Chapter 15: Cables PDF

Chapter 15: Cables Section 1: General 15.1.1 Railway signalling circuits shall be carried on cables. (a) Cables for signalling circuits shall be of approved types. (b) Extant guidelines from Railway Board, RDSO and...

Chapter 15: Cables Section 1: General 15.1.1 Railway signalling circuits shall be carried on cables. (a) Cables for signalling circuits shall be of approved types. (b) Extant guidelines from Railway Board, RDSO and PCSTE for cable laying to be followed. 15.1.2 Planning for Cabling (a) While planning for cabling on a route, the number of conductors required, depending upon the circuits should be first determined. Recommended core sizes as per specifications shall be used. (b) 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. The spare conductors shall be provided on the outermost layer. (c) 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. (d) 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. (e) 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 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. (f) Cable route plan shall also be approved by Engineering and Electrical departments. Approval of S&T open line is also required where ever it is prepared by other than open line. In case of Construction works cable route plan shall be signed by Engineering and Electrical departments of executing agencies as well. (g) As far as possible low lying areas, platform copings, drainages, hutments, rocky terrains, points and crossings, shall be avoided. Proximity to Electrical Sub Stns/Switching stns shall be avoided. (h) Separate cables of suitable size shall be laid for point operation. Chapter 15: Cables Page 314 of 530  (i) In case of Tunnel, provision of cable duct should form part of the Tunnel design. (j) Provision of suitable duct/pipe/other arrangements shall be incorporated in the bridge design itself for laying of cables on bridges. 15.1.3 Storage and Transportation of Cable (a) Cable drums shall not be stacked on flat side. Suitable stoppers shall be placed for stability. (b) Cable drums shall have access for lifting and moving. (c) 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. (d) The drums shall not be rolled over objects that could cause damage to the protective battens of the cable. (e) 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. (f) 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. (g) It is desirable that cable drums are stored in covered shed to protect against direct exposure to sun. Section 2: Paying Out, Trenching & Laying of Cables 15.2.1 Paying Out and Testing of Cable (a) For paying out cables, the cable drums shall be mounted on cable wheels. It should be ensured that no kink is formed while paying out the cable. (b) The drum on the wheel shall be brought to one end of the trench, the end of the cable freed and the cable shall be laid along the trench. (c) 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. (d) 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 in the trench. Record of insulation and loop resistance must be maintained. (e) 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. (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 purposes. Chapter 15: Cables Page 315 of 530  (g) Whenever mechanized equipment is used, the work shall be carried out by a trained operator under the supervision of SSE/JE(Signal), in charge of the work. (h) Where the cable drum is in damaged condition the cable may be placed on a horizontal revolving platform and the cable paid out in the same manner as given in paras above. (i) Paying out of cable should be done by rotating the cable drum and not by pulling the cable with excessive force. 15.2.2 Trenching (a) The width of cable trenches should commensurate with number of cables. The minimum width shall be kept as 0.3 meters. The bottom of the cable trench should be levelled and got rid 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 meters thickness previously deposited at the bottom of the trench. In both the above cases, the cable should be covered with a layer of sand or sifted earth of 0.10 meters thickness and thereafter a protective cover of trough or a layer of bricks or split DWC-HDPE pipe of approved type or any other approved means should be placed. (b) Bottom of Trench shall be cleared in such a way, so as to remove all the boulders having sharp edges. In rocky soil, the bottom of the trench shall be filled with river sand or any other soft material and cable shall be laid on smooth surface. (c) In block section horizontal directional drilling method may also be used based on site conditions for the laying of Quad and OFC cables across the track at sufficient depth to avoid damage due to future work of doubling etc. (d) Where it is not feasible to achieve required depth due to rocky soil/other obstructions, protective measures as shown in Drg. No.15-D2 shall be taken. (e) Where feasible, trenching may be done with suitable machinery, with due precautions towards safety of the running trains. For carrying out such works, the rules governing the working of machinery along the track shall be followed scrupulously. Suitable instructions in this regard shall be issued by the Railways in the form of a joint circular. 15.2.3 Laying Of Cables (a) Cables shall be laid generally as per instructions given in this chapter. 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 Department(where applicable) of the Railway. (b) Cables may be laid underground, either in the trench, in ducts, in cement troughs, in pipes or in any other approved manner. Chapter 15: Cables Page 316 of 530 (c) The main cable laid parallel to the track shall normally be buried at a depth of 1.0 meters from top of cables to ground level, including those laid across the track (1.0 meter below the rail flanges). The depth shall not be less than 0.50 meters for tail cables. In theft prone areas, the cables may be laid at a depth of 1.2 meters with anchoring at every 10 meters. (d) Half Cut DWC-HDPE pipe/RCC or any other approved type of ducts/pipes shall be used while laying the cable for protecting it. (e) The ducts being used shall be of such design and length to prevent/minimise damages to cable by any other future digging activities in the vicinity. The ducts shall have suitable covers to prevent water collection in the duct. (f) When cables are to be laid in rocky area, where depth of 1.0 metre is not feasible, it is desirable that such cables are protected as shown in Drg. No: 15-D2. (g) Cables belonging to other department must not be laid in the same trench along with Signal & Telecommunication cables. (i) A distance of approximately 10 cm must be maintained between cables of other department and signalling cables. (ii) The signalling cables must be separated from LT power cables by a row of bricks or any other approved means and from HT power cables a minimum of 3 meters separation shall be maintained. (h) 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 (iii) Power cable (i) Signalling cables for outdoor circuits should not normally be laid above ground. In exceptional 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 sag. (iii) In station yards, cable shall be laid in ducts suitably protected. (iv) Indoor signalling cable should normally be laid on ladders, channels or in any other approved manner. The cables should be neatly tied/laced. Note: For laying cables in RE area, please refer to Section 3 of this Chapter. (j) Where it is necessary to take the cable between the tracks, it shall be carried in trunking/Duct/pipe kept sufficiently below the ballast level. Chapter 15: Cables Page 317 of 530  (k) While laying the cables in accordance with the above instructions, the following instructions should be adhered- (i) Outside the station section, the cables should generally be laid at not less than 5.5 meters from the centre of the nearest track. (ii) Within the station section, the trenches shall preferably be dug at a distance of not less than 3 meters from the centre of the track, width of the trench being outside the 3 meters distance. (iii) At each end of the main cable an extra loop length of 6 to 8 meters should be kept. (l) After laying the cables, back filling of the trenches should be done properly. The soil excavated shall be put back on the trench, rammed and consolidated. (m) Cable joints of approved type shall be used. (n) Cable markers of approved type shall be provided which should be placed at suitable interval and at diversion points to mark the route. (o) Where the cables are entering the Cable room/Relay room/apparatus case etc., the cables shall be firmly held with suitable clamping arrangement, so as to avoid downward displacement. Suitable ducts, ladder supports, cable guides etc., shall be provided for the cables inside the Cable room/Relay room. Sharp cable bends shall be avoided. 15.2.4 Cable Crossing (a) When a cable has to cross the track, is 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. (iii) The cable is laid in concrete/GI/DWC-HDPE pipes of approved type, suitable ducts or in any other approved manner while crossing the track. (iv) Wherever feasible horizontal directional drilling method may be used. (b) Wherever practical, the cable may be taken underground across the drain bed at a suitable depth for crossing small culverts with low flood level, horizontal directional drilling method may be used where ever feasible. (c) When the cables have to cross any roads, high banks etc. where necessary, horizontal directional drilling method may be used. (d) When cables have to cross a metallic bridge, they should be placed inside a metallic trough/GI pipe which may be filled, as an anti-theft measure, with sealing compound or any other suitable means. 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 meters shall be made available at the approaches of bridge. (e) It is desirable that the excavation of the trenches is not done in long lengths and does not remain uncovered for long period. It is preferable that cables are laid and refilling done on the same day. Chapter 15: Cables Page 318 of 530  (f) During excavation, the soil of the trenches should not be thrown on the ballast. The soil should be thrown by the side of the trenches away from the track. (g) 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. (h) 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). Section 3: Cable Laying in RE Area 15.3.1 Only unscreened approved type underground cables shall be used for signalling purposes. The following precautions shall be taken: (a) 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 DWC-HDPE/Concrete 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. (b) 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. As far as possible, the cable shall be laid on the side of the track opposite to the feeding post. In addition, the cable shall be laid in concrete or DWC-HDPE pipes (approved type)/Split RCC pipes or other approved means for a length of 300 meters on either side of the feeding point. (c) 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 may be reduced to one metre provided the cables are laid in concrete pipes/DWC-HDPE-pipes of approve type/ducts or any other approved means. (d) Where an independent Earth is provided for an O.H.E 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. (e) 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 nearest Track. Chapter 15: Cables Page 319 of 530  (f) The use of G.I pipes or any form of metallic pipes is 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) Section 4: Insulation Resistance Testing of Signal Cables 15.4.1 These instructions apply only to the cables used for Railway Signalling and do not cover internal wiring. (a) The insulation resistance tests should be made when conductors, cables and insulated parts are clean and dry. (b) A 500 V insulation tester should be used for insulation testing of signalling cables and 100 V insulation tester shall be used for Quad cables. (c) Any metallic sheath or metal work of any rack or apparatus case should be bonded to earth during test. (d) Disconnect all cores of a cable at both ends. The disconnection may be made through links of ARA/Modular terminals, if provided. (e) Connect one terminal of the insulation tester to the conductor under test and other terminal to all the other conductors being bunched together and connected to earth. (f) Similarly test remaining conductors of the cable one by one as in above Paras. (g) Insulation Resistance so measured should not be less than 5 mega ohms per km at buried temperature, if the insulation resistance is found to be lower than 5 mega ohms, the cause should be investigated and immediate steps taken to repair or replace it. (h) Insulation Resistance tests should be made in such a manner that safe operation of trains is not affected. It should be ensured that no unsafe conditions are set up by the application of test equipment. (i) All conductors in signalling cables must be tested for their insulation before commissioning. (j) The conductors of the cables may accumulate electrostatic charge. The cable conductors should be shorted or earthed to completely discharge any accumulated charge. (i) Before connecting the insulation tester while commencing the test. (ii) After the insulation tester is disconnected when the test is completed. This is in the interest of safety of personnel and protection of equipment. (k) The results of the insulation resistance tests should be recorded in approved proforma. A comparison of test results between successive tests carried out on a cable under similar conditions will give an indication of the trend towards deterioration of the cable. Chapter 15: Cables Page 320 of 530  Section 5: Maintenance of Cables 15.5.1 Testing of Cables (a) All conductors in signalling cables must be tested for their insulation in dry weather once in three years provided cables are monitored through ELD else annually preferably before monsoon as per instructions specified in section 4. Reading shall be recorded as per the format mentioned in Annexure: 15-MS1. Tail cables should be tested for insulation once a year. A comparison of the test results between successive tests carried on a cable under similar conditions will give an indication of the trend towards deterioration of the insulating material over a period of time. If a sudden fall in insulation is observed, the cause should be investigated and immediate steps taken up to repair or replace the cable. (b) In addition to the regular testing of cables in dry weather, random tests in wet weather may also be carried out, where considered necessary, to localise any sudden deterioration in insulation of cables. (c) All cables termination devices, pillar boxes, cable heads and glands shall be kept clean and dry. These parts shall be frequently inspected and any tendency for moisture or water leak shall be immediately attended to. (d) No excavation in the vicinity of underground signal cables shall be undertaken without a representative of the signal & telecommunication department present and without taking suitable precautions for the safety of the existing cables. Suitable instructions in this regard shall be issued by the Railway in the form of a joint circular. (e) The protective works provided for the cables at places like track crossings, culverts, bridges etc shall be regularly inspected by the maintenance staff, special attention being paid to these protective works soon after the monsoon. (f) Earth Leakage Detector (ELD): Shall be provided in all signalling installations and shall be interfaced with Datalogger (where ever feasible) for remote monitoring. Note: For Maintenance Schedules of ELD, please refer to Annexure: 15-MS2. 15.5.2 Periodical Testing of Signalling cables shall be as under; (a) First measurement of insulation of the cable should be carried out after laying of the cable and after first monsoon for all the conductors. (b) After major work in a yard, all cables should be meggered afresh. (c) In all other cases, Insulation Resistance shall be tested periodically as given below. Type of Cable Periodicity i) Main Cable Every 2 years ii) Tail Cables – Signal/Track/Points etc Once in 1 year iii) Spare conductors Once in 1 year Chapter 15: Cables Page 321 of 530  Note: This Chapter has under mentioned Annexures in Appendix I S.No Annexure Description No 1 15-MS1 Maintenance Schedule of Cable, Cable Insulation Resistance Test Sheet, Instructions for Insulation Resistance Testing of Signalling Cable. 2 15-MS2 Maintenance Schedule of Earth Leakage Detector (ELD). Note: This Chapter has under mentioned Drawings in Appendix II Drawing S. No Description No 1 15-D1 Drawing for RCC cable marker. 2 15-D2 Drawing for cable laying when rock faced at; 300 mm (Sheet 1 of 3), 400 mm (Sheet 2 of 3), 600 mm (Sheet 3 of 3). 3 15-D3 Drawing for RCC duct 500 mm (Sheet 1 of 2) & Drawing of RCC split pipe. (Sheet 2 of 2). 4 15-D4 Drawing of DWC split pipe (120 mm dia). 5 15-D5 Drawing for Road/Track crossing. 6 15-D6 Drawing for Cable trough for metallic bridge. 7 15-D7 Drawing for Cable laying on culverts. 8 15-D8 Drawing for Cable laying on culverts with high flood level. 9 15-D9 Cable core plans for a; 4-Road station with PI (Sheet 1 of 3), 6-Road station with Distributed EI (Sheet 2 of 3), 6-Road station with PI with either side cable Huts. (Sheet 3 of 3 ). 10 15-D10 Cable Plan for Electric Lifting Barrier (ELB) at Station. Chapter 15: Cables Page 322 of 530