Chapter – 4

Signalling Cable: Planning & Laying 4.1 Introduction 4.1.1 Scope of the Chapter

This chapter covers planning for cable (Quantity & core) and cable route; cable laying including protection, termination of cable.

4.1.2 Cables used in signalling installations

The cables used in signalling installations (out door), RDSO specification and the usage core-wise are given in fig.4.1:

Core & Cross section RDSO Specification Usage

2 Core X 25 Sq.mm IRS S 63/89 & IS 1554(Amdt.4) Power cable

6 Core X 1.5 Sq.mm IRS S 63/89 (Amdt.5) Tail Cable

12 Core X 1.5 Sq.mm IRS S 63/89 (Amdt.5) Tail Cable/LC Gate cct.

19 Core X 1.5 Sq.mm IRS S 63/89 (Amdt.5) Main Cable

24 Core X 1.5 Sq.mm IRS S 63/89 (Amdt.5) Main Cable

30 Core X 1.5 Sq.mm IRS S 63/89 (Amdt.5) Main Cable

2 Core X 2.5 Sq.mm IRS S 63/89 (Amdt.5) Track Cct lead connections

Fig. 4.1 Cable used in Signalling Installations

4.2 Determining requirement of cable

a) Requirement of cable conductors is to be determined depending upon the circuits run from CT room/Relay room to function. It is desirable to use separate cable linewise and if necessary; functionwise from relay room/CT room to facilitate easy testing of cable without much disruption of traffic (Para 15.3.3 of SEM Pt.II). A typical cable distribution plan is shown in fig.4.2 for information and guidance.

b) Cable size to be determined keeping spare conductors to a minimum of 20% of total conductors used in, each cable

working between the outermost facing points of the station and a minimum of 10% of the total conductors used in each cable working beyond the points area and up to outermost signals (Para 15.3.2 of SEM Pt.II).

c) A cable core distribution plan to be prepared for each installation.

d) The approximate cable requirement for a typical four line PI station using three pole lamp is shown in fig.4.3 :

Type of cable Double line Single line

Signalling Cable 24 Core 9 km 1 km

Signalling Cable 19 Core 10.6 km 2.4 km

Signalling Cable 12 Core 10.5km 12.7 km

Signalling Cable 6 Core 5.7 km 3.3 km

Power Cable 10 Sq. mm 8.6 km 7.7 km

Fig.4.3 Approximate cable requirement for a typical four line station

e) Numbering of cable to be done in ascending order from right hand

Side of the cable core distribution plan.

f) Style of numbering should be indicated with specific information, as for example 0112(4) here 1st two digit „01‟ next two digit 12 indicate 12 core cable and 4 in bracket indicate, number of spare conductor. All the cores of the cable should be numbered with

plastics markers. These markers should generally tally with the terminal numbers. g) Number of location boxes should be kept minimum and shall be as per typical cable distribution plan enclosed. For a

typical four line station with double distant signal the number of location boxes required are 32 approximate. h) It is preferable to install masonry or pre-fabricated goomty (approx. size 10‟ft.x10‟ft) at 500 m on both side of PI building

for maintenance ease and reduction in location boxes.

i) All cable core shall be terminated on ARA terminal in location boxes. In relay room/CT room, cable core shall be

terminated on “ARA or other approved Type” termination (Disconnection type preferable).

j) Cable should be laid in split DWC/RCC pipe or in a pre-casted duct from Home Signal to Home Signal and DWC/GI pipe on track and road crossings.

4.3 Cable Route Plan:

a) Foot by foot survey to be done along the track to determine best possible cable routes. Cable route plan is to be prepared showing the actual alignment of track giving offsets from P/Way and permanent structure. Diagram should include road and track crossing, crossing with power cables, water & sewage main and other points of importance.

b) Cable route plan thus prepared should also be approved by Engineering & Electrical department. c) Clearance from Maintenance wing of S&T to be obtained for cable route plan when alteration works/new works are

taken up on existing installations/in the vicinity of existing installations.

d) Cable Marker in regular interval shall be provided to identity the route. 4.4 Cable Laying 4.4.1 Cable laying in station section and beyond

a) Cables should be laid underground, either directly in the trench, in ducts, in cement troughs or in pipes. b) Main signal cable from relay room/CT room to Home Signal on either side shall be laid inside 6” dia split DWC/RCC pipe

at 1 m depth or in pre-casted duct. Laying in split pipe will reduce chances of cable damages due to outsider digging trenches in cable area. The RCC pipe have the required strength to withstand impact etc but it has no flexibility while laying in trenches which have some up or down in trench bed and lateral curves in trenches. Further, in long run due to soil settlement RCC pipe tends to develop cracks. DWC pipe have flexibility, longer life, light in weight and possess required mechanical strengths. Till RDSO issues specifications and list of approved firms, the supply of DWC pipe shall be taken as per specification given in Para 4.5 to ensure good quality. The approximate requirement of split pipe of 6” dia would be about 1.5 km per station.

c) There must be holes on the bottom of the split pipe for draining away water that may collect.

d) The track crossing, road crossing by main signal cables & tail cables shall be done through GI/DWC-HDPE pipe of 50 mm dia/75 nun dia at the depth of 1 meter below Rail flange (Para 15.12 SEM Pt.II). This depth shall be ensure to avoid cable cuts for various reasons. Cable in GI/DWC – HDPE pipe should crosses the track or road at right angle. It should not cross the track under points & crossings. Extreme care should be taken to ensure that outer PVC insulation and armouring of cable shall not get damaged while taking through pipes.

e) Cable shall be laid at depth of 1 m parallel to the track, for cables laid between Home Signal and at 1 m below rail flange

while track crossing and at 1.2 m depth for cables laid beyond Home Signals and Automatic Signal area, IBH & Level crossing gates.

f) For Safety of track, cable should be laid at 5.5. m from centre of nearest track in area outside station limit and 3 m from

centre of nearest track within station limit.

g) The width of the cable trench shall normally be 0.5 metre. A layer of shifted earth or sand or 0.075 m (3”) shall be spread over the ground before laying the cables. Also, cables shall be covered with shifted earth or sand of 0.075 m (3”) thickness.

h) Cable should be laid with ends having been sealed to avoid water entering through bare end and damaging the cables.

i) Laying the cables in ducts: i) In big yard, the cables may be laid in RCC ducts or brick channels with removable top cover.

ii) The location of cable duct should be such that due to derailment there is no possibility of damage of cable inside the duct.

iii) The area should not be a theft prone area. iv) There must be holes on the bottom of the duct for draining away water that may collect. v) The ducts shall have suitable cover.

4.4.2 Laying different cables in the same trench

a) Different cables in same trench can be laid in the following order from the main trackside, to facilitate recognition of

cable in urgency. i) Derivation cable for axle counter. ii) Signalling cables. iii) L.T. Power cable (less than 60 volts, if necessary) b) Power cables laid with other cables should be separated by brick continuously placed vertically lengthwise. c) Power cables of Electrical department & Telecom Cables of BSNL etc must not be laid in the same trench along with

signalling cables. d) 2nd Class brick should be used wherever required. 4.4.3 Paying out the cables

a) Cable drum shall be mounted on cable wheel. b) Wheel to be brought to one end of the trench. c) End of the cable freed and laid in trench; d) The cable wheel shall then be drawn along the road or track. e) A party of labour follow the drum and guide the cable from the road into the trench carefully. f) 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 purpose. g) Ensure no kink is formed while paying out the cable. h) Cable shall not be unfolded from the drum by keeping the cable drum flat on the ground and twisting the cables.

4.4.4 Cable laying on culverts & bridges

a) Cable laid along culverts shall be suitably protected and supported. b) Cable shall be taken on the culvert, through a G.I. pipe not less than 2 “ dia. c) The entry and exit ends of the cable from the pipe to the diversion point of the cable shall be laid in concrete duct. d) Cable laid along a metallic bridge should be placed inside a metallic trough which may be filled, as an anti theft

measure, with sealing compound. e) Should be protected in a manner, which would involve minimum vibration and facilitate maintenance work.

f) Extra length of 6 m to be kept at each end in the form of coil. 4.4.5 Laying Cable in solid and rocky soil If the terrain is hard rocky, normal dimensions of the trench cannot be ensured. In such cases a chase of 255 mm depth

and 150 mm width is to be cut on rocky soil. Sharp edges on the sides must be smoothened out and bottom of the chase should be leveled and the cable laid in sand or soft earth which should be filled and pressed down upto the step. A row of bricks should then be placed lengthwise on the top and jointed with cement mortar and a layer of concrete with cement plaster should be provided on the top of the same.

4.4.6 Cables leading to cabin/station building/Relay room/Goomties

a) In the Cabin/Relay room/Goomty/Location hut, the entry point of cable from outdoor should be protected by masonry and plasterto-guard.

b) The area enclosing the base of cables should be filled up with layer of sand in addition a thin layer of cement plaster with good top finish should be provided.

4.4.7 Jumper cables for track circuits There are numerous instances of jumper cable cut due to Engg. Staff working. Such instances can be minimized if jumper

cable is tied with the nearest sleeper. This should be done on wooden sleepers using iron clamps/hooks. On PSC sleepers jumper cable shall be tied using Track Circuit bonding kit using clamp, resin & hardener. A typical drawing for track jumper and continuity bond connection by Exothermic Welding is shown in figure 4.4(a) & 4.4(b) for information and guidance. Where sleeper ends, cable shall be buried under ground in the line of sleeper and taken to TLJB.

4.4.8 Testing of cables before laying

a) Visual inspection. b) Insulation test. c) Continuity test. d) Bedding & armouring shall also be inspected to see that there has been no damage during transit or in storage. e) Insulation measurement should be done before cable is unwound from the drum by removing the end seals. f) A cable register should be opened station and test results on cable insulation should be recorded after cable laying in

the format of fig.4.5

Cable No. Type Size Make Date of installation

Date of Test

Core No. Insulation against earth

Insulation against conductor

Result of continuity Test

Remarks

Fig. 4.5 Record of Cable Insulation Test 4.4.9 General Precautions to be taken while laying cable

a) Excavation of the trenches should not be done in long lengths and does not remain uncovered overnight. Preferably dugging of trenches, laying of cable and refilling are to be done on the same day.

b) Shoring materials should be kept ready in hand for shoring the bank where ashes or loose materials are encountered. c) Back filling of the trenches should be done properly, rammed and consolidated. d) During excavation, the earth of the trenches shall not be thrown on the ballast instead it should be thrown by the side

of trenches away from the track. e) Excavation work for cables laid close to the track or arrangements for track crossing of cable (like GI/DWC-HDPE pipe

laying under track) should be done only just before laying the cables in the presence of an official from Engineering Department. Caution order, messages may be issued wherever necessary.

f) The work shall be personally supervised by an S&T official not below the rank of JE-II. g) Extreme care should be taken to ensure that outer PVC insulation and armouring shall not be damaged while taking

through pipes. h) All materials used for cable laying and terminations shall be of RDSO/IS specifications and from RDSO approved

manufacturers. 4.5 Protection of Cable 4.5.1 Double Wall Corrugated (DWC) pipes of HDPE for underground Signalling Cable protection 4.5.1.1 Description of DWC HDPE Pipe

The Double Wall Corrugated (DWC) High Density Polyethylene Pipe (HDPE) shall be used for protection of underground signalling cable. Its outer wall shall be corrugated in longitudinal direction imparting high ring stiffness to the pipe. The

stiffness should be such that it can withstand high degree of impacts caused by train movement. The inner wall shall be plain with solid permanent lubricant for easy insertion of cables. It shall have anti rodent property. The DWC Pipe shall confirm to IS:14930 (Pt.I&II). The material of HDPE shall also confirm to approved grades or specifications. The material used for DWC pipe shall be such that in normal use their performance is reliable and without danger to the user or surroundings. The pipe shall have normal service life of at least 30 years. It shall have strength to withstand the stresses likely to occur during transport, storage and installation. The DWC Pipe shall be marked at eve4ry 1 mtr length in such a way that manufacturers name, Vendors name and year of manufacturer can be easily identified. The marking shall be durable and easily legible. The DWC Pipe is available in the sizes tabulated in fig.4.6

Nominal size Outside diameter mm Minimum inside diameter mm

50 50 37

75 75 63

90 90 75

120 120 100

150 150 130

Fig. 4.6 Sizes of DWC-HDPE Pipe

4.5.1.2 Construction of DWC-HDPE Pipe Within Conduit System there shall be no sharp edges, burrs or surface projections, which are likely to damage cables or

inflict injury to the installer or user. The material used in manufacture of DWC Pipes shall contain UV stabilizer of approved type and shall be minimum of 0.15.

The anti rodent & anti oxidant used shall be physiologically harmless. 4.5.1.3 Mechanical properties of DWC Pipes Compression strength – The deflection of owe pipe should be less than 5%, when compressed withy applied force of 450

N. Also no crack should develop during this test. Test as per IS 14930 Pt.2. Impact strength – A 5 kg striker load falling freely on owe pipe shall not crack or split the owe pipe when falls from a height

of 300mm for pipe upto 60 mm dia, 400mm for pipes 61-90mm dia & from 570mm for pipes 91-140. Bending strength – With DWC Pipe bent by 90 degrees, the sample ball should pass through the pipe without any

hindrance. Test as per IS 14930 Pt.2. Thermal Properties – Resistance to Flame Propagation: The DWC pipe shall have adequate resistance to flame

propagation. On removing the sources of flame the fire should extinguish. Test as per IS 14930 Pt.2. External Influences – DWC Pipe shall have Protection against ingress of dust and water when tested as per approved test

methods. Test as per IS 14930 Pt.2. Rodent Repellant Properties – The resistance to rodent bites at least 10 nos. shall not cause any crack or splitting of pipe.

This shall be tested in approved lab like CAZRI, Jodhpur. 4.5.1.4 Quality Requirement The manufacturer shall be certified under ISO9001 and shall submit copy of certificate. The manufacturer shall submit source of raw materials used with content proportion in DWC Pipe of approx. 100 Mtr

lengths. Based on above raw materials used, manufacturer shall submit Mechanical properties of DWC pipe tested by Govt. approved authorized laboratories. Any change in raw material sources and content proportion not permitted, thereafter.

The normal life of DWC Pipe under normal use shall be 30 years. A test report in support shall be submitted. 4.5.1.5 Test The following shall constitute the type tests:

a) Dimensions b) Construction c) Mechanical Properties d) Quality criteria

4.6 Cable Termination Termination of signalling cable on CT rack in relay room and in location boxes shall be done as per drawing shown in

Fig.4.7. Marking on cable and on conductors/ARA terminals shall be done as detailed in the Drawing. This will enable easy identification of conductors in case of any failures or cable disconnections or cable cut done by outsider/miscreants. A proper marking and termination practice ensures quick easy restoration during failures.