Railway Signalling Cable Planning

General Information

• Railway signalling circuits must use approved cables.
• Follow guidelines from Railway Board, RDSO, and PCSTE for cable laying.

Planning for Cabling

• Determine the required number of conductors based on the circuits during cabling route planning
• Recommended core sizes as per specifications should be used.
• Provide a minimum of 20% spare conductors in each main cable up to the farthest point zone.
• Beyond that, provide a 10% minimum of spare conductors.
• Spare conductors should be on the outermost layer if the total number of used conductors is 3 or less, otherwise no spares are needed.
• Distribute circuits so that cables can be disconnected for maintenance with minimal traffic disruption.
• Provide line-wise and function-wise cables, and place auxiliary signals in different cables.
• Conduct a foot survey along the track after determining conductor size and number to find the best cable route.
• Clearly show the route on a cable route plan, including the actual track alignment and offsets from permanent structures.
• Indicate road/track crossings, power cable crossings, water/sewage mains, and other important points on the diagram.
• It's preferable to chart it on a route plan showing existing routes of power cables.
• Incorporate changes into the chart/plan.
• Engineering and Electrical departments must approve the cable route plan.
• S&T open-line approval is required if prepared by other than open line.
• Engineering and Electrical departments of executing agencies must sign the cable route plan for construction works.
• Avoid low-lying areas, platform copings, drainages, hutments, rocky terrains, and proximity to Electrical Sub Stations/Switching stations where possible.
• Lay Separate cables of suitable size shall be laid for point operation.
• Cable ducts form part of tunnel design in tunnels.
• Incorporate duct/pipe arrangements in bridge design for cable laying on bridges.

Storage and Transportation of Cable

• Cable drums should not be stacked on their flat side and should have suitable stoppers for stability.
• Cable drums must allow access for lifting and moving.
• When rolling cable drums for unloading or transportation, rotate the drum in the direction of the arrow marked on it.
• Avoid rolling drums over objects that could damage the protective battens of the cable.
• Use a fork lifter or ramp when unloading from a vehicle to avoid impact damage.
• Seal cable ends with an end cap or any other approved method to prevent water from entering during all storage stages.
• It's recommended to store cable drums in a covered shed to protect against direct sun exposure.

Paying Out and Testing of Cable

• Mount cable drums on cable wheels for paying out cables.
• Ensure no kinks form while paying out the cable.
• Bring the drum on the wheel to one end of the trench, free the cable end, and lay the cable along the trench.
• A party of labourers shall move along the trench carrying cable at suitable intervals so that cable is not damaged due to dragging along the ground or bent unduly.
• Visually inspect the cable for damage before laying it in the trench.
• Test for insulation and continuity of cores.
• Lay the cable in the trench after testing.
• Maintain records of insulation and loop resistance.
• If wheels aren't available, mount the drum on an axle at one end of the trench, and have labourers pay out and carry the cable.
• The drum shall not be rolled off on to the road for laying the cable and the cable dragged on the ground for laying purposes.
• Work involving mechanized equipment must be carried out by a trained operator under the supervision of SSE/JE(Signal).
• If the cable drum is damaged, place the cable on a horizontal revolving platform and pay it out.
• Rotate the cable drum for paying out cable, avoid pulling with excessive force.

Trenching

• Cable trench width must match the number of cables with as minimum of 0.3 meters in width.
• Level the trench bottom to remove sharp materials.
• In soft ground, lay the cable at the bottom of the levelled trench.
• In rocky ground, lay the cable on a 0.05 meters layer of sand or sifted earth deposited at the trench bottom.
• Cover the cable with a 0.10 meters layer of sand or sifted earth
• Add a protective cover of trough, bricks, split DWC-HDPE pipe or another approved method after the layer of sand or earth.
• Remove sharp-edged boulders from the trench bottom.
• Fill the trench bottom with river sand or soft material in rocky soil, then lay the cable.
• Use horizontal directional drilling in block sections for laying Quad and OFC cables across the track at sufficient depth to avoid damage.
• Implement protective for rocky soil/obstructions, as shown in Drg. No.15-D2, where required depth cannot be reached.
• Trenching may be done with machinery if feasible, with precautions for train safety.
• Railways will issue instructions for machinery operation near the track via a joint circular.

Laying Of Cables

• Cables should be usually laid as per the instructions in this chapter
• Special precautions to be detailed in a joint circular by relevant departments for station yards with other utilities.
• Cables may be laid underground in trenches, ducts, cement troughs, pipes or other approved manners.
• Main cables parallel to the track should typically be buried at 1.0 meters depth, including those across the track.
• Tail cables should be at least 0.50 meters deep.
• In theft-prone areas, lay cables at 1.2 meters depth with anchoring every 10 meters.
• Use Half Cut DWC-HDPE pipe/RCC or other approved ducts/pipes to protect the cable.
• Use ducts designed and sized to prevent damage from digging activities, complete with covers to prevent water collection.
• Protect cables in rocky areas where 1.0 meter depth isn't feasible, as shown in Drg. No: 15-D2.
• Cables belonging to the other departments should not be laid in the same trench as Signal & Telecommunication cables.
• Maintain approximately 10 cm of distance between cables of another department and signalling cables.
• Separate signalling cables from LT power cables with a row of bricks.
• Maintain a minimum separation of 3 meters from HT power cables.
• Place cables in the following order from the main track side in the same trench to aid failure recognition:
  • Telecommunication cable
  • Signalling cable
  • Power cable
• Avoid laying signalling cables for outdoor circuits above ground.
• Take the following precautions if doing so is unavoidable:
  • Suspend cables in wooden cleats, from cable hangers, or in an other approved manner to prevent mechanical damage.
  • Space cable supports to prevent sagging.
  • Protect cables in ducts in station yards.
  • Neatly tie/lace indoor signalling cables laid on ladders or channels.
• Cables taken between tracks should be carried in trunking/Duct/pipe below the ballast level.
• Adhere to the following instructions when laying cables:
  • Outside the station section, lay cables at least 5.5 meters from the centre of the nearest track.
  • Within the station section, dig trenches at least 3 meters from the track centre, with the trench width outside the 3-meter distance.
  • Keep an extra loop length of 6 to 8 meters at each end of the main cable.
• Properly backfill trenches after laying cables.
• Ram and consolidate the excavated soil back into the trench.
• Use approved cable joints.
• Place approved cable markers at intervals and diversion points to mark the route.
• Firmly clamp cables entering the Cable room/Relay room/apparatus case to prevent displacement.
• Provide ducts, ladder supports, and cable guides inside the Cable room/Relay room, and avoid sharp cable bends.

Cable Crossing

• Ensure that the cable crosses the track at right angles.
• The cable must not cross the track under points and crossings.
• Lay the cable in approved concrete/GI/DWC-HDPE pipes, suitable ducts, or via another approved method while crossing the track.
• Use horizontal directional drilling method where feasible.
• Use horizontal directional drilling method and take the cable underground across the drain bed at a suitable depth for crossing small culverts with low flood level where practical.
• Use horizontal directional drilling method where necessary to cross roads and high banks.
• Place cables inside a metallic trough/GI pipe filled with sealing compound on a metallic bridge for anti-theft.
• Support the cable across the bridge to minimize vibrations and facilitate maintenance work.
• Provide adequate cable length (2 to 3 meters) at the approaches of bridge.
• It is preferable that cables should be laid and refilling done on the same day that excavation of trenches is done, and that this should not be in long lengths.
• During excavation, the soil of the trenches should not be thrown on the ballast, but the soil should be thrown by the side of the trenches away from the track.
• In places where cables to be laid within 1 meter from sleeper end, digging beyond 0.50 meter shall be done in the presence of an official from Engineering Department, and the laying of the cable and refilling of trench should be done with least delay.
• The work shall be supervised at site personally by an official of the Signal and Telecommunication Department not below the rank of a JE/SSE (Signal).

Cable Laying in RE Area

• Only unscreened approved type underground cables used for signalling purposes

Precautions

• Lay the cable at least one meter from the nearest edge of the mast or live conductor if the cable's depth is not exceeding 0.5 meters.
• Maintain a 3 meters minimum distance between the cable and O.H.E structure edge when the cable depth is greater than 0.5 meters.
• If these distances are hard to achieve, use DWC-HDPE/Concrete Ducts within 3 meters of the Mast on either side.
• The distance between the cable and mast may be reduced to 0.5 meters when ducts are used.
• These precautions are necessary to avoid damage to the cable in the event of the failure of an overhead insulator.
• In the vicinity of traction sub stations and feeding posts, the cable shall be at least one metre away from any metallic part of the O.H.E and other equipment at the substation, which is fixed on the ground, and at least one metre away from the substation earthing and laid In concrete, DWC-HDPE, Split RCC (approved types), or any other approved means for a length of 300 meters on either side of the feeding point.
• Near switching stations, lay cables at least one meter from any fixed metallic body and 5 meters from station earthing.
• The 5-meter distance may be reduced to one meter if cables are laid in approved concrete pipes/DWC-HDPE-pipes/ducts.
• Independent Earth is provided for an O.H.E, the cables must be at least one metre away from it.
• Cable trenches near O.H.E structures should be at least 5.5 meters from the nearest track's center if possible.
• G.I. pipes or any form of metallic pipes are prohibited within a distance of 300 meters from feeding post. Similarly galvanized iron metallic pipes are prohibited in close proximity to switching station earth or traction mast. (Para 20706 (vi) of ACTM)

Insulation Resistance Testing of Signal Cables

• These instructions apply only to Railway Signalling cables, excluding internal wiring.
• Conduct insulation resistance tests with clean, dry conductors, cables, and insulated parts.
• Use a 500 V insulation tester for signalling cables, and a 100 V tester for Quad cables.
• Bond metallic sheaths or metalwork of racks/apparatus cases to earth during testing.
• Disconnect all cable cores at both ends, using ARA/Modular terminal links if available.
• Connect one insulation tester terminal to the conductor under test. Connect the other terminal to all other bunched conductors and earth.
• Test all remaining cable conductors in same manner.
• Insulation resistance should be at least 5 mega ohms per km at buried temperature. Investigate and repair/replace if lower.
• Conduct insulation resistance tests to avoid affecting train operations. Ensure test equipment doesn't create unsafe conditions.
• Test all conductors for insulation before commissioning.
• Short/earth cable conductors to discharge accumulated electrostatic charge before connecting the insulation tester and after disconnection for personnel and equipment safety.
• Record results in approved proforma. Comparing results from similar tests indicates cable deterioration trends.
• Excavation soil must be thrown away from the track's ballast during excavation not on it.
• An official from Engineering Department must be present for digging beyond 0.50 meter in places where cables to be laid within 1 meter from sleeper end.
• And the laying of the cable and refilling of trench should be done with least delay.
• Site work should be overseen by a Signal & Telecommunication Department official of JE/SSE (Signal) rank or higher.

Maintenance Of Cables

• Test all conductors in signalling cables for insulation in dry weather once every three years if monitored through ELD, or annually before the monsoon as per section 4.
• Record readings as per Annexure: 15-MS1, and test tail cables annually for insulation.
• Comparing successive tests indicates insulation deterioration trends.
• Investigate and repair/replace cables if insulation drops suddenly.
• In addition to testing in wet weather cables may be randomly tested for insulation where necessary
• Keep all cable termination devices clean and dry. Inspect them frequently and address any moisture or water leaks immediately.
• A signal & telecommunication department representative must be present during excavation near underground signal cables with the necessary safety precautions. The Railway will issue suitable instructions via joint circular.
• Maintenance staff shall regularly inspect protective works at track crossings, culverts, and bridges, paying special attention post-monsoon.
• Provide Earth Leakage Detectors (ELD) in all signalling installations with Datalogger interfacing (where feasible) for remote monitoring.

Periodical Testing Of Signalling Cables

• Measure cable insulation after laying and after the first monsoon for all conductors.
• Megger all cables in the area afresh after major work.
• Insulate Resistance should be tested in all other cases:
  • Main cables should be tested every two years.
  • Tail Cables for SIgnal/Track/Points tested once a year.
  • Spare Conductors every year.