Underground Copper Cable Systems PDF

CHAPTER VII LINE PLANT SYSTEMS – UNDERGROUND COPPER CABLE 7.1 SYSTEM 7.1.1 Railway departmental telecommunication lines are usually laid underground between railway offices in railway colonies, large workshops, station yards and in the...

CHAPTER VII LINE PLANT SYSTEMS – UNDERGROUND COPPER CABLE 7.1 SYSTEM 7.1.1 Railway departmental telecommunication lines are usually laid underground between railway offices in railway colonies, large workshops, station yards and in the block sections alongside the track. 7.1.2 SPARE CAPACITY All telecom lines shall, as far as possible, be laid in a manner that due provisions are kept for any future extensions or extra connection which can be catered for without considerable alteration to the existing circuits or reconstruction of the entire alignment. 7.2 LINE PLANT (UNDERGROUND COPPER CABLES) 7.2.1 TYPES & PERFORMANCE PARAMETERS 7.2.1.1 TYPES OF CABLES USED UNDER VARIOUS SCENARIOS The following types of underground cables are generally used for various telecommunication circuits as indicated. a) Quad Cable 0.9 or 1.4 mm conductor dia as per IRS specification No. IRS:TC 30/05. These are 6 quad polythene insulated jelly filled cable suitable for underground laying and are used for control circuits and block interfaces. 1.4 mm conductor dia cable is used for longer block sections. It is desirable to provide 1.4 mm Quad cable in block sections longer than 12 kms. b) Multi pair (from 10 pairs to 200) Multi Dia (0.5mm/0.63mm/0.9mm) PIJF (Polythene insulated Jelly Filled) Cable as per IRS specification No. IRS:TC 41/97. This is suitable for underground laying and is generally used for exchange subscriber lines or branch cables branching off from the main Quad cable. c) Twisted Pair Switch Board Cable of sizes 0.5 mm / 0.6 mm copper conductor dia as per IRS/TEC specification. These are not designed for underground laying and are generally used for indoor applications such as distribution to various telephone subscribers in a building, MDF to exchange wiring etc. d) If RE cable containing paper as well as polythene insulated copper quads is still available, it should be planned to replace the same at the earliest. 7.2.1.2 SIZES OF CABLES The different sizes of cables to be used for various telecommunication circuits are detailed in the following table: Indian Railways Telecom Manual - 2021 Page 72  a) OUTDOOR UNDER GROUND Sizes of conductor Circuit for use 0.5 mm cond Dia twisted Pair PIJF Subscriber's connection up to 5 or 1.83 kg/km (6.5 lb/mile) kms. 0.63 mm cond. Dia. twisted Pair Subscriber's connections up to 10 PIJF or 2.81 kg/km (10 lb/mile) km. b) INDOOR Sizes of conductor Circuit for use 0.5 mm Annealed Tinned Local subscriber's connection in a building, Copper (ATC) Switch Board exchange to MDF wiring etc. cable1.76 kg/km 0.6 mm ATC Switch Board Trunk connections etc. cable 2.52 kg/km c) The size of the telephone exchange cables, shall be specified in a manner indicating the number of pairs, dia. of conductor, type of insulation/sheath, jelly filled, armoured or unarmoured as illustrated below: (i) 50 pair, 0.63 mm cond. dia armoured polythene insulated polythene sheathed jelly filled armoured telephone cable as per IRS : TC- 41/1997. (ii) In underground laying, only Jelly filled armoured cables to be used. 7.2.2 TESTING CABLE BEFORE LAYING a) Before the cable is laid, it shall be tested for insulation and continuity of the cores. Continuity of armour and screen of the cable need to be checked before laying. b) Bedding and armouring of the cable shall also be inspected to see that there has been no damage during transit or in storage. 7.2.3 LAYING OUT THE CABLE a) For laying out cables, the cable drums shall be mounted on cable-wheels b) The drum on the wheel shall be brought to one end of the trench and the end of the cable freed and put into the trench. c) The cable-wheels shall then be drawn along the road or track. d) A party of labours shall follow the drum and guide the cable from the road into the trench carefully so that the cable is not damaged or bent unduly. e) In case where the wheels are not available, the drum shall be mounted on an axle at one end of the trench and cable laid 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. Indian Railways Telecom Manual - 2021 Page 73 7.2.4 GENERAL a) While excavating earth for trenches or making other pits necessary for installation of cable junction boxes in between the tracks or in close vicinity of the track the Permanent Way Inspector or his representative shall be present. In 'Quad' type of cables, conductors diagonally opposite shall form one circuit. b) In telephone cables, electro-static and electro-magnetic induction between different pairs of conductors shall be minimized by a lead or aluminium sheath and by the provision of twisted pairs. c) Whenever a road-crossing or rail-crossing is encountered in busy areas, HDD (Horizontal Directional Drilling) method should be used to lay all types of cables in DWC pipes or any other approved protection arrangement. d) Where concrete large size duct is provided in the station section for laying signalling cables, the same may be utilized for telecom cables also following due precautions. 7.2.5 CABLE TERMINATION a) Cables can be terminated in any of the following methods: (i) DP Box of approved type. (ii) Direct termination. b) PIJF cable of various sizes shall be terminated through DP Box of approved type. 7.2.6 JOINTING OF PIJF CABLE: (i) Jointing should be done by a skilled and experienced person using the correct RDSO specified jointing kit to ensure quality. (ii) The entire cable laying and jointing to be done under close supervision of telecom staff. To expedite work, use of video recording may be resorted to ensure quality of laying and jointing of cables and the same may be submitted in the form of DVD or other suitable form to the concerned Railway officials by the agency carrying out the cable laying work to ensure proper depth of trench and quality of joints. (iii) Thermo shrinkable jointing material shall be used for jointing armoured PIJF cable with thermo shrinkable jointing technique using RDSO's code of practice. (iv) The jointing material is readily available in the form of a jointing kit. For different sizes of cable (No. of pairs and cond. dia.) the kits are different e.g. TSF-1, TSF-2 etc as per latest RDSO specification. For quad cable, only Reinforced Thermo Shrink Jelly Filled kit (RTSF) type jointing kit to be used as per latest RDSO specification. (v) Quad cable joint may normally be kept underground or it may be housed inside a location box of proper size avoiding sharp bends as per local requirement of Railways. Wherever joint is kept inside the Location Box, Indian Railways Telecom Manual - 2021 Page 74  EC Socket also should be fixed on that location box itself and that location box should be painted with black & yellow stripes (vi) The screen and armour of copper cables to be jointed shall be made through with suitable wires. This is essential to get the specified screening factor in association with its earthing at stations. This should be done first to avoid any electric shock due to induction. (vii) The copper cable screen and armour shall be earthed with a low value earth (