i) For train detection requirements associated with ground frames that are not within interlocking areas, see Section j) In the case of direction lever working, continuous train detection should be provided between the entrance and exit signals (in both directions) through the direction lever section, in accordance with GK/T Station Limits in Non-Track Circuit Block The requirement for continuous train detection, given in Section 3.3.1, may be relaxed, as permitted in GK/T0042 or GK/T0051, provided that any length of track not clearly visible from the controlling point is provided with train detection, and it is demonstrated that risks are controlled so far as is reasonably practicable, taking account of fog conditions. The following considerations and minimum requirements should apply: a) Where track sections are provided within station limits, they should generally extend to the next signal ahead, or its overlap, (unless provided solely to lock movable infrastructure) and should be indicated in the signal box. Section 3.3.1, items (c) to (h), should also be considered, where applicable in station limits. b) Where a track section is provided, it should be divided at each signal to provide an overlap, which should generally be as follows: i. block overlap at 400m beyond the home signal; ii. intermediate block home signal overlap at 400m; iii. overlaps of other signals within station limits (where the signal in rear is subject to the restricted approach arrangement when the signal is on) at 90m, wherever reasonably practical. F31

114 ailway Group Guidance Note Page F32 of 191 Withdrawn Document The 400m overlap may be reduced to 180m where the distant signal is colour light (see Figure F13). The restricted approach arrangement may be avoided for a colour light signal that is signal spacing distance beyond a signal capable of displaying a first caution aspect, by providing a 180m overlap. See also Section c) Train detection (track circuit or FPL bar, etc.) should be provided between a junction signal and the facing points ahead, to ensure that, once a train has passed the signal, the points cannot be unbolted or moved until the whole train has passed clear of the points. Where reasonably practicable, this should also be applied to other movable infrastructure. Such train detection may be used both to release the signal approach locking and to apply route holding. d) Track sections should be provided to track lock any power operated points. Where reasonably practicable, this should also be applied to other movable infrastructure. e) For train detection requirements associated with in-section ground frames, see Section f) In the case of non-token systems, a berth track section should be provided at the home signal, generally commencing between 180m and 230m on the approach side (but not less than 180m). Sighting of the signal should be ensured from the commencement of the track section to facilitate use of the restricted approach arrangement. An audible annunciator may be associated with the berth track section where necessary to alert the signaller in order to avoid undue delay. A separate track section should be provided, where reasonably practicable, from the home signal to the block overlap (or to the next stop signal, if situated in the overlap). A block overlap track section should always be provided, and included in the block controls, where there is no conflicting movement within the overlap, unless an additional signal intervenes. g) In the case of non-token systems on bi-directional lines, additional train out of section proving should be provided in accordance with GK/T0051. h) Where reasonably practicable in absolute block, and elsewhere as required by GK/T0051, suitable train detection should be provided beyond the section signal to detect a train entering the section and/or to automatically replace the section signal. i) For intermediate block home signals, continuous train detection should be provided from the section signal to the overlap beyond the intermediate block home, with a separate overlap track section, in accordance with GK/T0042. F32

115 ailway Group Guidance Note Page F33 of Estimation of Train Position or Speed by Expiry of an Elapsed Time Length of Berth Track Section Track Section Timer a) elease of Locking 50m 13s Figure F7 should be used 60m 14s to determine the timed 80m 18s release of opposing route 100m 21s locking and overlap 120m 23s locking necessary to 140m 25s prove a train at a stand. 160m 28s 180m 30s 200m 32s 250m 34s 300m 39s 350m 42s 400m 45s 500m 51s 600m 55s 700m 60s 800m 65s 900m 68s 1000m 72s b) Approach Control of Subsidiary Signals Figure F7 Length of Berth Track Section Timing to a Stand Track Section Timer Figure F8 should be used to determine the timed <55m 0s approach release of signal 75m 7s aspects necessary to 100m 11s prove a train nearly at a 120m 13s stand (speed reduced to a 140m 15s nominal 15mph). 160m 18s 180m 20s However, under the 200m 22s restricted approach 250m 25s arrangement, a slightly 300m 28s higher approach speed is 350m 32s preferable, as described 400m 35s below. 500m 40s Figure F8 Timing to Nearly at a Stand c) Approach Control of Warning Aspects Figures F9 and F10 should be used to determine the timed approach control of aspects (delayed yellow) where the length of a restricted overlap ahead of the next signal in advance is not less than 55m. The aspect may then be released when the train speed has been reduced to that appropriate to the overlap available, in accordance with GK/T0078. F33

116 ailway Group Guidance Note Page F34 of 191 Withdrawn Document The signal clearance point can be obtained from the overlap length in Figure F10. The approach release time can then be read down from the signal clearance point and across from the berth track section length in Figure F9. The approach speed should not generally exceed 30mph under the restricted approach arrangement. See also Section If the overlap available is less than 55m in length, the train should be brought nearly to a stand in accordance with Figure F8 (non-preferred). d) Approach Control of Junction Signals Figure F9 should also be used to determine the timed approach control of main aspects on junction signals, where required by GK/T0035 (generally where the main aspect is visible before the route indicator is readable). The aspect is held at red or yellow until the train is at the sighting point of the route indicator, i.e. until the indication is readable. The readability of different types of route indicators are given in GK/T0031. The achievable sighting distance for each signal is recorded by signal sighting committees in accordance with GK/T0037. e) Proving of epeat elays and Timers Such time releases should be initiated by track section occupation or by operation of a discrete train detection device, in accordance with GK/T0011. The track repeat relay, or other device, initiating operation of such time delay or effecting approach control without time delay (including temporary approach control) and the timing device (if it requires proving) should be proved in its normal position in the aspect controls of the main signal(s) in rear, as described in Appendix F2:4.2. See Part D for further details of timing devices. f) Application of the Timings The times given in Figures F7 to F9 will generally suffice for all ranges of approach speed and gradient, and for the braking and acceleration performance of all permitted trains. Nevertheless, each application should be checked to ensure that the worst combination of these factors cannot give rise to an unsafe situation. For instance, a slow train will take longer to travel from the timer initiation point to the signal clearance point than a fast one. Consequently, the timing of trains over distances greater than 275m should be avoided where there is a danger of relatively slow trains seeing the aspect clear too early (e.g. before the route indication is readable, unaware of the need to brake to the turnout speed). This applies to the shaded region of Figures F8 and F9. An additional track section should instead be provided within 275m of the clearance point. If a treadle is used, it should be at least 75m from the clearance point so as to require a timer (and prevent the driver anticipating the clearance as he passes the treadle), it requires the track section occupied and it should be proved normal in the signal(s) in rear. Signal clearance should not be unnecessarily delayed by extending the times given in the table to cater for occasional slow trains. Figure F11 is a similar table for use with reduced overlaps which are considered in Section F34

117 ailway Group Guidance Note Page F35 of 191 Signal Clearance with Train Approaching Length of Signal Clearance Point on Approach to Signal Berth Track 60m 75m 100m 140m 180m 200m 230m 250m 285m 300m 340m 400m 500m 600m 700m 800m Section(s) Track Section Timer 60m 0s 75m 4s 0s 100m 7s 4s 0s Use timer on track section(s) in rear, 140m 11s 6s 4s 0s summing length of all track sections. 180m 16s 11s 8s 4s 0s 200m 18s 13s 10s 5s 0s 0s 230m 20s 15s 12s 7s 4s 4s 0s 250m 21s 17s 14s 9s 5s 4s 0s 0s 285m 22s 18s 15s 10s 6s 5s 4s 0s 0s 300m 24s 20s 17s 12s 8s 7s 5s 4s 0s 0s 340m 27s 23s 20s 15s 11s 10s 8s 6s 4s 4s 0s 400m 31s 27s 24s 19s 15s 14s 12s 10s 8s 7s 4s 0s 500m 36s 32s 29s 24s 20s 19s 17s 15s 14s 13s 10s 6s 0s 600m 41s 37s 34s 29s 25s 24s 22s 20s 19s 18s 15s 11s 6s 0s 700m 46s 42s 39s 34s 30s 29s 27s 25s 23s 22s 19s 15s 10s 6s 0s 800m 50s 46s 43s 38s 34s 33s 30s 28s 27s 26s 23s 20s 14s 10s 8s 0s 900m 54s 50s 47s 42s 38s 37s 35s 33s 32s 31s 28s 24s 18s 14s 11s 10s 1000m 58s 54s 51s 46s 42s 41s 38s 36s 35s 34s 31s 27s 22s 17s 14s 12s 1100m 60s 56s 53s 48s 45s 44s 42s 40s 39s 38s 35s 31s 25s 20s 18s 16s 1200m 64s 60s 57s 52s 48s 47s 45s 43s 42s 41s 38s 35s 30s 24s 21s 20s 1300m 67s 63s 60s 55s 52s 51s 48s 46s 45s 44s 41s 38s 32s 27s 24s 23s 1400m 70s 66s 63s 58s 55s 54s 51s 49s 48s 47s 44s 41s 35s 29s 27s 26s eadability Junction Indicator - maximum readability 300m to 800m, depending on angle of sight of Standard oute Indicator Indicators Miniature t Ind Figure F9 Track Section Times to be Used for a Given Signal Clearance Point Note: Shading represents non-preferred area of table. For details see text. elease Speed and estricted Overlaps <55m 55-59m 60-69m 70-74m 75-79m 80-89m m m m m ange of estricted OLs for Early Clearance of Signal 15mph 20mph 25mph 30mph 35mph 40mph 45mph 50mph 55mph 60mph elease Speed for Signal Clearance use Fig F8 60m 75m 100m 140m 180m 230m 285m 340m 400m Signal Clearance Point on Approach to Signal OL generally limited to 30mph Figure F10 Signal Clearance Point to be Used for a Given elease Speed or estricted Overlap Length educed Overlaps 15mph 20mph 25mph 30mph 35mph 40mph 45mph 50mph 55mph 60mph Unrestricted Approach Speed 45m 55m 60m 70m 75m 80m 90m 105m 125m 135m educed Overlap Length Figure F11 educed Overlap Length to be Used for a Given Unrestricted Approach Speed F35

118 ailway Group Guidance Note Page F36 of 191 Withdrawn Document Foul Track Sections Where it is not practicable to extend track sections over S&C up to all applicable clearance points, the track sections between those in the direct line of a signal route (including the overlap) and the clearance points should be regarded as foul track sections. Where it is only possible for such track sections to be foul when occupied with points on the flank of the route in a certain position, the foul track section control may then be conditioned upon the lie of the flank points. a) Track Locking of Points Point track locking controls should be extended to prevent points being called to any position that would allow a route to be set with a track section occupied that was foul of the route, i.e. points may be allowed to move into the line of an occupied track, but not away from it. Where such foul track section control is conditioned upon the lie of other flank points, those points should be proved set and locked (and, if necessary, detected - see subsection c, below) with the track locking, unless the foul track section is clear. This will generally prevent any route being set with an occupied foul track section (except where it is possible for a train to ease back and re-occupy a foul track that had been cleared) and also provide protection for hand signalled movements. (Where it would not be unduly restrictive on other movements, points may be dead locked by foul tracks, rather than conditionally, provided that route setting could not be prevented by a train proceeding on a parallel route.) For example in Appendix F5, considering the branch line junction, the track locking on 707 points (N>) requires (CC clear or 708N) and (FC or 706) and (>N) DH clear, as well as track DG in dead. Points 708 track locking (N>) requires (DG clear or 707N) and (>N) DH clear, and track CC in dead. Considering the double junction and assuming the joints in the ten foot are foul, the track locking would be as follows if each set of points were treated separately: Points Dead Locking N to to N 709 BD, BE, CD, CE (AC O 712N), (DE O 710N) 710 DE (BE, CD O 709) (CE O 709N) 711 BE (BD, CE O 709) (AC O 712N), (CD,CE O 709N) 712 AC (BD O 709) (BE O 709N) However, considering that each route requires at least two sets of points, the track locking can be simplified as follows, whilst still preventing points being called to a position that would allow a foul route to be set: Points Dead Locking N to to N 709 BD, BE, CD, CE (DE O 710N) 710 DE CE 711 BE AC 712 AC BE b) Foul Tracks in Signal Aspect Controls Generally, foul tracks should also be proved directly in the signal aspect controls, to ensure that any unauthorised movement foul of the route replaces the signal. Providing it does not restrict other permissible movements, signal routes should set and lock (and, if necessary, detect - see sub-section c, below) flank points upon which foul tracks are conditioned. For example in Appendix F5, considering the branch line junction, routes from 105 set and lock points 707 normal, and route 212B sets and locks 708 normal. Considering the double junction: route 51 requires 711N; 56A F36

119 ailway Group Guidance Note Page F37 of 191 requires 711; 56B requires 712N; and 105B(M) and 203B(M) (and shunt routes) require 710N and 711N. Where flank points are called by the route, they should be held by route locking until the movement has passed beyond the place at which the track section was foul. Only those foul track sections that have not been conditioned out by calling flank points then need to be proved in the signal aspect controls. Where such foul track section control is conditioned upon the lie of flank points that are not called by the route, those points should be proved set and locked (and, if necessary, detected - see sub-section c, below) in the signal aspect, unless the foul track section is clear. (Such foul tracks may be provided dead in the aspect, rather than conditionally, except where a train proceeding on a parallel route would replace the aspect.) For example, considering the branch line junction, 203 aspect requires DH clear or 707, and 212A requires DH clear or 708. Considering the double junction: 56 (B route) aspect requires CE or 710N; 105 (A route) and 203 (A route) require CE or 710; and 214 requires CE or 709N. In the case of foul tracks over diamond crossings, flank points on adjacent track sections may be used for conditioning, but it is preferable to use the sequential operation of track sections if the foul track could be occupied by an overrun, rather than conditioning by flank points unrelated to the overrun. (This type of overrun protection is considered further in Section ) c) Detection of Flank Points Where flank points are called by a route to give flank protection from SPADs (see Section 3.4.4), as well as to condition out foul tracks, they should be detected at time of signal clearance. Points that have to be swung away, because they are facing points within a flank overlap, should also be detected at time of clearing, when the flank overlap is locked, as described in Section 3.4.2(d). Otherwise, where foul track section controls are conditioned on the lie of flank points, it will not generally be necessary to include point detection in the conditioning, unless it is considered, after balancing the following risks, that continuous detection, or detection at time of signal clearance (for foul tracks in signal controls), is necessary: i. the likelihood of a collision between a signalled movement and a hand signalled movement; ii. the permissible speed of any movement that might conflict; iii. hand operation of power operated flank points destroying the foul track controls for a signalled movement; and iv. where continuous detection is provided, the secondary hazard created by detection failure. The minimum requirements are summarised in Figures F16 and F Overrun Protection and Mitigation Main Overlaps An overlap should be provided beyond every block signal that acts as a destination for a movement from a main aspect, in accordance with GK/T0078 (see also GK/GN0678). Overlaps have two purposes: to maintain a minimum distance between following trains; and to prevent conflictions occurring immediately ahead of a train approaching a signal at danger. F37

120 ailway Group Guidance Note Page F38 of 191 Withdrawn Document a) Length Overlap length should be determined by the risk of a SPAD and the likely overrun in that event. Generally an overlap length of 180m will be sufficient for stop signals where the related caution signal(s) are colour light, or 400m where any related caution signal is not colour light. See Figures F12 and F13 for details. Consideration may be given to reducing these distances in the following circumstances to avoid restrictions to other movements: i. educed Overlap Where the maximum attainable approach speed under clear signals (from 400m in rear of the signal whose overlap is under consideration) does not exceed 60mph (with no local reduction in permissible speed), Figure F11 may be used to derive the overlap length. See also GK/GN0678 for further guidance on this subject. ii. estricted Overlap (OL) Where a train has been brought nearly to a stand at the signal in rear, under the restricted approach arrangement (see Section 3.2.5) a restricted overlap should be provided. estricted overlaps are provided in addition to a full overlap. Although a minimum length is not prescribed, for new work and otherwise where reasonably practicable, the restricted overlap should be 45m beyond a colour light signal or 90m beyond a semaphore signal. It is preferable, if a longer restricted overlap length is available, for approach control on the signal in rear to be relaxed in accordance with Figure F10, on the assumption that the train will not accelerate before sighting the next signal at danger. F38

121 ailway Group Guidance Note Page F39 of 191 Overlap Type Full OL educed OL OL Shunt OL Destination Signal Minimum Length Separate Track Section OL equired Clear OL equired Locked Level Crossing in OL Colour light stop signal with colour light caution(s) 180m generally, but see Section 3.3.1(b) ü ü locked within first 50m #4 Stop signal/board with any 400m ü ü ü locked within non-colour light distant first 50m #4 Non-colour light stop signal 180m, but 400m in ü #3 ü ü locked within with colour light caution(s) fog & falling snow first 50m #4 Colour light stop signal with 45m to 135m #1 generally, but see ü ü locked within colour light caution(s) Section 3.3.1(b) first 50m #4 Any non-colour light stop or where specially ü ü ü locked within distant signal authorised #1, #2 first 50m #4 Colour light stop signal 45m to 70m #1 may combine with not unless separate ü not locked (for new work) first track past sig track Non-colour light stop signal 90m where points, etc., ü ü not locked (for new work) in overlap Shunting signal or LOS with 180m not applicable no ü not locked passenger movement (or 45m #2) confliction in overlap Shunting signal or LOS with 45m not applicable no ü not locked non-passenger movement confliction in OL Main signal ahead of shunt move with confliction in OL high risk signals only #2 Figure F12 not applicable no ü not locked Types of Overlap - Track Circuit Block Overlap Type Destination Signal Minimum Length Train Detection #5 OL equired Clear OL equired Locked Level Crossing in OL Block Colour light stop signal with colour light caution(s) 180m where BOL clear of fouling point in block controls or by instruction by signaller s instruction no restriction #4 Overlap (BOL) Stop signal/board with any non-colour light distant 400m where BOL clear of fouling point in block controls or by instruction by signaller s instruction no restriction #4 Non-colour light stop signal with colour light caution(s) 180m, but 400m in fog & falling snow where BOL clear of fouling point, #3 in block controls or by instruction by signaller s instruction no restriction #4 Colour light stop signal with colour light caution(s) 180m required for IBH, otherwise #6 where train detection provided ü locked within first 50m #4 Full OL Stop signal/board with any non-colour light distant 400m required for IBH, otherwise #6 where train detection provided ü locked within first 50m #4 Non-colour light stop signal with colour light caution(s) 180m, but 400m in fog & falling snow 400m required for IBH, otherwise #6 where train detection provided ü locked within first 50m #4 educed OL All cases where specially authorised #1, #2 (see appropriate cases above) Colour light stop signal 45m to 70m where provided not unless separate ü not locked OL #1, #6 track #7 Non-colour light stop signal 90m #6 where provided where train detection provided ü not locked Shunting signal or LOS with 180m not applicable no ü not locked passenger movement confliction in overlap (or 45m #2) Shunt OL Shunting signal or LOS with non-passenger movement confliction in OL 45m not applicable no ü not locked Main signal ahead of shunt move with confliction in OL Figure F13 high risk signals only #2 not applicable no ü not locked Types of Overlap - Non-Track Circuit Block Notes: #1 = depending on approach speed. #2 = subject to risk assessment. #3 = 400m track, or 180m track with instructions for double block working, or two tracks (for 180m & 400m OL) with fog switch. #4 = preferred arrangement is for stop signal to be 50m clear, or OL provided, so as not to unduly delay road traffic. See Section 3.4.2(h). #5 = separate OL track sections for BOLs, IBH OLs and where there are points, etc., in the OL (see Section 3.3.2). #6 = where reasonably practicable, but not mandatory. #7 = also applies to stop signals beyond the home signal within station limits and related to the same distant signal(s) as the home. F39

122 ailway Group Guidance Note Page F40 of 191 Withdrawn Document iii. Train Interactive Systems Where a trainstop, automatic train protection (ATP), or train protection and warning system (TPWS) is provided to reduce the risk of SPADs, overlap lengths should be appropriate to the system. If inter-running of trains equipped for different systems is permitted, the overlap should cater for the worst case. See Section Factors to be considered as reasons for not reducing the overlap length to the degree permitted above are given in GK/T0078. b) Proving the Overlap Clear Full overlaps (and reduced overlaps) should generally be proved clear (including foul tracks) with a separate track section or sections, except where combined overlap and berth tracks are permitted. See Section 3.3.1(b). Overlap track sections may be longer than the required overlap, but the actual length should be shown on signalling/scheme plans if it differs from the standard 180/183m. Overlap track sections may not be necessary in nontrack circuit block (see Section 3.3.2) where the overlap is directly visible to the signaller, but, where provided, overlap track sections should be proved clear. An example of a combined berth and overlap track is given at signal 54 in Appendix F5. estricted overlaps (OLs) do not generally have to be proved clear, unless a suitable track section otherwise exists. See example OLs at signals 203 and 214 in Appendix F5. For restricted phantom overlaps (POLs) see Section 3.4.2(g). c) Suitability Any line may be used as part of an overlap provided there is continuous train detection, and, where applicable, route holding, between the destination signal and the end of the overlap, irrespective of whether any route of any class of the destination signal reads over the line. However, where certain lines are selected as preferred overlaps, these should be set, if available at time of route setting. Cancellation of such a route ahead should not change the overlap position. Preferred overlaps should be identified on the control tables. Alternative permitted overlaps over trap points reverse that usually protect the overlap, should not be set unless a route ahead has been set over the trap points, or the points are locked by the signaller s individual control device. (It should not be possible to move points to a non-permitted overlap, e.g. to a line without continuous train detection, until the route in rear and its overlap are normalised.) The sharing of overlaps for opposing main signals is not permitted, but a common track section may be shared, provided that its length is at least equal to the sum of the lengths required for each overlap. d) Block Overlaps In non-track circuit block, the end of the block overlap (BOL) beyond the home signal is known as the clearing point. The block overlap is locked only by instruction, as shown in Figure F13. Except in the case of restricted acceptance (see Section 3.2.5), the signaller should ensure that the block overlap is clear with no conflicting movement authorised before accepting a train. (See the B30062 series of regulations.) F40

123 ailway Group Guidance Note Page F41 of 191 Where there is no signaller present, the requirements of GK/T0078 may be satisfied by the provision of a home signal in the form of a stop board instructing the driver to stop and proceed if the platform line (or loop, etc.) is clear. With ETB, the distance between the stop board instructing the driver to obtain token and the train clear marker should equal the maximum train length plus an appropriate overlap, unless a separate home signal stop board, as above, is provided. e) Terminal Lines Buffer stops acting as a destination for a movement from a main aspect should provide an acceptable arresting arrangement in lieu of an overlap. Stop boards acting as a destination for a movement from a main aspect and acting in lieu of buffer stops should be provided with an appropriate overlap or a retarding device suitable for the approach arrangements, as described in Section 3.4.5(b). Track circuit interrupters may be used where necessary in these situations (see Section 3.4.5(f)) Locking of the Overlap Where points, ground frames, level crossings or movable bridges are situated in the overlap, or where opposing routes apply, overlap route locking should generally be provided as described in Section All signalling functions, except facing points that act as a hinge for a permitted alternative overlap, should be set and locked in the appropriate position until the route and overlap locking are normalised. Such locking may be conditional upon the position of the hinge points. Overlap locking also applies to trap points required to protect the overlap (but see Section 3.4.1(c)) and flank points required to condition out foul tracks (unless the conditioned foul track is included instead, see Section 3.3.4(b)), but points required solely to provide flank protection should not be set or locked. Point locking and proving is summarised in Figures F16 and F17. For the release of overlap locking see Section a) Facing Points in the Overlap Power operated facing points may be moved in order to swing the overlap to a permitted alternative when that is available. (Available means track sections clear, trailing points set or free, and no conflicting route or overlap, or, on route setting systems, locked by another overlap that can be swung away.) Signalling functions, particularly trailing points, beyond such facing points in the overlap are locked conditionally by the signal in rear and may be released when the facing points have been swung to the new overlap (or, on route setting systems, are about to swing once the trailing points have been released from their old position to allow the new overlap to be established). The counter of this conditional locking prevents the hinge points moving to an overlap that is not available. Signals should lock mechanically operated facing points in the overlap in either position with the FPL in. F41

124 ailway Group Guidance Note Page F42 of 191 Withdrawn Document b) Time of Operation Locking Time of operation locking should be applied to facing points in the overlap situated within 20m of the commencement of the first track section ahead of the signal, to ensure that, should a train pass the signal at danger, it would not reach the points until they had completed any movement in progress. This point locking should be effective only when a main class route is set up to the signal (or unrestricted main aspect selected for non-route setting systems) and requires the signal berth track section clear, or occupied for sufficient time to prove any approaching train at a stand. c) Swinging Overlaps on oute Setting Systems On route setting systems, facilities should be provided for overlap swinging either by individual point control device or by the setting of a second route that is foul, or its overlap is foul, of the first overlap. Where a point control device is used to swing an overlap, the remainder of the new overlap should set automatically without any further action by the signaller. An overlap may also be swung by the setting of a route onwards from the destination signal. (However, where this would swing to a non-permitted overlap, the first route would have to be normalised before setting the onward route.) d) Proving the Overlap Points The detection requirement of signalling functions in the overlap is the same as if they were in the route. Signal aspects should not replace momentarily as an overlap is swung. If, when an attempt is made to swing an overlap, the detection of the points that are required to move is not made up within a nominal five seconds, the entrance signal should be replaced. Points that have to be swung away, because they are facing points within a flank overlap, should be detected at time of clearing, when the flank overlap is locked. e) Examples of Swinging Overlaps In Appendix F5, signal 214 requires DG clear, 707 detected N or, ([DH clear, 708 set and locked normal, and 705 set and locked normal and detected at time of clearance, or locked reverse by a conflicting overlap that is free to be swung away] or 707 set and detected normal), ([FC clear and 706 set, locked and detected normal] or 707 set and detected reverse); 705 and 707 control ineffective for 5s after overlap starts to swing. (Points 708 are included to condition out CC track which is foul, so detection is not generally required. Points 705 are included for trapping protection and so should be detected. The latter can be swung when locked reverse by another overlap; hence the 5s inhibition in the detection requirement. Note, however, that 705 cannot be locked reverse by the overlap if 103 is an auto signal, as considered below.) Points 705 and 708 are set and locked normal, when 214 is set and 707 is set reverse. Similarly, points 706 are set and locked normal, when 214 is set and 707 is set normal. When 214 is set, hinge points 707 are called normal, if the new overlap is available, by: point control device; route 212A; a route from 105 which requires 705 and 708 reverse; or a route up to 105 when 705 is locked reverse. They are called reverse, if the new overlap is available, by: point control device; route 212B; or routes 505B or 506 which require 706 reverse. The point locking thus includes: 707 is set and locked normal by 214 route when 705 or 708 are locked reverse; and 707 is set and F42

125 ailway Group Guidance Note Page F43 of 191 locked reverse by 214 when 706 is locked reverse. To swing the hinge points 707 (N>) when 214 is set, the counter conditional locking (proving new overlap available) requires DH clear, 708 set normal or free, and 705 set normal, free, or locked reverse by a conflicting overlap that is free to be swung away. Similarly, 707 (>N) requires FC clear and 706 set normal or free. Exactly the same locking is required for 56A route, as 214 above. For a second example, consider if 103 were a controlled signal leading up to 105. Signal 103 would require EL clear, 705 detected N or, (DH clear or 705 set and detected normal), ([707 set and locked normal, and detected at time of clearing, or 705 set and detected normal] when routes 56A or 214 are set); 705 and 707 control ineffective for 5s after overlap starts to swing. Points 707 would be set and locked normal at time of setting route 103, when 705 is set reverse, for overlap flank protection. When 103 is set, hinge points 705 would be called normal by: point control device; route 212B; or routes 56A or 214 when 707 is locked reverse. They would be called reverse, if the new overlap were available, by: point control device; or routes from 105. To swing them reverse when 103 is set, the counter conditional locking would require 707 set normal, free, or locked reverse by a conflicting overlap that is free to be swung away. In fact the controls can be simplified by making 103 an automatic signal, as shown on the layout plan. Facing points 705 in the overlap would then be free of controls of 103, but required to be swung normal for trapping purposes by: 212B route; 201 main, but not warning route; routes from 203; and routes up to 212 when 707 is set reverse. If considered necessary, 103 could detect 707 normal when 705 reverse and route 56A or 214 set. (The aspect controls for 103 are included in an example of safety analysis in GK/T0701, Part.) f) Swinging Overlaps on Lever Frames In the case of power operated facing points on lever frames, the trailing points have to be moved first to establish the new overlap before the hinge points lever becomes free, but otherwise the controls are as stated in items (a), (b) and (d) above. The counter conditional track controls are provided in the selection lock and point locking in the interlocking lock. (Mechanically operated facing points should be locked by the signal in rear, because continuous motion is not guaranteed.) g) Phantom Overlaps Where the overlap track section is extended beyond the required overlap length, then any facing points situated beyond the required overlap length need not be proved in the rear signal controls. Similarly, the overlap track section may be allowed to extend foul of another line, but without restriction to movement on that line. In both such cases the required overlap length should be marked on signalling/scheme plans as a phantom overlap (POL). An example is given in Appendix F5, where the overlap from 105 signal, with 705 reversed, conflicts with route 212B, but does not conflict with routes from 203 signal. A similar situation occurs where OLs have no separate overlap track section. Because it is not necessary to prove the OL clear (see Section 3.4.1), the extent of the OL may be defined on the plan by a restricted phantom overlap (POL) symbol. An example is given in Appendix F5 at 203 signal, where the POL is clear of routes over 708 reversed. F43

126 ailway Group Guidance Note Page F44 of 191 Withdrawn Document h) Level Crossings in the Overlap Signals should preferably be situated 50m clear of a level crossing. This distance may be reduced to 25m where the risks of a SPAD are controlled so far as is reasonably practicable, e.g. where the crossing is situated immediately beyond a station platform or where the protecting signal is a stop board. Exceptionally, a non-block protecting signal may take the form of a red target mounted on the crossing gates with a worked distant signal. Where the above is not practicable, a controlled level crossing should generally be proved closed to road traffic before the signal in rear can clear. However, where there is a requirement for trains to approach the protecting signal with the crossing open to road traffic, so as to avoid undue delay to road users, a restricted approach arrangement may be provided, as described in Section Alternatively, the crossing may be closed to road traffic to allow the signal in rear to be cleared and re-opened once the train has come to a stand at the protecting signal. In non-track circuit block, a controlled level crossing situated in the block overlap should not control the block, but the level crossing operation should be regulated by the signaller. Any additional restrictions at existing level crossings should not be relaxed, except as part of an overall review of the crossing protection arrangements. i) Movable Bridges in the Overlap Signals should preferably be situated full overlap clear of a movable bridge. Where this is not practicable, the bridge controls (see Section 3.9.1) should be locked by the signal in rear. However, where there is an operating requirement for trains to approach the protecting signal with the bridge open to water traffic, trap points should be provided in lieu of an overlap, together with a retarding device suitable for the approach arrangements, as described in Section 3.4.5(b). j) Passing Loops At passing loops on single lines, section signals (or stop boards) in the loop should preferably be situated overlap clear of the single line connection. Where this is not practicable, the opposing home signals should be locked to prevent simultaneous entry to the loop. However, where there is an operating requirement for trains to enter simultaneously, trap points should be provided in lieu of an overlap, together with a retarding device suitable for the approach arrangements, as described in Section 3.4.5(b) Shunt Overlaps Simplified overlaps are required for shunting movements on running lines, but the overlap does not have to be proved clear. Only the following functions in the overlap are required to be locked: a) conflicting passenger movements, i.e. (M), (W) and (C) routes, generally within 180m of the destination signal (but not their overlaps); and b) conflicting non-passenger movements, i.e. (S) routes, within 45m of the destination signal. F44 Where necessary for operating reasons, and the risk is acceptable (i.e. the cost of provision is grossly disproportional to the safety improvement gained), item (a) may be relaxed to within 45m. The infrastructure controller may relax all

127 ailway Group Guidance Note Page F45 of 191 requirements where the destination signal is equipped with a main red aspect and has a low risk of SPADs, except where regular propelling movements take place. It is generally simpler in free-wired systems to lock the necessary routes normal, rather than locking points in the overlap, although geographical systems generally apply overlap locking via the points. Overlap route lights are only required on the signalling display (and overlap symbols on the signalling/scheme plan), if the locking is accomplished through the points. So, for example in Appendix F5, 510B generally locks 105A(M) and 105B(M), when 707 reverse, but does not lock 105C(S) or 105D(S) in the overlap, and does not require DG, DH, or FC tracks clear. (However, in practice all routes from 105 will call 707 points normal in order to give flank protection, as described in Section ) Conversely, 505A locks 105C(S), 105D(S), 203C(S) and 203D(S) because they conflict within 45m, but does not lock 216, even with 713 reverse, and does not require DC or DD clear, unless a SPAD is detected at Flank Point Setting (Flank Protection) Where suitable points exist in a layout, overrun protection should generally be provided by setting, locking and detecting points on the flank as if they were in the line of route, so as to protect that route, or its overlap, from a SPAD. equirements and relaxations are given in GK/T0078. Generally, for new work, detection of flank points is only required at time of signal clearance. Flank points that do not provide overrun protection, but are set so as to avoid having to prove foul tracks, do not generally require detection, as described in Section 3.3.4(c). For example in Appendix F5, considering the branch line junction, routes from 105 call points 707 normal, to protect against a SPAD at signal 212. Flank protection is achieved at the double junction by giving both facing points the same number, 709. In the event of a failure in the setting, locking, or detection of flank points, the signal may still be allowed to clear where the interlocking system can automatically inhibit routes over the failed points and routes up to the appropriate protecting signals. So, if 707 points cannot be set, locked or detected normal, routes from 105 would lock routes 56A, 214 and 510B Trap Points (Trapping Protection) Trap points may be provided in lieu of overlaps, flank point setting and enhanced overrun protection, to protect authorised routes from unauthorised movements. The following features should be considered: a) Provision Trap points (or derailers where speeds are extremely low) should generally be provided, unless other connections serve the same purpose (see Section 3.4.4), in the following circumstances: F45

128 ailway Group Guidance Note Page F46 of 191 Withdrawn Document i. where sidings and terminal platform lines join passenger running lines, particularly where there is shunting not under the signaller s control, or where vehicles could run away on a falling gradient (see GK/T0078); ii. where trains regularly come to a stand at a signal and there is a risk of a SPAD after the overlap locking has released (see GK/T0078); or iii. in lieu of an overlap at movable bridges, passing loops, the convergence of a non-passenger running line with a passenger line, etc. (see Section 3.4.2). b) etardation Guide rails should be provided at trap points to minimise the risk of vehicles fouling other running lines. Where such trap points are situated within the required overlap length for a running movement, i.e. (M) or (W) route, they should lead to a retarding device, e.g. a sand hump or interlaced sand drag, designed to arrest any likely unauthorised movement, such as vehicles travelling at up to 20mph. See example at 705 trap points in Appendix F5. Otherwise the trap points would have to be reversed and an appropriate overlap provided before the signal in rear could be cleared. c) Proving outes should generally require normal (trap position) any trap points, or other connections (see Section 3.4.4), that would prevent vehicles from fouling the route or its overlap. Such routes should prove trap points set, locked and detected. Generally, for new work, detection of trap points that are not in the line of route is only required at time of signal clearance. Where power operated trap points are situated on the flank of the route and their setting would be unduly restrictive to traffic movements, the following relaxations should be considered: i. the provision of controls to inhibit the proving when a train is proceeding over the points reverse, away from the route requiring protection; or ii. if the distance from the points to the converging clearance point on the protected route sufficiently reduces the risk of a fouling movement, setting and proving may be totally dispensed with. Distances in excess of 200m may generally be considered to reduce the risk sufficiently. d) Illustration For example in Appendix F5, 714 points provide trapping protection. They are situated in the route of 214, which requires them set, locked and detected in the usual way. They are also on the flank of 56A route, where there are two options, depending on the relaxations granted: i. set and locked normal and detected at time of clearance; or ii. set and locked normal and detected at time of clearance, except when train moving away (routes 105D(S), or 203D(S) clear of CE track, or 507B clear of DE track). Points 705 (set, locked and detected at time of clearance) provide trapping protection on the flank of routes from 203, 201(M) and 212B. (These points also act as facing points to be swung away when flank overlap locked, for 212B route which conflicts with the overlap. outes from 203 do not conflict with the overlap because of the POL.) See the examples in Section 3.4.2(e) for overlap trapping protection provided by 705 points. F46

129 ailway Group Guidance Note Page F47 of 191 e) Normalisation Normalisation of trap points, and other flank points providing similar protection, should be ensured by one or more of the following means: i. protected routes require such points normal, as described in item (c) above; ii. where all authorised movements over trap points are in the trailing direction, the points may be train operated and/or spring controlled to the trapping position; iii. the signaller should be required to return the point lever/switch to its normal position, in accordance with signalling instructions, after the passage of each train over the points reverse (see Part L for details of the signaller s reminder alarm), or iv. exceptionally, power operated points may be self restored where the risk of a fouling movement warrants it, to take effect 5 to 10s after the release of all locking on the points (see Part L for details of the failure alarm). Self restoration is generally only required in high risk situations, e.g. where the ruling gradient from the trap points falls towards the next signal section and vehicles are left unattended. f) Interrupters At trap points fitted with track circuits, an interrupter should be provided to maintain the track section concerned in its occupied state, in the event of vehicles passing over the trap points whilst set in the normal (trap) position. See GK/C0752 for further details of interrupters. Signals protecting adjacent lines that could be fouled by such a movement should prove the interrupter intact, unless they are controlled by the track section concerned (see GK/T0078). For example in Appendix F5, 706B interrupter controls FC track section, which is in the aspect controls of 212 (A route) and 505, but, if considered necessary, the interrupter may also be proved in signal 105. The interrupter at 705 controls EL track section, but should also be proved in 212 signal (B route), and possibly in 203 signal as well. Similar protection may be afforded by an axle counter track section Overrun Detection using Flank Track Sections Where it is not practicable to provide flank protection by setting flank or trap points, and a significant safety benefit would arise, the provision of flank track section overrun detection at vulnerable signals should be considered, either in conjunction with enhanced overrun protection (Section 3.4.7) or separately. It may be initiated by overlap track section, or treadle, occupied without signal having cleared, or by sequential operation of track sections (e.g. overlap track occupied after berth track occupied). It may effect automatic replacement of conflicting signals and/or actuation of a signaller s SPAD alarm (see Part L). Further considerations are given in GK/T0078. In Appendix F5, the following overrun detection might be provided: SPAD at signal 51 replaces signals 105 and 203, or points 709 normal; at signal 56 replaces 214 or 709N; at 203 replaces 105 and (51 or 709N); and at 214 replaces 56 or 709N. F47

130 ailway Group Guidance Note Page F48 of 191 Withdrawn Document At a diamond crossing, it can be preferable to use the sequential operation of track sections for foul track proving in the signal aspect (e.g. foul track clear after flank track in rear occupied, until both tracks clear), rather than conditioning a foul track section by flank points unrelated to any possible overrun (see Section 3.3.4(b)). Signal 214 controls in Appendix F5 include: (CE clear and no SPAD at 56) or 709N. However, if 709B points did not exist to divert the overrun as shown above, the foul track proving could become: (CE clear after BD occupied, until BD, CE clear), or alternatively with full SPAD protection: (BC, BD, CE clear) after (BC and BB occupied, unless 56 used). Track BB occupied is only included to protect against a right side failure of BC track. Each case should be judged on the simplicity and effectiveness of the protection, considering also secondary hazards in the event of a right side track section failure Enhanced Overrun Protection When a train comes to a stand at the signal before an onward route has been set, the overlap locking may be released in accordance with Section 3.7. This removes any protection against passing the signal at danger. The provision of enhanced overrun protection, described in GK/T0078, should be considered at high risk signals such as these. See also GK/GN Train Interactive Systems Full details of train interactive systems are given in Part S. The special controls required for each system should be specified in control tables, in accordance with GK/T0202. AWS should generally be provided in accordance with GK/T0016 and GK/T0364. In addition to the basic controls of signal at green and alight (with economisation where required), the following controls should be provided, either locally or from the interlocking: a) to energise an AWS suppressor for movements that do not require the AWS, particularly on bi-directional lines, e.g. by sequential operation of train detection devices, or using route sticks; and b) to prevent the energisation of an inductor on a permissive line when a second train is entering the section, either by requiring track sections between the inductor and the signal replacement point clear, or by inhibiting the inductor on clearance of a permissive signal. Where trainstops are provided in accordance with GK/T0017 and GK/T0363, the overlap length should be sufficient to accommodate an emergency brake application made at the permissible speed on passing the trainstop. Special controls may be necessary to make the trainstop mechanism ineffective for movements in the opposite direction, but the mechanism should only be lowered when the opposing movement is being made, using similar controls to those provided for AWS suppression. TPWS should generally be provided in accordance with GK/T0090. F48

131 ailway Group Guidance Note Page F49 of Controls for Points and Other Movable Infrastructure Points operated from a signal box, ground frame, or other control point should be set (by signaller s individual point control device, or route setting system), locked (by signal control, or route set) and detected in the signal controls, as summarised in Figures F14 to F17. Note that when the control point can be closed with the line remaining open to traffic, the combination of mechanically operated signals and electrically detected points is prohibited by GK/T0039. The controls for each set of points should be specified in control tables, in accordance with GK/T0202. See also Section in connection with overlap swinging, Section for flank point setting and Section for trap points. For trackside point operation and detection, see Part P Control and Numbering Points on passenger lines should be operated by one of the following means: a) signal box control, in accordance with GK/T0062; b) ground frame control, in accordance with GK/T0061; or c) the passage of trains, in accordance with GK/T0065. On non-passenger lines, hand points may be used. Facing hand points should be detected in signals reading over them, up to 100m beyond the destination, or beyond the limit of train detection. Trailable points on non-passenger lines need not be set or locked for movements over them in the trailing direction. Hybrid methods of control are not generally permitted, but an electrical release may be given from a second control point, either by individual control device, or by route setting over the points reverse. If it is considered that preselection presents a risk, then the release should be given before the points are called by the controlling signal box. Where two portions of a route are set by different signal boxes, then both portions of the route should be set before the points concerned may be called. (This is particularly applicable to crossovers between running lines controlled by different signal boxes.) F49

132 ailway Group Guidance Note Page F50 of 191 Withdrawn Document Controls and Facilities E Q U E S T Mechanical or Electro-Mechanical Interlocking - Level All-Electric (Miniature) Lever Frame - Level elay or Electronic Interlocking - Level Points requested by operation of point lever, switch or tracker ball, or called automatically by route setting equipment when switch in centre position. Mech l Interlocking Electric Selection Lock, if provided Selection Lock Lock elays or Logic Conditions Mech l or Electrical Operation Interlocking Lock Operation equires See Section or Part Operation equires ü 3.5 Part L Point lever normal or reverse, lock relay energised, or logic conditions fulfilled. ü Point switch in centre position immediately before normal or reverse. (Anti-preselection.) ü Track locking track sections clear, including flank tracks which may be conditional on lie of Clearance points, or clearance bar not occupied. bar All signals normal reading over the points, requiring the points for flank protection. All signals (This may be provided through the route locking in route setting systems.) normal All signals normal with these points in the overlap, or overlap swung away, except in the case All sigs of power operated facing points, which are only locked if an alternative overlap is unavailable. normal (This may be provided through the route locking in route setting systems.) (conditionally for trail'g pts in an alternative OL) Track locking Counter conditional locking of facing points in OL All authorised movements over the points, or requiring the points for flank protection, at a ü stand in platform or clear of points, with signal normal. (oute locking.) All authorised movements with points in the overlap at a stand at the signal ahead, with ü signals normal, or overlap swung away, except in the case of power operated facing points, which are only locked if an alternative overlap is unavailable. Any release from another control point given. elease Electrical lever release To move reverse, points releasing these points are required reverse. (Point to point locking.) (N) lock To move reverse, points locking these points are required normal. (Point to point locking.) (N) lock To move normal, points released by these points are required normal. (Point to point () lock locking.) Where provided for route holding or sequential locking, trailing points require signal ahead normal. ü Mechanically operated facing points require FPL plunger out and FPL lever in unlocked position (where separate lever). ü ü 4.3 FPL levers require all signals normal reading over the points in a facing direction, including points in the overlap, and track locking clear. They are locked both ways by signals in a trailing direction. Signal locking Track locking Figure F14 Point and Facing Point Lock (FPL) Controls (all systems) Where more than one point end is required to operate together (e.g. crossovers, a plain lead with a swing nose crossing, both ends of switch diamonds, two ends of single or double slips, both switches of wide to gauge trap points, etc.), they should be given a common point number with different suffix letters, in accordance with GK/T0009. This is to simplify the point locking, facilitate flank protection and reduce the incidence of run-throughs. For instance, giving the facing points at left hand double junctions the same number provides significant flank protection (see Section 3.4.4). F50

133 ailway Group Guidance Note Page F51 of 191 Controls and Facilities Such an arrangement should, wherever practicable, be restricted to two point ends, in order to simplify testing and corrective maintenance. Thus, in Appendix F5, points 711 and 712 have separate numbers. Common numbering may be extended to three point ends where it is particularly expedient, subject to the agreement of the infrastructure controller, e.g. points 713 and 714 in Appendix F5. Under certain circumstances, however, it may be beneficial for them to be operated separately, in order to improve availability or maintainability. Common numbering should only be used where each point end is operated by the same signaller s control device. So, for example, where the facing end of a crossover is operated from a signal box, but the trailing end is train operated, then each end should be separately numbered. Mechanical or Electro-Mechanical Interlocking - Level All-Electric (Miniature) Lever Frame - Level elay or Electronic Interlocking - Level Mech l Interlocking Interlocking Lock Electric Selection Lock, if provided Selection Lock Lock elays or Logic Conditions Mech l or Electrical Operat-ion Operat-ion equires Operat-ion equires See Section or Part Lever frames require point lever replaced normal after use, as in Figure F14. ü Points giving trapping protection may be self restored on route setting systems. ü Where indication locking is provided, detection must be obtained to move beyond the checklock. (NBD) lock 5.3 Ground frames and lockout devices generally require local levers/switches replaced normal before release can be given back. (GF signals and slots are proved on in their backlocks.) GF proved closed Any signal requiring GF reverse: normal. ü GF normalisation requires signal box lever/lock relay normal (or control device restored for noninterlocked signals), GF closed, power operated GF points in running line or for flank protection detected normal, and mechanically operated facing points detected normal. Normalisation of other releases require signal box release lever/lock relay normal (or control device restored for non-interlocked signals), lockout devices locked in traffic mode and gate locks/bridge bolts detected in, etc. Figure F15 elease normal elease normal Normalisation (of Points and Ground Frames, etc.) GF closed, detection Detection Split Detection Where two or more point ends work together, and a detection failure on one end would unduly restrict train movements over the other end(s), split detection may be provided. In such cases, the point end(s) in the direct line of route should be detected in the signal aspect, whilst any other end should be treated as flank points and the degree of detection described in Sections 3.3.4(c) and applied. Where flank detection is omitted, in the event of detection failure at one end of a set of points, signalled movements may be made over the end still detected. Where flank detection is provided, under similar circumstances, hand signalled movements may be made over the end still detected, without the points being secured, so long as the signaller has observed the appropriate point indication. F51

134 ailway Group Guidance Note Page F52 of 191 Withdrawn Document Signal to Signal In the Overlap See Set Locked Detected Set Locked Detected Sec n Permitted hinge facing points Not applicable Not applicable Not applicable To preferred No Except when OL if provided swinging Other points in direct line ü ü ü Conditional on hinge points. Conditional on hinge points. Conditional on hinge points Facing points in conflicting overlap to be swung away when flank overlap locked Flank overrun protection, where applicable, and trap points <200m from conflict point Flank points locked by track section in direct line of route Flank points called to simplify foul track section proving below Foul track sections conditioned by flank points above ü ü At time of signal clearing Or train moving away if provided Or train moving away if provided At time of signal clearing or train moving away if provided At time of setting Or train moving away if provided At time of setting Or train moving away if provided At time of signal clearing At time of signal clearing or train moving away if provided Only if req d for overrun protection ü ü Only if req d for overrun protection Only if req d for overrun protection Only if req d for overrun protection ü ü Optional ü ü Optional In signal aspect controls, and track locking of points Optional In signal aspect controls, and track locking of points Optional Note that where indication locking is provided, detection in the signal controls is only required for facing points in direct line. 5.5 Figure F16 Minimum equirements for Proving of Power Operated Points Set by Point Lever Signal to Signal Locked by Signal Lever, etc. Facing points in direct line ü Or by FPL lever, if provided Detected in Signal Controls For passenger moves, and where no FPL Set by Point Lever ü In the Selected Overlap Locked by Signal Lever, etc. Or by FPL lever, if provided Detected in Signal Controls For passenger moves, and where no FPL Facing point lock on above By FPL lever ü Pass gr By FPL lever ü Pass gr 4.3 moves moves Other points in direct line ü ü Optional ü ü Optional Flank overrun protection, where applicable, and trap points <200m from conflict point ü ü At time of signal clearing ü ü At time of signal clearing Flank points locked by track section in direct line of route Flank points called to simplify foul track section proving below Foul track sections conditioned by flank points above See Section ü ü Only if req d for overrun protection Only if req d for overrun protection Only if req d for overrun protection Only if req d for overrun protection ü ü Optional ü ü Optional In signal aspect controls, and track locking of points Optional In signal aspect controls, and track locking of points Note that mechanical detection is only appropriate for mechanically operated signals. Figure F17 Minimum equirements for Proving of Mechanically Operated Points Optional Split detection should not be provided for the two ends of switch diamonds and is generally not practicable for other situations using a common operating mechanism, such as adjacent ends of double slips. Where normal detection is split, reverse detection may, nevertheless, be common for more than one end. Part P The provision of separate point indications for the signaller is described in Part L Lie of Points The lie of points has most significance for lever frames, where levers are generally returned to their normal position in the frame after the passage of a train. The following principles should be applied: F52

135 ailway Group Guidance Note Page F53 of 191 a) trap points should lie with the normal position set for trapping; b) points providing flank protection should, wherever practicable, have the normal position set to give maximum protection, e.g. see the lie of 707 points at the double junction in Appendix F5; c) where single lines become double, the facing points should normally lie in the appropriate position for a train leaving the single line; d) where there is a risk of an unauthorised movement running onto a running line in the wrong direction, points should, wherever practicable, normally lie in a position that would divert vehicles away from the wrong line; and e) other points should lie normally in the most regularly used position. These general principles should, where appropriate, be maintained for route setting and other systems as well Setting of Points a) Non-oute Setting Systems On lever frames, ground frames and certain individual function switch (IFS) panels, point to point locking forms the basis for all other locking. Control table design should therefore commence with the point to point locking. General principles may include: i. Scissors crossovers, or facing and trailing crossovers, should lock one another. ii. Where slip points, switch diamonds, or swing nose crossings are worked by separate levers, they should be released by the points within which they lie. iii. If crossovers are not worked by one lever, one end should be released by the other. iv. Tandem points should be locked as if they were two following leads. v. If the lie of the points shown at the simple double junction in Appendix F5 cannot be achieved for some reason, then the facing points should release the trailing points, to provide flank protection. vi. In left hand four road double junctions, as in Appendix F5, the two trailing points should be released by their respective facing points. ight hand double junctions should work as two independent crossovers. vii. The levers of FPLs fitted with an FPL bar, should be locked both ways, by all signals leading over the points in a trailing direction. viii. Where trailing points between the arrival and departure lines at terminal stations lie set to divert an unauthorised movement away from the wrong line, towards the departure line, it may be necessary for the crossover to lie such that either end locks the other normal. ix. Other points may also lock or release one another, in such a way that will not restrict traffic movements, where this simplifies signal locking. x. Where a signal requires several sets of points normal or reverse, any points that lock or release other points that in turn release the signal, should not lock the signal directly. b) oute Setting Systems (route calling) On route setting systems, points should be free of any point to point locking. Setting a route should call (initiate the setting of) the following points, provided the individual point control device for each is in the centre or in the required position (N or ) and the points are free to move accordingly (or locked by an overlap that is free to be swung away): F53

136 ailway Group Guidance Note Page F54 of 191 Withdrawn Document i. all points in direct line of route and overlap to the correct position; ii. facing points in the overlap to the preferred overlap position, or, if not available, to an alternative position; iii. trap points to the trapping position, where necessary (see Section 3.4.5); iv. facing points in a conflicting overlap to swing the overlap away (see Section 3.4.2(c)); v. flank points that condition out foul track sections (see Section 3.3.4); vi. other points giving flank protection to the protecting position (see Section 3.4.4); and vii. points not in the direct line of route that are locked by a track section in the direct line of route, to allow parallel movements. Such points should be called by the route (set and locked only) to the position that will allow a parallel route to be set. For example in Appendix F5, points 713 or 714 should be called normal by route 56A, because 714 points are track locked by DD, FA, and (>N) CE or 713N. Otherwise, 509 and 510A routes could not be set if 714 were reverse and CE track occupied by a train on route 56A. (Points 714 may be set, locked and detected normal, in any case, to give trapping protection in accordance with Section ) c) Other Calling The following events should also call particular points: i. operation of the appropriate individual point control device; ii. operation of a individual control device for facing points in a locked overlap calls the subsequent points in the alternative overlap (route setting systems only); iii. setting a flank route calls facing points in a conflicting overlap to swing the overlap away (route setting systems only) see Section 3.4.2(c); and iv. where necessary, certain power operated trap points self restore after the passage of a train, once a time delay has elapsed (see Section 3.4.5). These should be identified in the control tables Anti-Preselection Where an unacceptable risk is presented by the preselection of a signalling function by the signaller prior to the conditions becoming available, so that it is automatically set when some other function is restored, measures should be provided to effect anti-preselection. This applies particularly to points and signal routes that call points. Legitimate swinging of overlaps should not be inhibited by this control feature. Anti-preselection should only be omitted where the cost of provision is grossly disproportional to any safety improvement gained Locking of Points and Other Movable Infrastructure a) Track Locking Points should generally be locked when a train is passing over the points, or standing foul of a route over the points. This should be achieved by one of the following means: i. For mechanical signalling systems without continuous train detection, the retraction of facing point lock (FPL) bolts may be prevented by the occupation of an FPL bar on the approach to the facing points. Where it is necessary to prove that a train is not standing foul, a clearance bar may be used. F54

137 ailway Group Guidance Note Page F55 of 191 ii. Where train detection is provided, points, ground frame releases, level crossings and movable bridges, etc., should be track locked by occupation of the track section(s) in which the infrastructure is situated and, in the case of points, by certain flank track sections, in accordance with Section The latter may be conditional upon the lie of the points concerned, or of adjacent points. Track locking that is not conditional is known as dead locking. However, once points have started to move they should be allowed to complete their movement. b) oute Holding Signals and routes that require points (as described in Section 3.5.4), ground frame releases, controlled level crossings and movable bridges, etc., to be set in a particular position, should also lock them. This does not apply to power operated facing points in the overlap, which should be free to swing to any permitted overlap that is available (see Section 3.4.2(a)). Where FPLs are provided, the locking may be accomplished by the signal levers locking the FPL levers in the bolt in position, and the FPL levers (bolt in) locking the point levers normal, reverse, or both ways, as appropriate. The locking should not be released until the protecting signal(s) are on and free of approach locking and, in route setting systems, the route has been cancelled. This also applies to the locking of directly opposing signals and routes (see Section 3.5.9). The direct locking between signals and movable infrastructure should generally be extended to provide route holding of infrastructure in the route and overlap. Once the route is set, infrastructure should be locked until the train has passed over it; or, for flank points, clear of the place where the protection was required (or the flank track section was foul); or until overlap locking (including time of operation locking) release conditions have been fulfilled. On route setting systems where sectional route locking (option iv, below) comprehensively locks all necessary infrastructure and opposing routes, the direct locking between signals and infrastructure may be omitted, provided that risks arising from the right side failure of track sections, necessitating a release of locking, are adequately controlled. See Appendix F2:6.4. The route holding should be achieved by one of the following means, and should be specified in control tables: i. Where the signal is close to the infrastructure concerned, the signal locking should be prevented from being fully normalised until the train has locked the infrastructure by occupying the dead locking track section, or FPL bar. This may be accomplished by the signal backlock circuit being extended to require the intervening track sections clear (see Section 5.3(b)), or it may be associated with an approach lock release circuit. Track locking of points may also be extended, where necessary, to meet the extended backlock. (This option should generally be used at electro-mechanical interlockings and non-block signals protecting ground frames or level crossings, etc.) Examples are given in Figure F1:12. ii. For mechanical signalling systems without continuous train detection, where facing points are less than a train length apart and are provided with FPL bars, each subsequent FPL should be released by the previous one. Trailing points within 440m of the next signal ahead may be locked both ways by that signal, thus providing route holding when a train is signalled through. F55

138 ailway Group Guidance Note Page F56 of 191 Withdrawn Document iii. Where continuous train detection is provided from the protecting signal to the infrastructure concerned, basic route locking may be provided, by which a route stick relay is de-energised when the signal is selected (or route set) until the signal is normalised and all the track sections between the signal and the infrastructure (or furthest point of conflict with an opposing route) are clear. See Section for application details. Examples are given in Figure F1:12. iv. Where continuous train detection is provided throughout the interlocking, sectional route locking may be provided, as described in Section This is the preferred option for operational flexibility. v. In non-track circuit block, route holding of ground frames should be accomplished by means of the arrangements described in Sections or oute holding for opposing movements should be achieved by a recognised method of single line control permitted by GK/T0051 or GK/T0054. Examples of options i) and iii) are given in Figure F1: elaxation of Point Locking, etc. Track locking and route holding of trailing points and other movable infrastructure (but not interlocking by signals and/or routes) may be relaxed where the section of track concerned is clearly visible from the controlling point and it is not reasonably practicable to provide train detection and/or electric lever locks. This relaxation generally includes track locking and route holding of controlled level crossings, where the protecting signal is within 100m of the crossing. oute locking of directly opposing movements clearly visible from the controlling point (but not interlocking of signals and/or routes) may be relaxed, provided that the signals aspects are controlled by the intervening track sections that would otherwise require route locking. An example appears in Figure F1:10, where opposing signals 23 and 31 have extended backlocks and the intervening track sections, DE and DF, are required in both aspects. For all relaxations, it should be demonstrated that risks are controlled so far as is reasonably practicable. (The cost of provision would have to be grossly disproportional to the safety improvement gained.) See Section for relaxations at ground frames. See Section for relaxations in approach locking oute and Overlap Locking This section describes both basic route locking and sectional route and overlap locking. See Section for the release of the locking, including special releases for infrastructure in the overlap and opposing routes. a) Application In the case of basic route locking, a route locking section may be applied to a group of track sections where the release of the section requires the whole group clear. In the case of sectional route locking, a separate route locking section should generally be provided for each track section separately indicated (except as described in Section 3.5.9). This provides a consistent signalling display, and allows points and conflicting routes to be released as soon as possible after a train has passed clear, so as to prevent other movements being unnecessarily delayed. oute locking and overlap locking should be applied in one of the following ways: F56

139 ailway Group Guidance Note Page F57 of 191 i. individually setting all the sections of route and overlap locking at the same time when the route is set (as with SSI); or ii. setting the first section when the route is set and then cascading the setting of each subsequent section in sequence (as with route relay interlockings, where each route section is set by de-energising its route stick relay); or iii. setting the route locking when the signal is ready to clear (as with some non-route setting interlockings). See Section for further details. b) oute Locking Provision oute locking should be provided, as necessary, to: i. prevent the setting of a second route for a directly opposing movement, whilst a train is passing between the protecting signal and the end of the first route; ii. maintain the overlap locked, whilst a train is passing between the protecting signal and the end of the route; iii. lock points in the route, whilst a train is passing between the protecting signal and the dead locking track sections over the points; iv. lock trap and flank points protecting the route from unauthorised movements, whilst a train is passing between the protecting signal and the place beyond which the protection is required; v. prevent the operation of a lockout device, whilst a movement is taking place in the wrong direction or in either direction, as appropriate; vi. lock controlled level crossings in the route, whilst a train is passing between the protecting signal and the dead locking track sections over the crossings, but see Section i) for locally locked protecting signals; vii. lock movable bridges in the route, whilst a train is passing between the protecting signal and the dead locking track sections over the bridges; viii. lock the releases for ground frames that control points in the route, whilst a train is passing between the protecting signal and the track sections that directly lock the releases, but see Section i) for locally locked protecting signals and Section 3.6 for alternative methods of route holding; ix. lock the releases for ground frames that control trap and flank points protecting the route from unauthorised movements, whilst a train is passing between the protecting signal and the place beyond which the protection is required, but see Section i) for locally locked protecting signals and Section 3.6 for alternative methods of route holding; and x. lock the route, as in items i) to ix) above, for a train departing from a ground frame without a departure signal, from the time the release is given. See Section 3.6.1(b). c) Locking the Overlap Overlap locking should extend beyond the route destination signal only as far as is required to provide the necessary locking for the overlap concerned, which may vary according to: i. the route set (entrance signals with different approach conditions may require different lengths of full overlap); ii. the class of route set (full overlap for main class, or restricted overlap for warning class); and iii. for warning class routes, whether the route has stepped up to a main class, thus requiring full overlap locking. F57

140 ailway Group Guidance Note Page F58 of 191 Withdrawn Document d) Overlap Locking Provision Overlap locking should be provided, as necessary, in case the train for which the route has been set inadvertently passes the destination signal and occupies the overlap. Until the overlap locking is released, it should: i. prevent the setting of a route for a directly opposing movement; ii. lock points in the overlap; iii. lock trap and flank points protecting the overlap from unauthorised movements; iv. lock the releases for ground frames that control points in the overlap, or trap and flank points protecting the overlap from unauthorised movements; v. lock controlled level crossings within a 50m overlap, but see Section 3.4.2(h) for alternatives; and vi. lock movable bridges in the overlap, but see Section 3.4.2(i) for alternatives. e) Proving of oute and Point Locking In relay interlockings, the locking of points should be proved effective in the aspects of signals reading over them. This should be accomplished by the following means: i. for sectional route locking, the last route stick relay to be de-energised when the route is set should be proved down to prove the integrity of the route stick chain (this proves all the points route locked) see also Appendix F2:2.4; ii. for basic route locking, the route stick relays actually locking the points should be proved down in the appropriate signals; iii. where points free relays are used, these should be proved down in the point detection used in the aspect circuit Opposing Locking and Bi-Directional Lines Directly opposing signals and routes should be locked and route holding provided as described in Section 3.5.6(b). (This also applies to other conflicting routes which are not locked by means of point locking, e.g. those that conflict at diamond crossings.) Indirectly opposing routes are those that initially conflict at points, but, after a train has proceeded through the route over the points and released the route holding on the points, can become directly opposing. If sectional route locking is not provided, additional route holding may be necessary to protect against this eventuality and should be shown in control tables. In Appendix F5, 216(M) route does not lock 203C(S) because it requires points 713 normal, whereas 203C(S) requires 713 reverse. However, once a move from 203 clears DD track, 713 can be normalised and route holding is necessary to prevent 216(M) route from being set. The same example for a system without sectional route locking appears in Figure F1:10 with indirectly opposing locking between signals 15 and 32. In this case, the additional route locking should be separately provided and shown in the control tables (Figure F1:12). Opposing locking may be omitted from directly opposing shunting signals for operating purposes (illustrated by signals 509 and 510 in Appendix F5). Opposing main signals generally create a bi-directional line. Bi-directional lines should be controlled in one of the following ways: F58

141 ailway Group Guidance Note Page F59 of 191 a) In track circuit block, where both ends of the line are controlled by the same signal box, route locking should be provided to prevent the setting of a second route for a directly opposing movement, whilst a train is passing between the protecting signal and the end of the first route, as described in Section An indication of route set (e.g. signaller s white route lights) should generally be provided in a manner consistent with the signalling display. b) As method (a), but with intermediate signal sections, generally provided with automatic signals. The aspect of the intermediate signals should be controlled by entrance route set, or, alternatively for the predominant direction, opposing route not set. oute locking should be maintained until the train enters the exit route at the other end of the line, although neither exit route should be locked by the occupation of the intermediate section(s). A directional indication of route set (e.g. white arrow) should be provided for the intermediate section(s) in lieu of route lights. c) In track circuit block, where both ends of the line are controlled by different signal boxes, directional interlocking (using, for example, direction levers or lock relays) should be provided to prevent the setting of a route for a directly opposing movement, in accordance with GK/T0041. The directional interlocking should be maintained until the train reaches the exit signal, although neither exit signal should be locked by the occupation of the line between them. A directional indication of the interlocking (e.g. white arrow) should be provided at both signal boxes. d) As method (c), but with intermediate signal sections, generally provided with automatic signals. The aspect of the intermediate signals should be controlled by the directional interlocking. e) In non-track circuit block, by a recognised method of single line control permitted by GK/T0051, or GK/T0054 (ETB). Separate route locking controls should be provided for each direction for methods (a) and (b). However, the intermediate track sections on bi-directional lines may be grouped for sectional route locking purposes. The route locking release should be enhanced, to protect against wrong side track section failures, as described in Section With methods (b) and (d), where there is a predominant direction of traffic, the signalling in the non-predominant direction may be simplified as permitted by GK/T Ground Frames and Gate Boxes Shunters releases, ground frames and gate boxes should be provided as required by GK/T0061, and equipped with the facilities listed therein, as summarised in Figures F15 and F18. The controls for each release should be specified in control tables, in accordance with GK/T0202. Ground frames and gate boxes should be regarded as interlockings in their own right, and the full requirements of this part of the Guidance Note should apply to each. Details of mechanical ground frames are given in Appendix F1:8 and switch panels in Appendix F2:10. In all instances the release requires the protecting signal(s) on and free of approach locking. F59

142 ailway Group Guidance Note Page F60 of 191 Withdrawn Document Controls and Facilities Ground Frames in Interlocking Areas and Station Limits For station limits at a token control point, see Section instead. For locking and normal proving at the main signal box, ground frames in interlocking areas should be treated as power operated points. Mechanical or Electro-Mechanical Interlocking - Level All-Electric (Miniature) Lever Frame - Level elay or Electronic Interlocking - Level Mech l Interlocking Electric Selection Lock, if provided Selection Lock Lock elays or Logic Conditions Mech l or Electrical Operation Interlocking Lock Operation equires See Section or Part Operation equires elease requested by operation of signal box lever, switch, push button or tracker ball, or called automatically by routes requiring the GF reverse. ü Centrally interlocked protecting signals: signal box release lever reverse or reverse lock relay energised. elease given Locally locked protecting signals: signal box control device operated. elease given All signals normal reading over the GF points normal, with GF in the overlap (or overlap swung away), or as required for flank protection. (Interlocked signals are proved on and free of approach locking in the backlock/approach lock release of the signal locking. For locally locked signals this proving is applied locally to the GF release instead, or a special timer provided in lieu of approach locking.) (Signals reading over GF points reverse should be controlled or slotted by the GF.) Interlocked signals normal Local approach lock release 3.6 All authorised movements over the GF points normal, or as required for flank protection, at a stand in platform or clear of points, with signal normal. With GF in the overlap, movements required at a stand at signal, with signals normal, or overlap swung away. (oute locking.) Interlocked signals Local route locking Figure F18 Ground Frame eleases (Applies similarly to Lockout Devices, Controlled Barrier Crossings, Interlocked Gated Crossings and Movable Bridges, etc.) (all systems) a) Locking the elease The ground frame release should thus be locked normal in the following circumstances: i. when a route is set (or signal selected in a non-route setting system) that requires ground frame points in running lines normal (including trap and flank points, points in the set overlap and in an alternative overlap when it swings); ii. when ground frame points in running lines are track locked; iii. when ground frame points in running lines are route locked. b) Giving the elease The ground frame locking should not be released until the protecting signal(s) are on and free of approach locking and, where applicable, the route has been cancelled. (This may require a timed release of route locking with a train in the section, as described in Section ) Any points located between the protecting signal(s) and the ground frame should be locked in the appropriate position by the ground frame release being given. Where there is no signal to control the departure of trains from the ground frame, the release should additionally prove any track sections or other signalling functions in the route up to the signal ahead, or LOS, (including an appropriate overlap if departures are regarded as running movements), and should initiate route locking unless the relevant functions are track locked by a departing train. F60

143 ailway Group Guidance Note Page F61 of 191 Where necessary, train detection may be overridden by a train at a stand waiting to use the ground frame, as described in Section 3.6.2(c), or the appropriate track section omitted from the controls (e.g. if timed release of route locking is provided, or if the portion of line is clearly visible from the signal box). The ground frame release should be given either: i. by operation of the signaller s ground frame release device, in which the giving of a release to the ground frame sets and locks the ground frame reverse in the interlocking; or ii. by the signaller setting a route through a ground frame controlled connection in the reverse position. The latter, route operated, release should generally be provided, where required by the infrastructure controller, where a movement into or out of the ground frame would pass over power worked points, move against the normal direction of traffic, or foul other lines. Such routes require a signal box controlled entrance signal, which is slotted by the ground frame, and proves the ground frame release set. The release should be withdrawn when the route normalises. c) Ground Frame Signal Controls Facilities may be provided for ground frames to have sole control of certain routes of a signal, other routes of which may be controlled solely or jointly by the main signal box. Ground frame signals that read to or from running lines should be provided with approach locking, route holding and train detection appropriate to the method of block working, including overlaps for running movements. d) Protecting Signal Controls Protecting signals and routes reading over the ground frame points normal require the ground frame release controls at the signal box normal, as described in (e), below. The signal aspect controls should provide continuous detection of the ground frame points in the same way as other points (see Figures F16 and F17), as follows: i. power operated ground frame points in the running lines set, locked and detected normal; ii. mechanically operated facing points in the running lines set, locked and detected normal (and FPL bolts detected in for passenger movements); iii. any flank or trapping protection afforded by the ground frame proved effective at time of signal clearance. Note that a combination of electrically detected points and mechanically operated protecting signals controlled from a ground frame is prohibited, to prevent a detection failure remaining unnoticed (see GK/T0039). e) Normalising the elease Normalisation of the ground frame release (ground frame closed state) requires at time of restoration: i. power operated ground frame points in the running lines set, locked and detected normal; ii. mechanically operated facing points in the running lines set, locked and detected normal (and FPL bolts detected in for passenger movements); iii. mechanically operated trailing points in the running lines set and locked normal; F61

144 ailway Group Guidance Note Page F62 of 191 Withdrawn Document iv. trap points set, locked and detected in the trapping position; v. slots operated by the ground frame normal, unless required when the ground frame is closed; and vi. ground frame release lever normal (and lock proved in, where necessary), or closed plunger operated for a switch panel. The signaller also requires a verbal assurance from the ground frame operator that it is safe to normalise. For lever frames, the detection should generally be proved in the release lever backlock. For ground frame normal indications see Part L. Where ground frames control more than one connection to the running lines, each may have a separate release. In such cases the controls stated above should only refer to the relevant connections, slots and releases in each case. Similarly, the ground frame may control internal shunting movements when the release(s) are normal emote Ground Frames: Track Circuit Block and Intermediate Block Sections The same principles should be followed as for ground frames in the interlocking area, but modified as follows: a) Protecting Signals In track circuit block (see GK/T0041), ground frames are often protected by block signals that carry no other interlocking. They may be designated semiautomatic provided they are not further than 800m from any facing ground frame points. Otherwise they should be designated controlled (see GK/T0035). Approach locking of any semi-automatic signals protecting the ground frame should be released by a timer that runs when all such signals have been replaced by operation of the signaller s release. See Appendix F2:10 for details. Where there is no block signal within a reasonable distance of the ground frame and there is a requirement to detect the ground frame points (see Figures F16 and F17), a non-block signal or remote ground frame marker may be provided for the purpose. This prevents the loss of block proving in the event of ground frame detection failure. Ground frame markers or nonblock signals are not appropriate in areas of continuous 3 or 4 aspect signalling. b) Protecting Signal Controls The protecting block signal requires the ground frame release controls at the signal box normal (see Section 3.6.1(e)) and continuous detection of the ground frame points (Section 3.6.1(d)). Where a non-block signal is provided closer to the ground frame, the continuous detection of the ground frame points should be applied to the nonblock signal instead of the protecting block signal. In the case of a ground frame marker, the detection requirements should apply to the distant signal associated with the marker. F62

145 ailway Group Guidance Note Page F63 of 191 c) Giving the elease When it is necessary to release a ground frame with a train in section, the release should generally prove the safe position of a train for ground frame operation. It is necessary to provide a separate release track section for approximately 100m on the facing side of the ground frame point(s) in the running line(s). For example, the release of a ground frame operated crossover would require: i. protecting signals on and free of approach locking; AND ii. where there is no departure signal, track sections clear up to the overlap of the signal ahead, together with any other ground frame or level crossing within the signal section normal (with route locking initiated by this release, unless the relevant functions are track locked by a departing train); AND iii. up line section clear and down line section clear (including the overlap of the signals ahead); O iv. up line section clear and down line release track section occupied for a time sufficient to ensure that the train has come to a stand; O v. down line section clear and up line release track section occupied for a time sufficient to ensure that the train has come to a stand. The time sufficient to ensure that the train has come to a stand may generally be taken to be 60 seconds. To guard against track section failure giving a premature release, sequential operation of track sections should be proved wherever practicable, e.g. release track section occupied for 60 seconds after release track clear and an adjacent track section occupied. The release track section(s) do not need to be separately indicated at the signal box. d) Direction Lever Working With direction lever working the ground frame release may require a direction lever reverse, in addition to the requirements of item (c) above, to maintain the integrity of the interlocking. Where the direction lever gives a one train release on the respective entrance signal to the bi-directional line, this should be cancelled by the ground frame release being given In-Section Ground Frames: Absolute Block and Single Line Block without Tokens For ground frames within absolute block sections (see GK/T0042), or tokenless block or one train working without train staff sections (see GK/T0051), the same principles should be followed as for remote ground frames within track circuit block, but modified as follows: a) General equirements Ground frames should be released by a signal box that controls entry to the block section. `Where there is more than one ground frame or other signalling function on the same line within the block section, then each should be released or supervised from the same signal box, so as to allow the route to be proved up to the overlap of the signal ahead, either in the ground frame release, or in a ground frame departure signal. In the case of interlocked absolute block on bi-directional lines, use of the ground frame should only be authorised for movements in a single direction, away from the releasing signal box. F63

146 ailway Group Guidance Note Page F64 of 191 Withdrawn Document Trains should only be permitted to depart from the ground frame when the block section is clear (see Section (c), below) and no other movements can be signalled into it. Operation of the ground frame release in the signal box should lock the section signal(s) and, conversely, clearing a section signal should prevent the ground frame release being given. Where a shutting-in facility is provided, sufficient continuous train detection on the running line should be provided in accordance with GK/T0042 or GK/T0051, as applicable, so as to prove that a train has been completely shut-in. Where more than one track section is provided, sequential operation may be used to prove a train completely shut-in and protect against a wrong side failure. isks should also be controlled by the provision of train detection throughout the section or from the section signal to the ground frame, or otherwise by the provision of signal box local instructions. Shutting-in is not permitted where the one-train system without train staff is in use. b) Giving the elease The ground frame release conditions should be as follows: i. protecting signals on and free of approach locking; AND ii. where there is no departure signal, any other ground frame or level crossing within the block section normal (with route locking initiated by this release, unless the relevant functions are track locked by a departing train); AND iii. ground frame track section(s), where provided, occupied for a time sufficient to ensure that the train has come to a stand and block indicator at TOL/TIS (not enforced for one-train working); O iv. where a shutting-in facility is provided, ground frame track section(s) clear and block indicator at LC/TA. c) Block Controls Where there is a shutting-in facility, controls should be provided to ensure that a LC/TA release can only be used for one train, by one of the following means: i. The occupation of any running line track section maintains the respective block indicator at TOL/TIS. (With this option, a track failure would prevent clearance of the section signal.) ii. Giving the ground frame release cancels the LC/TA release (nonpreferred). iii. A train entering the block section at the ground frame cancels the LC/TA release. iv. A departure signal is provided at the ground frame, which requires a LC/TA release. d) Normalisation Where sequential operation of track sections is provided, ground frame normalisation may additionally include: i. (ground frame points detected reverse, AND ii. track section over points occupied and adjacent track clear, AFTE iii. adjacent track occupied and points track clear), THEN iv. ground frame closed, as in Section 3.6.1(e). F64

147 ailway Group Guidance Note Page F65 of 191 e) Protecting Signals The protecting block signal should either be: i. a section signal, but not an intermediate block home (IBH); or ii. a signal that performs the role of an IBH, but is not so designated. f) Protecting Signal Controls Clearance of the protecting block signal requires: i. block indicator at LC/TA (at time of clearance); ii. ground frame release controls at the signal box normal (see Section 3.6.1(e)), unless proved in the opposing normal block indication for interlocked absolute block; iii. continuous detection of the ground frame points (see Section 3.6.1(d)), unless there is a non-block signal closer to the ground frame; and iv. any running line track sections clear, unless their occupation automatically puts the block indicator to TOL/TIS (see option (c)i, above). This is optional, as there is not generally a requirement for continuous proving of train detection in non-track circuit block, because a track failure would prevent clearance of the section signal. Where a non-block signal is provided (see Section 3.6.2(a)), it should continuously detect the ground frame points. g) Signal Box Indications At the signal box controlling the ground frame release, the running line track section(s) should be indicated, unless their occupation maintains the block indicator at TOL/TIS. More than one track section on the same line (and associated with the same ground frame) may have a combined indication. As these track sections do not control the block, it is the responsibility of the signaller to ensure the safety of each movement. For further details of block operation, see Part K In-Section Ground Frames: Key or Token eleases a) General equirements Such ground frames are released by one of the following means, in accordance with GK/T0051, and require no train detection: i. unlocked by the electric token for the block section; ii. unlocked by the train staff (one-train systems); or iii. unlocked by Annetts key, or similar apparatus (see GK/T0039). The key should be held captive while the ground frame is in use, and the points should be locked normal for the running line (and, where necessary, detected normal) before the key can be withdrawn. Where a train can be shut-in at a ground frame, an intermediate token instrument should generally be provided for token working. Otherwise, means should be available to transport the token or train staff to the signal box or another instrument. (See GK/T0054 for details of the arrangements with radio electronic token block.) It is the responsibility of the train crew to ensure that the train is clear of the running line before the token is returned. F65

148 ailway Group Guidance Note Page F66 of 191 Withdrawn Document b) Controls The following controls should be provided only if there is a requirement to detect the ground frame points (see Figures F16 and F17). These should apply to the section signal, unless a non-block signal is provided for the purpose (see Section 3.6.2(a)). i. ground frame release controls at the ground frame normal; and ii. continuous detection of the ground frame points (see Section 3.6.1(d)). Where applicable, the ground frame release may be interlocked with the section signal by requiring the Annetts key, etc., not released, at time of clearance. For further details of key releases see Appendix F1:7.5. In the case of ground frames at token control points remote from the controlling signal box, the ground frame should be protected by the home signal, or stop/instruction board that protects the station limits of the token control point. The ground frame may be released by any appropriate means to ensure security elaxation in Interlocking Principles for Ground Frames Approach locking (if the signal is clearly visible from the ground frame), track locking and/or route holding may be omitted, as permitted in GK/T0061, if the ground frame is protected by the method of block working, or it can otherwise be demonstrated that risks are controlled so far as is reasonably practicable. (The cost of provision would have to be grossly disproportional to the safety improvement gained.) This is likely to be the case in non-track circuit block sections (unless train detection is required for the operation of the ground frame), or if the ground frame is only required for emergency or engineering use (possibly during a failure of train detection). Where necessary to control risks (e.g. if a release may be given with a train anywhere in the section, or other locking is omitted, to give operating flexibility), the signaller s ground frame release device should feature a security arrangement, e.g. captive key, sealed release or swipe card. 3.7 Signal eplacement and oute Normalisation Generally, stop signal replacement is effected by the withdrawal of any aspect control (except those required at time of clearing only), including signaller s control device and/or route set. Full details are given in Section The signal remains locked until the approach lock release conditions are fulfilled, and also, where provided in lieu of route locking, the backlock release conditions. See Sections 3.7.2(d) and 3.5.6(b)i). estoring the signaller s control device once the approach lock, and/or backlock, release conditions are fulfilled releases the locking of conflicting signalling functions and initiates the normalisation of the route locking behind a train passing through the route. See Section estoring the signaller s control device before the approach lock release conditions are fulfilled initiates a separate release, usually involving a time delay, to prove that any approaching train has come to a stand at the signal. See Section 3.7.2(e). Where train operated route release (TO) is provided, route normalisation should occur without the signaller s control device being restored once the signal replacement and approach locking release conditions are fulfilled, i.e. signal on and free of approach locking. See Section F66

149 ailway Group Guidance Note Page F67 of Signal eplacement a) Manual eplacement Signal replacement should be effective on any signal at any time by normalising the signaller s control or replacement device, in accordance with GK/T0060. (Where, consistent with previous standards, certain automatic signals have no replacement device, a replacement facility is provided at the signal instead.) Where mechanically interlocked signals are released by other signals, e.g. distant signal or preceding signals, signalling instructions require the signaller to normalise the first signal lever immediately after the passage of the train, so that the subsequent signal(s) are not locked reverse. Other signals that are not automatically replaced should similarly be normalised immediately behind the train. Wherever a signalling system is subject to common mode failure, an independent emergency replacement (all-signals-on) facility should be provided for each area concerned, as required by GK/T0025. This can apply, for example, to electronic interlocking systems, remote control systems, interface systems and VDU based control systems. It does not apply to systems, such as power supplies, where any failure automatically restores all signals. The facility may be provided in conjunction with remote control override systems (see Section ). b) Automatic eplacement Signal replacement should be provided automatically for all power operated signals where suitable train detection exists. For the positioning of the first track section beyond the signal, and situations where berth and overlap track sections may be combined, see Section For the replacement of nonblock and automatic signals, see Section For the replacement of distant or banner repeating signals, see Section One of the following replacement conditions should be provided: i. Standard replacement for main signals and subsidiary signals (PLS or semaphore): First wheel on the first track section beyond the signal, generally commencing within 5.5m to 20m of the signal. ii. Where the first track section starts less than 5.5m beyond a main or subsidiary signal: First wheel on the second track section (or off the first track, where there is no second track), O the last wheel off the signal berth track section (where provided). iii. Where facilities are required for a train to be driven or assisted from the rear: Last wheel off the berth track (where provided), O last wheel off the first track, O first wheel on the first track section that is a train length beyond the signal (where provided). iv. Standard replacement for an independent shunting signal (PLS or semaphore) is the same as condition iii) for a main signal. (Note that such signals should generally be located 2m in rear of the track section joint approaching the first set of points over which they are to read, or at the clearance point, whichever is the further from the points.) Where opposing locking is omitted (Section 3.5.9), automatic replacement may be inhibited. The replacement conditions for independent shunting signals cleared as pre-set shunt signals are specified in Section F67

150 ailway Group Guidance Note Page F68 of 191 Withdrawn Document c) Last Wheel eplacement Where delayed replacement conditions (b) ii) or iii) are provided for a main signal, special precautions are required as follows: i. Such signals are depicted with an L symbol in the table of signal routes. ii. The train detection device, or repeater thereof, that is required clear to replace the signal, e.g. the berth track, should, wherever practicable, be proved clear in the signal in rear, so that a right side failure cannot create an unsafe situation. iii. Where a signal in rear of a signal equipped with last wheel replacement is not controlled by the berth track section of the signal ahead, as is the case with a call-on or shunt route, such routes should lock the signal ahead, or other controls should be provided, to prevent a second train approaching a signal that has not been replaced after the first train, in the event of the berth track failing in the occupied state. It is preferable for the signal controls to be arranged to give first wheel replacement when a permissive move is set in rear. iv. Where a main signal in rear is not controlled by separate track section(s) in the overlap, e.g. for a warning route, such that it would clear at the same time as the signal ahead were replaced, it should be controlled by signal ahead on, or first track beyond it clear to prevent a momentary false aspect sequence. v. Where an automatic signal, without a separate overlap track section, is provided with last wheel replacement, it is essential that the berth track section of the signal ahead is not bypassed by the signal replacement controls. d) e-stroking A route may be capable of being re-initiated (re-stroked) and a proceed aspect obtained at any time subsequent to the replacement of the signal. When the train has occupied and cleared the replacement track section of the route it should be possible to re-stroke the same route for which the signal has been cleared for the same class of aspect irrespective of the approach locking release and track section occupancy at the time. The signal would therefore clear when track section occupancy permitted Approach Locking Approach locking should be provided on all signals carrying interlocking (including local locking with ground frames and signal regulation at level crossings), in accordance with GK/T0063. a) Provision One of the following types of approach locking should be employed for each signal: i. applied when the signal clears (approach locked when cleared); or ii. for main aspects, applied when the signal clears and a driver could sight an aspect at a previous signal that would indicate that the signal concerned was displaying a proceed aspect (comprehensive approach locking); or iii. for an independent shunting signal (PLS or semaphore), applied when the signal clears and the approach track section(s) within at least 45m of the signal are occupied. (Where this signal is the exit of other routes, the proving may be extended back to the signal(s) in rear, for TO purposes.) F68

151 ailway Group Guidance Note Page F69 of 191 b) Comprehensive Approach Locking The use of comprehensive approach locking should be considered wherever enforced time delays might occur sufficiently frequently to be detrimental to train or level crossing operation. The type of approach locking required and the track sections that apply comprehensive approach locking should be identified in the control tables for each signal. Such track sections should extend back to the sighting point of the main signal(s) that would display the first caution, but may be conditioned out by the lie of points, or intervening signals being on and free of approach locking. The train detection may extend back further to avoid the provision of an additional track section. Conditioning to discount a train moving away from the signal is generally only necessary where trains regularly reverse on the approach to the signal. c) Proved Effective Clearance of the signal in relay interlockings should prove the approach locking applied, by proving the relay which applies it in the appropriate state. d) Approach Lock elease Both the following types of approach lock release, (e) and (f), should be provided. Either may effect the release, provided the signal (and any related distant and/or banner repeating signals) are proved on at the time. e) Timed elease A reasonable assurance that any approaching train has come to a stand may be obtained by the expiry of a time delay. The selection of suitable time delays is considered in GK/T0063 and the chosen period should be stated on the control tables. The time release should generally be initiated by the restoration of the signaller s control device for a signal, when approach locked. Alternatively, it may be initiated by the replacement of the signal, provided that the route locking is not released until the signaller s control device is restored. f) Train-In-Section Proving The train should be proved to have passed the signal by one of the following methods: i. Standard method: occupying concurrently the first and second track sections beyond it and subsequently clearing the first track section; ii. Long train release to release opposing locking, or the overlap beyond the signal ahead (where it contains trailing points), when the first track section is still occupied: as standard method, but with alternative condition of all tracks occupied between the signal and the next signal ahead (with the berth track of the signal ahead occupied for the time required to release the overlap); iii. No second track provided, but not where trains may divide on the signal berth track: occupying concurrently the berth and first track sections and subsequently clearing the berth track section; iv. No second track provided, where there is no berth track either, or trains may divide on the berth track: the first track clear after being occupied for a time (the time taken to traverse the track section at permitted speed, less 2 seconds equipment operation time); or v. Any other method that addresses the relevant situations and risks, and provides the appropriate degree of integrity. See Section 5.4. F69

152 ailway Group Guidance Note Page F70 of 191 Withdrawn Document The train-in-section proving may be omitted where continuous train detection is not provided, e.g. in non-track circuit block, in which case the timed release would be used to normalise the signal after the passage of every train. This is not appropriate for signals protecting level crossings because of the delay to road users. g) Special Features The releases should allow for: i. right side train detection failure not giving a premature release; ii. delayed signal replacement (the release requires signal on) see Section 3.7.1; and iii. for a release to be given when a train sets back behind the signal, having partially moved into the section ahead. h) Protection Protection against the following risks should also be incorporated: i. power supply restoration protection (see Part D); ii. very short track sections: for short fast trains, two adjacent tracks may be treated as one; and iii. very long track sections: a treadle, proved not operated before operated, may be used to avoid excessive delay in TO (its failure should not prevent the signal from clearing). iv. Wherever practicable, checks should be included to ensure protection against irregular sequences of events. Where approach track section occupancy applies approach locking, clearance of such track sections, once approach locking has been applied, should not release the approach locking. This guards against the risk of train detection response times that are not sufficient to cater for short fast trains, or other transient wrong side track section failures. i) Local Interlocking Signals protecting ground frames and controlled level crossings (or associated with signal regulation at automatic level crossings) are required to have approach locking, but where there is no other interlocking on the signal, this approach locking should instead be applied locally to the ground frame or level crossing concerned (thus rendering route locking unnecessary). For signals protecting ground frames see Section 3.6.2(a) and for signals associated with level crossings see Section 3.8. j) Distant Signals without Worked Stop Signals Where worked distant signals protect ground frames or gated level crossings (Section 3.2.3(a)), the requirements for both approach locking and route holding may be satisfied by proving a track section clear (or occupied for a time to bring a train to a stand) from the sighting point of the distant signal to the infrastructure concerned, before the distant signal can be fully normalised. F elaxation of Approach Locking The requirement to approach lock signals associated with low speed nonpassenger movements (e.g. shunting signals) may be relaxed, as permitted in GK/T0063, where the section of track concerned is visible from the controlling point. This relaxation may also be applied to other signals (e.g. non-block signals) if it is not reasonably practicable to provide train detection.

153 ailway Group Guidance Note Page F71 of 191 It should be demonstrated that risks are controlled so far as is reasonably practicable. (The cost of provision would have to be grossly disproportional to the safety improvement gained.) Train Operated oute elease (TO) TO should be provided on route setting systems where required by GK/T0063. It may be applied either as a safety-critical control within the interlocking, or as a safety-related interface with the signal box control system, provided that a consistent response is presented to the signaller. The operation of TO requires: a) signal proved on and free of approach locking; b) signal disengaged, i.e. prevented from reclearing; c) signal was off when passed; d) signal not set to work automatically; and e) except where the risk is minimal, as specified in GK/T0063 (i.e. no conflicting routes ahead of the signal involving passenger movements at speeds in excess of 15mph), one of the following should be provided: i. Proof of no train approaching, where provided for comprehensive approach locking (see Section 3.7.2). This requires the clearance of the signal in rear for a subsequent movement to approach the signal to be delayed until after TO has operated for the previous movement. ii. Proof of train having passed the signal, by a different train detection sequence or method from that used to release the approach locking, as specified in GK/T0063 (such that a common mode failure could not both release the approach locking and operate TO), but addressing the same situations and risks (see Section 3.7.2). f) Sequential Operation Note that in the design of sequential train detection, events should occur in the following order: i. signal disengaged (signal off when passed); ii. signal replaced (Section 3.7.1); iii. approach locking released (Section 3.7.2); iv. TO operated elease of oute and Overlap Locking This section describes the release of sectional route and overlap locking, but may equally be applied to the release of basic route locking, where applicable. The restoration of the signaller s control device, or operation of TO, with the signal on and free of approach locking, should initiate the normalisation of the route locking behind a train passing through the route. In route setting systems, the routes for all signals reading over the appropriate section should also be proved normal. The first route locking section beyond a signal should be released when its own track section (or sections) become clear, once the signal is proved normal, on and free of approach locking. Each subsequent route locking section should be released when its own track section(s) become clear, provided that the previous route locking section has already been released. F71

154 ailway Group Guidance Note Page F72 of 191 Withdrawn Document Where there is a particular risk of a wrong side track section failure giving a premature release (e.g. in high leaf fall areas), or where the consequences of such a failure are potentially severe (e.g. on bi-directional lines), the following enhancement should be applied to the track section clear release condition: (track section required clear for 15 seconds O track section required clear with track section next in advance occupied). Commercial operating requirements may be balanced against the whole-life cost of provision to determine whether a simplified option would be satisfactory: (track section required clear for 15 seconds). This enhancement may be provided as standard within a signalling system. It does not apply to overlap locking. Where an opposing call-on or shunt route may be required to set up to an occupied track section (or a ground frame release given), that route locking section may be released after a sufficient time has elapsed that the movement may be assumed to have come to a stand. The track section occupied timer should not operate until the previous track section has cleared behind the train, in order to avoid a premature release caused by track section failure. Note that this control is applied only if the next track section has not been occupied. It is represented as follows and may be further conditioned by a set of brackets, for example in Appendix F5 for 505A route: outes Normal Clear or Occupied Secs 214 DG, DC, DD, (DE, DF O DF- - 20) This would indicate that the applied route locking is released when DF track has been occupied for 20 seconds, DG is still clear and the back of the train has cleared DD track. The first overlap locking section beyond the destination signal should be released when the previous route locking section is released (see above), provided that its own track section(s) are clear, and the main and warning class signals requiring the overlap are proved normal, on and free of approach locking, for the destination concerned. It may also be released without the previous section being released, after a sufficient time has elapsed that the movement may be assumed to have come to a stand. Usually this control is applied where there is a set of trailing points in an overlap. In this case all the tracks in the route are generally bracketed, for example in Appendix F5 for 706 points N>: outes Normal Clear or Occupied Secs 214 O 707 DG, FC, (DC, DD, DE, DF O DF - 20) The necessary release times are given in Section 3.3.3(a). Each subsequent route locking section should be released when the previous overlap locking section is released, or an alternative available overlap is being set, provided that its own track section(s) are clear. Note that facilities may be required to release all or part of the overlap locking for a second train when a main route steps down to (or is overset by) a warning route, or a main or warning route is overset by a call-on or shunt route. F72

155 ailway Group Guidance Note Page F73 of Level Crossings Provision should be made for the locking and control of level crossing gates and barriers operated from the signal box, including those supervised by closed circuit television (CCTV), as summarised in Figures F15 and F18. The controls for each level crossing should be specified in control tables, in accordance with GK/T0202. Controlled level crossings may have local locking between non-interlocked signals and the level crossing controls, which includes approach locking and route holding. See Section For route holding see Section Special approach locking is described in Section 3.7.2(i)&(j). For level crossings in the overlap see Section 3.4.2(h). For gate boxes see Section Interlocked Gated Crossings Generally, level crossing gates should be interlocked with the signals or routes reading over the crossing. The gate stops (or gate lock) function should only be released when the protecting signals are normal (on and free of approach locking), and vice versa. Track locking should be applied by the track section(s) in which the crossing is situated, and route holding should be provided where necessary (see Section 3.5.7). Gate operating mechanisms may be mechanical (e.g. by wheel), or motorised with a separate signaller s control device. For further details of gate wheel interlocking, see Appendix F1:7.8. Detection of level crossing gates that are locked by gate stops or gate locks is not required. For the use of key lock and Annetts key releases see Appendix F1: Controlled Barrier Crossings Barriers are not required to be interlocked with signals or routes, but should be proved down at the time of clearing the aspect of signals reading over the crossing. The proving should include barrier mechanism doors closed and the signaller s crossing clear device operated. For crossings that are not adjacent to the signal box, it should also be proved that the booms are intact and remote control is selected on the local control unit. The barrier raise controls should only be released when the protecting signals are normal (on and free of approach locking) and all track sections between the signals and the far side of the crossing are clear. Main signals that have no interlocking other than the crossing should have their approach locking applied directly to the crossing as described in Section 3.7.2(i). In the event of a train passing a protecting signal at danger, the road light sequence should be initiated, but the barriers should not be lowered. This may be effected by an overrun treadle if there are no suitable track sections. Where a gated crossing operated from a mechanical interlocking is converted to barriers, the lever that locks the signals (gate lock lever or gate stop lever) may be retained to release the barrier controls, unless the infrastructure controller considers its retention to be detrimental to train or level crossing operation. F73

156 ailway Group Guidance Note Page F74 of 191 Withdrawn Document Automatic Crossings Automatic crossings are not interlocked with signals unless a signal is situated within the strike-in distance, in which case some form of approach locking and overrun detection should be provided. For delayed clearance of signals situated within the strike-in distance, see Section Miscellaneous Facilities Movable Bridges Movable bridges should be protected by interlocked signals equipped with approach locking and, where necessary, track locking and/or route holding, in accordance with Section 3.5.6, as summarised in Figures F15 and F18. The signal interlocking requires the bridge set for the railway, bolted and controls locked. Additionally to clear the protecting signals, the bridge bolts should be detected in. Where the risk of an overrun warrants it, trap points should also be provided to divert an unauthorised movement away from an unsecured bridge (see Section 3.4.5). Where a movable bridge is situated in an overlap and trap points are provided as described in Section 3.4.2(i), the bridge may be omitted from the controls of the signal in rear of the protecting signal. Otherwise, the same controls should be provided as for the protecting signals. To release the bridge bolts, the protecting signals should be proved on and free of approach locking, with route holding normal; the track locking track sections should be clear; and trapping protection should be proved effective Lockout Devices Lockout systems should be provided on bi-directional lines which are not regularly used in the wrong direction, and elsewhere as required by the infrastructure controller, in accordance with GK/T0030. Protected areas should be protected by signals equipped with approach locking, and route locking for the inhibited routes, in accordance with Section 3.5.8, as summarised in Figures F15 and F18. To clear the protecting signals, all the enabling devices should be proved in the normal (traffic) state. To give a lockout release, the protecting signals should be proved on and free of approach locking, with route locking normal. Where only wrong direction routes are inhibited, this may be achieved by maintaining the route locking in the right direction route set state. The diagram required to be provided adjacent to each fixed trackside enabling device should be presented in a consistent manner for all protected areas with a common user. It should give a representation of the layout of the protected area that is geographically correct and orientated in relation to the user. Any movements that are not inhibited should be clearly stated, e.g. Area Covered by the Lockout, except for the following movements: All right direction movements Train Activated Warning Systems (TAWS) TAWs should be provided where required by the infrastructure controller, in accordance with GK/T0029. The controls for each system should be specified in control tables, in accordance with GK/T0202. The basic controls to operate the warning generally consist of: a) any approach track section (within strike-in point) occupied (when moving away routes not set, for bi-directional line); or F74 b) any protected area track section occupied.

157 ailway Group Guidance Note Page F75 of 191 Wherever practicable the signalling should be arranged so that no signal, station platform, or other place where trains regularly reverse, intervenes between a strike-in point and the commencement of the protected area. Where this is not practicable, additional controls may be necessary to address the risk of excessive or spurious warnings encouraging users to fail to respond. Signal controls are described in GK/T0029. Special safeguards or warnings may be necessary if it is possible for a second train to strike-in before the first train has cleared the protected area, to ensure that users remain in a position of safety after the passage of the first train Interfaces and Transmission Systems The internal and external interfaces of the interlocking should be controlled, in accordance with GK/T0206, so as to satisfy the safety integrity requirements of the respective signalling system or sub-systems. See Section 3.1 for the signaller s interface Safety Integrity equirements Safety integrity requirements for signalling functions may be determined qualitatively from the following examples: a) Examples of Safety-Critical Functions Functions where operational safety or the integrity of the interlocking is directly affected, may be deemed to be safety-critical. These may include: i. signaller s replacement control on automatic signals; ii. CCTV crossing clear circuits; iii. ground frame releases in interlocking areas (see Section 3.6.1), also remote ground frame releases that prove signals on and free of approach locking; iv. emergency ground frame releases that bypass safety-critical controls (see Section 3.6.5); v. block circuits; vi. the control of signals, points and other signalling functions between the interlocking and the trackside; vii. the proving of signals, points, train detection and other signalling functions back to the interlocking; viii. automatic warning system (AWS) and automatic train protection (ATP); ix. right away and off indicator circuits; x. main interlocking logic; xi. ground frame local interlocking circuits; xii. level crossing local circuits; xiii. automatic signal control circuits. b) Examples of Safety-elated, but not Safety-Critical Functions Functions which may be protected by the interlocking, but where human intervention is part of the process and misleading information could create an unsafe situation or allow one to remain unnoticed, may be deemed to be safety-related (but not safety-critical). These may include: i. signalling display indications of safety-critical functions, including route locking, that can be used for operating purposes in the event of a failure; ii. signaller s control device repeating circuits of safety-critical functions; iii. remote ground frame releases where the signal proving is included at the ground frame (see Section 3.6.2); iv. emergency box to box alarms and other signaller s operational alarms; v. train describers; F75

158 ailway Group Guidance Note Page F76 of 191 Withdrawn Document vi. voice communication systems used in the operation of trains, including signal post telephones and cab secure radio; vii. supplementary systems, such as remote control override and all-signalson circuits (see Section ) and signal passed at danger (SPAD) indicators. c) Examples of Non-Safety-elated Functions Functions where operational safety and the integrity of the interlocking are not directly affected, may be deemed to be non-safety-related. These may include: i. signalling display indications and signaller s control device circuits, not associated with safety-critical functions; ii. train ready to start and close doors circuits; iii. point heater circuits; iv. maintainer's control panel circuits; v. fault monitoring circuits Transmission Systems The sub-system interfaces described below should use approved transmission systems that comply with the respective safety integrity requirements. It should also be determined that the system response time is adequate for the intended use. The correct application of the various available systems is identified in Part J. Diverse routing should be used for critical systems where necessary to ensure availability. See Appendix D2 for interference considerations. a) Interlocking to Location Data to be transmitted between an interlocking and an associated lineside location, generally includes safety-critical functions, such as signal control and proving, point operation and detection, and train detection, as listed in Section (a). An appropriate remote control system is vital FDM (frequency division multiplex). The circuits are generally the same as for a direct wired multicore link, except that inputs are formed by a closed contact in a loop to an FDM transmitter and outputs are obtained over a contact of a reed follower relay. b) Interlocking to Signal Box Data to be transmitted between an interlocking and the signalling control and display system at its controlling signal box generally includes safety-related signaller s controls and the functions that create the indications, as listed in Section (b). Appropriate remote control systems include less-vital FDM, duplicated nonvital FDM, or duplicated time division multiplex (TDM) systems. (The lessvital FDM system uses double tuned reed filters and safety reed follower relays in an otherwise non-vital system.) However, the requirement for duplication is satisfied by functions that require two changes of state to operate, such as: i. point controls that require NN or N energised and CN de-energised to move the points; and ii. signal controls that require an entrance and exit button operated to clear the signal. F76

159 ailway Group Guidance Note Page F77 of 191 Thus where a non-vital FDM or TDM system is not duplicated, any signal push button that can alone clear a signal, including individual replacement facilities, should be individually duplicated (e.g. using two TDM channels in different addresses), such that the two outputs are required to be operated simultaneously. In addition, certain controls where the signaller has the sole responsibility for safety unprotected by the interlocking, such as those listed in Section (a), items i) to iii), should be transmitted in a safety-critical system. Further details of signalling control and display facilities are given in Part L. See Section 3.1 for interface arrangements. c) Signal Box to Location Data to be transmitted between the signalling control and display system at a signal box and a lineside location generally includes safety-critical and safetyrelated signaller s controls and indications that are not directly associated with an interlocking. Vital or less-vital FDM systems are particularly useful for dropping off functions intermediately, such as remote ground frame releases (vital or lessvital - see Appendix F2:10), emergency releases (vital) and automatic signal replacement (vital). Indications include ground frame and replacement proving, and track indications for automatic sections (all less-vital). d) Signal Box to Signal Box Data to be transmitted between signal boxes includes emergency box-to-box alarms (safety-related) and block circuits (safety-critical). The systems described in items (a) to (c) above may be used, if suitable, or a dedicated link may be provided, e.g. for a train describer system emote Control Failure a) General A signaller s alarm and indications should be provided to warn the signaller of any failure of the remote control equipment to a remote interlocking that may affect his reliance on the display indications. Facilities should also be provided so that in the event of a failure of the remote control system (including all forms of panel multiplex or VDU control systems): i. all signals can be restored in the area of failure, using an independent allsignals-on facility (see Section 3.7.1(a)); ii. through routes can be set for automatic working with a limited choice of alternatives available to the signaller, by means of an override system (where required in (b), below); iii. any route set will remain set until the route is normalised by the passage of the train and the signal, if not already off and subject to approach control, will clear and remain off until replaced by the train; iv. routes may be set on a local control panel at the interlocking, the switch operations reproducing the button operations that would normally be transmitted from the signal box control system (where required in Section ). F77

160 ailway Group Guidance Note Page F78 of 191 Withdrawn Document b) emote Control Override System Where necessary to satisfy the infrastructure controller s availability requirements (see Part P of GK/C0701), an override arrangement should be provided for each remote control system. Override is generally required unless the main remote control system is duplicated. A supplementary non-safety-related system is generally of a sufficient integrity for a safety-related function (see GK/T0206). This allows override control to be transmitted either by direct wire, by an independent (usually non-vital) FDM system, or by an independent TDM system. Where reasonably practicable, diverse cable routes should be used for each remote control or override system. The minimum requirement is for all-signals-on and automatic working facilities using a three position switch capable of switching directly between any two positions without passing through the third (labelled signals-on/normal/ auto). The position of the switch should be transmitted to the interlocking in such a way that will revert to all-signals-on in the event of a failure. Operation at the interlocking should be confirmed by appropriate indications adjacent to the switch. At the interlocking, the automatic working control should disable those signalling functions which are required normal in override (delayed to allow the passage of any train approaching signals provided with comprehensive approach locking) and enable those that are required to work automatically (so that they set when their interlocking is free). These categories of signalling functions should be respectively defined on control tables. estoring the override switch to normal should cancel the automatic working facility, but not replace any signals. The all-signals-on control should replace to danger all signals controlled over the main remote control link, including automatic signals with individual replacement facilities. Selective routing with single push button control for each alternative route, or set of routes, may be provided if required by the infrastructure controller for operating purposes. As many non-conflicting routes as possible should be grouped to each push button and, once set, they should continue to work automatically until the button is pulled. Exceptionally, for heavy traffic conditions, the following features may be considered: i. one button per route; ii. effective for one movement only (with TO), and/or iii. pre-selection of routes, effective 5 seconds after the release of conflicting routes. Automatic platform or junction working may also be initiated by the override system, as described in Section (c). Where required by the infrastructure controller to permit hand signalling without clipping points in the event of a local failure preventing signal clearance, a routes set indication, proving all override routes correctly locked and detected, may be provided on the signalling display. In such cases, any selective routes should be proved in the push button lamp. The controls for each system should be specified in control tables. F78

161 ailway Group Guidance Note Page F79 of Maintainer's Facilities a) Layout of acks The layout of equipment racks and interlocking housings should be designed, in accordance with Part G, to facilitate: i. inspection of relays and other equipment to determine their state; and ii. access to check voltages on circuit connections. b) Provision Either of the following should generally be provided at each new interlocking: i. a maintainer's monitoring and fault indication panel with wiring for a test panel; or ii. an electronic maintainer's terminal and display. Where a signal box controls an interlocking that is local to the signal box, the equivalent facilities may instead be provided on the signalling display. Maintainer's monitoring panels should be wired to the standards given in Part L. Where provided, maintainer's terminals and technician's display systems (TDSs) should be in accordance with the appropriate electronic interlocking or display systems standards. An SSI maintainer's terminal will serve up to six SSI central interlockings and will provide all the facilities listed in (c). c) equirements The following facilities (described in Sections to ) should be provided to the degree necessary to satisfy the infrastructure controller s specified maintainability requirements (see Part P of GK/C0701): i. monitoring of indications being transmitted to the signalling display; ii. means of taking local control; iii. failure monitoring, giving indication of faults; iv. operation monitoring, including event recording equipment and data loggers; v. maintenance facilities to assist the tracing of faults; vi. isolation devices to allow off-line resetting of equipment; and vii. means to set restrictive controls. Where it is necessary for maintainers to release certain equipment to permit degraded operation under failure conditions, it should be ensured that any interlocking that must be maintained cannot be inadvertently released. See also Section Indication Monitoring The following indications should be provided on a simplified layout diagram, using colours that are consistent with GK/T0025: a) track occupation, using one indication per track section (subdivisions of track sections may be monitored here to avoid the requirement to indicate them separately at the signal box); b) entrance (to flash when the entrance is registered, become steady when the route is set and locked, and be extinguished as the route cancels); c) route set for each track section (extinguished by each portion of the route releasing); F79

162 ailway Group Guidance Note Page F80 of 191 Withdrawn Document d) main, distant and position light signals on or off; e) point detection; f) slot; g) ground frame or lockout release; h) level crossing indications; i) direction indicator; j) auto working; k) individual auto signal replacement; and l) train ready to start, etc. Monitoring panels should be equipped with an appropriately rated on/off switch to extinguish the indications Local Control Panel A lockable and/or transportable control panel fitted with plug-couplers (key coded in accordance with GK/T0330, where necessary) may be provided for test purposes, or for the use of local operating personnel. Provision should be made adjacent to the panel for some form of communication with the signal box that is independent of railway cable routes. A two position key operated rotary switch (labelled signal box/local) should be provided to enable local control to be taken. No action from the signal box should be required. The key should be captive while the switch is in the local position. Where override is provided and local operating personnel may be available, an additional three position rotary switch (signals on/normal/auto) should be provided for use when the interlocking is under local control (see Section ). ows of coloured three position toggle keys, or equivalent, with provision for labelling, may be provided, consistent with GK/T0025 push buttons and switches, as follows: a) route setting, auto working and signal replacement - non-locking with centre return: depress to make F contact; push up to make FM contact; b) points, etc. - locking in each position: depress to make contact; push up to make N contact; restore to centre to make C contact. Alternative types of panel may also be provided. For electronic interlockings, these facilities may be provided through the maintainer's terminal Failure Monitoring Monitoring of the following items should be considered, either locally or remotely, at a site where the state can be readily observed by a maintainer, but this list is not exhaustive: a) signal lamp main filament failure indications (where arranged in groups, the groups should not exceed six signals); b) level crossing failure; c) main power supply non-availability; F80

163 ailway Group Guidance Note Page F81 of 191 d) standby power supply non-availability; e) busbar earth fault (where vulnerable); f) under voltage detectors (for secondary cells); g) electronic system failure (including remote control amplifier monitoring); and h) pulse generator operation (where ratchet impulse timers are in use). Where necessary, a stick feature, with reset button, should be provided to store a previous or intermittent fault, particularly for filament failure and earth fault detectors. Controls may be required for earth fault detector remote reset and power supply changeover, etc. Where equipment is duplicated by redundancy with automatic changeover, a three position switch should be provided (labelled one/auto changeover/two) to enable one item at a time to be taken off line for maintenance purposes. The following colours should be used: red = fault; white/yellow = previous fault stored; or available (off line) for duplicated equipment; or release from signaller to allow resetting (see Section ); green = working or fault cleared. These monitoring functions should be repeated on a common fault indication panel at the signal box. For this purpose the power failure functions for each interlocking may be grouped together. Where 24 hour maintenance cover is not provided at the signal box, the functions should be included in an appropriate indication on the signal box display. As this monitoring is regarded as being non-safety-related, it may be transmitted to the signal box by any convenient means. The maintainer should be able to observe the grouped filament failure and earth fault indications at the same time as the track and signal indications associated with the passage of trains. If necessary, these circuits should be capable of being switched through to the signal box display, to allow this observation. For electronic interlockings, these facilities should be provided through the maintainer's terminal. Means of remote interrogation may be provided Operation Monitoring Commercially available event recording equipment may be used to assess the operation of a complex system, such as a level crossing controller. Data loggers using magnetic tape are generally used for electronic systems. Where these facilities can be used to investigate incidents, it should be ensured that there is an appropriate degree of security and processes are in place to prevent the required data from being overwritten. Where a temporary monitoring system is provided, this should conform to the requirements for temporary work given in Part B. Otherwise, the installation of the system should be subject to the full requirements of GK/T0201 and GK/T0221. For electronic interlockings, these facilities should be provided in conjunction with the maintainer's terminal. F81

164 ailway Group Guidance Note Page F82 of 191 Withdrawn Document Maintenance Facilities Maintenance facilities, in the form of fixed or specialised equipment and wiring, may be required to provide assistance in fault finding. The infrastructure controller should specify which of the following are required to facilitate the tracing of faults: a) comprehensive common equipment indications appropriate to the circuitry in use to indicate the stage that route selection has reached within each PBI ring, e.g. equipment quiescent, entrance registered, exit awaited, exit registered, etc. b) means to inhibit the function that effects the rejection of route initiation attempts (known as DJ hold) (with this facility in use signal clearance should be prevented within the affected PBI ring); c) level monitoring unit for geographical systems; d) facilities to inhibit automatic operation of equipment; e) facilities to interrogate an electronic system, with provision of fault diagnostic information; f) a condition monitoring system to detect impending random failures; g) computer aided diagnostic and simulation systems; or h) specialised test equipment for electronic systems esetting and estoration esetting and restoration is a two stage process required by GK/T0027. Where resetting systems presents a hazard, and automatic resetting is not provided, a means of manual isolation should be provided, so that the signaller has to request its restoration after it has been reset. For electronic interlockings, this facility should be provided through the maintainer's terminal estrictive Controls Means should be provided at each interlocking to enable a maintainer to readily comply with the requirements of Section E of the ule Book, GO/T3000, in applying restrictive controls, as specified in GK/T0060, including: a) temporary approach control; and b) aspect and/or route disconnection. The controls provided for each function should be specified in the appropriate control tables, in accordance with GK/T0202. Temporary approach control, releasing the signal from red by occupation of its immediate berth track section, should be provided for all power operated controlled signals. In the case of junction signals, this should prevent the signal clearing for any route until after the route indication is readable (or absence of indication is apparent), to ensure trains obey temporary speed restrictions for the route they are taking, for the situations described in GK/T0038, Part D. Generally, standard railway signalling terminals fitted with disconnection links, in accordance with Part J, should be provided. They should be fixed so as to enable ready access and operation and should be clearly and durably labelled so as to identify the function of each. For electronic interlockings, these facilities should be provided through the maintainer's terminal. F82

165 ailway Group Guidance Note Page F83 of Application to Mechanical Signalling Systems 4.1 General On basic mechanical lever frames, both the interlocking and operation are mechanical. Signal arm controls require lever reverse, with mechanical point detection and mechanical slots off, whereas point operation requires lever operated with facing point lock (FPL) plunger out. See Section 5 for enhancements to the basic mechanical interlocking, including the provision of train detection and electric locks. Purely mechanical signalling systems have the following attributes: a) long life span; b) minimum power supply requirement (assuming no track circuits, etc.); c) particular housing requirement for the interlocking (mechanical locking attached to a lever frame); d) the control point is at the interlocking (a signal box); e) all trackside signalling equipment should be close to the interlocking and, except where additional protection or proving is provided, should be clearly visible to the signaller; f) particular design, installation, test and maintenance skill requirement; g) interfacing with adjacent interlockings (signal boxes) by simple block systems; h) only suitable for simple track layouts; and i) only suitable for low speed lines with low traffic density, where approved by the infrastructure controller. 4.2 Mechanical Control and Interlocking The signaller's control device is a lever generally connected to a tappet passing through a locking box, where the mechanical interlocking locks levers, depending on the state of other levers. (Other mechanical arrangements may also be used to achieve the same result.) The levers are also physically connected to the trackside signalling equipment which they operate mechanically (using wires for signals and slots, and rodding for points, FPLs and level crossing bolts). This arrangement is only capable of maintaining the basic requirements: a) interlocking between points and signals; and b) in conjunction with a simple block system (which may be three position absolute block, using polar line circuits), a safe distance of separation between trains. These together fulfil the minimum regulatory requirement (Section 2.1), but are not generally appropriate for new work, without some form of electrical control (see Section 5). Point to point locking forms the basis of the interlocking. See Sections and The design of mechanical locking frames is described in Appendix F1. See GK/T0039 for further details of mechanical signalling. F83

166 ailway Group Guidance Note Page F84 of 191 Withdrawn Document 4.3 Point Locking Point locking is required on facing points as described in Part P, achieved with mechanically operated points by means of a facing point lock (FPL), generally operated by a separate lever interlocked with the point lever. It is preferable that the points are unlocked when the FPL lever is normal in the frame, but, in the case of ground frames, the points should be locked when the FPL lever is normal in the frame. Thus operation of facing points from a signal box frame involves replacing the FPL lever to withdraw the lock plunger, moving the point lever to the correct position and then pulling the FPL lever again to relock the points. FPLs may be omitted on non-passenger lines so long as the points are detected in the signal selection. Track locking may be provided by means of an FPL bar on the approach to facing points. Where points are situated less than a train length apart, route holding may be achieved by interlocking the FPL bars that protect each set of points. A degree of route holding may be provided by trailing points or ground frame releases being locked by the signal in advance, to prevent their movement until a train has passed through the section and the signal replaced behind it. See Section 3.5.6(b)ii) for further details. 4.4 Indications Indications should be provided to show the state of signalling equipment that is not clearly visible to the signaller. These may take the form of needle indicators to specification B 925, repeating the position of signals, slots, train waiting treadles, etc. They may be worked directly over polar line circuits. See GK/T0025 for further details. 4.5 Sequential Locking and Other Proving Non-reciprocal sequential locking between adjacent signal levers and between the section signal and the block should be provided to ensure that each signal is replaced before a following train can approach. This may be achieved in one of the following ways: a) non-reciprocal mechanical locking, but not for new work (see Appendix F1:4); b) signal ahead normal lever contact (and arm proved on, where repeated) in the normal lever lock of the signal in rear (see Section 5.3); or c) a stick circuit to store the fact that option (b) has taken place, for use with signals that are approach controlled. The locking of trailing points in the signal section in rear (see Section 4.3), will also prevent the sequential locking being defeated by a train approaching on a different route. Mechanical detection should be used to prevent a signal clearing until a point switch is correctly closed, in accordance with Figure F17. Further details are given in Part P. Signal arm proving, and train waiting detected at home signal, may be provided in the block circuit, using polar moving iron relays to specification B 923 in series in the repeater circuits. Further details are given in Part S. Electric lever locks should be fitted with a force down feature, as described in Appendix F1:7.1. F84

167 ailway Group Guidance Note Page F85 of Numbering Associated with Lever Frames Signalling functions controlled from a lever frame should take the number of the controlling lever. They should be allocated with ergonomic considerations, so that as far as possible they are pulled in ascending or descending numerical order. The need to pull, or replace, a lever between two levers lying reverse is prohibited (except in the case of miniature lever frames). It is usual to place up and down line running signals at opposite ends of a small frame (the end from which trains approach), or towards the centre of larger frames. Points are laid out in geographical order from left to right. Shunting signals and FPLs are numbered next to the points to which they apply. Level crossing functions are allocated to levers at the end of the frame nearest to the crossing. On new frames a minimum of ten per cent spare levers should be provided, evenly distributed and preferably in small groups to cater for future signalling. An illustrative layout is given in Appendix F1 (Figure F1:10). 4.7 Lever Nomenclature Plates The description should be that shown on the locking tables, with the lever number shown boldly at the top. Subject to locking constraints, the order of pulling details should be written in the same order that the signaller will pull them, avoiding unnecessary walking. Where optional routes are available, the first left route should be given first, then the next in order over to the right. When a nil move occurs among other options, the nil pull should be quoted in the appropriate order. Levers retained solely to maintain locking following alterations and that have to be pulled to release other levers should be plated Interlocking Lever or For elease of Mechanical Locking, according to regional practice. When undertaking alterations at an existing installation, plates should be manufactured (e.g. from xylonite, aluminium, cast iron, or brass) and painted or engraved to match existing plates. An illustrative set of nomenclature plates is given in Appendix F1 (Figure F1:13). 4.8 Lever Painting Lever painting details are prescribed in GK/T0005. Stripes or bands should generally be 75mm wide on full levers and 6mm wide on miniature levers. Stripes should be arranged with the darker coloured stripe nearest the quadrant. On bi-directional lines, chevrons should point upwards on the up side of the lever and downwards on the down side, or alternatively point upwards on the top half of the lever and downwards on the bottom half. Where levers bear two colours, the top colour relates to the function that operates first. Quadrants should be painted black. Levers should not be painted white until all locking has been removed from them. F85

168 ailway Group Guidance Note Page F86 of 191 Withdrawn Document 5 Application to Electro-Mechanical Signalling Systems 5.1 General Electro-mechanical signalling systems essentially comprise a mechanical interlocking with the addition of electric lever locks to provide a second level of locking, known as electrical or selection locking. This may involve track circuits and/or electrical point detection. Mechanically operated signals have aspect (arm) controls applied through the selection lock, whereas power operated signals generally incorporate the controls in the operating (aspect) circuits. This is summarised in Figures F1 and F2. Alternatively, frames may be equipped with all electric locking using either separate (preferred, see Appendix F1:4), or combined (not for new work), electrical interlocking and selection locks. Miniature lever frames may have either mechanical or electrical interlocking, but only power operation of points and signals. (See Section 6 for all-electric frames.) There is, therefore, a power supply requirement, but the trackside signalling equipment does not have to be so close to the interlocking, as it can be power worked over much longer distances, by means of circuit controllers attached to the levers. Likewise, by use of electrical point detection, more complex layouts can be signalled. A home signal berth track section to place the block indicator at "train on line" is a minimum requirement for a block system. The provision of track sections between signals and points enable route holding to be provided. Track sections over the points are generally necessary for track locking. These features make the system more suitable for use on passenger lines. See Section for the minimum train detection requirements. The line capacity between signal boxes may be increased by the addition of an intermediate block section, with a track section extending from the most advanced starting signal to the overlap of the intermediate home, as described in GK/T Interlocking The interlocking is generally accomplished mechanically, as in Section 4.2. However, signals are not required to lock trailing points in rear (see Sections 4.3 and 4.5), provided that: a) the signal is automatically replaced, O this signal is proved on in all signals in rear; AND b) route holding and track locking are provided, O the points are over the maximum train length from the signal ahead. 5.3 Electric Selection Locking Electric lever locks, fitted to those levers that require electrical locking, should be used to apply the additional controls that enable a signalling function to be selected. See Figure F19(b) for the basic circuits. a) Signal Selection A signal lever is generally fitted with a normal and back lock, the normal position, (A), releasing the lever, the lock being energised by the following, as necessary, in accordance with the electrical control tables: F86

169 ailway Group Guidance Note Page F87 of 191 i. electrical point detection (mechanically operated signals); ii. track sections in signal section, overlap and flank (non-permissive mechanically operated signals); iii. approach control track occupied (diverging or subsidiary mechanically operated signals) - see Section ; iv. line clear release (mechanically operated signals); v. sequential locking (main signals) - see Section 4.5; and vi. route locking (opposing signals) - see Section Where mechanically operated signals are approach controlled, an audible warning of an approaching train may be provided to remind the signaller to pull the lever. Alternatively, particularly where there is no berth track section, the signal concerned may lock the main signal in rear to prevent a high speed approach. For power operated signals it is preferable for point detection, train detection, lamp proving and block conditions to be provided as electrical controls (see Section 5.5), so that the signal lever is free to be pulled, and so protect the route by means of the mechanical interlocking, even if any of the electrical conditions should fail. b) Signal Backlocks The back, (B), position should be used where any of the following are provided, in order to backlock the lever and prevent it being replaced in the frame until the conditions are met: i. track section(s) clear between the signal and points, in lieu of route locking (see Section 3.5.6(b)i), and ii. power operated signal proved on (proved instead in the approach locking for new work), or, for new work, proved free of approach locking (see Section 5.4). c) Point Selection Point levers should be locked both ways with an (AE) lock, the lock being energised by the following, in accordance with the electrical control tables (see Section 3.5.6): i. track sections over the points to provide track locking; and ii. route locking, where there are several tracks between signal and points. d) Point Checklocks Where it is the practice to provide indication locking to prove the point operation before releasing the interlocking, ABDE locks (often referred to as NBD) should be provided to hold the lever in the checklock position until the appropriate detection is obtained. See Figure F19(c) for the basic circuits. F87

170 ailway Group Guidance Note Page F88 of 191 Withdrawn Document 1 G 1 G 1 HGP 1 GP 1 ALS 1 GP 1 GS 1 ALS 1 AJ 1 NA LOCATION 1 H 1 H 1 H AB TP 1 B AC TP 1 ALS Double cutting and polar circuits not shown. 1 ALS 1 AJ 1 ALS 1 B 11 WJ 11 NA 11 E 11 NWK 11 WK 1 HGP 1 GS 11 NA 11 E 11 NWK 11 WK AA TP 11 NK 11 K 11 W J Correspondence proving 11 NA 11 E AB TP LOCATION 11 WM 11 NWM 1 GS 11 NWM 11 WM Contactors LOCATION 11 NK 11 K Combines signal stick and train-insection proving 11 WM 11 NWM (PO) J 1 53 ECP 11 NWK AB TP AC TP AD TP AA TP 1 TACL 1 GS 1 G 1 AJ (a) Circuits Common to All Systems 1 ALS AB TP 1(B)L AC TP BE TP CD TP 11(AE)L Extended backlock in lieu of route locking (b) Lever Frame with Mechanical Interlocking Extended track locking in lieu of route locking from signals 2 & 10 1 ALS AB TP 1(B)L AC BE CD TP TP TP 11 NA 11(ABDE)L 11 Detection of trailing points (11 NWK) is omitted from 1G. Feeds to point contactors are fed over NB and D contacts, rather than NA and E. Detection without correspondence proving 11 NK 11 K E 11 BC 11 DC (c) Lever Frame with Indication Interlocking Point to point locking (A)L (AE)L (AE)L N A A N A These interlocking lock circuits are additional to the selection lock circuits shown in items (b) or (c). 2 N 10 N 11 E 11 N 14 N 12 E F88 (d) Lever Frame with Electrical Interlocking Figure F19 Basic Interlocking Circuits (Lever Frames) to Demonstrate Principles See Figure F1:10 for Layout Plan; Figures F1:11 & 1:12 for Control Tables

171 ailway Group Guidance Note Page F89 of 191 Locks should be economised, as described in Appendix F1:7.2. Where necessary, track sections should be conditioned by the lie of points (see Section 3.3.4). A list of lever lock and controller positions is given in Figures F1:17 and F1:18. Lever notation is defined in GK/T Approach Locking and Signal Disengaging The provision and release of approach locking should be in accordance with Section Where continuous train detection is provided, the approach locking should either be extended back to the sighting of the first caution, or become effective as soon as the signal is ready to clear. Without continuous train detection, the approach locking should become effective as soon as the signal is ready to clear. The signal backlock requires the approach locking to be free. Where track circuit replacement is provided, a signal disengaging stick should prevent controlled signals clearing a second time until the lever is replaced and pulled again. The signal is generally disengaged by the berth track and first track past the signal being occupied whilst the signal is off, and is reset when the lever is normalised. The signal stick may also be used to prove that the train has passed the signal in order to release the approach locking, provided that it is designed to fulfil the necessary requirements. In addition, a manual timed approach lock release should be provided, initiated by the lever in the backlock position, when approach locked. Where the provision of train detection cannot be justified, a timed release alone may suffice. See Figure F19(a) for the basic circuits. 5.5 Electrical Control and Operation Levers controlling power operated equipment or electrical releases should have shortened handles to warn the signaller of the reduced force necessary to pull the lever. This does not apply to levers retained solely to maintain locking (Section 4.7), which should be marked in a temporary manner. Power operated trackside signalling equipment should be designed to revert to a safe state in the event of a control being removed, e.g. signals return to danger and point mechanisms complete their movement. Power operated trackside signalling equipment should generally be controlled over lever contacts on the circuit controller. In order to take advantage of the safety integrity of the equipment, the selection controls (point detection and train detection) should be transferred to the operating circuit. Thus, if any of the controls are lost, the equipment is made safe. This continuous monitoring will result, for instance, in motorised semaphore signals being automatically replaced in the event of a disconnection in the circuit. Signals should thus be replaced by track sections, avoiding the need for sequential locking. F89

172 ailway Group Guidance Note Page F90 of 191 Withdrawn Document a) Signal Controls Signal controls should generally contain the following: i. signal lever reverse ( or E lever contact); ii. track sections in signal section, overlap and flank; iii. approach control track occupied (diverging or subsidiary signals); iv. electrical point detection; v. signal ahead lamp proving; and vi. signal disengaging stick (where signal is track replaced). Point detection of trailing points may be omitted where indication locking is provided. Where colour light signals are provided, the control circuits operate a signal relay at the interlocking, which in turn operates the aspect relay(s), conditional upon the aspects of the signals in advance, in accordance with GK/T0032. The aspect relay(s) are generally situated in a lineside location adjacent to the signal. See Part S for full details of signal control circuits. b) Point Controls Point controls contain the following: i. point lever normal or reverse (NA or E lever contacts); ii. selection controls, as in the lever lock (optional). The point control circuit generally energises a contactor situated in a lineside location adjacent to the points. Point operating currents should not be fed over ordinary relay contacts, or lever contacts. See Appendix F2:6.3 for features to be incorporated into all point control circuits. See Part P for full details of point operating circuits. c) Track Locking Circuits should be arranged to prevent point movement when the track locking is effective, but allow any movement in progress to be completed. This may be accomplished either: i. by the use of special stick relays, where the armature is held up by the point operating current flowing through a separate winding; or ii. by arranging the point control circuit to operate in the direction set by the point lever, until the appropriate detection is obtained. Note that, in selection circuits, course lever contacts, such as (NA) and (E), are more reliable than fine, (N) and (), contacts. 5.6 Proving Proving should be provided as in Section 4.5. The appropriate form of point detection should be provided for mechanically operated facing points (except for certain non-passenger movements) and all power worked points, in accordance with Figures F16 and F17. Wherever practicable, signal on proving (signal aspect relay de-energised for colour light signals) should be provided in the signal lever backlock (via the approach lock release circuit for new work). Sequential locking is not required where signals are automatically replaced to danger by the passage of the train, but a signal stick should be provided as described in Section 5.4. Colour light signals should be proved alight in the aspects of the signal in rear in such a way that will facilitate degraded operation. Junction signal aspect relays should prove route indicators alight as necessary. F90

173 ailway Group Guidance Note Page F91 of Indications Indications for semaphore signals, etc., should be provided as in Section 4.4. Where several track sections are provided, they should be indicated by more than one lamp per track section on an illuminated diagram, arranged in the correct geographical orientation as seen by the signaller. Where track section occupation is indicated by lamps, the availability of the power supply should also be indicated. Point detection relays should be repeated by indication lamps, generally located on the block shelf. The state of colour light signals (on or off) should be indicated similarly. They should repeat the aspect relay and include lamp proving. (Alternatively the individual aspects may be repeated instead.) Where necessary, a white lamp should be provided to indicate that a lever is free to be moved, i.e. lock ready to be energised. See GK/T0025 for further details, including signalling display options. 5.8 Sealed Emergency eleases at Signal Boxes Where it is necessary for maintainers to release certain equipment to permit degraded operation under failure conditions, it should be ensured that any interlocking that must be maintained cannot be inadvertently released. A sealed emergency release should be provided for mechanically operated points and FPLs, to override any track locking or route locking, in the event of a failure of train detection equipment. It should only bypass track section controls. Where route locking is overridden, the signal lever normal and free of approach locking controls should be included separately in the point (and FPL) lever locks. Sealed releases should not be provided at ground frames. 6 Application to All- Electric Non-oute Setting Interlocking Systems 6.1 General One example of an electrical non-route setting system is a lever frame or miniature lever frame where all signalling functions are power operated. It is preferable for each lever to have two electric locks, the interlocking lock and the selection lock, as explained in Section 6.8. (See Section 5 for the case where some functions are mechanically operated.) Another example is an individual function switch (IFS) panel, with separate switches for each function. Power operated ground frames often use this type of panel. Here lock relays are used to combine the interlocking and selection lock functions in the lock relay operation and release circuits. Where such an interlocking is combined with colour light signalling and continuous train detection, the signalling system becomes suitable for medium density, high speed traffic, with reasonably complex layouts. Continuous train detection between signal boxes is a requirement of track circuit block (see GK/T0041). Automatic signals may be provided, as necessary, to increase the line capacity with additional signal sections. F91

174 ailway Group Guidance Note Page F92 of 191 Withdrawn Document 6.2 Interlocking Lever Frames With lever frames, the interlocking should be accomplished electrically by means of interlocking lever locks (see Section 5.8), with lock slides cut for the (A) and/or (E) positions. The locks should be energised by contacts of the appropriate levers in either the (N) or () positions. All converses and counter conditional locking, where necessary, should be specifically wired and identified on special locking tables. Fine (N) and () contacts should be used, because, in conjunction with the force down feature, these prove that the locks are effective. Further details are given in Appendix F1. See Figure F19(d) for the basic circuits Switch Panels with Latched elays Switch panels use similar circuits to operate two position latched lock relays, which perform the interlocking and imitate the action of a lever. Unlike a lever, a switch is not interlocked to prevent its movement, but it is only able to throw down its respective lock relay when permitted by the interlocking circuit. Only if the selection conditions (e.g. track locking) are correct can the lock relay for the opposite position be operated and so release the interlocking and operate the function concerned, in the same way as a lever completing its stroke. Where points are equipped with indication locking, a further stage is added, by which the points are operated if the selection is made, but the lock relay is not operated until detection is obtained. This, however, requires additional relays. The latched relay armatures should be mechanically or electrically interlocked to prevent both being operated at the same time. The equivalent of the mid stroke position of a lever, where locking has been performed but no locking has been released, may be achieved by both lock relay armatures being thrown down. In systems where the integrity of latched relays is such that they can only be thrown down by operation to the opposite position, and a mid stroke position is not required, a single latched relay or magnetic stick relay may be used instead of separate normal and reverse latched relays. See Figure F20(a) for the basic circuits. Signal lock relays thus represent the (A) and (B) lock positions. The reverse lock relay operated (preceded by normal lock relay thrown down) requires the switch reverse and interlocking free, including route locking (equivalent to signal lever reverse). The normal lock relay operated (preceded by reverse lock relay thrown down) requires the switch normal and approach locking free, and should release the signal interlocking (equivalent to signal lever normal). Both armatures thrown down together thus maintain the signal interlocking with the signal on, waiting for an approach lock release. The reverse relay does not have to be latched and the substitution of a ordinary acting relay will ensure the immediate replacement of the signal if the switch is restored, or any interlocking condition is lost. Similarly, point lock relays represent the (A) and (E) lock positions. The reverse lock relay operated (preceded by normal lock relay thrown down) requires the switch reverse and interlocking free for the points to go reverse (including track and route locking) and should release the normal interlocking, and vice versa. Both armatures thrown down together maintain the normal and reverse interlocking and prevent the points from moving. F92

175 ailway Group Guidance Note Page F93 of Alternative Arrangements Magnetic stick relays (see Part D) are used in place of latched relays in some systems. Alternatively, conventional stick relays may be used for point locking and the approach lock stick relay (ALS) for signal locking. The signal relay may combine the route and aspect requirements, but, if anti-preselection is provided, the signal cannot be set until the aspect controls are satisfied, so any approach control tracks should be included in the outgoing signal feed, rather than the signal relay. See Figure F20(b) for the basic circuits oute Locking Where required (see Section 3.5.6), route stick relays should be de-energised by the release of the signal normal lock relay (NL). If there are no lock relays, the ALS should be used instead to de-energise the route sticks. See Figure F20(c) for the basic circuits. The final route stick relay should be down proved in the aspect controls (see Section 3.5.8(e)). If the signal relay combines the route and aspect requirements, the route stick relay should be included in the outgoing signal feed, rather than the signal relay, as the route stick is not de-energised until the signal relay energises, thus de-energising the ALS. F93

176 ailway Group Guidance Note Page F94 of 191 Withdrawn Document 1 1 ALS/AJ as Figure 19(a), but with 1 NL (front contact) instead of the NA lever contact and 1 N (front contact) instead of the B contact. 1 GS as Figure 19(a), but with 1 N (back contact) instead of the B lever contact. 1 H, HGP and GP as Figure 19(a). 11 NWM/WM/WJ as Figure 19(a), but with 11 NL and 11 L (front contacts) instead of the NA and E lever contacts, respectively. 11 NWK/WK as Figure 19(a), but with 11 NL and 11 L (front contacts) instead of the NA and E lever contacts, respectively. 1 IFS relays for each function 1 1 N N 1 1 L 53 ECP Interlocking 12 NL 1 ALS 11 NWK AB TP AC TP AD TP AA TP 1 TACL Extended Track locking backlock 1 AC BE CD 12 1 L TP TP TP L AB TP 1 N 2 NL 1 GS 10 NL Extended Backlock 1 NL track locking Interlocking (a) Individual Function Switch (IFS) Panel with Point to Point Locking (Conventional) 1 G Point to point locking 11 L 11 NL 1 ALS/AJ as Figure 19(a), but without the NA lever contact and with 1 N (front contact) instead of the B contact. 1 GS as Figure 19(a), but with 1 N (back contact) instead of the B lever contact. 1 HGP and GP as Figure 19(a). 11 NWM/WM/WJ as Figure 19(a), but with 11 NW and 11 W (front contacts) instead of the NA and E lever contacts respectively. 11 NWK as Figure 19(a), but with 11 NW (front contact) and 11 W (back contact) in series, instead of the NA lever contact. 11 WK as Figure 19(a), but with 11 W (front contact) and 11 NW (back contact) in series, instead of the E lever contact. 1 AJ N AC TP BE TP CD TP 1 ALS 37/38 ALS 2/3/4 ALS 9/10/15 ALS 11 L 11 L NW 11 W Track locking Ns and s as in item (a). Approach control here to allow antipreselection to be incorporated in G 1 TACL AA TP 13 NW Interlocking using ALSs Prove points locked 11 L 12 L 1 G 13 W 1 ALS Points free relay LOCATION 1 H 11 L 11 N 11 W 11 NW 11 W Point control stick relays 11 NW 1 2/3/4 ALS 9/10/15 ALS Use ALS front contacts here to prove any opposing locking. EL TP DH(DN) US DH(DN) US oute sticks initiated by ALSs CC(DN) US DH TP CC TP CC(DN) US CD TP CD(DN) US 53 ECP (b) DH(DN)US CC(DN)US CD(DN)US 11 NWK 12 NW AB TP AC TP AD TP 1 GS 1 G Flank points (not detected) required here in lieu of point to point locking IFS Panel with Stick elays and No Point to Point Locking AC TP BE TP BE TP Track locking AC TP AC(DN) US BE(UP) US BE(DN) US AC(DN) US BE(UP) US Use AC(DN)US (back contact) in 1 H to prove points locked, rather than 11 L and 12 L, as shown in item (b). Other circuits as in item (b). BE(DN) US Interlocking using USs 37/38 ALS N BC TP BD(UP) US 11 NW 11 W 11 NW 11 W BD TP 1 AJ 11 W 11 NW BD(UP)US CD(DN) US BE TP BE(DN)US 1 ALS AB TP AC TP AC(DN)US BD(UP) US 11 NW BE(UP)US 13 NW BE(DN) US AC(DN) US 13 W BE(UP) US (c) Figure F20 IFS Panel with oute Locking and No Extended Backlocks or Extended Track Locking Basic Interlocking Circuits (Non-oute Setting Systems) to Demonstrate Principles See Figure F1:10 for Layout Plan. Anti-preselection is not shown. F94

177 ailway Group Guidance Note Page F95 of Anti-Preselection Anti-preselection should be incorporated into the switch operation, as required by Section 3.5.5, to guard against risks of premature release of locking and incorrect operation of switches. 6.3 Selection Locking For lever frames, selection lock circuits should be provided as in Section 5.3. Where lock relays are provided, all electrical locking (approach locking, backlocking, route locking, checklocking and track locking) should be in the lock relay circuits (see Section 6.2). All route proving for signals should be in the signal control circuits (Section 6.5). 6.4 Approach Locking Approach locking should be in accordance with Sections Signals should be proved free of approach locking as follows: a) in the backlock of levers; or b) in the normalisation of the signal lock relay(s). 6.5 Control and Operation Selection (or control) circuits should be provided as in Section 5.5, initiated either by lever contacts or by lock relay contacts, as appropriate. Where lock relays are provided, all electrical locking should be in the lock relay circuits. The signal control circuits should include the following: a) train detection; b) point detection and correspondence with the point lock relay; c) signal ahead lamp proving; d) any other route proving; e) signal not disengaged; f) signal lock relay reverse; and g) signal switch reverse, to allow manual replacement (not required if the signal reverse lock relay is not latched). See Section for alternative arrangements, combining the route and aspect controls, epeat relay(s) may be used in operating and proving circuits to extend the operating distance as far as necessary. See Part D. Alternatively, a safetycritical transmission system may be used, such as vital FDM. See Section (a). 6.6 Proving Proving should be provided as in Section Indications Indications should be provided as in Section 5.7, on the block shelf and illuminated diagram, or on a control panel. F95

178 ailway Group Guidance Note Page F96 of 191 Withdrawn Document 6.8 Separate Electric Locks For new lever frames, or newly relocked frames, where the interlocking is to be accomplished electrically, separate interlocking locks and selection locks should be provided. Where separate locks exist, the interlocking lock (body and cover) should be painted red, as a warning to the maintainer that they must not be released to facilitate degraded operation. 7 Application to oute Setting Interlocking Systems 7.1 General oute setting interlockings generally register a route request if the locking is free (i.e. points available), and then automatically call the points to the required position. The route request with the points correctly called sets the route, which, in turn, locks the points. In electronic systems, these actions may be accomplished at the same time: the route request controls the points and sets the route, if the points are free to move, with no separate locking. Examples of route setting systems include free-wired route relay, geographical route relay, or electronic interlockings, controlled from one control switch (OCS) or entrance exit (NX) panels, integrated electronic control centres (IECCs), or other VDU based systems. By using a signaller s control device that does not remain in the position in which last set, e.g. a push button, automatic route setting (AS) is possible. This should be specified where AS might be a future requirement. (The requirements for control and display systems are given in GK/T0025.) oute setting signalling systems are suitable for complex layouts and, where incorporating AS sub-systems, they are suitable for particularly high density traffic. Considerable space, however, is required for route relay systems (even more for geographical interlockings) and power consumption is heavy. Little space and less power consumption is required for electronic interlockings, but data preparation skills are required. Electronic systems, due to their flexibility, present the opportunity for incorporation of advanced safety features, particularly to allow for the safe passage of trains under degraded conditions, as described in GK/T0206. However, they can be less flexible as regards alterations and slow to respond due to cycling time. Interlockings should be designed to prevent an unsafe state occurring during power supply failure or restoration, as described in Section Signaller's Controls In addition to the route setting devices, individual three position point control devices are required to control points for maintenance purposes or during failures, to select an alternative route, to swing an overlap, or to inhibit point movement. In order to permit route setting, the point control device must be left in the centre position. The signaller s control devices may be switches, push buttons, tracker ball, mouse, keyboard, or some combination thereof. There is no longer a requirement for points free indications on route setting systems. The signaller s workload may be reduced by the provision of special facilities, such as: F96

179 ailway Group Guidance Note Page F97 of 191 a) automatic route setting (see Section 3.1.3); b) automatic working facilities for controlled signals (see Section ); c) automatic platform working at simple terminal stations (see Section (c)); d) override controls (see Section ); e) through setting of several consecutive routes by one action; and f) route demand storage, but unavailable routes should not be stored to await conditions becoming available, unless measures are taken to address the risks arising from preselection (see Section 3.5.5). Several interlockings may be controlled from a single signal box control system by means of remote control transmission links. See Section (b). 7.3 oute Setting The BS-SW67 free-wired route relay system is described in Appendix F2. The requirements for geographical relay interlockings are given in Appendix F3 and for electronic interlockings in Appendix F4, which also defines the solid state interlockings (SSI) filenames used in this section. Simplified circuits showing the basic requirements are shown in Figure F21. oute setting interlocking systems are broadly configured on four levels (in geographical systems these levels may relate to specific lines in the geographic cables connecting the functional sets), viz: oute Initiation (or egistry) Level This is basically the interface with the signaller s route setting devices, by which entrances registered await a valid exit. If any of the points in the route are unavailable, the request should not succeed. Further details of the signaller s interface is given in Section 3.1. With some systems, such as OCS, the route setting device(s) simply energise a route relay or route reverse lock relay, if the points are free, which in turn calls the route. In the AEI-GS geographical system, an entrance device registered in a signal set sends out a feed, both ways at any available facing points, until a registered exit is found in another signal set. These systems require no special control panel interface. See Figure F3:10 an application of the basic circuits to the example in Appendix F Completion Level The completion level checks route availability, selects or calls the route, and sets the points. This may be regarded as part of the signaller s interface system (see Section 3.1). F97

180 ailway Group Guidance Note Page F98 of 191 Withdrawn Document OCS relays for each function (centre position for points only) 51 N C 51 N C 712 C 712 NL 712 C 712 L AC TP 712 L 712 L BE TP Track locking 712 NZLP Points free or appropriately locked relays 712 ZLP AC(DN) US BE(UP) US These six summation relays should be provided as necessary 712 L Points locked and detected relays BE(DN) US 712 NWK 712 WK 712 L oute locking including all conflicting and opposing routes (a) Circuits Common to All Systems 712 NKLP 712 KLP 51 G 51 U 56B U 105A(M) U 203A(M) U 51 ALS 712 NCU oute calling summation relays 712 CU LOCATION 51 H 51 ALS/AJ as Figure 19(a), but with 51 NL (front contact) instead of the NA contact and 51 N (front contact) instead of the B contact. 51 GS as Figure 19(a), but with 51 N (back contact) instead of the B lever contact. 51 HGP and GP as Figure 19(a). 712 NWM/WM/WJ as Figure 19(a), but with 712 NL and L (front contacts) instead of the NA and E lever contacts, respectively. 712 NWK/WK as Figure 19(a), but with 712 NL and L (front contacts) instead of the NA and E lever contacts, respectively. 51 Points normal or free 711 NZLP 51 ALS 51 L 712 NZLP 53 ECP 712 NKLP 711 NW Ls prove points locked Use route NLs or USs here to prove any opposing locking 711 L 51 L 51 NL AC(DN) US N AB TP oute stick relay chain as Figure 20(c), but initiated by route NLs instead of ALSs. AC TP AD TP Last US proves all locking effective Locking 712 L AA TP 51 TACL 712 L 712 NL 51 GS oute calling 712 CU 712 NCU 51 G C 712 N 51 AJ (b) One Control Switch (OCS) Panel with Latch elays 51 ALS/AJ as Figure 19(a), but without the NA lever contact and with 51 U (back contact) instead of the B contact. 51 GS as Figure 19(a), but with 51 U (front contact) instead of the B lever contact. 51 HGP and GP as Figure 19(a). 712 NWM/WM/WJ as Figure 19(a), but with 712 NW and W (front contacts) instead of the NA and E lever contacts respectively. 712 NWK as Figure 19(a), but with 712 NW (front contact) and W (back contact) in series, instead of the NA lever contact. 712 WK as Figure 19(a), but with 712 W (front contact) and NW (back contact) in series, instead of the E lever contact. 51 U Points normal or available 711 NZLP C 712 L 712 N 53 ECP 712 NZLP oute calling 712 CU 712 C 712 NCU 712 NKLP Use USs here to prove any opposing locking Locking 712 L 711 NW Ls prove points locked 712 NW 712 W everse stick path is converse of normal pick up path 711 L 51 U 712 W AC(DN) US 51 AB TP 712 N 712 C 712 L 712 AC TP 712 NCU 712 C 712 CU AD TP Last US proves all locking effective oute stick relay chain as Figure 20(c), but with a back contact of the respective U in series with each ALS to initiate the route locking as soon as the U picks. 712 L AA TP 51 TACL 712 W 712 NW Normal stick path is converse of reverse pick up path 51 GS 712 NW 51 G 51 AJ 51 N is not required. 712 NZLP and ZLP as item (a), but with NW and W contacts instead of NL and L. F98 Figure F21 (c) One Control Switch (OCS) Panel with Stick elays (see Figure F3:10 for an application of this circuitry to a geographical interlocking) Basic Interlocking Circuits (oute Setting Systems) to Demonstrate Principles See Appendix F5 for Layout Plan and Control Tables. Anti-preselection is not shown.

181 ailway Group Guidance Note Page F99 of 191 oute availability should be tested by checking the position of the point lock or point free relays, or by the P file (see Figure F4:9) in the SSI interlocking multi-processor module (MPM). This may be done at the initiation level. If all the points are free (SSI PFM file - see Figure F4:8), or locked in their correct positions, and any directly opposing routes are normal with route locking free, the required route is set and the points called (by the operation of the route reverse relay in free-wired interlockings). Where there are alternative routes from a signal to a given destination, a preferred route may be identified on the control tables. The preferred route should set whenever the route is requested, if it is available. If it is not available a non-preferred route should set. This may be achieved by delaying the setting of the non-preferred route(s). Particular alternatives should be selected either by the use of the individual point control devices, or, where required by the infrastructure controller, by the provision of additional push buttons. In geographical systems, paths through S&C that do not comprise a valid route should, if necessary, be inhibited, e.g. divergences at switch diamonds oute Locking Level When the route is set (normal lock relay released) route sticks in the route should be de-energised (subroutes set in the FOP file of the SSI MPM - see Figure F4:10). The points that have been called by the route setting should be locked (normal or reverse lock relays prevented from being released) by the last route stick (or subroute) over the points. This is accomplished within SSI by the points free to move (PFM) file. In freewired relay interlockings points are also locked by the appropriate route lock relays, although this may be unnecessary where sectional route locking is provided. The actual interlocking (Section 6.2) is a two stage process by which firstly the route is proved available (Section 7.3.2) and then, if successful, conflicting functions are locked. Directly opposing routes, including those over diamond crossings, should be required normal before a route can be set, but conflicting routes are interlocked through the point locking (i.e. one route requires points normal; the conflicting route requires them reverse). Point to point locking should not generally be provided. Main (M), warning (W), call-on (C) and shunt (S) class routes from a main signal should be interlocked with one another, but provision should be made for warning routes to be stepped up to main routes should the track occupancy conditions change and stepped down after use in automatic working mode (see Section 3.2.5) Aspect (or oute Proving) Level This is equivalent to the signal control circuits described in Section 6.5. The SSI equivalent is the OPT file (see Figure F4:11). Call-on class routes require the permissive track occupied in the aspect level (not replacing signal) as well as the route locking level, so as to force re-stroking to main class routes should the track occupancy conditions change before the signal clears (see Section 3.2.6). F99

182 ailway Group Guidance Note Page F100 of 191 Withdrawn Document In a route relay interlocking, the signal aspect should prove points locked (i.e. not free to move) as well as detected, because they are not proved locked when the route is set at the completion level, but only available. This is achieved by proving the points free relay de-energised. Where sectional route locking is provided, the last route stick relay to be deenergised when the route is set should be proved down in the signal relay to prove the integrity of the route stick chain (see Section 3.5.8(e)). 7.4 oute eleasing Manual releasing is accomplished by the signaller operating a device, such as pulling an entrance button, which stores the normalise request. If the train has passed the signal, or when the signal becomes free of approach locking, the normal route lock relay re-energises (route becomes unset in SSI) and the route sticks energise (subroutes unset) as the track sections clear behind the train. Approach locking should be as described in Section 6.4. Provision should also be made, until the approach locking becomes free, for the signaller to cancel the normalise request by re-stroking the route (see Section 3.7.1(d)). Where required, train operated route release (TO) is provided in accordance with Section Points should not be restored to their normal position by the route releasing, except where required for trapping purposes in accordance with Section Operation elay operating circuits should generally be provided as in Section 6.5, unless trackside signalling equipment is to be operated directly from trackside functional modules (TFMs) in accordance with SSI applications (see Appendix F4:3.6), or by some other safety-critical means. TFMs are connected to the interlocking by a safety-critical data link. The OPT file in the SSI MPM is used to address the TFMs via the data link. The requirement for signalling equipment to revert to a safe state is achieved in SSI by the provision of a "red retain" output from the signal TFM. The most restrictive aspect of every signal should be connected to this output to prevent the signal being completely extinguished in the event of a failure of the data link. 7.6 Proving Trackside signalling equipment should generally be proved as described in Section 6.6, or by some other safety-critical means. Where TFMs are used, the equivalent proving should be provided in accordance with the SSI applications manual. The IPT file for this purpose in the MPM is addressed via the data link. The proving of relay circuits should be as described in Part D. The outputs from electronic processor interlocking systems duplicated by diversity should be proved to be in correspondence. Single processors should have a self checking capability. 7.7 Identification in oute Setting Systems All routes should be identified in accordance with GK/T0009. oute sticks (known as subroutes and suboverlaps in SSI) are directional, and so require a directional label after the track section name. Conventionally the labels (Up) and (Dn) have been used, but in some systems a more comprehensive identification is necessary. F100

183 ailway Group Guidance Note Page F101 of 191 The SSI system is based upon the orientation of the subroute/suboverlap plan (see Figure F4:7), on which the extremities of each track section are labelled A, B, C, etc. in a clockwise direction (starting at twelve o'clock), thus identifying the direction of travel as -AB, -AC, etc. For other SSI nomenclature, see Appendix F4:3.4. Geographical systems have to be based on the orientation of each individual set, e.g. whether points are facing or trailing. As the sets are generally named after the main function (signals and points), track repeaters may be given special names such as A (approach track) and F (first track past signal). Point ends of crossovers are specially labelled A & B or P & Q, in order to identify the track sections and also the normal routes through each point end. A consistent method should be adopted for each geographical system and, in addition, the actual names of the track sections should be clearly displayed on each set. 8 Hybrid Systems Hybrid systems are generally acceptable (e.g. points mechanically operated from a lever frame with other functions controlled from an IFS panel), but for novel combinations it should be demonstrated that risks are controlled so far as is reasonably practicable. Any combination of interlocking types may be controlled from a single signal box, subject to the constraints given in this Guidance Note. F101

184 ailway Group Guidance Note Page F102 of 191 Withdrawn Document Lever Frame Interlocking Guidelines Appendix F1: F1:1 Introduction This appendix describes the design of specific types of lever frames and associated interlocking. The design details required for a mechanical interlocking are described in Part N of GK/C0701. Examples relating to the typical layout shown in Figure F1:10 are given in Figures F1:11 to F1:14. Most of the locking terms used in this Appendix are illustrated in the figures. Where other former regional terms are found describing these items, care should be taken to avoid ambiguity. For instance, locks and notches are also known as nibs (or wedges) and ports. Tappets can be known as swords, irons or blades. Locking bars can be referred to as bridles, and studs as drivers. Note that imperial dimensions are used in this appendix, viz: 1 inch (") = 25.40mm; 12" = 1 foot ('); 3' = 1 yard. F1:2 Lever Frames The main development of the mechanical locking frame was from the 1860s to the 1920s, but installation and reconditioning of lever frames has continued, albeit at a decreasing rate, until modern times. Currently in the region of seven hundred mechanical frames remain in use on ailtrack controlled infrastructure, comprising some fifty distinct types. These are listed in Figure F1:1 and some of the most common are illustrated in Figures F1:2 to F1:9. Their life expectancy can be seen from the fact that many of the frames in use today are over a hundred years old. There is no prohibition on the introduction of new or reconditioned mechanical locking frames, provided the necessary risk assessment is undertaken in accordance with Section 2.2. The signaller's control device is a lever connected to mechanical and/or electrical interlocking that prevents movement of levers, depending on the position of other levers. The levers may be connected to trackside signalling equipment which they operate mechanically (using wires for functions requiring pull only with the return usually being self-acting, e.g. signals, and rodding where both pull and push forces need to be transmitted, e.g. points), or electrically as described in Section 5. F102

185 ailway Group Guidance Note Page F103 of 191 Commonly Found in Areas Lever Centres (inches) Method of Operation/ Actuation Type of Frame Type of Illustrated Locking British Power (power slide frame) ABP 2 or 2½ lever (r/t) tappet Fig F1:9(c) Cheshire Lines Committee (similar to Stevens Tappet) 5 lever (d/a) tappet Dutton or 4½ catch handle tappet Dutton Combination 4½ c/h & lever tappet Evans O Donnell 4 catch handle tappet Gloucester Wagon Company 5 lever tappet (r/l) Great Central (similar to SCo LNE Standard) GC 4½ lever (d/a) tappet Great Northern - East Lincolnshire 4¼ lever (d/a) tappet Great Northern Duplex (aka McK & Holland No.26) sim to S&F c/h & lever tappet Great Western 3 Bar Horizontal Tappet GW 4 lever (r/t) tappet Fig F1:2(a) Great Western 3 Bar Horizontal Tappet GW 5¼ or 5½ lever (r/t) tappet Great Western 3 Bar Vertical Tappet GW 4 lever (r/t) tappet Fig F1:2(b) Great Western 5 Bar Vertical Tappet GW 4 lever (r/t) tappet Great Western Double Twist GW 5¼ lever tappet (r/l) Great Western Stud (mostly relocked) GW 4 or 5¼ lever (grad) LLB/DN Lancashire & Yorkshire (v sim to ailway Signal Company Tappet) L&Y 5½ lever (d/a) tappet London & North Western Tappet LNW 5½ catch handle tappet London & North Western Tumbler 1876 (Bar & Stud) LNW 5½ lever (esc) LLB/BC Fig F1:3 London Midland 1943 LM 4½ or 6 catch handle tappet Fig F1:4(b) London Midland & Scottish 1938 (development of LNW Tappet) 4½ catch handle tappet London, Brighton & South Coast 1880 (similar to S&F 1874) LBSC 5 lever (d/a) tappet London, Brighton & South Coast 1905 LBSC 5 lever (d/a) tappet London, Brighton & South Coast Bosham Pattern 5 lever (d/a) tappet London, Chatham & Dover 4¼ lever (d/a) tappet Manchester, Sheffield & Lincolnshire 6 lever (d/a) tappet (r/l) McKenzie & Holland 1873 Hook, Cam & Soldier LM 5 or 6 lever (esc) LS McKenzie & Holland No.11 (5 ) / No.12 (4 ) 1886 T-Bar E, NE 4 or 5 lever (esc) LS Fig F1:5 McKenzie & Holland Cam & Tappet 4 lever (r/t) tappet McKenzie & Holland / Westinghouse No.16 (5 ) / No.17 (4 ) NE 4 or 5 lever (d/a) tappet Fig F1:6 McKenzie & Holland / Westinghouse No.17A (deep locking boxes) E 4 lever (d/a) tappet McKenzie & Holland No.21 (aka Brettell Duplex Tappet) 4 lever (d/a) tappet Midland Tappet M 6 catch handle tappet Midland Tumbler M 6 catch handle LLB/TS Fig F1:4(a) North London Tappet (similar to Stevens Tappet) 5½ lever (d/a) tappet ailway Executive Committee LMS 4½ catch handle tappet ailway Signal Company / Edwards 1877 (Bar & Stud) 5½ lever tappet (r/l) ailway Signal Company Tappet E, LM 5½ lever (d/a) tappet Fig F1:7(a) ailway Signal Company London & North Eastern Standard 4 or 4½ lever (d/a) tappet ailway Signal Company Great North of Ireland E 4 lever (d/a) tappet Saxby & Farmer 1874 ocker & Gridiron (mostly relocked) E, S 4 or 5 catch handle LLB/TS Saxby & Farmer 1888 Duplex E, S 4 c/h & lever tappet Saxby & Farmer 1905 Duplex E, S 4 or 4½ c/h & lever tappet Fig F1:7(b) South Eastern Cam / Brady 5 lever (d/a) tappet (r/l) South Eastern Tappet (Old Pattern) SE 4½ lever (d/a) tappet Stevens Knee Frame S, Sc 4 # /& lever (d/a) tappet Stevens Tappet E, S 4 to 5¼ lever (d/a) tappet Fig F1:8(a) Stevens / Caledonian (similar to Glasgow New Pattern) Sc 4¼ or 5¼ lever (d/a) tappet Stevens Glasgow (Old Pattern) Sc 4¼ or 5¼ lever (d/a) tappet Stevens Glasgow (New Pattern) Sc 4¼ or 5¼ lever (d/a) tappet Stevens / Glasgow & South Western (New Pattern) Sc 4¼ lever (d/a) tappet Stevens / McKenzie & Holland No.28 (similar to No.17 & Stev Tap) 4 lever (d/a) tappet Sykes & Hallam (aka South Eastern & Chatham New Pattern) 4½ lever (r/t) tappet Tyer Direct Tappet 4 lever (d/a) tappet Tyer Knee Frame 5½ lever (d/a) tappet Westinghouse 1924 Type A2 / 1948 Type A3 E, S 4 catch handle tappet Fig F1:8(b) Westinghouse Style K / Style N (miniature lever power frame) LT 2½ lever (vert) LLB/TS Fig F1:9(a) Westinghouse Style L (miniature lever power frame) S 2½ electrical electric Fig F1:9(b) Figure F1:1 Existing Types of Lever Frame continued (notes)... F103

186 ailway Group Guidance Note Page F104 of 191 Withdrawn Document Notes Method of Actuation:- Type of Locking (non-tappet):- Lever Locking: d/a = direct action LS = longitudinal rotating shafts; or r/t = reduced travel LLB = longitudinal locking bars (non-tappet) esc = escapement gives initial & final motion with motion transmitted by: grad = gradual motion gives early lock & late release BC = bell cranks; vert = vertical shaft DN = diagonal notches; or TS = transverse rotating shafts. Duplex Locking: c/h & lever = catch handle and lever locking r/l = all surviving examples relocked with tappet locking Longitudinal means running parallel to the length of the frame. Transverse means in the plane that the lever moves and at right angles to the length of the frame. Ground frames are not included in the table. Some frames were made by different manufacturers and the parts are not necessarily interchangeable, e.g. parts for the McK&H No16/17 frames made by Butterworth & Dickinson. Figure F1:1 Existing Types of Lever Frame The levers should be arranged in a frame, so as to give the signaller a clear view of the line and as much of the trackside signalling equipment being controlled as reasonably practicable. Indicators should be provided for any equipment that is not clearly visible to the signaller, or where electrical proving is provided for other purposes. Except where track circuit block is provided to all adjacent signal boxes, the frame should be arranged to give the signaller ready access to the signal box windows. The frame is generally elevated to permit the mechanical locking and other apparatus to be situated within the space below the operating floor. The frame should be adequately supported. Alternatively, ground frames may be provided, as described in Section F1:8. F1:2.1 Actuation of Locking The locking apparatus is generally actuated as follows: a) by the motion of the lever (direct action or lever locking) with the locking acting on the lever (see Figure F1:14, for example); b) by moving the catch handle (catch handle locking) with the locking acting on the catch handle, e.g. Figure F1:8(b); or c) by some combination or permutation of the above, e.g. duplex locking, which may have one set of tappets connected to the lever and another to the catch handle. See Figure F1:7(b). F1:2.2 Prevention of Confliction The locking should generally be effected at or before the start of each stroke and should release only at or after the end of each stroke. Additionally, it should not give rise to confliction during the travel. This may be achieved by one of the following means: a) by the use of catch handle locking, where the catch handle operates a rocker that is attached to the locking, e.g. Figure F1:4(b); b) by incorporating a reduced travel mechanism, such as a cam, into lever locking, so as to give escapement with initial and final motion, as shown in Figure F1:2(a); or c) in the case of direct action lever locking tappet frames (i.e. where the tappet stroke is directly related to the motion of the lever), by taking special precautions to avoid conflicting notches (see Section F1:5.1). F104

187 ailway Group Guidance Note Page F105 of 191 Cam Plate oller Locking Boxes Drive Bar Locking Boxes 3 Bar Horizontal Locking Bars 3 Bar Vertical 5 Bar Vertical Lock (various profiles) Locking Box (a) GW Horizontal Tappet Frame (b) GW Vertical Tappet Frame Figure F1:2 Great Western Tappet F105

188 ailway Group Guidance Note Page F106 of 191 Withdrawn Document Tumbler Lever Tail Counterbalance Weigh Bell Cranks Hook ack Back Tail Locking Bars Point Connections ocker Lever (to balance weight) Signal Connections Figure F1:3 London and North Western Tumbler Frame (non-tappet locking) See Section F1:3.2 for details F106

189 ailway Group Guidance Note Page F107 of 191 Locking un Identification ( 5 bars per run) Tumbler (standard tumblers have 4, 7, 10, or 13 nibs - not 6 as shown) Nibs (rear view) Catch Handle Stud for tumbler actuation Drive od E D C B A Lever Pin to engage in tumbler pocket Cover Plate Pocket Tumbler (right hand locking tumbler shown) (a) Midland Tumbler Frame (non-tappet locking) See Section F1:3.3 for details Locking Bar Notation Bars T B 4 2 Lock Towards Levr Studs (sliding) ivets (fixed) X o = Top Bars = Bottom Bars Two 4 Channel Locking Boxes (with identification letters) Cover Plate Contact Box H G F E D C B A ocker Floor Level (b) London Midland 1943 Frame (catch handle locking) Figure F1:4 Midland Type Frames F107

190 ailway Group Guidance Note Page F108 of 191 Withdrawn Document Cam Cam Shaft T-Bar with lock notches Drive Link to Operate Soldiers otating Soldier and Lock Shafts Two Tiers of Locking are shown here Figure F1:5 McKenzie & Holland 1886 T-Bar Frame (non-tappet locking) F108

191 ailway Group Guidance Note Page F109 of 191 Arrangement with 8 Two Channel Locking Boxes Catch Handle Catch Handle Spring Box Quadrant (or Floor Plate) Tappets Electric Lock (SGE type) Lock Slide (showing notches cut for lock) A B Locking Box Identification C D E F Economiser (showing roller that locates in small notches on lock slide) Circuit Controller (rotary type) Figure F1:6 McKenzie & Holland/Westinghouse No. 16/17 Frame (lever locking) F109

192 ailway Group Guidance Note Page F110 of 191 Withdrawn Document Drop Box Spring Catch Box Notch for Drop Box Tappet Catch Handle Actuated Tappet Locking Box Lever Actuated Tappet Figure F1:7(a) ailway Signal Co Tappet Frame Figure F1:7(b) Saxby & Farmer 1905 Frame (lever locking) (duplex locking) F110

193 ailway Group Guidance Note Page F111 of 191 Curved Tappets Locks Locking Bar Notation Alternative Arrangement Ten Channel Locking Tray (with identification letters) Figure F1:8(a) Two Channel Locking Box Stevens Tappet Frame (lever locking) Bars Lock 1 4 T B 2 3 ivets (fixed) Studs (sliding) Towards Lever Lever Normal Catch Handle Lever Normal Catch Handle Lever everse Catch Handle aised Figure F1:8(b) Westinghouse A2 Frame (catch handle locking) Lever everse Catch Handle Lowered F111

194 ailway Group Guidance Note Page F112 of 191 Withdrawn Document Lock Slide Miniature Lever moves through 60º Signaller s Indications Selection Lock Lever Contact Shaft Mechanical Locking Square Vertical Shafts Locking Bars Selection Lock Interlocking Lock (sealed) Bevel Gearing rotating contact shaft through 120º Toothed Segment Lever Contacts Cross Lock Lock (a) Westinghouse N Frame (b) Westinghouse L Frame (similar to the K Frame) See Section F1:3.4 for details Free Lamp Indication Magnet (actuates check locking) Latch Cam Plate Circuit Controller Even Levers Odd Levers Safety Magnet Vertical Tappet Locking (c) British Power Slide Frame Figure F1:19 Miniature Lever Frames F112

195 ailway Group Guidance Note Issue Two Page F113 of 191 Basic equirements Mechanical locking frames should have the following attributes, as far as reasonably practicable: a) simple construction; b) minimising the number of pins or links between the lever or catch handle and the locks, so as to reduce the risk of slack locking; c) strong and effective locks; d) broad wearing surfaces for wearing parts; e) accessibility of locking for maintenance and alteration; f) arrangement of the frame to allow for easy extension and replacement of parts; g) locking design not to limit the size of frame that can be conveniently constructed. F1:3 Mechanical Interlocking Levers are generally interlocked by one of the following methods: a) longitudinal shafts that rotate as the lever moves, e.g. Figure F1:5; b) longitudinal locking bars. In this case, motion is transmitted from the plane of the levers by means of: i. diagonal notches (see Section F1:3.1); ii. bell cranks (see Section F1:3.2); or iii. transverse rotating shafts (see Section F1:3.3). The mechanical locking should be sufficiently robust to withstand a signaller s pulling of a locked lever, or, in the case of catch handle locking, a signaller s grasping of a locked catch handle (a lesser force). All components of the locking mechanism (tappets, locks, lock bars, steadies and holding down bars, etc.) should be uniquely identified with a suitable marking, so as to avoid confusion and comply with GK/T0009. The orientation of each loose component should be defined by the orientation of the marking. The rationale of the identification system should be recorded on the locking chart, as shown on Figure F1:14. Mechanical locking is generally reciprocal and special arrangements have to be made when this feature is not required (see Section F1:5). It is generally easier to provide non-reciprocal locking electrically, as explained in Section F1:4. F1:3.1 Tappet Locking The most common type of locking is known as tappet locking, whereby each lever is connected to a tappet that passes through a locking box. The tappets have diagonal notches cut from them which bear on locking pieces with diagonal bevels. These locking pieces, known as locks, are connected to longitudinal locking bars that slide in channels in the locking box, in order to effect the interlocking. Generally, several locking boxes extending the length of the frame are arranged in tiers and supported on brackets attached to the frame standards. Locking boxes for direct acting frames usually contain two channels. A maximum of two or three locking bars are located above and below the tappets in each channel. F113

196 ailway Group Guidance Note IssueTwo Page F114 of 191 Withdrawn Document Alternatively, particularly on reduced travel frames, a wide locking tray, often inclined at an angle for accessibility, may contain a large number of locking bars in close proximity. Figure F1:8 illustrates both arrangements. See Figure F1:14 for a typical locking chart and detail drawing. Further details of tappet locking are given in Section F:1.5. F1:3.2 London & North Western Tumbler Locking The most widely found design of non-tappet locking is Webb s London & North Western Tumbler frame of A rocking piece, known as a tumbler (widely replaced now by a more recent method of actuation), is pivoted on the lever below the floorplate, such that, when the lever is pulled, it raises a hook rack coupled to it. The shape of the tumbler and the lugs that it rides over effects a partial movement of the hook rack at the beginning and end of each stroke, thus providing reduced travel for the locking. The bar and stud interlocking is arranged with horizontal locking bars crossing in front of the vertical hook racks for each lever. The hook racks have a series of ports cut at 2 inch centres into which riveted studs on the locking bars engage to perform the locking. Motion is transferred from the hook racks to the locking bars, as necessary, by means of bell cranks bolted to the structure of the frame. One end of each crank is permanently engaged in a port in a hook rack, whilst the other end locates around a stud riveted to one of the locking bars. The general arrangement is illustrated in Figure F1:3. See Figure F1:15 for a typical locking chart and detail drawing. F1:3.3 Midland Tumbler Locking A very different form of non-tappet locking is known as Midland Tumbler. This consists of two horizontal transverse rotating shafts, also known as tumblers, for each lever. (These tumblers bear no similarity with the LNW tumblers.) The tumblers are able to tilt to the left or to the right, one located on either side of the lever beneath cover plates on the operating floor. At the rear of the frame, appropriate lengths of locking bars are directly connected between vertical projections, known as nibs, on the top and bottom of the tumblers, in order to provide the necessary interlocking between levers. The locking bars are connected to the top to move one way or to the bottom to move the other way. When each lever is normal, a pin holds its left hand tumbler in the left hand position and, when reverse, holds its right hand tumbler in the right hand position. (The right hand tumbler is free when the lever is normal, and the left hand is free when the lever is reversed.) The locking is actuated by the catch handle. To raise the catch handle with the lever normal, the right hand tumbler must be free to rotate to the right, which then occurs, and conversely, to raise the catch handle with the lever reversed, the left hand tumbler, if free, is rotated to the left. In this way the right hand tumbler effects the locking; and the left hand tumbler the releasing. Levers that are not released do not require a left hand tumbler. The general arrangement is illustrated in Figure F1:4(a). See Figure F1:16 for a typical locking chart and detail drawings. F114 F1:3.4 Miniature Lever Frame Mechanical Locking Finally, a more modern type of non-tappet locking is found with mechanically locked miniature lever frames (e.g. Westinghouse Style K or N). Here the vertical locking box, which is integral to the frame at the front, contains horizontal locking bars and vertical square shafts, each of which is rotated by means of a bevel gear when its miniature lever is pulled. Where necessary, a toothed segment is provided on the square shaft to engage in a ratchet on the bar, so as

197 ailway Group Guidance Note Issue Two Page F115 of 191 to slide the bar to the right as the lever is reversed. The locking is effected by vertically sliding bars, known as cross locks, in which notches are cut. The general arrangement is illustrated in Figure F1:9(a). F1:4 Electrical Interlocking As an alternative to mechanical locking, levers may be interlocked electrically using lever locks energised by circuit controller contact bands in the appropriate positions (see Section F1:7). Such locking is non-reciprocal, i.e. requires the converses to be separately provided. Counter conditional locking, to prevent conditions from changing, is also often required to be separately provided. Electrical interlocking is particularly common on miniature lever frames, although any frame may be relocked with electrical locking. Separate interlocking and selection locks should be provided as described in Section 6.8. Further details are given in Section 6. An all-electric miniature lever frame (Westinghouse Style L) is illustrated in Figure F1:9(b). F1:5 Locking equirements Mechanical locking tables for a typical layout are given in Figure F1:11. The following locking requirements are distinguishable: a) dead locking (one lever locking another); b) releasing (one lever released by another); c) both-way (B/W) locking (one lever locking another in either position); d) conditional locking (or special locking); and e) sequential locking (non-reciprocal, restoration or rotation locking). Mechanical locking charts showing how these locking requirements may be accomplished for different types of mechanical interlocking are given in Figures F1:14 to F1:16. The design of mechanical locking charts requires certain knowledge about the type and manufacture of the mechanical interlocking concerned. F1:5.1 Conflicting Notches In the case of tappet locking, the travel of the tappet affects the arrangement of locking boxes, in order to avoid notches that are cut for use in one channel from conflicting with an adjacent channel as the tappet is moved. With direct acting lever locking the travel is around 9 to 18 and the number of channels is generally limited to two per set of tappets. This problem is less prevalent with reduced travel locking because the stroke is reduced to between 1 and 2½. Consequently, a locking tray can be used consisting of a number of channels (perhaps ranging from 4 to 18). Conflicting notches only occur if the travel is equal to or exceeds the pitch of the channels. On some frames the travel equals the pitch of the channels, allowing a notch to perform locking in two adjacent channels. The locks and notches on such frames are nose shaped with two diagonal faces, i.e. double bevel, although various sizes of nose may be found. On frames where conflicting notches are a problem (generally between adjacent channels), there should be a technique for overcoming it, such as selecting locks and notches with large or small noses (or other mutually exclusive configurations), or riveting pieces with separate notches to the top of tappets and using locking pieces with high and low noses (i.e. normal and inverted). F115

198 ailway Group Guidance Note IssueTwo Page F116 of 191 Withdrawn Document The general rules for avoiding conflicting notches on direct acting lever locking frames with two channel locking boxes are as follows: a) locks in the channel nearest the rear of the frame to have small notches; b) locks in the channel nearest the front of the frame to have large notches; c) wherever practicable, releases to be in the rear channel and have large notches; d) where unavoidable, releases may be placed in the front channel and should have small notches, but in such cases only another release (with a large notch) can be placed in the rear channel; e) both-way locks (in either channel) to be double bevel with small notches; f) two both-way locks cannot be used on the same edge of a tappet; g) where used in combination with a release, the both-way lock to be in the front channel and the release (with a large notch) in the rear; and h) where used in combination with a lock, the both-way lock to be in the rear channel and the lock (with a large notch) in the front. F116

199 5 EG GZ 5 EH B EJ DOWN BANCH UP BANCH FG FF AA JZ CA CB 8 DJ 4 3 EK FE 110 BH X AB AC AD 11A 11B DOWN FAST BF BE 12A 12B BC BB 13B UP FAST CP CP 9 SPAD 9 54 BD A 13A CP CP 9/10G CD CE CF DOWN SLOW 16A POL 46m CC 7B 33G DG DF 14 DE 18 19A 16B OL 91m DD DC DB 32G 19B 16C UP SLOW DH 26 POL C m FC 29 EL 24A 24B UP SIDING FA NECK A 23 Opposing Locking Omitted FD A TANNE OW TW Extract of Signal Box Notes: Elevated lever frame: 38 levers. Spare levers: 21, 22, 34, 35, 36. Track circuit block with train describers to adjacent signal boxes. Signals working auto when lever reverse and switch operated: 1, 38. Machine operated points: 11, 12, 13, 14, 16, 19. Telephones provided at all main signals, and at shunt signals: 20, DA BA KZ Figure F1:10 Signalling Layout Plan to Illustrate Examples (not to scale) eleased By 12 (16, 18 w 19), (23 w 19, 24), 24), 19 B /W 24 No. Locks eleased By No. Locks 1 20 (23 w 19, 6, 7, SPAE 6, , SPAE 6, 7, 16 4 (33 w 19), 19 B /W 23 25, 26, 29, (14, 27 w 24), (20 w 19, 24 ), (20 w 19, 24),(31 w 27), 24 B /W , 29, (31, 37 w 27) 6 7 B /W , 10, 15, , 24, 27, , 26, 29, (23 w 24) 9 7, 13, B /W , 24, 26, , , 16, 18, 19, (23, 24 w 27) 13 3, 9, 16, , 18, 19, , 31, (23 w 24) 33 32, (4, 15, 18 w 19) , (33 w 19), 19 B /W 34 SPAE 16 3, 9, 13, 18, 31, 32, (20 w 19) 35 SPAE SPAE 18 16, 31, 32, (20 w 19), (33 w 19), 19 B /W 14, (24 w 27) 19 14, 17, 31, Figure F1:11 Mechanical Locking Tables

200 equires (B) Lock Lever oute To oute Function Signal Ahead Train Detection Points & GFs Detected oute equires Locked when Signal Off until e- Lever No. Indic- Arm or Aspect Track Circuits/ Lock- Track Track Ccts Or marks No. ation Alight Aspect Alight Treadles Occupied Track Circuits Clear Normal everse ing Circuits Clear Signal On Occ & Clear 1 53 Y 53 AA$7 AB, AC, AD$16 11A/B AB 1 AB AC 120 $1 1 G Y O G 2 53 POS Y 53 EK$7 EL, DH, CC, CD, BE, AC, 27 6, 7A/B, 13A/B, EL, DH, 2/3/4, 3B EL DH G Y O G AD$16, (CE O 14) 12A/B, 11A/B CC Y 205 EK$7 EL, DH, CC, CD, CE, 13A/B, 16A/B/C, 6, 7A/B EL, DH, 2/3/4, 3B EL DH G Y O G CF$16 27 CC 3B Y O G 2/3 EK X $25 PL 511 EK EL, DH, CC, CD, CE, DD, DC, DB NECK N $25 PL EK EL, DH, CC, CD, CE, DD, FA 13A/B, 19A/B/C, 27 13A/B, 27 6, 7A/B, 16A/B/C, 19A/B/C After Occ Time $46 6, 7A/B, 16A/B/C O EL, DH, CC 2/3/4, 3B EL DH /3/4 Y 2/3 EG$7 EH, EJ, EK$16, EL, (27 O 7N$37), 6, 5, 5 EH EJ B (DH O 7N) (7A/B O 7A/B) G Y O G 2/3 3B OFF 5 Y O G 5 EG 6 (E) LOCK EL 6 7 (AE) LOCK CC, EL, DH (8 LEVE O #4) 7 8 9/10/15 (A) LOCK (7 LEVE O #4) 8 CA CB Y#4, Y O G 9/10 JZ FO 15 ($46) CA, CB$16 Y#5 9/10 JZ$7 CA, CB$16, CC 7A/B G#5 Y O G Y 205 CB$7 CC, CD, CE, CF$16 7A/B, 13A/B CC 9/10/15 CC CD G Y O G SPAD 9 (X O 9/10/15 USED) POS Y 53 CB$7 CC, CD, BE, AC, AD$16, 7A/B 13A/B, 12A/B, CC 9/10/15 CC CD G Y O G 53 CB (CE O 14) 11A/B 11 (AE) LOCK AC, BE, CD (AE) LOCK BE (AE) LOCK BD, BE, CD, CE (AE) LOCK DE, CE # X $25 PL 511 CB CC, CD, CE, DD, DC, DB 7A/B, 13A/B, 19A/B/C 16A/B/C O CC 9/10/15 CC CD NECK N $25 PL CB CC, CD, CE, DD, FA 7A/B, 13A/B 16A/B/C, 19A/B/C 16 (AE) LOCK CE, DD, CD # NECK PL FA#1 19A/B/C 17 FA# PL 511 (DD, DC)$40, DB 19A/B/C, 16A/B/C O 18 DD DC 30 (DE, 18 NECK PL (DD, FA)$40 16A/B/C 19A/B/C 18 DD FA 30 DD)#3 19 (AE) LOCK FA, DD, (CD, CE O 16N) # UP SDG PL FA#1 19A/B/C O 20 FA# /29/30 PL 26/30 (FA, DD, DE)$40, DF$16, 16A/B/C, 14 19A/B/C FA, DD 20 FA DD 30 FA#3 (CE O 13N) Figure F1:12 Electrical Locking Tables continued

201 equires (B) Lock Lever oute To oute Function Signal Ahead Train Detection Points & GFs Detected oute equires Locked when Signal Off until e- Lever No. Indic- Arm or Aspect Track Circuits/ Lock- Track Track Ccts Or marks No. ation Alight Aspect Alight Treadles Occupied PL (FC, DG, DF)$40, DE, (DH O 7), (CE O 13N) Track Circuits Clear Normal everse ing Circuits Clear 24A/B, 27, 14 O Signal On Occ & Clear After Occ Time $46 FC, DG 23 FC DG 30 (FD, FC)#3 UP SDG PL FC$40 24A/B 23 FC# (AE) LOCK FC, (DG O 27) (#8 O 27 $37) PL 110 FC$40, (DG O 27) 24A/B 25 FC FD 30 FC# (A) LOCK FD, FE 26/29/30 DG FC 120 (DF, 26 POS Y 110 DF$7 (DG, FC, FD)$40, FE$16, 27, 24A/B 28 DG)#3 1 G Y O G 110 (DE O DF) FF, (DH O 7) 27 (A) LOCK DG, DH, (FC O 24) 27 (E) LOCK DG, DH, (FC O 24) (24A/B w 31 O 37 USED)#8 28 (E) LOCK DG (A) LOCK (FD O FE) 26/29/30 DG FC 120 (DF, 29 B $25 PL DF, (DG, FC)$40, (DH O 7) 27, 24A/B 28 DG)#3 (FD O FE)$ Y 210 DF$7 DG, DH, DJ$16, 7 27, 28 26/29/30 DG DH G Y O G (FC O 24) 31 26/29/30 Y 26/30 DB$7 DC, DD, DE, DF$16, DG, (CE O 13N), (DH O 7), 16A/B/C, 19A/B/C, 14, (7 O 27N$37), 28, DC, DD 31 DC DD G Y O G (FC O 24) (24A/B O27$37), (27 O 27) (A) LOCK #9 32/33 DA DB Y 31 KZ$7 DA, DB$16, DC, DD 16A/B/C, 19A/B/C G Y O G (A) LOCK #9 32/33 DA DB Y, Y O G 31 KZ FO 15 ($46) DA, DB$16, DC 37 26/29/30 POS Y 26/30 BB$7 BC, BD, CE, DE, DF$16, DG, (DH O 7), (24A/B O27$37), (7 O 27N$37), 13A/B, 14, 28, BC, BD, CE /38 BC BD G Y O G 26/30 BB (FC O 24) 19A/B/C, (27 O 27) Y 54 BB$7 BC, BD, BE, BF$16 13A/B, 12A/B BC 37/38 BC BD 120 $1 38 G Y O G eferences oute Locking $1 Provision for automatic working. After oute Locking eleased by $7 Temporary approach control. eference Signal Signal On and Track Circuits $10 At time of clearing. Used Clear Occ Time $16 Signal ahead approach control TP proved energised. $46 $25 oute indication NOT proved alight in signal controls. #6 (23 O 24$37) FC, DG, DF $37 Points set and detected. #7 32 DA (DB O DB 20) $40 equired clear for proceed aspect; replaces signal except under last-wheel or other special replacement conditions. #8 31, 37 DE (DF O DF 20) $46 Time in seconds; timing tolerance of 0% to +20%, or 0 secs to +3 secs, whichever is greater. #9 (4, 15 O 19$37) CD, CE, DD, DC, DB #1 Automatic replacement and signal stick inhibited when opposing route set. #2 Occupied for 15 ($46) and clear. #4 No.8 main/warning switch operated to warning. #3 Track circuits occupied for $40 to inhibit replacement. #5 No.8 main/warning switch operated to main. Figure F1:12 Electrical Locking Tables See Figure F1:10 for Layout Plan; Figure F1:11 for Mechanical Locking

202 1 DOWN FAST TO No.53 SIGNAL 20 SHUNT NECK TO UP SIDING NIL O UP SLOW 19 2 DOWN BANCH TO DOWN FAST SPAE 3 DOWN BANCH TO DOWN SLOW DOWN BANCH SHUNT TO UP SLOW O NECK DOWN BANCH TO No.3 SIGNAL AND DISTANT 6 O FP LOCK FO No.7 TAPS UN- LOCKED - LOCKED 7 DOWN BANCH - DOWN SLOW POINTS AND TAPS 8 DOWN SLOW TO No.9 SIGNAL 9 DOWN SLOW TO No.205 SIGNAL 10 DOWN SLOW TO DOWN FAST DOWN FAST TAILING POINTS AND SWING NOSE UP FAST SWITCH DIAMOND DOWN SLOW - UP FAST FACING POINTS 14 UP SLOW TAILING POINTS DOWN SLOW SHUNT TO UP SLOW 16 O NECK UP SLOW - DOWN SLOW COSS- OVE AND SLIPS 17 SHUNT UP SIDING TO NECK 18 SHUNT BACK ALONG UP SLOW NIL O UP SLOW TO NECK SPAE 23 SHUNT UP BANCH TO UP SLOW NIL O UP SIDING 24 UP SIDING - UP BANCH POINTS AND TAPS 25 SHUNT UP SIDING TO UP BANCH UP SLOW TO UP BANCH UP SLOW - UP BANCH FACING POINTS 28 FP LOCK FO No.27 POINTS UN- LOCKED - LOCKED 29 UP SLOW CALL-ON TO UP BANCH UP SLOW TO No.210 SIGNAL UP SLOW TO No.30 SIGNAL UP SLOW TO No.31 SIGNAL 33 UP SLOW TO No.31 SIGNAL WANING 34 SPAE 35 SPAE 36 SPAE 37 UP FAST TO UP SLOW Lever Painting Key red white yellow Figure F1:13 Typical Lever Nomenclature Plates black blue See Figure F1:10 for Layout Plan; Figure F1:11 for Mechanical Locking Tables 19 UP SLOW - UP SIDING COSS- OVE AND SLIPS 38 UP FAST TO No.54 SIGNAL

203 Example of Mechanical Locking Chart: Direct Action Tappet Locking Lock #1 = 4D Locking bar #2 = 4/18 D3 See Figure F1:10 for Layout Plan; Figure F1:11 for Mechanical Locking Tables Figure F1:14 Examples of locking component identity: Withdrawn Document

204 Note: Double conditional locking not illustrated. For this purpose, tappets (acting through supplementary horizontal locking boxes) may be connected, by means of cranks, to the bottom of the hook racks. Hook ack Bell Crank Locking Bar Full Lock (elease Position) Notch VETICAL COSS SECTION Hook acks raised by levers ELEVATION Half Lock Full Lock (Lock Position) Dart Locking Example: 4 locks 1 both ways 1 released by 2 2 locks 3 5 locks 1 when 2 normal KEY Bell Crank Full Lock Full Lock (release) Half Lock (both ways) Shell Lock (conditional backlock) Dart (conditional) Half Bell Crank (conditional) Locking Bar Hook ack Figure F1:15 Example of Mechanical Locking Chart: London and North Western Tumbler Locking See Figure F1:10 for Layout Plan; Figure F1:11 for Mechanical Locking Tables