GK/GN0653. Guidance on Control of Unwanted Voltages on Telecommunications. Equipment at Stations. Rail Industry Guidance Note for GK/RT0053

Transcription

1 GN Published by: Block 2 Angel Square 1 Torrens Street London EC1V 1NY Copyright 2011 Rail Safety and Standards Board Limited GK/GN0653 Telecommunications Equipment at Stations Issue One: December 2011 Rail Industry Guidance Note for GK/RT0053

2 Issue record Issue Date Comments One December 2011 Original document Superseded documents Supply GK/GN0653 was developed to provide rationale and guidance on GK/RT0053, which resulted from the scope review of measures in GT/TDINT100, TD CAB 018, and TD INT 023 in accordance with the Railway Group Standards Code This Rail Industry Guidance Note does not supersede any other Railway Group documents. The authoritative version of this document is available at Uncontrolled copies of this document can be obtained from Communications,, Block 2, Angel Square, 1 Torrens Street, London EC1V 1NY, telephone or enquirydesk@rssb.co.uk. Other Standards and associated documents can also be viewed at Page 2 of 13

3 Contents Section Description Page Part 1 Introduction Purpose of this document Copyright Approval and authorisation of this document 4 Part 2 Guidance on the Control of Unwanted Voltages on Telecommunications Equipment at Stations Earthing system arrangements Applied voltage and transmission level for balanced-pair telecommunications cables 6 Part 3 Application of this document Application - infrastructure managers Application - railway undertakings Health and safety responsibilities 10 Definitions and Abbreviations 11 References 13 Page 3 of 13

4 Part 1 Introduction 1.1 Purpose of this document This document gives guidance on interpreting the requirements of Railway Group Standard GK/RT0053, issue one, Control of Unwanted Voltages on. It does not constitute a recommended method of meeting any set of mandatory requirements All requirements in GK/RT0053 are reproduced in the sections that follow. Guidance is provided as a series of sequentially numbered clauses prefixed GN immediately below the boxed text to which it relates. Where there is no guidance given, this is stated The requirements of this document apply to all new telecommunications equipment and alterations to the existing telecommunications equipment managed and operated by more than one infrastructure manager, that is to say, where the infrastructure manager (track) and infrastructure manager (stations) are different duty holders. Specifically, the requirements apply to the management of electromagnetic compatibility between systems managed and operated by one infrastructure manager, and telecommunications systems managed and operated by another infrastructure manager Specific responsibilities and compliance requirements are laid down in the Railway Group Standard itself. 1.2 Copyright Copyright in the Railway Group documents is owned by Rail Safety and Standards Board Limited. All rights are hereby reserved. No Railway Group document (in whole or in part) may be reproduced, stored in a retrieval system, or transmitted, in any form or means, without the prior written permission of Rail Safety and Standards Board Limited, or as expressly permitted by law Rail Safety and Standards Board () members are granted copyright licence in accordance with the Constitution Agreement relating to Rail Safety and Standards Board Limited In circumstances where Rail Safety and Standards Board Limited has granted a particular person or organisation permission to copy extracts from Railway Group documents, Rail Safety and Standards Board Limited accepts no responsibility for, nor any liability in connection with, the use of such extracts, or any claims arising there from. This disclaimer applies to all forms of media in which extracts from Railway Group Standards may be reproduced. 1.3 Approval and authorisation of this document The content of this document was approved by Control Command and Signalling Standards Committee on 21 July This document was authorised by on 21 October Page 4 of 13

5 Part 2 GN1 GN2 Guidance on the Control of Unwanted Voltages on The requirements in GK/RT0053 are intended to deal with those situations where new telecommunications equipment or alterations to the existing telecommunications equipment are managed and operated by more than one infrastructure manager. The legal requirements to ensure that the electromagnetic disturbance generated by electrical or electronic equipment does not exceed a level above which telecommunications equipment and other equipment cannot operate as intended, and that the equipment itself has an adequate level of immunity to electromagnetic disturbance, are set out in EMC regulations Earthing system arrangements Design of earthing systems The design of all earthing systems in buildings shall conform to the requirements set out in BS 7671:2008+A1:2011. GN3 GN4 GN5 Requirements for the provision of earthing arrangements in buildings can be found in Chapter 54 of BS 7671:2008+A1:2011. The same standard refers to BS EN :2006 for protection against lightning. Some low voltage supplies in stations are in scope for GL/RT1255. Requirements for the design of earthing and bonding of traction systems are set out in BS EN :2011. In particular the requirements for touch and body voltages is set out in section 9. Good practice in earthing design is given in BS 7430:1998, which sets out methods that may be adopted to earth an electrical system for the purpose of limiting the potential (with respect to the general mass of the earth) of current-carrying conductors forming part of the system, and non-current-carrying metalwork associated with equipment, apparatus, and appliances connected to the system. This is essential to the proper operation of the system and to protect against the danger to life from electric shock due to non-currentcarrying metalwork rising to dangerous levels. However, the section dealing with railways is out of date, and the whole of the section on railways and tramways should be considered as a reference to the BS EN series. A revision to BS 7430:1998 is planned. Earthing and bonding of information technology equipment in buildings in relation to safety, functional and electromagnetic performance is set out in BS EN 50310: Combined safety and functional earthing system resistance The maximum earthing system resistance for the purpose of combined safety and functional earth of telecommunications equipment shall be 4 Ω. GN6 An earthing system is provided for one or more of the following purposes: a) Safety earth earthing for the purpose of safety. For example, an earthing system that ensures the effective and rapid operation of protective equipment in the event of earth fault currents in an electrical supply system, which might otherwise cause fire and danger to life through shock due to non-current-carrying equipment and metalwork being maintained at a dangerous potential relative to earth. Page 5 of 13

6 b) Functional earth earthing provided to ensure correct operation of equipment and circuit. For example, to provide an earth for telephone systems employing an earth return signalling circuit. c) Reducing interference (both safety and functional earth), for example, earthing of metal screens of telecommunications cables and equipment. d) Lightning protection to provide a direct connection with earth for discharge tubes, lightning protectors etc. GN7 Combined safety and functional earthing are provided mainly to facilitate the correct operation of telecoms systems in limiting background noise. They may also provide safety protection in special cases of operational power supply distribution. For example, providing protection against earth fault leakage current caused by a transient suppression filter, which is used for preventing data loss or damage of telecommunications equipment by removing or reducing voltage spikes and transients. Section 5 of BS 6701:2010 provides guidance on earthing for installers of telecommunications equipment and telecommunications cabling. It advises the compliance of protective earth with BS 7671:2008+A1: Restricted locations The following locations shall be excluded from consideration as choice of sites for an earthing system for telecommunications equipment unless controls are in place to limit the touch and body voltages to those set out in section 9 of BS EN :2011: a) Locations within 100 m of electricity generating stations, sub-stations or railway traction feeder stations. b) Locations within 50 m of track sectioning cabins or return conductor / rail connections. In addition, cable sheath earthing systems shall not be located within 25 m, but preferably 50 m of telecommunications accommodation. GN8 The location constraints on earthing points provide physical separations of earthing points from electricity generating stations, feeder stations, track sectioning cabins, and lineside equipment rooms. This reduces the risk of a potentially dangerous longitudinal voltage causing electrical shock to staff and damage to equipment. GN9 The voltage limits are set out in section 9 of BS EN : Applied voltage and transmission level for balanced-pair telecommunications cables In-band noise levels The level of in-band noise in balanced-pair telecommunications cables shall not exceed that recommended by the Code of Practice for the Design of Private Telecommunication Networks (NICC NCOP040). Page 6 of 13

7 GN10 GN11 GN12 In-band noise is the noise contained inside frequencies between 300 to 4000 Hz. The limits for in-band noise are normally more stringent than the limits for wideband noise in order to avoid customer annoyance. The Voluntary Code of Practice for the Design of Private Telecommunication Networks (NICC NCOP040) recommends those factors and technical limits that should be considered for the design, development and evolution of Private Telecommunication Networks (PTN), in order that they may provide a high probability of satisfactory communications for the user for calls to and from a Public Switched Network (PSN). It has recommended that the telecommunication circuits should be designed to contain the inband noise within those limits specified by the relevant International Telecommunication Union (ITU) recommendations. The level of in-band noise and other characteristics of the end-user terminal for various types of access (for example, copper access or xdsl access) are covered in the relevant suite of ETSI standards Maximum permissible levels of signals The maximum permissible levels of signals to be transmitted by balanced-pair telecommunications cables shall be in accordance with: a) Section 4.2 of ETSI ES for terminal equipment connected to analogue interfaces of telephone networks. b) Section 4.2 of ETSI ES for terminal equipment incorporating a handset connected to the analogue interface of the Public Switched Telephone Network (PSTN) Telecommunications equipment shall comply with the voltage limits specified in sections 2.2 and 2.3 of BS EN :2006+A1:2010. The maximum voltage induced from the traction system shall not exceed the limits specified for touch and body voltages set out in section 9 of BS EN :2011. GN13 The limits on the levels of signals to be transmitted and induced voltage are required to ensure that: a) Users are protected from potential hazards of excess voltage. b) The signals applied are not at a level that could overload the circuit components, for example, amplifiers used in some telephone lines have a limited dynamic range. c) Signals outside of voice band are limited to improve signal-to-noise ratio. d) Crosstalk between cables are controlled. GN14 GN15 Section 4.2 of ETSI ES sets out the sending level limitations for terminal equipment intended to be connected to analogue interfaces of public or private, switched or non-switched telephone networks. Section 4.2 of ETSI ES sets out the sending limits to be provided by a single, handset telephony, terminal equipment which is intended for connection by two wires to an analogue interface of a PSTN. The safety issues relating to the terminal equipment connected to the telecommunication networks are addressed in BS EN Section 2 of BS EN sets out voltage limits for various types of circuits; section 6 sets out requirements for terminal equipment when connecting to a telecommunication network. Page 7 of 13

8 2.2.3 Maximum aggregate level of unintentional transverse voltage The maximum aggregate level of any unintentional transverse voltage in the transmitted signal on balanced-pair telecommunications cables shall not exceed -65 dbmp. GN16 GN17 GN18 The requirements set out above limit the transverse noise which disturbs the useful signals in the telecoms circuit. The noise is generated by unbalance in the circuit (for example, unbalance in conductor resistance, inductance, and capacitance being subjected to an electromagnetic environment, inducing different potentials between each conductor and earth or sheath). The same amplitude of noise at different frequencies disturbs telephone-type speech in different ways, because both the telephone and human ear are more sensitive to frequencies near to 800 Hz. Hence, harmonics at these frequencies will have a greater disturbing effect than those above or below this datum. A means of weighting different frequencies has been developed such that the disturbance for each frequency can be normalised. A psophometer is used to measure the weighted voltages. The required frequency weighting coefficients at various frequencies used by a psophometer are set out in Table 1 of ITU-T O Isolation of dangerous voltage If the telecommunications equipment contains potentials in excess of those set out in 2.2.2, the telecommunications equipment shall be transformer-coupled to the telecommunications cable, as follows: a) An earthed metallic screen shall exist between the transformer windings connected to the telecommunications cable and all the other windings. b) The earthed metallic screen shall be able to withstand the fault current produced by the equipment power source, due to an insulation breakdown in the transformer. c) Insulation between transformer winding connected to the telecommunications cables and all other conductive parts shall withstand proof test voltages of E V rms for 1 minute; where E is the peak a.c. or d.c. voltage to be isolated. GN19 GN20 The requirements set out above provide a protection barrier between protected telecommunication networks and potentially dangerous excessive voltages. Measures on the protection of telecommunication network service persons, and users of other equipment connected to the network, from hazards in the equipment, can be found in section of BS EN Page 8 of 13

9 Part 3 Application of this document 3.1 Application - infrastructure managers Scope The requirements of this document apply to all new telecommunications equipment at stations and alterations to the existing telecommunications equipment at stations It is permissible for the infrastructure manager to designate specific infrastructure projects, ongoing when this document comes into force, for which compliance with the requirements of this document applicable to the design, construction and commissioning of new or altered infrastructure is not mandatory. When designating such projects, the infrastructure manager shall consider: Exclusions from scope a) Its responsibilities under its current safety authorisation. b) The stage reached by the project at the time this document comes into force (for example, approval in principle). c) Whether compliance is necessary to ensure compatibility with other parts of the infrastructure. d) Whether compliance is necessary to facilitate safe interworking, having regard to changes to related requirements mandated on another infrastructure manager or a railway undertaking. e) The economic impact of compliance, but subject to its current safety authorisation in relation to the infrastructure in question There are no exclusions from the scope specified in for infrastructure managers General compliance date for infrastructure managers This Railway Group Standard comes into force and is to be complied with from 03 March 2012, except as specified in After the compliance dates, or the date by which compliance is achieved if earlier, infrastructure managers are to maintain compliance with the requirements set out in this Railway Group Standard. Where it is considered not reasonably practicable to comply with the requirements, authorisation not to comply should be sought in accordance with the Railway Group Standards Code Exceptions to general compliance date There are no exceptions to the general compliance date specified in for infrastructure managers. 3.2 Application - railway undertakings There are no requirements applicable to railway undertakings. Page 9 of 13

10 3.3 Health and safety responsibilities Users of documents published by are reminded of the need to consider their own responsibilities to ensure health and safety at work and their own duties under health and safety legislation. does not warrant that compliance with all or any documents published by is sufficient in itself to ensure safe systems of work or operation or to satisfy such responsibilities or duties. GN21 No guidance is associated with Part 3. Page 10 of 13

11 Definitions and Abbreviations a.c. Alternating current. Combined safety and functional earthing Earthing systems are provided mainly to facilitate the correct operation of telecoms systems in limiting background noise. They may also provide safety protection in special cases of operational power supply distribution. dbm Decibel referenced to one milliwatt: relative strength to a signal, calculated in decibels, when the signal is compared in a ratio to a value of one milliwatt. dbmp The additional p to dbm means that the considered value is a noise level which is measured by a psophometer with a special noise weighting filter specified by relevant standards. The required frequency weighting coefficients at various frequencies used by a psophometer are set out in Table 1 of ITU-T O.41 Psophometer for Use on Telephone- Type Circuits. d.c. Direct current. Earthing system One or more earth electrodes with their earthing conductors, capable of being connected to a main earthing terminal. Emf Electromotive force. ETSI European Telecommunications Standards Institute. Functional earth Connection to earth necessary for proper functioning of telecommunications equipment. ITU International Telecommunication Union. PSN Public Switched Network. PSTN Public Switched Telephone Network. PTN Private Telecommunication Networks. rms Root mean square. Safety earth (protective earth) Earthing of a point or points in a system or in an installation, or in equipment for the purpose of safety. Page 11 of 13

12 Telecommunications equipment Means of delivering a specific telecommunications application and its associated transmission method over telecommunications cabling. Telecommunications system Combination of telecommunications equipment and telecommunications cabling providing distribution of telecommunications applications within and / or between premises. Transverse voltage Transverse voltage is the voltage at a given location between two conductors of a group. xdsl Digital Subscriber Line, where x represents different bandwidths structures. Page 12 of 13

13 References The Catalogue of Railway Group Standards and the Railway Group Standards DVD give the current issue number and status of documents published by. This information is also available from Documents referenced in the text RGSC 01 Railway Group Standards Code Railway Group Standards GK/RT0053 GE/RT8015 GE/RT8270 GL/RT1255 Control of Unwanted Voltages on Telecommunications Equipment at Stations Electromagnetic Compatibility Between Railway Infrastructure and Trains Assessment of Compatibility of Rolling Stock and Infrastructure Low Voltage Power Supplies in Electrified Areas Other references BS 6701:2010 BS 7430:1998 Telecommunications equipment and telecommunications cabling Specification for installation, operation and maintenance Code of Practice for Earthing BS 7671:2008+A1:2011 Requirements for electrical installations. IET Wiring Regulations. Seventeenth edition BS EN :2011 BS EN 50310:2006 BS EN :2006 +A1:2010 BS EN :2006 Railway applications Fixed installations Protective provisions relating to electrical safety and earthing Application of equipotential bonding and earthing in buildings with information technology equipment Information technology equipment Safety Protection against lightning. General principles EMC Regulations 2006 The Electromagnetic Compatibility Regulations 2006 ETSI ES Speech and multimedia Transmission Quality (STQ); Requirements and tests methods for terminal equipment incorporating a handset when connected to the analogue interface of the PSTN ETSI ES ITU-T O.41 NICC NCOP040 Access and Terminals (AT); Harmonized basic attachment requirements for Terminals for connection to analogue interfaces of the Telephone Network. Part 2: Basic transmission and protection of the network from harm Psophometer for Use on Telephone-Type Circuits Voluntary Code of Practice for the Design of Private Telecommunication Networks, ND1406:1997/10 Page 13 of 13