Signal Cable

SIGNALLING CABLE 1.

INTRODUCTION A Cable can be defined as a number of insulated electrical conductors bunched in to a compact form by providing mechanical protection and electrical insulation. Cable can be classified as Underground Cable (laid under ground), Submarine cable ( laid under water), Aerial cable (laid over head) and Indoor cable ( laid along the walls of building. However, in Railways only Underground and Indoor Signalling Cables are used. This handbook covers Construction. Laying, Jointing, Testing, and Maintenance of Signalling Cables as per Indian Railway Standard Specifications No. S:63-89, S-35/93, S:76-89 and IS:1554. These Specifications cover the requirements and tests for armoured and unarmoured single core and multicore copper conductor, PVC insulated sheathed and unsheathed cables for Indoor and Outdoor Railway Signalling.

2.

BRIEF DESCRIPTION The Cable is circular throughout its length and is free from any physical defects. The measured length of cable on any drum should not vary by more than + 0.2% of drum length (CL.4.2 of S/63-89) Single core cables may be supplied in coils of 100 + 0.5 metres (CL.6.1 of S/63-89) . Unless otherwise specified, the multicore cable is supplied in length of 500 metres each. With the prior approval of cosignee, cable upto 9 cores may be supplied in length of 1000 metres each. Non-standard lengths each not less than 100 metres shall be acceptable upto 4% of the total quantity ordered (CL.6.4 of S/63-89). The cable ends are sealed to prevent moisture entry. The length of the cable is marked in a sequential manner over the outer sheath at intervals of one metre with an accuracy of + 0.2%. The Cable drum number shall be legibly embossed at every one metre or less on the PVC outer sheath throughout the length of cable (CL.4.4 of S/63-89). The following information shall be stencilled on the drum in black paint over yellow painted background (CL.4.3 of S/63-89): a) b) c) d) e) f) g) h) i) j) k) l) m)

Manufacturer’s name, brand name or trade mark. IRS Specification number. Type of cable and voltage grade. Number of cores. Nominal cross-sectional area of conductor. Colour of cores (In case of single core cable). Number of lengths on drums/in coils ( if more than 1) Length of the cable on the drum/coil. Initial and final sequential marking for the length. Direction of rotation of drum (by means of arrow). Approximate gross weight. Country of manufacture. Month and year of manufacture.

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2

Advantages of Underground Cable 1.

Overhead lines may come in contact with trees, bushes, etc. and cause low insulation.

2.

Due to natural causes and ravages of humans beings, overhead lines are prone to a higher fault incidence.

3.

Due to headway considerations the maximum number of pairs on a pole route is limited to 16. By using underground cable all these disadvantages can be minimised.

3.

TYPES AND USE

3.1

Outdoor Signalling Cable Signalling cables for outdoor circuits should be laid underground. Following types of underground cables are normally used in Railway Signalling.

A)

Main Cable These cables are used for extending signalling circuits from cabins to location boxes and between location boxes. Normally 2, 4, 6, 9, 12, 18, 24, 30 and 37 cores, armoured cables are recommended for use as main cable.

B) Tail Cable Tail Cables are used for extending signalling circuits from location boxes to signalling gears. Cables of 5 core to 12 core are normally used as tail cables. C) Power Cable These cables are used for extending 230/110 Volt AC supply. Normally aluminium cables 2/16 Sq.mm, 2/25 Sq.mm, 2/35 Sq.mm, 3/16 Sq.mm, 3/25 Sq.mm, 3/35 Sq.mm sizes are used. In addition, 2/10 Sq.mm. copper cable is also used. 3.2

Indoor Signalling Cable Indoor Signalling Cable is used for indoor wiring of signalling circuits. Following cables are normally being used for indoor signalling applications :

TABLE 3.1 : ‘TYPES OF INDOOR CABLES & USES’ Sr. No.

1 2 3

Type of Cable

Use

16/0.2 mm 3/0.75 mm 1/1.4 mm

Wiring of Q series and Shelf type Relays Wiring of shelf type Relays Wiring of lever lock, Circuit Controller

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7/1.4 mm

5 6

8

1/ 2.5 mm 40/0.6 mm 60/0.6 mm 24/1.0 mm 40/1.0 mm 60/1.0 mm 1/0.6 mm

9

1/1.0 mm

10

36/0.3 mm

7

3

Power Supply i.e Battery Room to Charger and Busbar Wiring of Boot leg (Track Circuit) Rack to Rack wiring in metal to metal type relay installations. For wiring from control or Relay rack upto Cable termination rack for outdoor circuits i.e signal and point. From tagblock to tagblock (except Signal and Point) From tagblock to tagblock For Signal and Point) For wiring of track relays from MDF

Note : Busbar conductors shall be so chosen that voltage drop is not more than 0.5% of busbar voltage between battery terminals & busbar in equipment room.

4.

CONSTRUCTION Construction of a typical 30 core, un-screened, armoured cable is shown below:

Conductors

PVC Armour Outer Sheath

SIGNALLING CABLE

PVC Inner Sheath

Core

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CONDUCTOR Circular conductors are used for Railway Signalling applications. The dimensions, nominal weights and resistance of conductors is shown in Annexure ‘A’ ( Page 55 ).

II.

INSULATION Conductor

Insulation PVC compound covering is provided on conductors for electrical isolation between them. Insulation should be free from any joints or repairs. It shall fit closely on the conductor but not adhere to it so that it is possible to remove it easily without damage to the coductor. The insulation resistance of each core shall not be less than 5.0 Megaohm /kilometre at 50 deg.C. For details see Annexure ‘D’ at page No.58. The average thickness of the insulation is shown in Annexure ‘B’ ( Page no. 56 ). III.

CORE A core can be defined as an insulated conductor. Cores of cables shall be identified by different colours of PVC insulation. Colour scheme shall be as follows (CL3.2.5 of S. 6389 ) : 1 Core - Red, Black, Yellow, Blue or Red 2 Cores - Red and Black 3 Cores - Red, Yellow and Blue 4 Cores - Red, Yellow, Blue and Black 5 Cores - Red, Yellow, Blue , Black and Grey cores in each layer above shall be blue and yellow. Remaining

6 Cores and

-Two adjacent cores shall be grey.

For a single core in the centre of a multicore cable, red or black colour is used. For 2, 3, 4 or 5 centre cores the colours correspond to those specified for 2, 3, 4 or 5 core cables, respectively, as described above. Alternatively, the cores of cables with 6 cores and above may be identified by numbers 1, 2, 3, 4, 5......... printed indelibly at intervals of not more than 50mm. In that case the insulation of cores is of grey colour and printing of number is black. The core is numbered sequentially in clockwise direction, starting with number 1 for the inner layer. The numbers are printed in Hindu-Arabic numerics on the outer surface of the cores. The numbers are legible and consecutive number is inverted in relation to each other. SIGNALLING CABLE

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When the number is a single numeral, a dash is placed underneath it. If the number consists of two numerals, these are disposed one below the other and a dash is placed below the lower numeral. LAYING UP OF CORES The core of twin, three and multicore cables is laid up together with suitable lay. The outermost layer has right-hand lay and the successive layers are laid with opposite lay. The cores of a layer is cross each other. The sequence of the cores is maintained throughout the length of the cable. The recommended plan for lay up of cores upto 37 is shown at Annexure ‘C’ ( Page No. 57). Example: A typical laying of core of 30 - core cable is shown below. As shown in Annexure ‘C’, there shall be 3 layers in 30 pairs cable. Lay up shall be 4 - 10 - 16 i.e. first layer, second layer and third layer shall have 4, 10 and 16 cores, respectively.

First Layer Second Layer Third Layer Colour Scheme Colour scheme of a typical 30 - core cable is shown below: G G G G G G G G G G G YR G G G G BL B G G G Y BL G G G BL G Y IV.

LEGEND R Y BL B

- Red - Yellow - Blue - Black

PVC COVER A PVC covering called inner sheath is applied over cores for protection of cores from armour.

V.

ARMOUR One layer of armouring of aluminium or galvanised mild steel wires is applied for protection. Armouring shall be applied over the insulation in the case of single core cables

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and over the inner sheath in case of multicore cables. Wire armouring is provided upto 9 cores. Above 9 cores armouring can be of wires or strips. VI.

OUTER PVC COVER A PVC cover is applied for protection from water penetration. It is also called outer sheath. Galvanised steel strips armouring is not used in up to 9 core cables.

5.

CABLE LAYING

5.1

Storing and Transportation of Cable • • • • • • •

5.2

Cable drums shall not be stacked on flat side. Suitable stoppers shall be placed for stability of the drums. Cable drums shall have easy access for lifting and moving. When rolling the cable drum either for unloading or transportation, the drum shall always be rotated in the direction of the “arrow” which is marked on the drum. The drum shall not be rolled over objects that could cause damage to the protective battens of the cable. When unloading is carried out from the vehicle the drum shall not be dropped on the ground directly to avoid damage due to impact. Fork lifter or ramp shall be used. During all stages of storage, it is essential that the ends of the cable are effectively sealed by end cap or in any other approved manner to avoid water entry into the cable. It is desirable that cable drums are stored in covered shed to protect against direct exposure to sun. Planning

•

While planning for cabling on a route, the number of conductors required, depending upon the circuits required should be first determined. Recommended core sizes as per specifications shall be used.

•

Adequate spare conductors to a minimum of 20% of the total conductors used shall be provided for in each main cable up to the farthest point zone, beyond this there should be a minimum of 10% spare conductors of the total conductors used. No spare conductors are required if the total number of conductors used is 3 or less.

•

Where a number of cables have been laid along a route, the circuits shall be so distributed that cables can be disconnected for maintenance purpose with the least possible dislocation to traffic. Line wise and, if necessary, function wise cable shall be provided. Auxiliary signals shall be taken in different cables.

•

After deciding the size and the number of conductors in the different types of cables to be used on a route, a foot survey along the track should be done to determine the best route for the cable.

•

The route shall be shown clearly on a cable route plan showing the actual alignment of track, giving offsets from permanent way or permanent structures. The diagram should indicate the various road and track crossings, crossing with power cables, water and sewage mains and other points of importance. It is

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preferable to chart the route on a route plan on which the existing routes of power cables, etc. are shown. Changes, if any, should be incorporated in the chart/plan. •

Cable route plan shall also be approved by Engineering and Electrical departments.

•

As far as possible, low lying areas, platform copings, drainages, hutments, rocky terrains, points and crossings, etc. should be avoided.

•

Separate cables of suitable size shall be laid for point operation.

5.3

Paying out of the Cable

•

For paying out cables, the cable drums shall be mounted on the cable wheels. It should be ensured that no kink is formed while paying out the cable. The drum on the wheel shall be brought to one end of the trench and the end of the cable freed. Cable should be laid along the trench. A party of labourers shall move along the trench carrying cable at suitable intervals so that the cable is not damaged due to dragging along the ground or bent unduly. Before the cable is laid in the trench, a visual inspection of cable shall be made to see that there is no damage to the cable. It shall be tested for insulation and continuity of the cores. Thereafter the cable shall be laid into the trench. Record of insulation and loop resistance must be maintained.

• • •

• • • • • •

In cases where the wheels are not available, the drum shall be mounted on an axle at one end of the trench and cable paid out and carried by labourers. In no case shall the drum be rolled off on to the road for laying the cable and the cable dragged on the ground for laying purposes. Whenever mechanised equipment is used, the work shall be carried out by a trained operator under the supervision of SE/JE (Signal) incharge of the work. Where the cable drum is in damaged condition the cable may be placed on a horizontal revolving platform. In no case shall the cable be unwound by taking off from the side of the drum as this will cause formation of twist in the cable. Paying out of cable should be done by rotating the cable drum and not by pulling the cable with excessive force.

5.4

Laying cable above ground

•

In AC electrified areas cables shall be laid underground only. Signalling cables for out door circuits should not normally be laid above ground. In exceptionable cases where it becomes unavoidable, the following precautions should be taken: (i) The cable should be suspended in wooden cleats, from cable hangers or in any other approved manner so that no mechanical damage occurs to the cable even under exposed condition. (ii) The cable supports shall be so spaced as to avoid

(iii) In station yards, cable shall be laid in suitably

SIGNALLING CABLE

sag.

protected ducts.

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(iv) Indoor signalling cable should normally be laid on ladders, channels or in any other approved manner. The cable should be neatly tied/laced. 5.5

Underground cable

Cables may be laid underground, either in trenchs, in ducts, in cement troughs, in pipes or in any other approved manner. 5.51

Laying the Cables in ducts

•

RCC or any other approved type of ducts may be used for laying the cable.

•

The ducts shall have suitable covers.

•

The ducts shall be of such design as to prevent water collecting in the duct.

•

When cables are laid in rocky area, it is desirable to protect them with split RCC ducts of suitable design.

•

Where it is necessary to take the cable between the tracks, it shall be carried in trunking kept sufficiently below the ballast level.

•

Where several cables of different categories have to be laid in the same trench, they shall be placed as far as possible in the following order starting from the main track side, so that in the event of failures the maintenance staff may easily recognise the damaged cables: i) Telecommunication Cable ii) Signalling Cable or Cables iii) Power Cable

RAILWAY TRACK TELECOM. CABLE SIGNAL CABLE BRICKS POWER CABLE •

Cables belonging to the Department of Telecomm. or the Electrical Department must not be laid in the same trench along with Signal & Telecom. cables. A distance of approximately 10 cm. must be maintained between telecommunication and signalling

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cables. The signalling cables must be separated from power cables, carrying more than 110 volts, by a row of bricks between them. 5.52

Laying

Cable shall be laid generally as per instructions given. However, special precautions to be taken in the station yards etc. where a number of other utilities may be existing, may be detailed in a joint circular issued by the Civil Engineering, Signalling and Electrical departments of the Railway. •

The cable laid parallel to the track shall normally be buried at a depth of 0.80 metres from ground level while those laid across the track must be 1.0 metre below the rail flanges. However, in case of rocky soil, the depth may be reduced suitably. When it concerns the laying of tail cables which serve the track apparatus, etc, the depth should not be less than 0.50 metres. In theft-prone areas the cables may be laid at a depth of 1.2 metre with anchoring at every 10 metre.

•

The width of manually made cable trenches should be commensurate with number of cables. The minimum width shall be kept as 0.3 metre. The bottom of the cable trench should be levelled and cleared of any sharp materials. In the soft ground, the cable should be laid at the bottom of the trench previously levelled. In the rocky ground, the cable should be laid on a layer of sand or sifted earth of 0.05 metre thickness previously deposited at the bottom of the trench. In both the cases the cable should be covered with a layer of sand or sifted earth of 0.10 metre thickness and thereafter a protective cover of trough or a layer of bricks should be placed.

5.53

Cable Crossing

•

When a cable has to cross the track, it should be ensured that:I) The cable crosses the track at right angles, ii) The cable does not cross the track under points and crossings, and iii) The cable is laid in concrete/GI/CI/PVC pipes, approved manner while crossing the track.

•

suitable ducts or in any other

Wherever practical, the cable may be taken underground across the drain bed at a suitable depth for crossing small culverts with low flood level.

When cables have to cross a metallic bridge, they should be placed inside a metallic trough which may be filled, as an anti-theft measure, with sealing compound. The cable should be supported across the bridge in a manner which would involve minimum vibrations to the cable and which will facilitate maintenance work. Adequate cable length to the extent of 2 to 3 metres shall be made available at the approaches of the bridge. • Cable markers wherever provided should be placed at suitable intervals and at diversion points. • While laying the cables in accordance with the above instructions, the following instructions should be adhered to for the safety of the track: i) Outside the station limits, the cables should generally be laid at not less than 5.5 metres from the centre of the nearest track. SIGNALLING CABLE

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ii) Within the station limits, the trenches shall preferably be dug at a distance of not less than 3 metres from the centre of the track, width of the trench being outside the 3 metres distance. iii) At each end of the main cable an extra loop length of 6 to 8 metres should be kept. •

It is desirable that the excavation of the trenches is not done in long lengths and does not remain uncovered for a long period. It is preferable that cables are laid and refilling done on the same day.

•

Back filling of the trenches should be done properly. The earth excavated shall be put back in the trench, rammed and consolidated. During excavation, the earth of the trenches should not be thrown on the ballast. The earth should be thrown by the side of the trenches away from the track. In places where cables are to be laid within 1 metre from sleeper end, digging beyond 0.50 metre shall be done in the presence of an official from Engg.Dept., and the laying of the cable and refilling of trench should be done with least delay. Cable joints of approved type shall only be used. The work shall be supervised at site personally by an official of the Signal and Telecommunication department not below the rank of a Sectional Engineer/Junior Engineer(Signal).

• • • •

6.

WIRING OF SIGNALLING CIRCUITS

The following instructions are to be followed for carrying out wiring of Signalling Circuits. •

Wiring or alteration of signalling circuits shall be in diagrams.

•

Alternations to existing circuits may be resorted to at site only in emergency cases under the direct supervision of an officer. In such cases the alteration should be immediately advised to approving authority for approved wiring diagrams.

•

“As made” circuit diagram must be submitted by divisions to HQs. on completion of alterations to wiring and the final diagram should be as per actual wiring at site. This should be signed by the Section Engineer (Signal) carrying out the works and the officer opening the works.

accordance with approved circuit

6.1 Principles of Wiring • • • • •

Wiring between any two points shall be done in one length and no joints shall be made in any wire run. Wire runs shall be as short as possible. Care should be taken to avoid damage to the conductor while peeling off insulation. Stripper-cum-cutter of approved design shall only be used. All wires in a wiring bunch shall be properly terminated and no loose wire shall be left in the bunch without being terminated. Conductors and terminals shall be cleaned before making connections. Bunching tape & button should be used. Wires shall not be pulled out after lacing of wires. This can damage insulation of other wires. Adequate spare conductors to a minium of 20% of the total conductors used shall be provided for each main cable upto the farthest point zone. Beyond this there should be a minium of

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11

10% spare conductors of the total conductors used. No spare conductors are required if the total number of conductors used is three or less.( CL 9.2 of S36-87). Suitable conductor sizes shall be used to ensure that the voltage drop on line is not more than 10% (CL 9.3 of S 36-87). When cables are to be terminated or jointed underground in outside location boxes, these shall be brought up over the ground and terminated or jointed in water-tight junction boxes (CL 9.4 of S 36-87). At least two cores cable shall be provided between two ends of the yard to cater for telephone communication for maintenance purposes in non-RE area (CL 9.5 of S 36-87).

6.2 Wiring Practices The following practices shall be adopted for wiring: • • • • • • • • •

The return negative of various circuit elements must be separately terminated at the negative busbars. In no case a common return (negative) wire shall be used. All terminals shall be screwed tight and washers shall be used under the screw head of terminal nuts. Ends of wires shall be bent round the terminal in clockwise direction unless an eyelet/lug is used. Precautions shall be taken to prevent kinks and twists in the wires used. If there is any kink it must be removed. Insulations must not be damaged and must be kept free from oil, grease, acid and alkali. When cables/wires are taken through a duct in the wall, proper PVC pipes must be provided or any other approved method should be adopted. The duct for wiring should not be closed on either side. Rodents may settle in the closed duct and damage the wiring. As a safeguard against rodent attack, the wiring from Circuit Controller/Lever Lock to the relay room should be taken through a cable without removing the PVC sheath and armour, in lieu of 16/0.2 mm. PVC wires. Terminal Blocks to RDSO design SA 23756 (Adv/Alt.2) shall only be used.

•

ARA terminals are to be properly fixed in vertical/ horizontal rows. Terminals of any special design to be used with specific approval of CSTE.

•

The terminals should be fixed on standard Relay Rack.

6.3

Wiring Materials The following wiring materials shall be used for different types of relay.

6.3.1 Wiring inside one rack (Intra-rack wiring) for shelf type and plug-in-type metal-to-carbon contact relays (Q series): •

3/0.75 mm wire shall be used for wiring of Shelf type relays and 16/0.2 mm wire shall be used for wiring of Q Series relays. Wiring between Shelf Type relay and Q Series relays shall be done with 16/0.2 mm wire.

•

The eyelets shall be connected to the wire on terminal by hand operated crimping tool.

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•

Appropriate eyelets and crimping tools shall be used.

•

For terminating the 16/0.2 mm wires to the connectors of plug-in-type relays (Non-proved type) with metal to carbon contacts, the wire head shall be first tinned, inserted into the connector and crimped. The wire shall again be soldered at the connector.

6.3.2 Wiring from one relay rack to another relay rack (Inter rack wiring) using metal to carbon contact plug-in-type and shelf type relays: •

Multicore (or alternatively single core) unarmoured cable of 1.0 mm (S-76 or S-63) shall be used for wiring. Intermediaries like terminal blocks, tag blocks etc. shall not be used.

•

If the use of intermediate terminal block/tag block is unavoidable, the same shall be of standard design of any type conforming to IRS specification No. S71/87. Spare contacts need not be wired.

6.3.3

Wiring of proved type (Metal to Metal contact) Relays:

For rack to rack/IDF wiring 60/0.6 or 40/0.6 mm cable shall be used. For wiring from rack to cable termination rack 60/1.0, 40/1.0, 24/1.0 mm size wire shall be used. Size of conductor shall be chosen based on circuit current to be carried by it. 1/0.6 and .1/0.1 mm cable shall be used for tag block to tag block wiring. 6.4 Essentials of wiring in relay rooms and location boxes. •

All wiring used in the Cabin and Locations shall be done in a neat manner so that the wiring does not in any way prevent the proper functioning over working parts and is easily accessible for maintenance (CL 10.2 of S 36-87).

•

At all locations and cabins wire entrance of adequate size, conveniently located for ease of approach to terminals and other equipment so arranged as to protect the wires from mechanical injury, shall be provided. Such wire entrance shall be plugged and sealed with suitable compound after the wiring is completed (CL 10.4 of S 36-87).

•

Relay to Relay wiring on the same rack should as far as possible be direct without intermediaries like tag blocks/terminals(CL 10.5.2 of S 36-87).

•

Identification Marker for Identifying the terminals and tags shall be provided at each terminal to identify the circuits for which it is used (CL 10.6 of S 36-87).

•

Relay racks shall have sufficient capacity to take additional equipment to the extent of 15% of equipment provided to permit additions and alterations (CL 10.7 of S 36-87).

•

Charts showing the positions of relays on relay racks and contact arrangement of relays indicating the spare and used contacts shall be prepared and kept in the cabin (CL 10.8 of S 3687). Marking and Labelling SIGNALLING CABLE

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•

Conductor marking and labelling shall be done by means of plastic ferrules with embossed letters. Alternatively, a chain of pre-embossed plastic ferrules can also be used.

•

Terminal numbers should be properly marked.

Bunching & Lacing •

All the inter-relay wirings and inter rack wiring shall be neatly bunched in a circular shape.

•

Black twine or plastic strip of suitable design shall only be used for lacing of the wires.

NOTE : In case power is to be fed to any outdoor equipment through common feeders from outside locations, a ring main shall be provided preferably in different cable and on different route, so that the failure of a part of the feeder or a fuse blowing off shall not affect the feed to the outdoor equipment in the whole yard (CL 12.5 of S 36-87).

6.5

Earth connections

•

Separate earth shall be provided for each block instrument at a station.

•

The resistance of earth for signalling circuits shall not exceed 10 ohms. If it is not possible to reduce the earth resistance below 10 ohms additional earth may be provided in parrallel.

•

Where more than one earth is used, the distance between earthing pipes shall not be less than 3 metre. The conductor leading to these earthings shall be electrically insulated from each other throughout and also from metallic structures connected to different earths. Method of obtaining Earth •

Earthing arrangement shall normally consist of one or more galvanized iron pipes of not less than 38 mm internal diameter and not less than 2.5 metre in length with a spike at one end and a lug at the other for connecting the earth lead or galvanized iron/steel rods of not less than 16 mm dia or copper rods of not less than 12.5 mm dia and of not less than 2.5 metre length. While the pipe is embedded vertically the rod electrodes are driven vertically in the ground .When a rocky soil is encounterd at a depth of less than 2.0 metres of the length of this electrode the electrode may be buried inclined to the vertical the inclination being limited to 30 degrees from the vertical. Earth electrodes shall not be buried in a position likely to cause an obstruction or where it is likely to be damaged.

•

The resistance of these electrodes in a soil of uniform resistivity decreases with depth but there is little to be gained by driving the rod to more than 3 to 3.5 metres. Also the decrease in the resistance with increase in rod diameter is not significant. It is therefore recommended to use the rod electrodes of such diameters as can easily withstand the strain of driving.

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Earthing Leads •

Earth wires shall be protected against mechanical damage and possibility of corrosion particularly at the point of connection of earth electrode.

•

The earthing lead shall be a mild steel flat of size 35mm x 6 mm. or copper wire of 29 sq.mm cross-sectional area (19 strands of 1.4 mm dia). In case the conductor is buried underground, it shall be protected from corrosion by an application of suitable anticorrosive paint or bitumen or varnish. The length of the cable so treated shall extend half a metre beyond the buried length.

•

The earthing lead shall be soldered or crimped on a lug which shall be bolted to the earth electrode.

6.6

Soldering Connections

6.6.1 Staff working in the installation and maintenance of S&T equipment shall be conversant in use of soldering iron/gun for making good soldering joints. 6.6.2 Care shall be exercised to avoid dropping of solder particles and wire clipping on adjacent terminals and apparatus. 6.6.3 In addition to soldering irons of adequate wattage for the type of work done, the following shall be on hand : a. A small file for dressing the soldering tip. b. A fire-proof pad for wiping the tip. c. A mica sheet of adequate size or a suitable stand

for soldering iron.

6.6.4 Electrical soldering irons shall be switched off when not in use over extended period. 6.6.5 While making a soldering joint, the surface shall be thoroughly cleaned, fluxed and tinned. 6.6.6 Use of too much solder shall be avoided to prevent lumpy connections. 6.6.7 Soldering iron shall not be held on the wire connection for too long to avoid damage to insulation. 6.6.8 Imperfect joints are the result of any one of the following causes, which should be avoided: a. Soldering iron not sufficiently hot. b. Soldering iron held on the connection for

insufficient time.

c. Unclean terminal or wire d. A solder of improper composition or inferior 6.6.9

fluxing

agent.

A newly soldered connection shall not be disturbed till the solder has thoroughly cooled.

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6.7 • • • • • • 6.8 • •

15

Wire Termination While terminating wires, care shall be taken to bend the wire in clock wise direction. Wire strippers shall be used for the purpose of stripping off the wire insulation. Cutting pliers shall not be used for this purpose. Washers and check nuts shall be used whilst fastening. Not more than two wires shall be terminated on one terminal, if avoidable. Multi-strand wires shall be terminated on terminal lugs and covered with insulation sleeves. Wires of cable shall be neatly terminated and properly bunched. Connections from and between Secondary cells For inter connections between secondary cells, standard lead strips, supplied by the manufacturer shall be used. Flexible multi-strand copper cable PVC insulated single core of nominal cross sectional area 10 Sq.mm. (7/1.4 mm.) shall be used for wiring between secondary cells to battery chargers/ terminal board. The ends shall be crimped with a copper ring conductor (eyelet) and then terminated. However, the voltage drop between battery terminal and bus bar shall not exceed 0.5 V under full load condition.

The following colour code of wires shall be used: a) Between Battery charger and and Black for

Red for positive

Batteries/ Terminal Board

negative b) Earth connections

Grey

c) AC side wiring

Blue for neutral and Yellow for phase.

6.9

Tools for Wiring

1. 2. 3. 4.

Stripper and cutter suitable for wires 0.6 sq.mm to 1.5 sq.mm. and 2.5 sq.mm. Crimping tool. Soldering iron or Soldering Gun of suitable wattage. Socket set consisting of 19 sockets and other accessories for maintenance of point machine. Socket driver tester set. Screw driver set Seven piece nut driver set of sizes 3/16”, 1/4”, 1/325/16”, 1”, 3/8”, 7/15” and 1/2”.CR 5, 6, 7, 9, 10, 11, 12 mm. for maintenance of Block Instruments.

5. 6. 7.

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16

JOINTING OF CABLE Since the length of the cable in a cable drum is 500 metres, so when more than above length is required, two drum lengths of cable are to be jointed. This type of joint is called straight through joint.

7.1

TOOLS REQUIRED FOR CABLE JOINTING

1. Crowbar ] 2. Spade ] for digging of pit 3. Shovel ] 4. Tent (complete set): for protection of joint 5. Megger (500V) : for cable testing 6. Tool Box : for keeping tools 7. Hack Saw : for cutting steel armour 8. Cutting Plier : for removing armour etc 9. Wire Nipper : for removing wire insulation and cutting the conductor. 10. Hack-Knife : for marking,cutting and sheath etc. 11. Clasp-Knife: for cleaning the sheath, cutting thread etc. 12. File Rasp : for removing the rough surface 13. File ( Triangular) : for smooth finish 14. Screw Driver : for terminating cable 15. Hammer Large ] 16. Hammer Small ] for cutting 17. Chisel ] 18. Adjustable Spanner : for tightening of nuts 19. Brass rule : for measurements 20. Dividers : for marking etc 21. Shave hock : for removing plumbing old joint. 22. Blow Lamp : for plumbing, heating etc. 23. Soldring Iron : for soldring the twisted joints 24. Measuring tape : for measuring the cable length. 7.2

metal from

CABLE JOINTING MATERIAL

1. Jointing Box 2. Jointing Kit Emery Paper 4. Resin Core 7. 3

opening of

5. Kerosene Oil 6. Copper Wire

3. PVC Sleeves

7.

8. Fire Wood

M - SEAL JOINT

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At the site of the cable jointing, a pit is to be dug up, the dimensions can be 51X 31 X 31 and a tent is to erected over the pit. Other necessary precautions should be taken to prevent entry of water in to the pit in the event of rain etc. M-seal Jointing is a technique for straight through joints. In this type of joint an epoxy Resin is mixed with another liquid called Hardener. The resultant compound is poured into the mould fixed at the jointing portion.

7.4

JOINTING PROCEDURE

1.

Cut and maintain the length of PVC outer and inner cover, armour and requirement according to the size of the kit.

sheath as per

2.

Keep both ends face to face leaving some space between them. This space is called jointing space. Jointing shall be started from first conductor of inner layer.

Insert the PVC sleeves on one end of the cable conductor and nip the insulation of both end cable conductor about 1”. Twist both conductors. Now solder the tip of twisted conductors. Bend the twisted and soldered portion to the opposite side of the PVC sleeve end, and draw over the PVC sleeve such that the bare portion of the twisted and soldered conductor is covered completely. Similarly, all conductors shall be jointed. 3.

The PVC sleeves of adjacent conductors shall be inserted on alternate sides to reduce the bulging at the centre. Now joint all conductors in sequence. Bind the conductors together with PVC tape to obtain sufficient clearance between sleeves and mould.

4.

Abrade the sheath and armour with emery paper and clean them thoroughly with a cloth soaked with mould adhesive-cum-solvent. Make earth continuity connection by tightly binding earthing wire to sheath and armour with binding wire. Seal bedding of cable with putty.

5.

Cut cable entry portions of the mould to match the diameter over outer sheath. Place bottom half of mould in position and support it by bricks etc. Ensure sufficient clearance between conductors and mould.

6. Stir the cable jointing compound to obtain a homogeneous mixture. Add hardener and mix both to a uniform mixture for about 2-3 minutes. Allow air bubbles, entrapped while mixing, to come up and remove them by pricking before pouring. If there is more than one container, mix and pour one by one and not all at a time. Ensure that only similarly marked and colour labelled containers of cable jointing compound and hardener are mixed together.

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7.

Liberally apply mould adhesive-cum-solvent on the flanges of both halves of the mould. Immediately place top half in position and press the halves with clips.

8.

Mix M-Seal putty and seal cable entry portions. If necessary, apply on the flanges also and leave undisturbed for about 15-20 minutes till putty hardens.

9.

Finished M seal cable joint should be protected from mechanical damage by covering it with sand and bricks. In case it is to lie in the open or in cable trenches or cable tunnel liable to heavy trampling, some form of metal protection over the joint is recommended.

8.

TERMINATION

•

Main cable and Tail cable shall be serially numbered.

•

All cables shall be taken vertically in the location boxes with armour. The armour shall be cut once, after taking the cable inside a location box. The de-armoured cable portion shall be taken vertically and laced to a ladder. Cables coming from each side shall be grouped separately.

•

Cables shall be terminated in horizontal/vertical rows. Cables commencing from relay room side shall be terminated on top side of the terminals and cables from the far end shall be terminated on bottom side of the terminals. All tail cables shall invariably be terminated on the bottom sides of the respective row.

•

Approved type of terminal shall only be used for termination. The terminals shall be fixed vertically in horizontal rows on hylam strips.

•

On cable termination rack (CT-Rack), cables shall be terminated on 8-way terminal strips procured from RDSO - approved sources.

•

All conductors of main and tail cables shall be terminated serially on terminals even if they are spare. Allocation of cable cores should be done in such a fashion that spares are available from CT-Rack to last location as far as possible.

•

The cables shall be suitably terminated in all location boxes such that far end functions are on the top row and near end functions on the bottom row.

•

Before termination, cables shall be tested and record shall be maintained at all installations.

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19

TESTING OF CABLE Signalling cable must be tested for continuity and insulation. The tests should be carried out before and after cable laying. For maintenance purposes these tests shall be performed after every one year for main cable and after every six month for tail cable.

9.1

TESTING PROCEDURE Before commencement of cable testing necessary disconnection from traffic shall be obtained. All working circuits and power supply shall be disconnected from the cable at both ends. Communication between the ends of cable under test shall be established by magneto telephones with other cable which is not under test if possible, otherwise by VHF sets. Competent staff, required instruments and material shall be available at both the ends. Testing shall be carried out when conductors and insulated parts like terminal blocks are clean and dry. Cable conductors shall be shorted/earthed momentarily to discharge the accumulated charge, if any, before the commencement and after the end of testing.

9.1.1 CONTINUITY TEST TOOLS & EQUIPMENTS REQUIRED 1. Multimeter 2. Wire nipper 3. Screw driver set Multimeter

E

1 2 3 4 5 6

Earth 1 2 3 4 5 6

LOCATION A

LOCATION B

This test is carried out to confirm that the core under test is either showing break between both ends or continuous. Testing can be commenced as per the following procedure:

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A.

Set the knob of multimeter to check resistance at 200 ohm range. (at Location A)

B.

Connect one probe of multimeter to earth and other probe to the end of cable limb as shown in above figure.

C.

Instruct staff at the other end ( at Location B) to connect earth to same limb of the cable. Deflection of multimeter needle shows that limb is OK, otherwise there is a break in limb under test..

D.

Repeat the procedures (b) and (c) for testing of other cores.

9.1.2. INSULATION TEST TOOLS AND INSTRUMENTS REQUIRED 1. Insulation Tester (Megger) 500V DC 2. Wire nipper 3. Screw Driver set. This test is carried out to measure the insulation resistance of the cable under test. insulation resistance measured between (1) conductor to conductor, called cross insulation, and (2) conductor to earth. Procedure is as follows: (1)

Coductor to conductor (Cross Insulation) Conductor A Line MEGGER 500 V DC

•

Earth • Conductor B

I) A 500 V Insulation Tester ( Megger ) shall be used for this test and kept at one end of the cable under test. II) Conductors for which cross insulation is being measured shall be connected to at Line and Earth terminals of megger as shown in figure. III) Now rotate the handle of megger or press push button of megger. The reading of meter will show the cross insulation between the conductors. Insulation reading shall be recorded after applying the test voltage for about a minute till a steady reading is obtained. IV) Replace the conductor connected to the earth terminal of megger by other conductor of cable and take measurement. V) Repeat the process IV for remaining conductos. VI) Now connect next conductor to Line terminal of the megger & connect the remaining conductors one by one to earth terminal of the megger and take measurements as per procedure III , IV & V. SIGNALLING CABLE

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VII) Record the measurements in the prescribed format as shown below.

CABLE MEGGERING CHART 1 1 X 2 X 3 X 4 X 5 X 6 X 7 X 8 X 9 X 10 X 11 X 12 X

2

3

4

5

6

7

8

9

10 11 12

X X X X X X X X X X X

X X X X X X X X X X

X X X X X X X X X

X X X X X X X X

X X X X X X X

X X X X X X

X X X X X

X X X X

X X X

X X

X

SIGNATURE II)

Conductor to Earth Insulation

LINE MEGGAR 500Volt

EARTH

CONDUCTOR

EARTH

I) By this we can measure individual insulation of conductors w.r.t. earth. II) Connect conductor under test to the Line terminal of the megger. III) Connect earth terminal of the megger to the earth. IV) Rotate the handle of megger or press push button of megger. The reading of meter will show the insulation resistance of the conductors. Insulation reading shall be recorded after applying the test voltage for about a minute till a steady reading is obtained.

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V) Replace the conductor at Line terminal of the megger by another conductor under test and repeat as process IV. VI) Record the mesurements in following format: Sr.No.

CONDUCTOR No.

INSULATION RESISTANCE

1 2 3 4 5 6 NOTE : These measurements shall be recorded in two copies. One copy each shall be kept in SE(Sig.) and Sr.DSTE’s office. Insulation Resistance should not be less than 5 Mega ohm per kilometre at 500C, irrespective of the size of conductor. For converting measured value of insulation resistance at any temperature to insulation resistance at 500C, multiplier constant is given in the table at page No. 49 Annexure ‘D’. Example: Insulation resistance of 5 mega ohm/km at 50 degree centigrade is equivalent to 500 mega ohm/km at 20 degree centigrade with multiplier constant 0.01. 9.2

GENERAL INSTRUCTIONS 1. All conductors of signalling cable must be tested for the insulation resistance every year for Main Cable and after every 6 months for Tail Cable. 2. Low insulation of cable will lead to inadvertent energisation or de-energisation of circuits. Check for insulation values periodically enables to ensure integrity of circuits. 3. A comparison of test results of successive tests carried on a cable under similar conditions will give an indication of the trend towards deterioration or otherwise of insulating material over a period of time. 4. If a sudden fall in the value of insulation is observed during the test, the cause should be investigated and immediate action shall be taken to repair or replace the defective cable. After completion of cable testing: •

Ensure that all conductors have been reconnected properly.

•

Test the functions of Points, Tracks & Signals connected through the cable for their correct response.

•

In case of signals, aspect should be verified personally.

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•

In case of points, verify positions at site.

•

Check whether any polarity of any feed taken through the cable has got earthed inadvertently.

Insulation of signalling cable can be measured by means of Earth Leakage Detector. Description of a typical multi-channel Earth Leakage Detector as per RDSO- specification No.RDSO/SPN/256/1971 is given on next page.

9.3

MULTI - CHANNEL EARTH LEAKAGE DETECTOR

Introduction It is an equipment which measures insulation of the bus bar cable w.r.t. earth and announces through audio-visual alarms if the value of the insulation drops below the set value. It is of 2, 4, 6, 8, 12 or 24 channels. All the channels of the equipment continuously monitor the insulation of the cable and an alarm is actuated along with a visual indication when the leakage value reaches the preset value. The audio alarm is common for all channels while the visual indication is separate for each channel. Each channel is in the form of a module thus making each module an independent unit which works alongwith the main unit. The main unit has a rotary switch for switching on a particular channel for reading leakage on an analogue meter and for switching certain controls which are common to all channels. Technical Specifications AC Mains : 110V/230V/50 HZ AC Signalling supply : 110V/24V AC and 24V/60V/110V DC or as required by user Leakage setting range: 50K, 100K, 150K, 200K, 500K & 1M ohms. Controls & Indications Normal

: Green LED glows when the insulation of the set limit

Fault : Red bulb glows, indicating the insulation limit. The Normal light extinguishes. Reset the unit Counter

: Micro push switch, when pressed after the

connected channel is within the has reached the set leakage fault is removed, brings

back to Normal Mode. : Counts number of reset operations.

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Simulated : An inbuilt testing facility in the instrument Leakage to check its working by simulating leakage used with Simulated Leakage Select on individual module. Power unit.

: Red neon on main unit indicates that

Meter : Selectable through a rotary switch for a reads insulation value. Mute Buzzer

: Mutes the buzzer announcing fault, indicating that fault is acknowledged.

Channel

: Used in conjunction with panel meter and Select

10.

power is connected to the particular channel

Simulated Leakage Test.

PRECAUTIONS

In order to safeguard against any unsafe situation arising due to wrong connection of cable conductors during insulation check or changing of defective cable cores, the following instructions are issued with immediate effect in respect of all installations already in service and those to be commissioned in future: 10.1

10.2

10.3 10.4

10.5

No alteration in any cable core, either working or spare, in any installation should be done by a maintainer independently. Changes where necessary to rectify a fault or for any redistribution of cores shall be done only in the presence of and in conjunction with a Section Engineer (Signal). The concerned SE (Signal) shall ensure that a disconnection memo is issued for the equipments controlled by the cable before any such work is undertaken. Proper communication and co-ordination between the staff at either end of the cable must be maintained either by telephone or by portable VHF to ensure that the connections are made correctly. Terminal markings shall be legible and core markers shall be available at the cable terminations identifying each core. The length of the cable core leading to the individual CLS transformers mounted inside the colour light unit must be to the exact length such that the conductor leading to the Red aspect transformer can not be shifted to the CLS transformer of less restrictive aspect. The tail cable from the location box should be taken direct to the transformer and there shall be no other termination or joint between the transformer connection and the cable termination in the location unit. Correspondance between a lever/knob and the actual aspect at the CLS unit must be verified by the Maintainer and Section Engineer (Signal) during their maintenance/inspections and invariably after every occasion when cable cores have to be changed.

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ANNEXURE “A” “ DIMENSIONS NOMINAL WEIGHTS & RESISTANCE OF CONDUCTOR” Nominal cross sectional area

No.of wires in conductor

mm. sq.

-

Dia Of Wire

Tolerance on dia. of wires

Weight per Km.

Mm.

mm.

kg.

ohms.

Ohms.

ohms.

Resistan -ce per kilometer at 20 deg. C

Maximum resistance of each conductor per km at 20 deg. C.

1.00

1

1.13

+0.020

8.89

17.241

17.689

18.04

1.5

1

1.40

13.68

11.20

11.540

11.77

2.5

1

1.80

22.62

6.775

6.978

7.118

2.5 4 4 6

3 1 7 1

1.06 2.24 0.85 2.80

23.55 35.03 35.28 54.74

6.664 4.375 4.414 2.800

6.843 4.506 4.591 2.884

6.980 4.596 4.683 2.942

10

7

1.40

97.47

1.627

1.660

1.693

16 25 35 50

7 7 7 19

1.70 2.24 2.50 1.80

+0.025 -0.015 +0.035 -0.015 +-0.016 +0.045 +0.012 +0.055 -0.035 +0.025 -0.015 +0.030 +-0.045 +0.050 +0.035

143.70 249.8 310.70 437.80

1.104 0.6357 0.5103 0.3633

1.124 0.6484 0.5205 0.3706

1.149 0.6614 0.5309 0.3780

ANNEXURE ‘B’ “AREA & THICKNESS OF CONDUCTOR” Nominal Area Conductor in mm. Square 1.0 1.5 2.5 4.0 6.0 10.0 16.0 25.0 35..0 50.0

SIGNALLING CABLE

of Nominal thickness of Insulation Single Core Multi Core in mm. in mm. 1.5 0.8 1.5 0.8 1.5 0.9 1.5 1.0 1.5 1.0 1.5 1.0 1.5 1.0 1.5 1.2 1.5 1.2 1.5 1.4

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NNEXURE ‘C’ “LAY UP OF CORES” No.of Cores 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

LAY-UP 2 3 4 5 6 1-6 1-7 1-8 2-8 3-8 3-9 3-10 4-10 5-10 5-11 5-12 0-6-12 1-6-12

SIGNALLING CABLE

No.of Cores 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

LAY- UP 1-7-12 1-7-13 2-7-13 2-8-13 2-8-14 2-8-15 3-9-14 3-9-15 3-9-16 4-10-15 4-10-16 4-10-17 5-11-16 5-11-17 5-11-18 5-12-18 0-6-12-18 1-6-12-18

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ANNEXURE ‘D’ MULTIPLIER CONSTANT FOR INSULATION RESISTANCE

Test Temp. ( in 0C ) 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Multiplier Constant 0.001 00012 0.0016 0.002 0.0026 0.0033 0.0042 0.0047 0.0063 0.006 0.01 0.0122 0.015 0.018 0.022 0.026 0.031 0.037 0.046 0.055 0.064

SIGNALLING CABLE

Test Temp. ( in 0C ) 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Multiplier Constant 0.080 0.100 0.120 0.140 0.170 0.195 0.225 0.260 0.300 0.340 0.380 0.430 0.480 0.540 0.600 0.670 0.750 0.820 0.910 1.00

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