Wiring Tools and Wire Joints

Transcription

1 206 UNIT 7 Wiring Tools and Wire Joints Learning Objectives To identify various tools used in wiring and know their applications. To learn about preparation of Joints 7.0 Introduction Electrician tool kit is the most simple and brief among other servicing engineers tool kits. As the electric wiring is a specialized job, so it requires a special kit. Some of the tools used for wiring are common with other trades. Overall the trades are not expensive and are available at almost all hard ware and electric shops. 7.1 Wiring Tools Screw Drivers A screw driver is a hand tool that is designed to loosen or tighten or to keep the screws in a position. It has two parts one is blade and shank made of high carbon steel or chrome-vanadittan steel and the other is plastic or wooden handle. The tip of the blade is hardened. Screw drivers are made in many sizes. Its size usually varies from 4.0mm to 600mm. A standard or common screw drivers as shown in fig 7.1 (a) is used to meet different types of jobs when plenty of room is available and the head of the screw is out in the open. A thin blade screw driver in fig 7.1 (b) is used for screwing and unscrewing the screws of switches, lamps, holders etc.

2 Paper - II Electrical Engineering Materials and Wiring 207 A heavy duty screw driver, fig 7.1 is of average length but is made with a heavy blade, the shank of which is square in cross-connection.. It may be required to augment hand pressure by using plier for turning stubborn or heavy screws. The shape of the bank permits the use plier or wrench to assist on turning a screw. A helical or spiral ratchet screw driver is used to turn screws, when there is a large opening and the head of the screw is in the open. It can be locked rigid and used as common screw driver, fig 7.2(a). Blade or Handle (a) Standard Screw Driver (b) Thin Blade Screw Driver (c) Heavy Duty or Square Blade Screw Driver 7.1 Types of Screw Drivers Offset screw drivers are used where it is impossible to use a common screw driver, such as in places only where a small opening is available to remove the screw and where the head of the screw is hidden, fig 7.2. Fig 7.2 Other Types of Screw Drivers

3 208 A Phillips type screw driver as shown in fig 7.2 (e) is specially designed to fit the heads of Philip screws. It differs from other screw drivers in that the end of the blade is fluted instead of flattened. It is made in several sizes from 75mm to 200mm. The screw drivers will not usually slip or burr the head of the screws if a proper size of screw driver is selected for a particular screw. On some of the screw drivers handles, voltage rating or grading will be mentioned, which represents that the screw driver can be used on the live line up to the specified voltage Pliers Pliers are used for holding or gripping small screw or bolts in position where it is inconvenient or unsafe to use hands They are also used for bending and cutting the wires. They are made in various types to suit different applications. The following are the most commonly used pliers: (a) Slide cutting plier or cutting plier: This plier is used for cutting wires, gripping operation by hand, holding jobs, twisting wires and a number of operations in electrical wiring. It is usually provided with snub-nosed jaw and have a cutting edge only one side as shown in fig 7.3. An insulated plier is used in lines of electricity. Insulated Handle Pivot Plier Insulated Plier Fig. 7.3 (b) Nose plier: pliers are made as the name implies, with a nose or jaws. These tools are used for bending and holding thin wires.they are also used for forming eyes of the wires which are to be used where they are held fast under the screw. It is also preferred for electrical radio and tv repair works for placing and removing small items in narrow place.

4 Paper - II Electrical Engineering Materials and Wiring 209 (c) Diagonal cutting: Diagonal cutting pliers or diagonals are special types of pliers and are exclusively used for cutting and stripping of electrical wires, where the wire terminates into holders, switches, sockets, etc.fig 7.4 shows the diagonals. (a) Long Nose Plier (b) Round Nosed Plier (c) Half Nose Plier (d) Fig. 7.4 Diagonals Fig. 7.5 Slip Joint Plier (d) Slip joint pliers fig 7.5 shows the common slip joint or combination plier. They are used for holding and gripping small articles in situations where it may be inconvenience or unsafe to use hands. It is not good practice to use plier in place of a wrench Hammers A hammer is of the man s earliest tools. They have been improved since the day when the stone-age man fashioned one by tying a stone to branch torn from a tree, but they still consist of major parts: head and handle. Several varieties of hammers are made that it would be impossible to mention them all in a limited space. This discussion therefore will be limited to the hammers which are used in electrical works are: (a) Ball pen hammer and (b) Claw hammer:

5 210 (a) Ball pen hammer: The ball pen hammer is shown in fig 7.6. It consist of a hammer face which is used to drive in nails into wooden batten or for general work and a ball peen (or cross peen or straight peen) end for cutting wall plaster and bricks when it is necessary to take wiring from one room to another and to drive the gutties etc. The eye is the name for the hole that receives the handle. The post is the portion between the face and the eye. The middle portion of the hammer head is known as cheek. The weight of the hammer is stamped on this cheek. (b) Claw hammer: It is dual purpose hammer. It has a hammer face which is used to drive in nails or general purpose or claw at the other end for pulling out nails from the wood as well as can be inserted behind, beneath or between boards to be removed. Cheek Claw Handle Face Eye Fig. 7.6 Claw Hammer Hammers or engineer hammers are designed by their weight and they varies from 375 gram to 675 gram. The use of a claw hammer is shown in fig 7.7. Fig. 7.7

6 Paper - II Electrical Engineering Materials and Wiring Hack Saw and Wooden Saw Hack saw is especially designed for cutting metals like conduit cables etc. It consist of a metal frame, in the ends of which are metal clips to hold the cutting blade. One clip is threaded on one end for a wing nut which is used for tightening the blade in the frame. Only two types of hack saws are used in ordinary practice. They are: 1. Solid or common hack saw 2. The adjustable hack saw Fig 7.8a shows a solid type hack saw which accommodates the blades of same length. Fig 7.8b shows the adjustable hack saw which is most useful and accommodates the blades of different lengths. Frame Handle Pin (a) Solid Type (b) Adjustable Type Fig 7.8 The commonly used blades are 0.65mm thick 12.5mm wide and 200 to 300mm in length. The blades are specified by its length measured between the centres of the two holes and pitch. Blades are available with 6, 8, 10, and 12 teeth per cm. Blades with coarse pitch are used for jobs or soft materials while finer pitch are for fine cuts or thinner jobs. The hack saw blades are made of high grades of steel such as tool steel, high speed steel or tungsten alloy steel. (c) Handle Blade Back Toe Heel Tooth Fig. 7.9 Tennon or Wooden Saw

7 212 When cutting with a hack saw full strikes while pushing the saw away from you and no pressure should be applied on return stroke. Wooden saw or tenon saw is used for cutting small jobs like cutting wooden batten, casing-capping, wooden blocks etc. It is the ideal saw for all types of wooden work. The saw available in different lengths ranging from 250mm to 400mm Chisels, Scratch Awl One of the earliest method of shaping a piece of wood, stone or metal was the chip away the unwanted material with a hammer and chisel. This practice is still common today for jobs which are done at the work bench and instances where it is not practical to do the work on a machine. For electrical work generally two types of chisels are used: 2. Wooden chisel 3. Cold chisel Wooden Chisel In wood work the use of Blade chisel is made in making various Handle Tang Ferrule connections of casing0capping or for cutting the side of the wooden boards from the centre in order to Cutting Edge allow the wires to be connected to switches, sockets etc. The Fig wooden chisel has a blade made of tool steel and is fitted in to a handle as shown in fig 7.10 cutting edge is hardened and tempered to increase the toughness. The chisel usually specified by the width of the cutting edge. Cold Chisels A cold chisel is a tool from hexagon or octagon shaped tool steel (or high carbon steel chrome vanadium steel). One end is shaped for the cutting operation and other end (head) is left blunt to receive the blow from a hammer as shown in fig The cutting edge is hardened and tempered. The cross-section of the shank is usually hexagonal or octagonal. The chisel is specified by the width of the cutting edge. In house wiring cold chisels are used for plaster cutting or for brick cutting only.

8 Paper - II Electrical Engineering Materials and Wiring 213 (a) Flat Chisel (b) Cape Chisel (c) Diamond Point Chiesel (d) Round Nosed Chisel Scratch Awl Fig Types of Chisels Scratch awls are generally made from forged tool steel as shown in fig It is difficult to insert a wooden screw into wood, unless there is a small hole or impression. With a scratch awl an impression is made into wood before screwing. As the scratch awl tool is very sharp, it should be handled carefully. Handle Hand Drill Hand Drill Fig 7.12 The making of whole in a piece of material can, in some instances, be a simple operation. But in some of the instances it is an important and precise job. A large number of different tools and machines have been designed so that holes may be speedily, economically and accurately in all kinds of material. A hand drill consists of a chuck with hardened steel jaws into which is placed the twist drill (drill bit). A crank and gear is used for increasing the speed of the drill as shown in the fig In house wiring, hand drill is often used in wooden batten, wooden blocks and wooden boards etc., to facilitate the passage of insulated wires which terminate into switched holders, sockets or other fittings. For such purpose a hand drill is useful.

9 214 Name Plate Turning Handle IDE Handle AW Drill Chuck Main Handle Main Handle Drive Wheel Pinion Jaw Chuck Plug Auxillary Handle Pistol Grip handle Cable (a) Hand Drill (b) Electric Power Drill Reamer Fig A hole that has been made by drilling is seldom accurate in size. It is usually slightly oversize. This is quite satisfactory for holes in which bolts or rivets are placed. When greater accuracy and a smooth finish are required, the hole is first drilled under size and then finished by reaming. Fig Reamer The reamer as shown in above figure is inserted into the spindle of the machine in the same manner as a drill Rawl Plug Jumper, Center Punch Rawl Plug Jumper It consists of a hard tube with a central hole called Rawl plug and a bit. It is generally used to make holes in stone walls or concrete walls, and should not be

10 Paper - II Electrical Engineering Materials and Wiring 215 used on metals. While drilling a hole are should be taken to tap it slightly with a rotary motion so that which each stroke it goes forward and throws out the dust or small stone pieces etc. Center Punch Fig 7.15 Rawl Plug Jumper A center punch is made of hardened tool steel. It is used to mark the location of holes to be drilled and also to help to start the drill in the correct spot. (a) Center Punch (b) Automatic Center Punch Fig Center Punch The automatic center punch makes punch marks of a uniform size without the use of a hammer. The knurled cap may be turned to control the depth of the punch mark or impression Files Filing is a method of removing small amounts of material from the surface of a piece of metal or other hard substance. A file is a hardened steel instrument (tool) having parallel rows of cutting edges or teeth on its surfaces. On the two wide surfaces, the rows are usually diagonal to the edge. One end of the file is shaped so that it may be inserted into a wooden handle. Handle Tang Heel Fig Files Face Length Tip

11 216 Often electrician requires a file for removing burrs on wires or joints etc. Usually a smooth half round files with serve the purpose of an electrician. Files are classified according to their length, teeth pattern, fineness of the teeth and shapes of the cross-section Pipe Vise A pipe vise is a vise with serrated jaws that are V-shaped to grip pipe and cylindrical bars firmly. Fig Pipewise Pipe vises are generally used in plumbing work for holding the hollow circular sections such as pipes, and cylindrical bars. An electrician also used the pipe vises (Portable) for holding the conduit during conduit cutting or for cutting threads on the conduits or for bending conduits etc. It has two V-shaped serrated jaws, one is fixed and the other is moved by rotation of handle. It grips the conduits or bars in between the jaws firmly as shown in fig (7.17) Pipe Cutter A pipe cutter is a tool especially designed to cut pipe. The cutting blade is a hardened-steel wheel. The cutter is adjustable for cutting various sizes of pipes. The pipe is held securely by the pipe cutter which is rotated round the pipe and after few rotations the cutter is again tightened against the pipe wall and further rotations are given to the cutter.

12 Paper - II Electrical Engineering Materials and Wiring 217 The process is repeated until the pipe cut. But the pipe bulges with a sharp edge at the cut which strongly affects the wires by spoiling their insulation. The sharp edges can not be removed completely but, can be improved by reaming the edges by means of a reamer (or use hack-saw for cutting Wrenches Fig Pipe Cutter A wrench is a tool for turning or twisting nuts or bolts. It is usually made of steel. Wrenches may consist of a slot, socket, pins or movable jaws for gripping the nut, accordingly the wrenches are classified as follows: (i) Single-ended wrench: A single-ended wrench is one that is made to fit one size of nut of bolt as shown in fig 7.19(a). This is the most inexpensive type of wrench and is quite efficient in ordinary situations. (a) Single - Ended Wrench (b) Double - Ended Wrench Fig (ii) Double-ended wrench: A double-ended wrench has two openings one at each end of the handle, to fit two different sizes of nuts or bolt heads as shown in fig (b). (iii) Closed end wrench: A closed-end wrench is similar to a single-ended wrench, but, as if entirely encloses a nut, there is little danger of the wrench slipping off the nut or of the jaws spreading apart. For these reasons it is preferred for some jobs. It is also known as a box-wrench.

13 218 (a) Closed - End Box - Wrench (b) 12 - Point Box Wrench (C) Comibination box and open end Wrench (d) Flare Nut Wrench Fig 7.20 Flare Nut Wrench (iv) Twelve point box wrench : A twelve point box wrench is one that is designed with twelve notches or points, inside each closed end. The points of a nut may be gripped by any one of the twelve notches of the wrench, which permits the turning of a nut where only short pull of the wrench is possible. (v) Adjustable open-end wrench : An adjustable open end wrench has a movable jaw which makes it adjustable to various size of nuts as shown in fig 7.21(a). A heavy type of adjustable wrench is the monkey wrench shown in fig 7.21(b). When using this type of tool, point the jaws in the direction of the force applied. This will prevent the jaws from springing apart, and the wrench will be less likely a slip off a nut. The movable jaw should be adjusted so that it is tight against the part to be turned. (vi) Lever-jaw wrench : A lever-jaw wrench is a combination gripping tool with adjustable jaws that may be locked in place. It may be used as a wrench, clamp, pliers, or vise as shown in fig (vii) T-socket wrench : A T-socket wrench is made in the form of T, as shown in fig The hole in the end or socket is made in a variety of shapes, such as shapes, such as square, hexagon, or octagon. It is generally used on jobs where there is insufficient space to permit the use of an ordinary wrench. The handle may be removed from the head of the wrench.

14 Paper - II Electrical Engineering Materials and Wiring 219 Fixed Jaw Handle Movable Jaw Thumb Screw (a) Adjustable Open - End Wrench (b) Monkey Wrench Fig (viii) Off-set socket wrench : An off-set socket wrench is made with the same variety of sockets as a T-socket wrench. It is designed to be used on nuts requiring great leverage or in places where a T-socket wrench cannot be used. Fig LEVER - Jaw Wrench (ix) Ratchet wrench : A ratchet wrench permits a nut to be turned in spaces only a short swing of the handle is possible. Another advantage of this type of wrench is that it is not necessary to remove it from the nut or bolt until it is tight. Fig Off Set Socket Wrench Fig T-Socket Wrench

15 220 Fig Ratchet Wrench (x) Hollow Set screw Wrench : A hollow set screw wrench, sometimes called an Allen wrench, is made of hexagonal shaped stock. They are used to fit set screws or head screws and are available in many sizes. Fig Hollow - Set Screw or Allen Screw (xi) Strap wrench: A strap wrench is used for turning cylindrical parts or pipes, or holding or revolving any job on which the surface finish must be preserved. Fig Strap Wrench (xii) Pipe Wrench : A pipe wrench is a tool designed to grip and turn a pipe or rod about its axis in one direction only. It has adjustable serrated jaws,

16 Paper - II Electrical Engineering Materials and Wiring 221 the serrated edges tend to cut into the metal being gripped, so care should be taken to protect plated or finished surfaces. Conduit Fig Pipe Wrench (xiii) Rib joint Wrench : A rib joint wrench. It has an adjustable channel with which one jaw can be adjusted. It can be used as a plier as well as a wrench. Adjustable Channel Straight Jaw Handle Nut Bolt (xiv) Chain Pipe Wrench : A chain pipe wrench. It is mainly used to grip the big size conduits. This chain pipe wrench or simply chain wrench is mainly used to install sub-mercible pumps in the tube wells. Fig Rin Joint Wrench Miscellaneous Tools Fig Chain Pipe Wrench Some of the following important tools, associated with an electrician or used in our daily life are:

17 222 (a) Voltage tester: The voltage tester used to find the supply in a live conductor or system. It should not be used as a screw driver except for small screws. (b) Wire stripper: The wire stripper used to remove the insulation of cables. It removes the insulation without any scratches or cuttings on the conductor. Neon Lamp Insulated Handle Insulated Blade Adjustment Wheel 7.2 Wire Joints Splicing or Joining of Wires Fig Stripper In house-wiring or in any wiring system, the splicing (jointing) of wires is essential. To make use of the wire pieces or to extend the length of a wire, another wire is to be spliced to it. The termination of wires is needed, as the wires are to be connected to switches, sockets, lamp holders, ceiling roses etc. As far as possible the splicing should be avoided in conduit runs or casing capping. But sometimes when repairing old wiring system splicing becomes necessary. Splicing should always be carried out at out lets i.e. in switches, ceiling roses or in junction boxes etc. Splicing should be mechanically strong; it should have 95% tensile strength and 100% electrical continuity. The following are the various operations for making a joint: (a) Removing of insulation (b) Cleaning of conductor (c) Twisting and over laying the conductors. (d) Splicing the conductors (e) Soldering the splice (f) Insulating (Taping) the splice.

18 Paper - II Electrical Engineering Materials and Wiring 223 (a) Removing of Insulation : For splicing two conductors together, first their insulation should be removed in a tapered fashion, which facilitates better splicing and insulation of the splice. While removing the insulation care should be taken such that conductor will not get any scratches or cuts. The insulation should be removed to the required lengths only i.e. 2.5 cm approximately. Fig Removing Insulation (b) Cleaning of Conductor : After removing the insulation, the conductor should be cleaned with the help of sand paper. So that enamel costed insulation present on the conductor will be removed. (c) Twisting and over laying the Conductors: The bare conductor after cleaning should be twisted properly. If it is a single core conductor twisting is not necessary. The overlaying of conductors in cross-position prevents the two wires being separated out under pressure. (d) Splicing the Conductors : Now with the help of plier or forefinger and thumb make four to eight turns on both sides of the cross position. Fig Twisting of Wires Fig Finished Joints (e) Soldering the splice: The splice should be soldered in order to make it strong and avoids the formation of carbon in between the turns. The soldering can be done with the help of soldering iron for small size splices and for large size splices (which are used for under ground cables) either blow lamp

19 224 will be used or solder will be heated and poured on the splice, with the help of blow lamp the splice will be heated to certain temperature such that the solder wire (lead and tin), which when place over the splice should melt. (f) Insulating the splice: The soldered splice should be provided with insulation. For house wiring splices, a rubber tape or black tape should be wrapped uniformly. Each turn of the tape should over lap a part of the previous turn. The tape should cover the entire splice and part of the insulation on the cable on either side of the splice also should be covered. Some of the common methods employed for jointing of cables are: 1. Western Union Joint: It is a straight joint and is used to increase the length of single core cables only. The western joint is well explained with the help of fig 7.32, 7.33 and fig It is also known as twisted joint. It is also used for bare conductor as shown in fig Two clean bare conductors pieces are placed one over the other as shown in fig 7.35(a). Leave a portion of 8 cm in the centre. Give a neck turn and twist one conductor around the other making 3 to 4 turn. Repeat the same on the other end and cut the surplus conductors as shown in fig 7.35(b). (a) Base Conductor (b) Completed Joint Fig Western Union Joint 2. Married Joint: It is also a straight joint but is used to join stranded cables. Let us consider a seven strand cable and follow the steps given below for the joint: (i) Remove the insulation of both cable upto a length of about 6 to 8 cm from one side of each cable in a tapered fashion as shown in fig 7.36 (a). (ii) Remove the also braid if present for about 1 to 2 cm on each cable. (iii) Scatter the strands by twisting the conductors in opposite direction leaving about 4 cm from the insulation end and bind it at this point with binding wire as shown in fig 7.36(b).

20 Paper - II Electrical Engineering Materials and Wiring 225 (iv) Clean each strand neatly with emery paper (sand paper) and cur off the middle strand. (v) Bring both the cables end to end and mix them intersecting with other at alternate strands as shown in fig 7.36 (c). Hold one cable in the left hand and wrap the one strand around the twisted portion of the other in opposite direction, and complete the wrapping of other strand also. Repeat the method of wraping strands on the other side of the conductor. Round off the ends of both the cables with the help of wooden hammer (mallet) or plier. (a) Removing of Insulation (b) Scatter the Wires (c) Intersecting the Strands (d) Finished Married Joint Fig Married Joint (vi) The joint is then soldered and insulated with insulation tape. 3. Britannia (Straight) Joint: This is also another straight joint and is suitable for bare overhead conductors. To make this joint, conductors are cleaned with the help emery paper for a length of 8 to 10 cm (even more depending upon the size of the conductor). The conductors are then made straight and a little bend is given at their ends. The conductors are then held together firmly and wound over tightly with a copper binding wire. The joint is then soldered (insulation tape will not be used). Fig 7.37(b) shows Britannia Tee joint. It is usually used for over head lines for tapping the electrical energy. (a) Britannia Straight Joint (b) Britannia Tee Joint Fig Britannia Joint

21 Tee-Joint: It is also known as single branch splice and is used for taking a tapping or connection from a straight through cable or over head line. (a) Running Cable (b) Branching Cable (c) Finished Joint Fig Tee Joint of Single Core Conductor Consider a running cable and branch cable. Remove the insulation of the running cable in a tapered fashion for a length of 2 to 3 cm. Also remove the insulation of the branching cable for a length of 3 to 4 cm as shown in fig () and fig () respectively. Clean the conductors with the help of a emery paper. Keep the branching wire in quadrature (90 ) with the running wire and turn the branching wire around the running wire and complete atleast 5 to 8 turns as shown in fig. 7.38(c). Now the joint should be soldered and insulated. (a) Running Cable (b) Turning of Branching Cable (c) Finished Joint Fig TEE Joint of a Stranded cable Fig 7.39 illustrates the tee joint or branch splich or a tap joint of a stranded cable. Remove the insulation of both the running and branching cable suitably and after cleaning the conductors with emery paper, separate the strands of the running cables as shown in fig 7.69 (a). Insert the branching conductors into the middle of the opening made in the running conductor. Divide the strands of the branching cable in to two equal groups and wrap them into opposite direction as shown in fig 7.39 (b). Now complete 3 to 5 turns by each group of the

22 Paper - II Electrical Engineering Materials and Wiring 227 branching cable in the opposite direction as shown in fig 7.39(c). Lastly solder the joint and insulate with the tape. (a) Staggered Manner of removing insulation for running cable (b) Finished Tee Joint Fig Tee Joint of a DCC Fig illustrates the tee joint of a double core (or twin core) cable. Some times it is necessary to provide a tee joint in a double (twin) core cable. In such cases remove the insulation of the running cable in a staggered and tapered fashion as shown in fig. 7.40(a). Remove also the insulation of the branching cable in a tapered fashion. Clean the conductors with emery paper and hold the two lengths of the branching cable at 90 to the running cable. Wrap the branching conductors over running conductors in the opposite direction and provide at least 5 to 8 turns as shown in fig 7.40(b). Now solder and provide the insulation tape. 5. Pig Tail or Rat Tail or Straight Joint: Pig tail is often required for termination of the conductor in switches, sockets, lamp holders, ceiling roses etc. Fig Pigtail Joint of a Single Core Cable

23 228 Fig illustrates a pig tail joint of a single core cable. Remove the insulation of both the cables for a legth of 3 t o5 cm in a tapered fashion. After cleaning the conductors keep the conductors with their insulation parallel and twist the two conductors by hand or with the help of plier, keep the length of the twist at least 2 to 8 cm and cut-out the remaining conductor. Now solder the joint and provide the inslation. Fig Pigtal Joint of a single core cable and flexible cable Fig 7.42 illustrates a pig tail joint of a single core cable and a flexible cable. In this case the flexible wire should be wrapped over the solid conductor over the solid conductor for a length of 2 to 3 cm, then the solid conductor should be bent back. After soldering for providing tape care should be taken to see that no part of the joint should be left without tape for this purpose tape should be started between the cables. 7.3 Soldering a Joint Soldering is a process of making joints between two metallic surfaces by a metal alloy which melts at lower temperature than that of the metals to be jointed. The material used as a solder for joining of conductors consists of an alloy of lead and tin in the ratio of 1:1 (or 50/50) and it melts at 200. The melting temperature can be reduced by increasing the tin quantity. The following are the various devices for soldering a joint: (a) Soldering iron (for small size joints) (b) blow lamp (c) ladle and pot (for larger size joints) (a) Soldering Iron: It is used for small size joints such as Radio, TV, Computer and other electronic field. When the soldering iron cord is connected to AC. Supply the copper bar gets heated and melts the solder placed over the tip of the bar for making joint. Before making a joint the wires should be cleaned and then only soldered.

24 Paper - II Electrical Engineering Materials and Wiring 229 Fig (b) Blow Lamp : The blow lamp is used for soldering the joints of large size such as under ground cable etc. It is capable of producing very high temperatures. Usually kerosene oil is used in the lamp. It directs the flame on to the job or joint and increased the temperature. When the solder is placed over the joint it melts and spreads over the joint. It is essential to heat the joint to a proper temperature; if it is under-heated proper soldering can not be done, and if it is over-heated the conductor joint becomes weak and brittle. Proper temperature can be tested with the help of solder. Which when placed over the joint should just melt. Fig Blow Lamp Fig 7.45 (a) Ladle and Pot (c) Ladle and Pot : This method is used to solder large size joints. First the solder is heated in a pot. After cleaning the joint the melted solder should be poured over the joint with the help of ladle until entire joint is soldered as shown in fig (). A dish or tray should be placed below the joint to collect the solder which flows through the joint.

25 230 (b) Melted Solder Pouring over the Joint Termination of Wires at Terminal Screws The bending of a cable conductor into a proper shape (circular fashion or fixing into a lug etc). is known as termination. The termination is needed as the cables or wires are to be connected to switches, sockets, holders etc. The terminals can be terminated by the following two methods: by using solder type terminal lugs or splicers. By using solder less terminals lugs or connectors. (a) Bending of a cable conductor (b) Conductor Terminal Connection Fig Consider a 1/18 cable conductor for termination in to the screw of a switch or socket. First the insulation of the cable should be removed in a tapered fashion, and the conductor should be bent in the form of a loop as shown in fig While bending care should be taken to see that the conductor must be bend in the (clock wise direction) same direction in which the terminal screw is to be turned for tightening. Such an action closes the loop in the process and keeps in a tight position. Fig 2.23(b) shows the terminal point, when the binding nut or screw is tightened, it also tends to tighten the conductor eye.

26 Paper - II Electrical Engineering Materials and Wiring 231 This method of termination is some times not desirable when, the conductor size is large or design requirements are rigid. Vent Tongue Barrel (a) Soldering Lug Fig When heavy conductors are to be terminated into a small nut and bolt screw, some times soldering lugs used as shown in fig The soldering lugs are also called as terminal lugs. They are available in different shapes and sizes. Each type of lug has a barrel (or sleeve) which is wedged, crimped, or soldered to its conductor. There is also a tongue with a hold or slot in it to receive the terminal post or screw. The conductor tip is stripped and also tinned, then inserted into the preheated lug. When mounted, the conductor insulation should butt against the lug barrel, so that there is no exposed conductor. When the termination is supposed to be opened very frequently, in such cases a solder less connection is made for lighter or heavier conductors as shown in fig Splicers and terminal lugs which do not require solder are more widely used than those which do require solder. Solder less connectors are attached to their conductors by means of several different devices. They are all squeezed (crimped) tightly onto their conductors. They afford adequate electrical contact, plus great mechanical strength. In addition, solder less conductors are easier to mount correctly because they are free from the most common problems of solder connector mounting; namely, cold solder joints, burned insulation and so forth Standard Wire Gauge (b) Joints between conductors larger than 7/0.44 must be made with substantial mechanical clamps of sweating sockets. (c) Solder - Type Terminal Lug Standard wire gauge is also known as British Standard Wire (BSW) gauge and is used to measure the size of the wires. The size of the wires are not measured in terms of areas, but are measured in terms of numbers, which are assigned to the wire sizes.

27 232 Fig Suppose we want to measure the size or wire (or cable), the wire should be inserted into suitable slot and that particular number marked on the slot into which exactly fits is its gauge number. The diameter and area of the wire can be determined from the table. The smallest wire gauge number is 40 having a diameter of mm ( inch); while the largest number is 00,00,000 (named as seven zero) or in short written a 7/0 having a diameter of mm. It should be remembered that the higher the number of wire gauge the smaller is the diameter. Fig () shows the wire gauge used for measuring the sizes of wires. Table () gives the diameter and the area of the British standard wire gauge Number of Strands and Current Carrying Capacity While giving the specification of an insulated wire we have to mention the number of strands and gauge number, type of insulation and the material of the conductor. For example: 3/20 VIR Aluminium wire The numerator 3 represents number of strands and the denominator 20 represent the gauge number with VIR insulation and the material is aluminium. Table () and Table () gives the current capacity of various size cables.

28 Paper - II Electrical Engineering Materials and Wiring 233 Table 2.1 British Standard Wire Gauge (S.W.G) Gauge No. 7/0 6/0 5/0 4/0 3/0 2/ Diameter (mm) Area (mm) Gauge No Diameter (mm) Area (mm)

29 234 Table 2.2 Current Carrying capacity of PVC Insulated : PVC sheathed, Aluminium conductor cable confirming to IS : 1554 (Part - I) Nominal cross sectional area (sq.mm) Nominal thickness of insulation (mm) Nominal thickness of outer sheath (mm) Approximate overall dia (mm) core (amp) core (amp) Current Rating In Ground In Duct In Air 2 core (amp) core (amp) core (amp) core (amp) Short Answer Type Questions (1) What is the difference between a wire and cable? (2) List the various types of cables. (3) Write short-notes on the following

30 Paper - II Electrical Engineering Materials and Wiring 235 (a) VIR cables (b) CTS or TRS cables (c) PVC cables (d) Weather-proof cables (e) Flexible cables. (4) What are the various operations for making a joint? (5) Explain the following with neat sketches: (a) Western Joint (b) Married Joint (c) Britannia Joint (d) Tee-Joint (e) Pig-Tail Joint (6) Explain the soldering of a joint with the help of soldering-iron and Blow-lamp. (7) What do you understand by termination of wire? (8) How you will measure the size of a wire? (9) What is the different between PVC and CTS wires? Long Answer Type Questions 1. Draw a screw driver and name the various parts. 2. What is the material used for the shank of a screw drivers? 3. State the applications of a screw driver. 4. List the various types of screw driver. 5. What are the various applications of pliers? 6. List the various types of pliers. 7. State the function of a diagonal cutting pliers. 8. With a neat sketch identify the various parts of a ball peen hammer. 9. How many types of hack-saw s are there and what are their functions?

31 Draw a wooden chisel and name the parts. 11. State the functions of the following: (a) Scratch Awl (b) Hand-drill (c) Ratchet brace (d) Auger-bits (e) Center punch (f) Rawl plug jumper 12. With a near sketch identify the parts of a file. 13. What is pipe-vise? How many types of pipe-vises are there? 14. Write short notes on the following: (a) Taps (b) Die and die set (c) Pipe cutter 15. How many types of conduit bending tools are there? Explain any one of them? 16. What is a wrench? And how many types of wrenches are there? Activities 1. Practice, usage of tools for different applications. 2. Prepare T Pig tail and straight joints and paste them.