Do’s & Don’ts for laying of Signalling Cables

Introduction

The laying of Signalling cables require laying of various types of Cables in the station yard as per the Signalling plan. Cables which are mainly used inside the building are called Indoor cables and cable which are laid in the outdoor are called Outdoor Signalling Cables.

To drive the Point, Signal and Track Circuits cables are laid from the Relay Room to actual gear/equipment installed in the field (outdoor). Thus, the cable laying require details planning as per the yard layout and signalling scheme of the station before laying of the cables.

References:

• Execution of Engineering work along the Railway Track- JPO of Rly. Board 01.06.17
• Joint Procedure Order No. 2004/Sig/G/7 – Railway Board
• SEM-II Chapter-XV Cable Laying practices
• Handbook on Laying of Signalling cables- CAMTECH

Planning for Laying of Signalling Cables

As per the function (gear) the cables are laid. All the gears as per Signal Interlocking Plan (SIP) should be listed and marked on the Plan.

Main cable is laid directly from Relay room to  the junction boxes in the field.

Tail cable is laid from the junction box to the signalling gear like Signal, Point Machine, Track, Axle counter detection point on the track side.

Documents to be prepared for Cable laying

Cable Route Plan
Cable Core Chart
Track Crossing Plan
Location Details
CTR Details
Cable Testing Records
Meggering Report
Cable Route Plan

A foot survey along the track should be done to determine the best route for the cable.

Following shall be shown on the cable route plan:

• Actual alignment of track
• offsets from permanent way or permanent structures
• Various road and track crossings
• Crossing with power cables
• Water and sewage mains

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

 This needs approval from the division.

Cable Core Chart

This is most important activity for starting of cable laying for any station. This requires thorough understanding of signalling plan and interlocking scheme of the station, like…

• No. of Point Machines, Signals, Track Circuits, and other equipments.
• Type of Track Circuiting ex. DC tracks, MSDAC, AFTC etc.
• Make of Equipments ex. different type of axle counter require different cables.

A cable core distribution plan is required to be prepared for each installation.  Detailed instructions are elaborated in below sections.

Track Crossing Plan

During laying, cables has to cross the track, thus for crossing the track either open trench is made under the track or boring is to be done under the track. As per instructions issued and for cable laying can be done as per JPO issued from the Railway Board.

Thus, the track crossing plan has to be prepared so that the P-Way Inspector can allow the track crossings of cables.

Now a days, open trench under the track is not permitted, so the track crossing by Boring Method is the only option.

Read about precautions to be taken during track crossing.
Location Details

The Location detail is prepared as per the Cable Termination  in the location boxes. It shows the information that how the functions are feed from the location box and how the cables are connected with other cables.

 
CTR Details

Cable Termination Rack (CTR) details are prepared for the termination of cables on the Cable Termination Rack.

Basically, CTR are used to connect the Outdoor (cables) with the Indoor (cables). On the CTR, Outdoor cable is connected on the one side of terminal, and the Indoor cable is connected on the other side of the terminal.

Cable Testing Records

The records of cable laying during the laying should be properly maintained in a cable laying register.

Details to be noted in columns-

1. Type of Cable (6C, 12C, 24C, 6Q etc…)
2. Manufacturer of Cable
3. Cable Drum Number
4. Length of Cable in Drum
5. Length of Cable used/laid in the trench
6. Top meter (reading from the cable)
7. Bottom Meter (reading from the cable)
8. From (Location box)
9. To (Location box)

Meggering Report

This is also an important document, which keeps the details of cable testings. With the megger, cable must be checked for its insulation with respect to other conductors and earth as well.

So, the meggering report must be prepared “Before the Cable laying” and “After the cable laying” for all the cables.

It should be jointly tested with the openline staff and record should be maintained.

Approval of Plans

The Cable Route plan, Track Crossing Plan must be got approved from the divisional officers as well like… Sr.DSTE, Sr.DEN and Sr.DEE. If the work is being executed by the construction department then the approval from Construction officers like Dy.CE/Construction, Dy.CEE/Construction is also required in addition to divisional officers.

The Cable Core Chart, Location Details and CTR details must be approved by the executing officials i.e. SSE, JS/SS and JAG officers.

The Cable Meggering Report must be jointly signed by the openline SSE and construction SSE, if the work is being executed by the construction organisation.

• Check List for preparation of Signal Interlocking Plan (SIP)
• Check List for approval of ESP (Engineering Scale Plan)

Cable laying precautions

General

• In AC electrified areas cables shall be laid underground only.
• Cables may be laid underground, either in the trench, in ducts, in cement troughs, in pipes or in any other approved manner.
• Cable is generally laid parallel to the track beyond Home signal with minimum deviations and on one side of the yard.
• As far as possible, cable shall be crossed only at two locations, i.e. one crossing on each side of the yard.
• The cable laid parallel to the track shall be buried at a depth of minimum 1.0 metre (top most cable) from ground level. Those laid across the track must be minimum 1.0 metre below the rail flanges.
• However, in case of rocky soil, the depth may be reduced suitably.
• For laying of tail cables the depth shall not be less than 0.50 metres.
• In theft prone areas the cables may be laid at a depth of 1.2 metres with anchoring at every 10 metres.
• The minimum width of manually made cable trenches shall be kept as 0.3 meters.
• The cable shall 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 shall be placed.
• Normally, not more than 12 cable are to be laid in one trench.
• It is recommended that cables are laid in RCC duct up to home signal on both side of the station and may be extended up to distant, if required. This will also help later for laying of additional cable later without carrying out trenching.
• Before starting cabling work location boxes shall first be erected so that cable after laying is directly taken inside location box.

(a) Cable laying near the Track

(i) Outside the station limits, the cables shall generally be laid at not less than 5.5 metre from the centre of the nearest track.

(ii) Within the station limits, the trenches shall preferably be dug at a distance of not less than 3 metre from the centre of the track, width of the trench being outside the 3 metre distance.

(iii)At each end of the main cable an extra loop length of 6 to 8 metre shall be kept burried at same depth as that of cable in the same trench to ensure that cable is free from theft/outside interference.

(b) Laying of different type of cables in same trench

Cables should be laid in the following order, starting from the main track side:
i) Telecommunication cable
ii) Signalling cable
iii) Power cable
Minimum separation between telecommunication cable and signalling cables -10 cm.

The signalling cables must be separated from power cables by a row of bricks between them.

Note: As per practice in some railways, before laying of cables, stripes, dots or any other symbol may be marked throughout the outer sheath of cable with different colour for different cables. This will help in easy and quick identification of ends when cables are cut due to theft or excavation work or any other reason, thereby reducing the restoration time.

(c) Cable laying in ducts

RCC, masonry or any other approved type of ducts may be used for laying the cable. The ducts shall have suitable covers and shall rest on walls of duct.

(d) Laying cable in solid & rocky soil

• In the rocky ground the cable shall be laid normally on layer of sifted earth of 0.05 metres thickness previously deposited at the bottom of the trench. Cable shall be covered with the layer of sand or sifted earth of 0.1 metre thickness.

• Alternatively, concrete/GI/CI/PVC/DWC-HDPE pipe shall be used if number of cables is small.

• If number of cables is large, RCC duct shall be used.

• A row of bricks shall be placed lengthwise on the top and jointed with cement mortar and a layer of concrete with cement plaster.

(e) Laying in special soil condition

If it is unavoidable to run cables through abnormally high acidic or alkaline soil or through sewages, cables may be laid in the concrete/GI/CI/PVC/DWC-HDPE pipes

(f) Cable laying in residential area

The cable shall be specially protected on both sides up to a distance of about 300 metres beyond the building line, protected by means of concreting of 50 mm.

(g) Cable laying in large yard and suburban area

Main signalling cable shall be laid in RCC ducts/DWC-HDPE pipes.

Tail cables shall be laid through DWC-HDPE pipes of suitable sizes and buried in trenches at a depth of not less than 1000 mm from ground level.

(h) Track crossing

How track crossings should be done.

• As far as possible, cable shall be crossed only at two locations, i.e. one crossing on each side of the yard.
• When a cable has to cross the track, is shall be ensured that.
• The cable crosses the track at right angles;
• The cable does not cross the track under points and crossings and
• The cable is laid in concrete/GI/CI/PVC/DWC-HDPE pipes or suitable ducts or in any other approved manner while crossing the track.
• Cable laid across the track must be 1.0 metre (minimum) below the rail flanges.
• No digging shall be done below the sleepers. Digging work while crossing a track shall be done between sleepers in the presence of a Railways representative.

(i) Road Crossing

The cable is laid in concrete/GI/CI/PVC/DWC-HDPE pipes, suitable ducts or in any other approved manner while crossing the road at the depth of 1 metre from the ground level. It shall extend 1 metre (minimum) on each side of the road keeping in view the future increase of width of the road.

• Suitable precautions may be observed while laying of pipes and refilling the trench depending upon the type of road (e.g. heavy or light traffic, broad or thin) so as not to block the road traffic for a longer period.

• Whenever a cable is laid across an important road, particularly one with a special surface, a spare pipe may be laid, through which a cable can be drawn when required. It will be advantageous to leave a lead wire of G.I. wire in the pipe for drawing the cable in future.

(j) Cable laying on bridges/culverts

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

• Where cable may not be taken underground across the drain bed, cable shall be taken on the culvert through GI/DWC-HDPE pipe of suitable sizes.

• When cables have to cross a metallic bridge, they shall be placed inside a metallic trough which may be filled, as an anti-theft measure, with sealing compound. The cable shall be supported across the bridge in a manner which would involve minimum vibrations to the cable and which will facilitate maintenance work.

• In case of arch bridges, cable shall be taken through GI/DWC-HDPE pipes on top of the arch adjoining the parapet wall. The pipe shall be covered with ballast.

(k) Laying near to sleeper

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 Engineering Department, and the laying of the cable and refilling of trench shall be done with least delay. Laying may be undertaken under block protection as needed.

(l) Jumper cables for track circuits

• Jumper cable should be tied with the nearest sleeper, on wooden sleepers using iron clamps/hook and on PSC sleepers using clamps.

• Cable shall be buried underground in the line of sleeper and taken to TLJB, where sleeper ends.

• Wherever required, cable may be laid in DWC-HDPE pipe.

• Jumper cable shall be laid at least 0.5 metre below ground level excluding ballast depth.

• Jumper cable shall be laid neatly in squared manner and shall not be kept in loose coils above the ground near TLJB.

• Top surface of TLJB shall not be 1 feet above rail level.

(m) Cable laying in monsoon season

It is not advisable to lay cables in monsoon. When however cable laying is necessary during the monsoon season, the cable ends shall be inserted in a pipe sealed at one end and the pipe buried. Termination work shall be started only when there is likelihood of a clear weather for three or four days.

(n) Entry of cable at cabin, relay room, location boxes etc.

• All cable entry points in cabin, relay room, battery room, SM’s room, location boxes, location huts, junction boxes, etc. must be closed with suitable masonry works, sand covered and plastering/RCC slab to prevent entry of rats etc.

• Cable shall be protected on both sides up to a distance of 10 metre beyond building line of cabin, relay room, battery room, SM’s room and 1 metre beyond location boxes, location huts, junction boxes etc.

The cable must not press against the edge of the solid support where the bed changes from solid support such as a foundation/masonry to soft support such as soft soil. The soft soil near the edge must be tamped and the cable raised slightly.

(o) Cable termination

All the core of the cable (used or spare) shall be terminated on approved type terminals in cabin/SM’s office or apparatus cases. Each core so terminated will be provided with identification ferrules with letters or/numbers embossed on them as per requirement of circuitry.

Termination of signalling cable on CT rack in relay room and in location boxes shall be done duly using identification marking on cable and on conductors/terminals. A proper marking and termination practice ensures quick and easy restoration during failures.

(p) Testing of cable

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 resistant must be maintained.

(q) Supervision of cable laying

• The work shall be supervised at site personally by an official of the Signal & Telecommunication Department not below the rank of a JE/SE/SSE (Signal).
• Orders will be given by the Inspector in charge only. He will be assisted by others at vulnerable places to inform him of the position and possible danger.
• All concerned staff shall have full knowledge of their duties and the material handled by them.
• No work shall be started unless all types of materials, tools consumable materials and staff are available. Location boxes and junction boxes shall be in position. If the cable ends are left in the ground unattended, damage is likely to take place.
• Following record shall be maintained by JE/SE/SSE in-charge of the work/section:-
  • Cable route plan

• Cable distribution chart

(iii)Cable termination diagram

• Cable Testing Record : Summary Sheet, including supply details etc.

(r) Special requirements in 25 kV AC electrified area

• Only unscreened cable shall be used.

• Screened signalling cable may be used on signalling installations where screened cable is already in use and site condition demand its further use.

• PVC insulated PVC sheathed and armoured unscreened cable to an approved specification (IRS-63) shall be used for carrying signalling circuits. Only approved type (IS-1554) power cable shall be used for signalling purposes.

• The screened cable, if used, shall be PVC insulated, armored and to an approved specification IRS S-35.

• The cable shall be so laid that it is not less than one meter from the nearest edge of the mast supporting the catenary or any other live conductor, provided the depth of the cable does not exceed 0.5 meters. When the cable is laid at a depth greater than 0.5 meters, a minimum distance of 3 meters between the cable and the nearest edge of the O.H.E structure shall be maintained. If it is difficult to maintain these distances, the cable shall be laid in concrete/heavy duty HDPE/Ducts or any other approved means for a distance of 3 meters on either side of the Mast. When so laid, the distance between the cable and the mast may be reduced to 0.5 meters. 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. In addition, the cable shall be laid in concrete or heavy-duty HDPE pipes/or other approved means for a length of 300 meters on either side of the feeding point. As far as possible, the cable shall be laid on the side of the track opposite to the feeding post.

• In the vicinity of the switching stations, the cable shall be laid at least one metre away from any metallic body of the station, which is fixed in the ground, and at least 5 meters away from the station earthing. The distance of 5 meters can be reduced to one metre provided the cables are laid in concrete pipes/ heavy-duty HDPE pipes/ducts or any other approved means.

• Where an independent Earth is provided for an OHE structure, i.e. where the mast is connected to a separate Earth instead of being connected to the rail, the cables shall be laid at least one metre away from the Earth.

• Where there are O.H.E structures along the cable route, the cable trenches shall as far as possible, be dug not less than 5.5 meters away from the centre of the Track.

• In a cable run, the number of circuits carrying 300V at any given instant shall not exceed three.

• Read more about IRSSE service
• Electronics Interlocking EI TAN and Specifications
• User Manuals for Signalling equipments
• Read more about IRSEE service