TC1 Cables PDF - Telecom Cables (Copper)

TC 1 TELECOM CABLES (COPPER) इ रसेट IRISET TC 1 TELECOM CABLES (COPPER) The Material Presented in this IRISET Notes is for guidance only. It does not over rule or alter any of the Provisions contained in Manuals or Railway Board’s directives INDIAN RAILWAY INSTITUTE OF SIGNAL ENGINEERING & TELECOMMUNICATION, SECUNDERABAD - 500007 April 2020 TC 1 TELECOM CABLES (COPPER) INDEX S.No. Chapter Page no. 1 Introduction of Telecom Cables 1 1.1 Introduction of Telecom Cables (copper) 1.2 Advantages of U/G cables over O/H lines 1.3 Comparison between U/G cables and O/H lines 1.4 Types of Telecom Cables 1.5 Special Features of Telecom Cables 1.6 Electrical characteristics of Telecom Cables 1.7 Important Terms 2 Paired Telephone Cables 2.1 Paired Cables 8 2.2 Types of Paired Cables 2.3 Telecommunication Switchboard Cables 2.4 Applications in Railways 2.5 Standard make of switch Board Cables 2.6 Technical Data 2.7 Double drop wire/Twin Flat wire 2.8 Field service (FS) Cable 2.9 Data Communication Cables 2.10 Coaxial Cable 2.11 RF Coaxial Cable 3 Underground PIJF Cables 3.1 Introduction 16 3.2 Brief Description 3.3 The colour code of conductors 3.4 Colour code scheme of 20 pair polythene insulated cables 3.5 Application 3.6 Technical Data 3.7 Advantages of Polythene Insulated Jelly Filled Cables 3.8 Marking on Cable 4 Effects of Railway Electrification on Telecom circuits 4.1 Effects of 25KV 50 Hz AC Traction on Telecommunications 21 4.2 Mechanism of Induction 4.3 Screening factor 4.4 I.T.U-T. Recommendations 4.5 Psophometric noise 4.6 Effects of 25 KVAC Traction on Telecom cable may be reduced 4.7 Precautions to be taken for the protection of staff and equipment in 25 KV 50 Hz AC traction territory 5 Telecom Quad Cables 5.1 Introduction 26 5.2 Construction of PIJF Quad Cable 5.3 Colour Code scheme for PIJF Quad Cable 5.4 General specification of 4/6 PIJF Quad cable 5.5 Specifications of 6 Quad Cable 5.6 Present Status of 6 Quad System in Railways 5.7 Quad cable along with OFC and without OFC 5.8 Guidelines for the use of OFC system and 6 Quad cable in IR 5.9 Difference between PIJF u/g Paired and Quad Cables 6 Cable laying practices 6.1 Introduction 32 6.2 Important stages in Telecom Cable laying 6.3 Survey Work 6.4 Points to be covered under the survey for cable route 6.5 Information in Cable Route Plan 6.6 Detailed Cable Route Survey 6.7 Length of 6 Quad Cables 6.8 Typical cable requirement calculation 6.9 Telecom cable laying/arrangement in major yards and stations 6.10 Storage of Cable drums 6.11 Basic methods of laying underground cables 6.10 Methods of laying underground cables 6.12 Special cable laying practices 6.13 Cable Markers 6.14 Power Crossing 11KV and above 7 Jointing of Underground Telecom Cables 7.1 Introduction 43 7.2 Preparation of Cable for Jointing 7.3 Jointing procedure of Quad Cable conductors 7.4 Important stages of making a Cable Joint 7.5 Various Types of Joints in Quad Cables 7.6 Jointing Procedure of PIJF u/g cables 7.7 Termination of 6 quad cables 8 Testing of Cables 8.1 Types of tests 57 8.2 Acceptance tests for 6 Quad PIJF cables 8.3 Standard values of various tests 8.4 Mandatory Check & Tests to be done before commissioning of BPAC/SSDAC/MSDAC applications on 4/6 Quad/PIJF cables 8.5 Causes for cable failures & precautions 8.6 Fault localisation tests 9 Quad Cable Maintenance 9.1 Typical 6 Quad cable failures & their causes 63 9.2 Important tools to protect u/g S&T Cables from damages 9.3 Quad Cable Maintenance Register 10 Annexure 73 11 Question Bank 89 12 Abbreviations / Acronyms 97 13 Glossary 100 Prepared by : N. V. Gopala Rao, ICT1 Reviewed by : D. Janardhana, L IT Approved by : C.Chandrasekhara Sastry, Sr.Professor-Tele DTP and Drawings : K.Srinivas, JE (D) Version No. : 1.0 April 2020 No. of Pages : 104 No. of Sheets : 53 © IRISET “This is the intellectual property for exclusive use of Indian Railways. No part of this publication may be stored in a retrieval system, transmitted or reproduced in any way, including but not limited to photo copy, photograph, magnetic, optical or other record without the prior agreement and written permission of IRISET, Secunderabad, India” http://www.iriset.indianrailways.gov.in CHAPTER-1 INTRODUCTION OF TELECOM CABLES 1.1 Introduction of Telecom Cables (Copper) In Indian Railways different types of Telecom networks exist and play a vital role by providing clear and distant voice and data services. Various types of telecommunication cables with RDSO specification are being used depending upon the requirements of Telecom and safety related Signalling circuits, which are under utilisation for functioning of administrative and train operation activities. For administrative purpose Telephone exchanges, Railnet (Intranet), UTS/PRS, FOIS (Freight Operations Information System), MIS (Management Information System) MMIS (Material management Information and IRPSM (Indian Railway Projects and Sanction Management) etc are in use. Whereas for Train operation various safety circuits like Block, LC gate communication, IB Phone (Intermediate Block), BPAC(Block Proving Axle Counter), EC (Emergency Communication) and Train Traffic Control communication etc. are in use. For all types of above Telecom networks, different types of Telecom links are established by using Telecom trunk cables and tail cables. The Telecom transmission media over Indian Railways is as follows: 1. Aerial Lines (Over Head Lines): GI wires & ACSR (Aluminium Conductor Steel Reinforced) are in use for Section Control Communication, Block Communication and LC gate Communication etc. These existing ACSR lines are under replacement with 6 Quad Underground Cables. 2. Micro Wave System: Analog & Digital Systems were in use for Radio Patching for Control Communication and long distance administrative trunk circuits. Analog MW systems became obsolete and closed down. However Digital MW systems are still in use. MW system functionality is under replacement with OFC system. 3. RE Main Telecom Underground Cable: 0+12+2, 0+17+3, 0+18+2 etc. are in use in RE areas for Section Control, TPC, RC, EC, Block etc circuits. Due to non availability and foreign exchange currency involvement, these cables are under replacement with 6 Quad with OFC cables. 4. Underground 4 Quad and 6 Quad Cables: These are in use as standalone or along with OFC in many Zonal Railways. 5. OFC Cable: Laying optical fiber cable along the Railway track utilizing Railways’ Right of Way (ROW) and provide modern communication system to improve Railways operation and safety through Memorandum of Understanding between the Ministry of Railways and RailTel Corporation of India Limited vide Rail board letter number No. 2001/Tele/MW/3 RCIL- MoU New Delhi, 09.01.2002. 24 Fiber Underground OFC Cable is in use for high bit rate Telecom traffic with enormous applications over Indian Railways. Railway is using only 4 fibers in which 2 fibers for working and 2 fibers for standby and remaining 20 fibers handed over to RCIL (RailTel Corporation of India Ltd.) as a policy between Railways and RCIL. 6. Leaky Coaxial Cable: leaky coaxial cable communication system is used inside tunnel in Railways for seamless communication for Distributed Power Wireless Control System. When the train enters the tunnel, communication ceases to exist between train crew due to absence of signal. The system comprises “leaky” feeder cables that provide both transmission and reception for the radio handsets in the tunnels and amplifiers for surface communications. IRISET 1 TC1 - Telecom Cables (Copper) Introduction of Telecom Cables 1.2 Advantages of U/G cables over O/H lines  Overhead lines may come in contact with trees, bushes, etc. and cause low insulation.  Due to natural calamities and ravages of human beings, overhead lines are Prone to a higher fault incidence. Hence, less liable to damage as well as faults.  Due to headway considerations, the maximum number of pairs on a pole route in Over Head Alignment is limited to 16.  Due to induced voltage effects from the 25 KV OHE system, Over Head lines are not fit for Telecommunication circuits in RE area.  Low maintenance cost.  General appearance is better. 1.3 Comparison between Underground Cables and Overhead Lines Underground Cables Overhead Lines Number of circuits is more. Number of circuits is limited. No noise and no cross-talk Prone to noise and cross-talk Less number of failures. More number of failures. For long distance circuits-4wire For Long distance circuits- 2-wire systems are required. system is required. Maintenance cost is less. More maintenance cost. Thefts are minimum. Thefts are maximum. More secrecy. No secrecy. Used in RE and- Non RE areas. Cannot be used in RE area 1.4 Types Telecom Cables: 1.5 Special Features of Telecom Cables Telecom cables are: a) PVC insulated d) Balanced cables b) Twin Twisted paired / quad cables e) Loaded Cables and c) Screened cables f) Colour coded IRISET 2 TC1 - Telecom Cables (Copper) Introduction of Telecom Cables Unlike electrical noise, cross talk is the main criteria in telecom circuits. Cross talk arises mainly from unbalanced electrostatic and electromagnetic couplings between the pairs of conductors and sheath with respect to earth. These effects are respectively be measured in terms of capacitance unbalance and mutual capacitance. At voice frequencies, capacitance unbalance is the major source of cross talk. In order to reduce the cross talk in cables, insulated wires are twisted together at regular intervals on their own axis helical throughout its length. Different twist lengths are used to transpose the circuits continuously with respect to one another pairs/quads. After laying the cable, if capacitance unbalance is persisting, it can be reduced by introducing the external fixed capacitors. This process is called as “BALANCING OF CABLES”. In star quad cables diagonally opposite conductors are formed as one pair and two wires of the pair are kept at an equal distance from the conductors of the remaining pair. 1.6 Electrical characteristics of Telecom Cables 1.6.1 The four primary elements The four primary elements of cable should be taken into Consideration while designing the circuits. R = Series Resistance L = Series self inductance C = shunt capacitance G = Shunt conductance [Leakage] These four quantities per unit length of a pair of telephone lines are called primary elements of the lines. Dig: Schematic representation of the elementary components of a transmission Line. Where R-is the resistance per unit length, L- is the inductance per unit length, G- is the conductance of the dielectric per unit length, C-is the capacitance per unit length. When alternating current flows through the lines, there will be voltage drop due to both resistance and inductance and so they may be assumed to be present in series in the lines and as capacitance and leakage are present between the lines, current is lost through them during transmission. Z0 = (L/C) are independent of frequency and as such all the frequency components are equally attenuated during propagation through line. All the different types of distortions that are likely to be introduced during transmission through long lines are thus eliminated when the condition GL = RC is satisfied. Telephone line is a balanced twisted pair transmission line and its characteristic impedance Z0 can be calculated from the data which was given by the manufacturer. IRISET 3 TC1 - Telecom Cables (Copper) Introduction of Telecom Cables 1.6.2 Defining the Impedance Vs Frequency. The impedance, which describes the combined effect of resistance (R), inductive reactance (X L) and capacitive reactance (XC) in an AC circuit, whether it occurs in a single component, or in a whole circuit. Because impedance is affected by reactance (X), as well as resistance (R), it is also affected by frequency (ƒ) and the value of impedance will change at different frequencies. The component or circuit will not have the same impedance at all frequencies. It is common for inputs and outputs on many types of equipment to have their impedances quoted in Ohms and to assume a common frequency for that particular type of equipment. For example, audio commonly uses a frequency of 1 kHz as the standard for measuring impedance. This is because 1 kHz is approximately the centre of an audio amplifier ś bandwidth, measured on a logarithmic scale, as shown in the above figure. The wiring to the subscriber in telephone networks is generally done in twisted pair cable. It is possible to manufacture this kind of cable to have a 600 Ω characteristic impedance but it will only be this value at one specific frequency. This might be quoted as a nominal 600 Ω impedance at 800 Hz or 1 kHz. Below this frequency the characteristic impedance rapidly rises and becomes more and more dominated by the ohmic resistance of the cable as the frequency falls. At the bottom of the audio band the impedance can be several tens of kilo-ohms. On the other hand, at high frequency in the MHz region, the characteristic impedance flattens out to something almost constant. 1.6.3 Loading of underground cable The distortion less condition, GL=RC, is not satisfied in usual cables. In telephone cables as the conductors are necessarily of thinner gauge and as the conductors are run side by side, both the values R and C are large compared to values L and G. Usually the cables contain a large number of conductors, and the dia. of the conductors are necessarily of smaller dimensions and so the value of R is much high. From expression, GL=RC, the capacitance, C value is much higher and inductance, L value is much lower. The L value has to be increased to satisfy the equation GL = RC. When the diameter of the conductors is increased, the value of R is reduced. This is not possible considering it’s size and cost. If the value of G is increased, the transmission loss will be increased which is not acceptable to a long distance transmission line. Therefore, there is one way to increase the value of GL by increasing the value of L. This is achieved by using the coils of suitable inductance value wound on dust cores are placed in series with the lines at suitable intervals. This is called coil loading or lump loading. IRISET 4 TC1 - Telecom Cables (Copper) Introduction of Telecom Cables Effect of using 118 mH loading coil in 6 Quad Cable The object of loading cables for voice frequencies is almost solely for the purpose of reducing the attenuation constant per Km. For long distance cables and for trunk cables 118 mH coils are used and spaced at regular intervalls of 2000 mtrs. Each (2000 mtrs) of such a cable then appears as one section of a low pass filter in which L = 118 mH(59 mH in each limb of a pair) and the shunt capacitance is C x S (C = Capacity per Km and S = spacing in Km) Attenuation Vs Frequency of one Loading section A cable has an appreciable amount of resistance, so that the attenuation characteristic of any one loaded section, would be as shown in above figure. Note: Unloaded cable has an attenuation of approx. 0.65 dB/ Km. This system of loading, increases the Zo from 470 ohms to approximately 1,100 ohms and reduces attenuation to 1/3 of its unloaded value i.e. 0.25dB/Km and this is the practice being followed in 6 Quad Cables. Loading Section of 4/6 Quad Cable Loading coil joint Condenser joint Loading coil joint 1. Loading section– 2000 Meters. 2. Condenser joint– 1000 Meters. 3. Normal Joint wherever requires. (At present quad cables drum length of 1000 meters. are in use, hence number of Normal Joints have been minimised) 1.6.4 V.F balancing of underground cable V.F balancing of underground cable is done to reduce noise and crosstalk in cables. This is necessary in 6 Quad Cables because the cables carry a number of important circuits. The process of measuring the capacitance unbalances between various quads and earth, within the quad and with adjacent quads and minimising the unbalances by connecting condensers is called V.F. balancing. Permissible limits of capacitance unbalance for full and half loading sections are 40 pF and 20 pF respectively. IRISET 5 TC1 - Telecom Cables (Copper) Introduction of Telecom Cables The capacitance unbalance exists between, a) Conductors of a quad and sheath (Earthed). This is called “Earth Coupling”. b) Conductors of a quad and between adjacent quads. This is called “Crosstalk Coupling”. Capacitive couplings cause cross-talk and Earth couplings cause ‘Noise’ in VF circuits. e1, e2, e3, e4 - earth couplings & c1, c2, c3, c4 - capacitive couplings 1.7 Important Terms 1. Core: Everything inside the sheath of the cable. 2. Pair: Two wires forming a single circuit, held together by twisting, binding, in Common jacket. 3. Quad: A structured unit employed in cable. A quad consists of four separately insulated conductors twisted together. 4. Unit: A Unit is made up of a number of pairs stranded together in layers. 5. Marker Pair/Quad: The conductors have different markings on their insulation to distinguish them from other conductors. The counting and numbering of a pair/quad of a layer commences from the marker pair/quad. 6. Paper-Insulated Cable: Cable in which the conductors are insulated with a paper ribbon. Either spirally or longitudinally is applied. 7. Plastic-Insulated Cable: Cable in which the conductors are insulated with Plastics, such as polyethylene and polypropylene. Note: PVC insulated conductors are not referred to as Plastic-Insulated Cables. 8. Insulated: A non-conducting material that can offer a high and permanent resistance, for separation from other conducting surfaces to the passage of current. 9. Interference: Any electrical or electromagnetic disturbance, man-made or natural, which causes, or can cause, undesirable response. 10. Jacket: A covering over a cable. It is usually the outer component of a composite sheath. 11. Dielectric: Any material used in a cable that will insulate one conductor from another or from shield. 12. Dielectric Strength: The maximum voltage that a dielectric can withstand without rupturing. Also called “electric strength” or “break-down strength. 13. Phantom Circuit: A superimposed circuit derived from two suitably arranged pairs of wires called side circuits. Each pair of wires is a circuit itself and, at the same time, acts as one conductor of the phantom circuit. IRISET 6 TC1 - Telecom Cables (Copper) Introduction of Telecom Cables 14. Twisted Pair: A cable composed of two small-insulated conductors twisted together without a common covering. 15. Cable: An assembly of one or more insulated conductors or optical fibers or combination of both, within an enveloping jacket. 16. Underground Cable: A cable installed below the surface of the earth in conduit or ducts. 17. Unit-type Cable: A cable in which the pairs are first formed into bound units and then the units are formed together to make the completed cable. 18. Moisture Barrier: In a cable, the material, usually in the form of an axially laid aluminium foil/polyethylene laminated film, placed immediately inside the sheath. Generally called Poly- Aluminium laminate moisture barrier. 19. Filling Compound (Jelly): It is a water resistance compound. The cable core shall be fully filled with jelly and this will be used in joints also. 19. Sheath: A protective covering made of metals or plastics over the cable core. 20. Wire gauge: It is a measurement of wire diameter. This determines the amount of electric current a wire can safely carry, as well as its electrical resistance. The following chart gives above information on different copper wire gauges. Copper wire gauge and conversion chart IRISET 7 TC1 - Telecom Cables (Copper) Paired Telephone Cables CHAPTER-2 PAIRED TELEPHONE CABLES 2.1 Paired Cables Paired cables are balanced, by using two closely spaced conductors twisted together. The purpose of twisting the wires is to reduce the electrical interference from neighbouring pairs. A ground shield is used to prevent high frequency noise and balanced wires also reject noise coming from ground loops. How Cross Talk is being eliminated in Twisted Pair The following representation shows potential difference between “Conductors without twist (Fig.A) and Conductors with twist (Fig.B)” Net induced voltages on L1 and L2 in twisted pair (figure B) are the same. Hence, no potential difference, no current flow at destination then no cross-talk from adjacent pair or circuit. IRISET 8 TC1 - Telecom Cables (Copper) Paired Telephone Cables Twisting arrangement in twisted copper cables 2.2 Types of Paired Cables Switchboard cables Underground PIJF cables PVC Twin flat-2 core 10 pair-0.4/0.5/0.63mm (dia of conductor ) 10 pair-0.4/0.5/0.63mm (dia of conductor ) 20 pair-0.4/0.5/0.63mm (dia of conductor ) 20 pair-0.4/0.5/0.63mm (dia of conductor ) 50 pair-0.4/0.5/0.63mm (dia of conductor ) 50 pair-0.4/0.5/0.63mm (dia of conductor ) 100 pair-0.4/0.5/0.63mm (dia of conductor) 100 pair-0.5/0.63mm (dia of conductor ) These cables are used for Indoor extension These cables are used for outdoor extension TEC Spec.No: GR/WIR/06/03 of March 2002 RDSO Spec. No:IRS:TC 41/97 (Amd. 2) 2.3 Telecommunication Switch Board Cables TEC Specification: GIR/WIR – 06/03 March 02 IRISET 9 TC1 - Telecom Cables (Copper) Paired Telephone Cables 2.4 Applications in Railways: These cables are used for indoor installation for the interconnection of telephones & electronic equipment, Telephone switching exchanges, Switch board & telephone wiring (MDF, SDH, DWDM, and DSLAM etc.) PDH/SDH systems, RS-232 Communication Systems and Digital Transmission networks. 2.5 Standard make of Switch Board Cables: Delton cables, Reliance cables, Finolex cables, Havells cables etc. 2.6 Technical Data Parameter Construction Technical Data Solid Annealed Tinned Conductor dia (mm) Conductor Copper in 0.4,0.5 & 0.6 mm 0.4 0.5 0.6 sizes. Max. loop Resistance at (Ohms/Km.) 286 184 128 20°C Insulation Polyethylene. Pairs are Min. Insulation Colour coded as per Resistance at specification. 50°C/Km. Mega 50 50 50 ohm/Km. Capacitance For 200 meter length in pF (pair to pair) Unbalance at 800/1000Hz 230 230 230 Assembly Pairs/units to laid up to form a round and compact cable. Core Wrap Non-Hygroscopic (against moisture) polyester tape with min. 15% overlap of width of the tape. Screening If required, shall be of Aluminium tape. The Al. tape of min. 0.04mm (Optional) thickness and a drain wire of solid tinned copper of 0.125 sq.mm shall be laid parallel touching the Al.surface throughout the length. PVC Sheathing Extruded PVC Type. It will be in Grey Colour. Rip Cord A non-metallic suitable Nylon thread shall be longitudinally placed under the sheath for the removal of sheath. Length Standard lengths of packing : 100 mtrs / 500 mtrs. +/- 5% 2.6.1 Conductors Each conductor shall consist of a solid wire of annealed high conductivity tinned copper circular in cross section, uniform in physical, mechanical and electrical properties. The conductor is free from spills, splits and defects of any other kind and shall conform to specification IS: 8130.The conductor is uniformly coated with tin. Characteristic impedance of the conductor is 600 Ohms 2.6.2 Insulation Each conductor is insulated with PVC. The PVC shall be applied by the extrusion process and shall form a compact homogeneous uniform core. The PVC insulation shall have distinct single colour for identification of each conductor. For a hundred pairs cable, each unit consists of 20 pairs and there are all-together five units. Mate colours of each unit is White, Red, Black and Yellow. The colour scheme of the 1st wire of all other units is the same as shown above for the first unit. IRISET 10 TC1 - Telecom Cables (Copper) Paired Telephone Cables Pair No. Lead A Lead B Pair No. Lead A Lead B 1 Blue White 11 Blue Black 2 Orange White 12 Orange Black 3 Green White 13 Green Black 4 Brown White 14 Brown Black 5 Slate White 15 Slate Black 6 Blue Red 16 Blue Yellow 7 Orange Red 17 Orange Yellow 8 Green Red 18 Green Yellow 9 Brown Red 19 Brown Yellow 10 Slate Red 20 Slate Yellow Colour of PVC insulation for identification of 20 pairs cable. 2.6.3 Twining: Two insulated conductors shall be uniformly twisted together with a right hand lay which shall not exceed 100mm.Twisted pair shall be laid up to form a compact and symmetrical cable. The lay of any two adjacent pairs shall be so chosen as to reduce the cross talk to the minimum possible extent. The cable core consisting of the required number of twisted pairs shall be stranded in concentric layers. The cable core shall be lapped with polythene tape. 2.6.4 Ripcord: A non-metallic suitable ripcord shall be laid longitudinally under the PVC sheath. It shall provide an effective means of ripping the PVC sheath longitudinally to facilitate the removal of PVC sheath. 2.6.5 Sheath: The cable shall be sheathed with PVC. 2.6.6 Identification mark: The PVC sheath shall be prominently embossed on the outside with IRS cable and the name/code of the manufacturer at intervals not exceeding 30cms to enable identification of the cable. The cables shall be supplied in standard lengths of 100/200/500 meters. A tolerance of + or - 5%of the standard real coil length is permissible. The cable shall be wound on suitable wooden drums/rolls /coils and shall be strong enough to withstand the stress and strain of transportation and handling. 2.7. Double Drop wire / Twin Flat Wire (IS 434-Part-1/1964) This wire is used to extend one Telephone connection from outside the distribution box to inside the house up to the Telephone instrument. It is available in copper conductors of 0.5mm and 0.9mmdia.The standard lengths of the cable’s coil are of 100 meters, 200 meters and 500 meters. In this wire L1 and L2 are separated by PVC insulation to prevent short circuit. 2.8. Field Service (FS) Cable (IS-694-Part /1964) This wire is used to extend telephone connection from outside DB to telephone instrument for outdoor applications. During emergencies like Railway accidents, Floods, Cyclones, etc., this cable is extensively used to provide temporary connections of the telephones as per requirement. This is a single core twin twisted of size 7/0.375mm. Out of 7 strands three strands are steel and four strands are copper with single PVC core called as L1. One more length has to be taken as L2. This is available in length of 500Mtrs. and 1Km drum lengths. Steel strands will provide additional mechanical strength. This FS cable is also called D8 Cable. IRISET 11 TC1 - Telecom Cables (Copper) Paired Telephone Cables 2.9. Data Communication Cables For data communication, two types of cable are used for LAN network: i. UTP: Unshielded twisted pair ii. STP: Shielded twisted pair 2.9.1 UTP Cable This type of cable is used in I.E.E.E (Institute of electronic and electrical engineering) Ethernet LANs. UTP wire offers an economical alternative for both Ethernet and Token ring networks. This cable is less expensive than a shielded twisted pair, less bulky and is also easier to work with. It is, limited to segments no longer than 100 meters and generally does not transmit as fast as its shielded relative. Unshielded twisted pair cabling comes in different grades that are assigned to six standard categories created by the Electronic Industries Association and the Telecommunications Industries Association (EIA/TIA). The Different UTP Categories and their specifications Category 1/2/3/4/5/6/7 – a specification for the type of copper wire (most telephone and network wire is copper) and jacks. The number (1, 3, 5, etc) refers to the revision of the specification and in practical terms refers to the number of twists inside the wire (or the quality of connection in a jack). CAT1 is typically used for telephone wire. This type of wire is not capable of supporting computer network traffic and is not twisted. CAT1 is also used by telco companies providing ISDN and PSTN services. In such cases the wiring between the customer's site and the telco’s network is performed using CAT 1 type cable. CAT2, CAT3, CAT4, CAT5/5e, CAT6 & CAT 7 are network wire specifications. This type of wire can support computer network and telephone traffic. CAT2 is used mostly for token ring networks, supporting speeds up to 4 Mbps. For higher network speeds (100 Mbps or higher) CAT5e must be used, but for the almost extinct 10 Mbps speed requirements, CAT3 will suffice. CAT3, CAT4 and CAT5 cables are actually 4 pairs of twisted copper wires and CAT5 has more twists per inch than CAT3 therefore can run at higher speeds and greater lengths. The "twist" effect of each pair in the cables ensures any interference presented/picked up on one cable is cancelled out by the cable's partner which twists around the initial cable. CAT3 and CAT4 are both used for Token Ring networks -- where CAT 3 can provide support of a maximum 10Mbps, while CAT4 pushed the limit up to 16Mbps. Both categories have a limit of 100 meters. The more popular CAT5 wire was later on replaced by the CAT5e specification which provides improved crosstalk specification, allowing it to support speeds of up to 1Gbps. CAT5e is the most widely used cabling specification world-wide and unlike the category cables that follow, is very forgiving when the cable termination and deployment guidelines are not met. IRISET 12 TC1 - Telecom Cables (Copper) Paired Telephone Cables CAT6 wire was originally designed to support gigabit Ethernet, although there are standards that will allow gigabit transmission over CAT5e wire. It is similar to CAT5e wire, but contains a physical separator between the four pairs to further reduce electromagnetic interference. CAT6 is able to support speeds of 1Gbps for lengths of up to 100 meters, and 10Gbps is also supported for lengths of up to 55 meters. Today, most new cabling installations use CAT6 as a standard, however it is important to note that all cabling components (jacks, patch panels, patch cords etc) must be CAT6 certified and extra caution must be given to the proper termination of the cable ends. In 2009, CAT6A was introduced as a higher specification cable, offering better immunization to crosstalk and electromagnetic interference. Organizations performing installations using CAT6 cabling should request a thorough test report using a certified cable analyzer, to ensure the installation has been performed according to CAT6 guidelines & standards. CAT7 is a newer copper cable specification designed to support speeds of 10Gbps at lengths of up to 100 meters. To achieve this, the cable features four individually shielded pairs plus an additional cable shield to protect the signals from crosstalk and electromagnetic interference (EMI). Due to the extremely high data rates, all components used throughout the installation of a CAT7 cabling infrastructure must be CAT7 certified. This includes patch panels, patch cords, jacks and RJ-45 connectors. Failing to use CAT7 certified components will result in the overall performance degradation and failure of any CAT7 certification tests (e.g using a Cable Analyzer) since CAT7 performance standards are most likely not to be met. Today, CAT7 is usually used in Data Centers for backbone connections between servers, network switches and storage devices. Conductor: Each conductor is made up of annealed copper of dia. 0.5mm.and PVC insulated. USE: UTP cable is connected with the connector known as RJ-45 and IO box. Eight no. of wires are connected to these RJ 45 connector or IO box. Thick Ethernet cable is also used to connect a 15-pin connector known as DB-15 or DIX. Different types of UTP Cables and application IRISET 13 TC1 - Telecom Cables (Copper) Paired Telephone Cables Different types of UTP Cables and it’s speed and frequency 2.9.2 STP Cable For high-speed data, the STP cables are used. The application of this cable is widely found in SDH rack wiring. In this cable each twisted pair is shielded and an earth wire is drawn along with it. The twisted pairs are to be bundled together and enclosed in a protective jacket to form a thicker cable. Below the jacket a tape of aluminium foil is used as a screen. Each conductor is made up of annealed copper of 0.9mm.or 0.6mm dia. and PVC insulated. 2. 10. Coaxial Cable Coaxial cable and parts Different types of Coaxial cables IRISET 14 TC1 - Telecom Cables (Copper) Paired Telephone Cables Coaxial cable often called coax is the round and flexible cable. Four separate elements are identified, by the cross-sectional view. In the center there is a copper wire, carrying the signal. Encasing this wire is a layer of non-conducting insulation made up of PVC or Teflon. Outside the insulation, forming a protective sleeve around the conducting wire and its insulation, another layer made up of a braided mesh of copper or Aluminium. This layer protects the transmitted signal from the electromagnetic interference known as noise that can distort the transmitted signal. Finally outside the braided sleeve is an outer shield or jacket, made of either PVC or a fire resistant material such as Teflon. The coaxial cable comes in various forms for networking a. Thin Ethernet or thin wire: Ethernet is based on the 3/8-inch coaxial cabling known as RG- 58. This Thinned cabling can carry a signal for about 185 meters. Above this the signal begins to degrade. Thin Ethernet LANs Coaxial cable is connected with the BNC (Bayonet Neill Concelman) connector to make connection with the equipment. b. Thick Ethernet: is based on less flexible coaxial cabling about ½ inch thick. Also known as RG-8. Thick net cabling can carry signals farther than Thinned cabling about 500meters and thus is often used as the backbone connecting. 2.11. RF Coaxial Cable The coaxial cable radiates the least power and picks up interfering signals to the least degree. the usual impedances are 40-50 ohms and 70-80 ohms, so the diameter remains reasonably small. The optimum conductor diameter ratios for different transmission line properties will vary from one to infinity, if the outer diameter “D” of the outer conductor is kept constant and inner diameter “ d’' is varied. Cross sectional view of RF co-axial cable RF Coaxial cable and parts A single compromise ratio is also desirable for certain fields of use because it simplifies manufacturing and merchandising problems. These considerations have led to standardization, in effect, of a single coaxial conductor diameter ratio for high frequency and microwave application. This ratio (2.3) results in a nominal characteristic impedance of about 50 ohms. The medium between conductors is assumed to be a gas. IRISET 15 TC1 - Telecom Cables (Copper) Underground PIJF Cables CHAPTER-3 UNDERGROUND PIJF CABLES POLYETHYLENE INSULATED, POLYETHYLENE SHEATHED, JELLY FILLED, UNDERGROUND CABLES (ARMOURED or UNARMOURED) 3.1 Introduction PIJF telephone cables are widely used in Railways for local loop and other networks due to improved technology and simplicity in installation and maintenance. Indian Railway Standard specification for Polythene insulated polythene sheathed jelly filled telephone. cable with Poly-Al Moisture Barrier is IRS-TC: 41/97 (RDSO spec) Cross section of PIJF Telephone Cable IRISET 16 TC1 - Telecom Cables (Copper) Underground PIJF Cables G B C D E F A A: Polythene Outer jacket B: Galvanised Steel Tape C: Polythene Tape D: Polythene Inner sheath E: Poly-Al-Laminated Tape F: Core wrapping (Polyester) tape G: Polythene Insulated Copper Conductor Construction of PIJF Telephone Cable 3.2 Brief Description Jelly filled cable is an underground cable having polythene as insulation on conductors and the inter-spaces between the conductors is fully filled with petroleum jelly. Petroleum jelly prevents ingress of moisture and water inside the core in the event of any damages to the cable. The Cable is circular throughout its length and is free from any physical defects. Jelly filled cable is wound on strong wooden drums. The length of cable on any drum is 500 / 1000 meter + 10% unless single longer lengths are specified by purchaser for specific application. The diameter of the yoke of the drums is not less than 20 times of the overall diameter of the cable. Both ends of the cable are kept inside the drum to get access to the cable ends battens are painted by red colour arrow. Number of pairs: The cable shall be of different sizes varying from 10 to 200 pairs and above with nominal conductor diameter 0.5mm or 0.63mm or 0.9mm.The Standard cable sizes shall be 10,20 50 100 and 200 pairs armoured / un-armoured. Conductor: Each conductor shall consist of a solid round wire of annealed high conductivity copper, smoothly drawn, normally circular in section, uniform in quality and free from defects. Insulation: Conductor insulation shall be polythene insulating grade and 100% virgin material as per ASTM (American Society for Testing and Materials) -D883. Twining/Pairing: Two insulated conductors shall be twisted together with uniform lay to form a pair. The length of the lay of any pair shall be different from the adjacent pairs. The lay of various pairs shall be so chosen as to satisfy the capacitance unbalance. Filling compound: (Petroleum Jelly): A cable core shall be fully filled with suitable water resistant compound like jelly, which is fully compatible with the polyethylene insulation, binders, and tapes used in the cable. Core wrapping: After application of water resistant filling compound, a closed helical or longitudinal lapping of a non hygroscopic and non wicking polyester tape or tape of any other suitable materials shall be laid over the cable core. IRISET 17 TC1 - Telecom Cables (Copper) Underground PIJF Cables Poly-Al Laminate moisture Barrier/Screen: Polythene coated aluminium tape shall be applied longitudinally on the core with a minimum overlap of 6mm. Thickness of the aluminium tape shall be 0.2mm + or –10% and that of polythene/ co-polymer coating on each side 0.05mm nominal. Thickness of composite tape shall be 0.3mm + or - 15%. Sheath: Cable shall be sheathed with polythene and containing a suitable anti oxidant system. The material shall be virgin and meet required specification. The sheath shall be reasonably circular and free from pin holes joints and other defects. The thickness depends on the size of the cable. Armour: The sheathed cable shall then be armoured with two applications of galvanized steel tape conforming to IS: 3975 each applied helically in the same direction with gap in the first tape of 25% + or – of the width of the tape, the second tape evenly covering the gap of the first tape. Thickness of the galvanized steel tapes used in two applications including zinc coating on each tape shall not be less than 0.5mm. Jacket: The armoured cable shall be tightly jacketed with polythene conforming to the requirements as specified for sheath. 3.3 The colour code of conductors: In 5 pair,10 pair, 20 pair cable, colour code specified as below in para 3.4 Stranding: A 50 pair cable consists of 5 numbers of 10 pair units A 100 pairs cable consists of 5 numbers of 20 pair units 3.4 Colour Code Scheme of 20 pair polythene insulated cables Main↓ / Mate→ White Red Black Yellow Blue 1 6 11 16 Orange 2 7 12 17 Green 3 8 13 18 Brown 4 9 14 19 Grey 5 10 15 20 Pair 1st wire 2nd wire Pair 1st wire 2nd wire no. Main colour Mate colour no. Main colour Mate colour 1 Blue White 11 Blue Black 2 Orange White 12 Orange Black 3 Green White 13 Green Black 4 Brown White 14 Brown Black 5 Grey White 15 Grey Black 6 Blue Red 16 Blue Yellow 7 Orange Red 17 Orange Yellow 8 Green Red 18 Green Yellow 9 Brown Red 19 Brown Yellow 10 Grey Red 20 Grey Yellow IRISET 18 TC1 - Telecom Cables (Copper) Underground PIJF Cables 3.4 The colour code scheme of polythene insulated cables Blue, Orange, Green, Brown & Grey are called the main colours. White, Red, Black and Yellow are called mate colour. The five pairs make one unit. In this way there are four units in twenty pair’s cable. A cable of 50 pairs and 100 pairs, the twisted pairs shall be arranged in units of 10 pairs and 20 pairs respectively. 4 No of 50 pairs super unit shall be assembled to form a 200 pair cable. Colour of binding tape: The different colours of the binding tape shall be used for identifying each unit as given in Table 3.4 Unit number 1 2 3 4 5 Colour binder Blue Orange Green Brown Grey Table 3.4 Colour of binding tape 3.5 Application: These cables are used for in transmission and distribution of networks designed to be used underground, not inside the water. Cables having 0.5 mm conductor diameter are used for short distance distribution networks, cables having 0.6 mm. conductor diameter are used for long distance networks. In Railways Polythene Sheathed Jelly Filled Cable with Ploy-Al moisture barrier is used for providing telephone connections to the subscribers and local lead / last mile connectivity of various circuits of both voice and data. These PIJF cables will be used in both RE and non RE areas depending upon application. Whereas in the RE area the usage of PIJF telephone cable may be limited to a maximum of 2 Km length due to induced voltage effects. 3.6 Technical Data Parameter 0.51 mm dia conductor 0.63 mm dia conductor Conductor resistance (20 C) 92 Ohms/Km 64 Ohms/Km Loop Resistance of pair(20 C) 184 Ohms/L.Km 128 Ohms/L.Km Insulation resistance 5000 M Ohms/Km 5000 M Ohms/Km (500 V Megger) Mutual Capacitance (800 Hz) 52 nF/Km 50 nF/Km Operating Voltage 300 V 300 V Attenuation at 800 KHz 1.379 dB/Km 1.107 dB/Km Min. Bending radius 15 X Cable diameter 15 X Cable diameter Weight 1.83 Kg/Km 2.81 Kg/Km Application Up to 5 Km for sub. loop 5 to 10 Km for sub. loop 3.7 Advantages of Polythene Insulated Jelly Filled Cables. 1. Counting pairs is easy and human mistakes are avoided. 2. Jointing is easy and requires no additional place. 3. Failures are less. 4. Entry of moisture / water is prevented by Jelly in the core. 5. Cables can be directly terminated on MDF/CTB/Tag Block/Equipments, thus avoiding additional joints decreasing the cost and time. 6. Handling of cable is easy not delicate like paper insulated cables. 7. Life of cable is more. IRISET 19 TC1 - Telecom Cables (Copper) Underground PIJF Cables 3.8 Marking on Cable To enable proper identification of the cable, the following information is embossed, engraved or printed on the polythene jacket in case of armoured cable, and on the sheath in case of un- armoured cable. All the markings are white or yellow. a) Name/Trade mark of the manufacturer b) IRS Specification number c) Year of manufacture d) Length (Sequential marking) e) Cable drum number f) No. of pairs/conductor size (Example: 20 pairs/0.63mm) This marking exists throughout the length at intervals of one metre. IRISET 20 TC1 - Telecom Cables (Copper) Effects of Railway Electrification on Telecom circuits CHAPTER-4 EFFECTS OF RAILWAY ELECTRIFICATION ON TELECOM CIRCUITS 4.1 Effects of 25 KV 50 Hz AC Traction on Telecommunications In the system of electric traction adopted by the Indian Railways, the catenary wire is fed at 25,000 V, 50 c/s, and single phase. The rails are being employed as the return conductor. Such an arrangement while resulting in several advantages in respect of power transmission and traction engineering, the power feed being inherently unbalanced, produces certain undesirable effects on communication circuits in the neighbourhood of the tracks, rendering them unsafe and unworkable. 4.2 Mechanism of Induction The mechanism of induction from the 25 KV AC traction system is due to electrostatic coupling and electromagnetic coupling. 4.2.1 Electrostatic Coupling (Capacitive coupling) Electrostatic induction:- cable conductor insulated from earth and situated in this field will get charged to certain potential with reference to the earth due to capacitance coupling. The magnitude of this potential depends on the catenary current and distance between track and conductor. With the catenaries maintained at 25,000 V an electric field is created in the vicinity of the tracks. An electric conductor, such as a communication wire insulated from earth and situated within this field will get ‘charged’ to a certain potential with reference to earth due to capacitance coupling. The magnitude of this potential depends on the voltage of the catenary and distance. 4.2.2 Electromagnetic Coupling Electromagnetic induction:- Due to vicinity of AC Traction and length of parallelism, the currents flowing in the catenaries return to the feeding point via rails, the rails are not specifically insulated from the earth therefore some portion of currents field a path or induces emf in cable sheath and conductors. It is dangerous to working people and equipment. The currents flowing in the catenary returns to the feeding point via the rails. The rails are not specifically insulated from the earth, therefore, provides an alternate path for the currents. Some portion of this current penetrates deeply into the earth, to find a path in other rails, cable sheaths, metal pipes and similar conductors parallel to the track. Near the feeder points the whole of the current must return to the secondary windings of supply transformer. The current in the catenary is the source of an alternating magnetic field. This field cuts any conductors parallel to the track and induces e.m.f.’s in them. The catenary system acts like a primary winding and each other parallel conductor acts like the secondary winding of a transformer. IRISET 21 TC1 - Telecom Cables (Copper) Effects of Railway Electrification on Telecom circuits Therefore, from the above, it should be evident that the inductive interference constitutes a hazard to personnel using or working on the lines as also to the connected equipment. The induced voltages also seriously interfere with the signalling arrangements on the telecommunication circuits causing them to be unworkable. Apart from the induction at the fundamental frequency 50 c/s another source of trouble is on account of the harmonic components of the catenary currents. 4.3 Screening factor Voltage induced in conductor in presence of metallic sheath Screening factor, K = ---------------------------------------------------------------------------------------- Voltage induced in conductor in the absence of metallic sheath The reduction in induced voltages that is affected by the various conductors parallel to the catenary system is expressed by saying that each such conductor has a screening factor. This is defined as follows: - Screening factor, K is the ratio of Voltage induced into the conductors of the cable core in the presence of the metallic sheath of the cable to which the screening factor refers to voltage that would be induced to the conductor of the cable core if the metallic sheath of the cable to which the screening factor refers, is absent. It follows from this definition that the screening factor is normally less than unity. Generally this value is as low as possible. The screening effect of current is the consequence of the magnetic field produced by current in that conductor (sheath). This conductor (sheath) can only provide a screening factor when it is carrying current. To achieve, it must be a part of a complete circuit. By considering the screening effect of a cable sheath, clear distinction should be made between "the voltage of the core to the sheath," and “the voltage of the core to earth". If the sheath is insulated from earth, identical voltages are induced in sheath and core, the voltage between them is zero. At the same time the sheath does nothing to reduce the voltage between core and earth. To do this the sheath must carry a return current, the field of which opposes the field induced by the current in the catenary. To carry such a current the both ends of the sheath have to be earthed. According to the above mentioned phenomenon, it is very clear that an induced voltage developed due to the difference of primary & secondary magnetic fluxes in the cable conductors as shown in figure shown below. IRISET 22 TC1 - Telecom Cables (Copper) Effects of Railway Electrification on Telecom circuits Induced Voltage in Cable conductors 4.4 I.T.U-T. Recommendations Recommendations on permissible voltages, calculating method and protective measures have been issued by the I.T.U-T. Accordingly the following voltages may not be exceeded in the circuit formed by cable conductors and ground. a) As regards electrostatic induction, the critical figure recommended by the I.T.U-T is 15 mille amperes current. b) When a person is in contact with both the earth and with the conductor of a telecommunication line. During the normal functioning of the power line, or electric traction system, the longitudinally induced voltage in the telecommunication circuits should not exceed 60V. c) During the abnormal functioning of the traction power line, the longitudinal induced voltage shall not exceed more than 150 Volts. d) During traction power line short circuit condition, the induced should not exceed more than 430V rms. e) As regards interference to speech transmission, the psophometric voltage in the communication circuits should not exceed 2mV. By the way of sectionalising all the communication circuits to break the metallic continuity of the conductors to prevent cumulative build up of induced voltages with the introduction of isolating transformers at every 17 Km on long distance communication networks and adoption of special maintenance precautions. The cables to be laid along the tracks should have aluminium sheath and steel tape armouring so as to have a screening factor of less than 0.1 in the anticipated range of magnetic field intensity. IRISET 23 TC1 - Telecom Cables (Copper) Effects of Railway Electrification on Telecom circuits 4.5 Psophometric noise When cable is in close proximity to strong electromagnetic fields, unwanted current and voltage may be induced on it. If the power level is high enough, the electrical "noise" can interfere with voice and data applications running on the cabling. In data communication, excessive electromagnetic interference (EMI) hinders the ability of remote receivers to successfully detect data packets. The end result is increased errors, network traffic due to packet retransmissions, and network congestion. For analog voice communication, EMI can create psophometric noise, which degrades transmission quality. This will be measured with a psophometric meter. Psophometric voltage readings, V, in mill volts, are commonly converted to dBm (psoph) by dBm (psoph) = 20 log10V- 57.78. Psopho curve 4.6 Effects of 25 KV 50 Hz AC Traction on Telecommunication cable may be reduced by ▪ Changing over Overhead system to Underground Cables is mandatory.. Isolation Transformers: It is considered that a normal field strength of 87.5 V/Km exists in the vicinity of a telecom cable. This induces a voltage of 8.75 V/Km in each conductor of cable, because of its screening factor of 0.1. As cable length increases this voltage also increases proportionately. If this longitudinally induced voltage exceeds 150V AC, the safety of working personal and equipment becomes hazardous as per the recommendations of ITU-T. It is essential to isolate all circuits from induced voltage, so that its value will not raise above 150volts. For that divide 150V by per-kilometre induced value i.e., 8.75V/Km of the cable, gives 17 Km of max. permissible length for cable circuits. Hence, Isolating circuits are provided physically by Isolation Transformers at a distance of 17 Km on each circuit at cable Hut. By doing this accumulation of induced voltage on the cable pairs is brought to Zero. ▪ Provision of Earthing and SPD`s for all telecom equipment as per RDSO guidelines. ▪ Using Aluminium Sheathed/Screened cables which are having good screening factor (0.1). ▪ Screening factor is the ratio of voltage induced in the conductor in presence of metallic sheath and voltage induced in the absence of metallic sheath. 4.7 Precautions to be taken for protection of staff and equipment in 25 KV 50 Hz AC traction territory. Any Telecommunication circuits in the vicinity of AC Traction running parallel to 25 KV lines are liable to be affected by AC induced voltage. Therefore precautions should be taken to eliminate the possibility of induced voltage affecting equipment and humans. IRISET 24 TC1 - Telecom Cables (Copper) Effects of Railway Electrification on Telecom circuits 1. Crossing of track, if any, should be negotiated by underground cables running at right angles to the track as far as practicable. 2. Special protective measures (viz. provision of G.D tubes, fuses and earthing etc) are required to be taken for telecommunication lines entering equipment rooms/OFC huts. 3. For the human safety considerations the safe working voltages should be 60 V under normal conditions and 150 V with special precautions and 430 V under fault conditions as discussed earlier. 4. Precautions are required to be taken on account of following, i) Proximity of live conductor. ii) Pressure of return current in Rails. iii) Induction in all metallic bodies situated close to overhead equipment. 5. Precautions to be taken by staff are i) Use Insulated Tools. ii) Use Rubber Gloves. iii) Use Rubber Mats. iv) Before cutting the armour or sheath of the cable an electrical connectivity is to be established between two ends of the cable through an external wire. IRISET 25 TC1 - Telecom Cables (Copper) Telecom Quad Cables CHAPTER-5 TELECOM QUAD CABLES 5.1 Introduction: At the time of conversion of Non RE Area into RE(Railway Electrification) Area of 25KVAC Traction Line, the Underground Quad Cables are utilized in place of Over- Head transmission line of metallic wires to avoid the effect of induced EMF on Over Head Alignment running parallel to the electrified traction lines. The existing PIJF cables are not fit for long distance communication; hence underground quad cables have been introduced. These underground Quad cables work excellently for good quality of speech. In non-RE areas the Telecom circuits are working on Overhead ACSR wires and its overall dia of the line wire is 4.5 mm with 0.038 dB loss per Km. The long distance Telecom networks on ACSR wire were working on 2 wire since no amplifier is used upto the length of 350-400 Km of Telecom network. Because of tremendous induced voltage effects in the Railway Electrification area the Telecom networks are changed to screened underground quad cables. Here the dia of the underground quad cable conductor is 0.9 mm with the loss of 0.63 dB per Km for unloaded cable and 0.25 dB per Km for loaded cable, due to this high attenuation of the conductors in cable, the amplification of the speech and signal became essential at every 40-50 Km length of cable section. Hence, 2 wires for Trans and 2 wires for Receive are used for amplifiers, totally four wires are used known as quad and circuit is modified as 4 wire circuit in RE area. “STAR QUAD” is four conductor balanced cable, two pairs form a tighter, more consistent pack will resist even more noise. IRISET 26 TC1 - Telecom Cables (Copper) Telecom Quad Cables PIJF Quad Cables 4 Quad cables 6 Quad cables 0.9 mm dia conductor 1.4 mm dia conductor RE cable and PIJF quad cable These RE Main Cables were specially designed for long distance communication networks in Railway Electrified areas. This cable is a combination of Paper and PVC insulated quads. Being paper is a very good insulator, these paper insulated quads are used for long distance Telecom circuits such as Section Control (CTO), Dy Control, Traction Power Control (TPC), Traction Loco Control (TLC), Remote Control (RC) and Emergency Control (EC). PVC insulated quads (PET) are used for signalling applications such Block, IB etc. In the present scenario the RE cable is phased out due to its limited bandwidth with limited route diversity and introduction of OFC with 4 quad /6 quad cable. All the long distance Voice Frequency (VF) circuits as mentioned above are transferred into OFC network and existing signalling circuits, such as Block, BPAC, IB, TAWS and Telecom circuits such as LC gate communication, EC sockets are working in 4 quad/6 quad underground cable. In addition to this, data circuits such as UTS/PRS, FOIS, Railnet, MIS, MMIS and Telephony trunking etc., are switched over to OFC network. The 4/6 quads Jelly filled cable of IRS-Specification No- 30/2005 version-2 (0.9mm dia conductor) affected from 1/1/2006 has been introduced. In addition to this, 1.4 mm dia copper conductor underground Railway jelly filled 6 or 4 quad cables for Signalling & Telecom installations have been introduced by RDSO under specification no: RDSO/SPN/TC/72/07 for long (more than 25 Km ) distance Block sections. 5.2 Construction of PIJF Quad cable 1. Conductor, 2.Petroleum jelly, 3. Dummy tube, 4. Binder, 5. Polyester tape 6. Poly aluminium tape, 7. PVC inner jacket, 8. Aluminium wire screen 9. Woven tape (yellow colour), 10. PVC intermediate jacket, 11. G.I. Steel armour 12 PVC outer jacket IRISET 27 TC1 - Telecom Cables (Copper) Telecom Quad Cables 5.2.1 Polythene Insulated conductor The conductor is composed of plain annealed high conductivity copper wire. The conductor is circular in cross-section, free from splits, cracks and corrosion. Each conductor is insulated with solid polythene. The insulation is applied closely and homogeneously on the conductor. The insulation resistance between each conductor shall not be less than 5000 Mega ohms per kilometre at room temperature when tested with 500 V megger. 5.2.2 Jelly The cable core is fully filled with a water resistant compound of jelly which is fully compatible with the polythene insulation of the conductors. 5.2.3 Polyester Tape After application of the filling compound a close helical or longitudinal lapping of a polyester tape is applied over the cable core. The tape is impregnated or flooded with jelly. 5.2.4 Poly Aluminium Moisture Barrier Polythene coated aluminium tape is applied longitudinally on the core with a minimum overlap of 6mm. 5.2.5 Inner Sheath Cable is sheathed with polythene. Sheath is circular, free from pin holes, joints and other defects. 5.2.6 Screen The cores with inner sheath are surrounded by a reasonably close fitted screen of aluminium in the form of wires/strips. IRISET 28 TC1 - Telecom Cables (Copper) Telecom Quad Cables 5.2.7 Woven Tape The aluminium screen is wrapped with a single layer of woven tape impregnated with barium chromate to protect the screen from oxidation. 5.2.8 Intermediate Sheath Further protection for the screening is provided by extruded PVC circular sheath over screening. The colour of this intermediate sheath is grey. 5.2.9 Armouring The galvanised steel tape armouring is applied tightly over the intermediate sheath with two layers. The direction of the lay of the armour is opposite to that of the outermost layer of screening. 5.2.10 Outer Sheath The outer sheath is applied over the armouring. The colour of this outer sheath shall be black. 5.3 Colour Code scheme for PIJF Quad Cable 5.3.1 4-Quad cable The colour code scheme of 4 Quad polyethylene-insulated quads Colour of insulation of conductor Colour scheme of the Quad No A-Wire B-Wire C-Wire D-Wire quad whipping Quad 1 Orange White Red Grey Orange Quad 2 Blue White Red Grey Blue Quad 3 Brown White Red Grey Brown Quad 4 Green White Red Grey Green 5.3.2 6-Quad cable Colour code scheme of conductor insulation of 6-Quad cable Colour of conductor insulation Colour scheme of Quad No A-Wire B-Wire C-Wire D-Wire the quad whipping Quad 1 Orange White Red Grey Orange Quad 2 Blue White Red Grey Blue Quad 3 Brown White Red Grey Brown Quad 4 Green White Red Grey Green Quad 5 Yellow White Red Grey Yellow Quad 6 Black White Red Grey Black Wire A and B shall form a pair and similarly Wire C and D shall form another pair. Conductors are diagonally opposite forming one pair and the remaining two diagonally opposite conductors forming the second pair of the quad. The quad shall be held together firmly by means of an open helical whipping of nylon yarn or coloured tape of suitable material of appropriate thickness. IRISET 29 TC1 - Telecom Cables (Copper) Telecom Quad Cables 5.4 General specification of 4/6 PIJF Quad cable 1.4 mm dia Sl.No. General Specifications 0.9 mm dia conductor conductor Characteristic impedance 470 Ohms (Unloaded) 310 Ohms (Unloaded) 1 at 800 Hz 1120 Ohms (Loaded) 2 Max. Loop Resistance 56 Ohms / Km 23.2 Ohms / Km Insulation resistance of the >100 M Ohms / Km >100 M Ohms / Km 3 PET Quad measured with 100V DC. Megger Transmission loss at 1 Kz 0.63dB/Km. (Unloaded) 0.3 dB/Km. (Unloaded) 4 0.25 dB/Km. (Loaded) 5 RDSO spec. IRS:TC: 30/2005 ver.2 RDSO/SPN/TC/72-07 Note: The value of attenuation shall not exceed 2 dB/km for any frequency in the frequency range 300 Hz – 3400 Hz at 20C. 5.5 Specifications of 6 Quad Cable RDSO spec. no: IRS-TC 30/2005 ver. 2. (w.e.f:1-1-2006) 1. Loop resistance: 56Ω/L.Km 2. Transmission loss: 0.25 dB/L.Km (loaded), 0.63 dB/ L.Km (unloaded) 3. Impedance: 470 Ω (unloaded) / 1120 Ω (loaded) 4. Insulation resistance: >100 MΩ /Km with100V Megger 5. Conductor diameter nominal: 0.9 mm 6. Minimum diameter of insulated conductor: 1.5 mm 7. Thickness of PVC outer sheath: 2 mm 8. Thickness of G.I. Armour tape: 0.8 mm 9. Thickness of PVC intermediate sheath (Grey colour): 1 mm 10. Thickness of inner PVC sheath: 2 mm 11. Thickness of Aluminum tape: 0.2mm±10% 12. Aluminium wires/strips used for screening: 36/12 no. 13. Mutual Capacitance of the pair: 50 pF/Km. 5.6 Present Status of 6 Quad Cable System used in various Railways 1. Conventional 6 quad cable system with loading, balancing and V.F repeaters at regular intervals of 40-50 Km. 2. Equalizer Amplifier System at all stations with unloaded 6 quad cable, balancing of cable at the stations. 3. 6 Quad cable with OFC. 5.7 Quad cable along with OFC and without OFC. The Railways are presently following two schemes of laying 6 quad underground Telecommunication Quad cables as under: a) 6 Quad cable only b) 6 Quad cable along with OFC Where the section is non-RE area only 6 quad cables was used for Train operational communication arrangements. However, additional Signalling sub-systems like BPAC, TAWS, IB Phone to improve safety and reliability are gradually being integrated into the Signalling systems. Railway board have considered this emerging need and decided that 6 quad cables shall be provided along with OFC in all future works on sections where communication based Signalling schemes are being planned. IRISET 30 TC1 - Telecom Cables (Copper) Telecom Quad Cables 5.8 Guidelines for use of Optical Fiber System and 6 quad cable on various routes in Indian Railways. (a) New Railway Projects – Gauge Conversion/New lines/Doubling/Railway Electrification. On A, B, C, D & D spl Routes, the following configuration should be used. 24 Fibers Optical Fiber Cable (as per RDSO Specification IRS.TC.55/ or latest) with Six Quad cable (as per RDSO Spec. IRS.TC30/2005 or latest). (b) Replacement of existing overhead /RE quad cable for control communication. (i) Existing RE Telecom Cable, whenever it is due for replacement on age cum condition basis, it should be replaced by Optical Fiber System with 6 quad cable (ii) Existing Overhead alignment on A, B, C & D-special should be replaced with Optical Fiber System with 6 quad cable. Tentative Quad allocation of a 6 Quad Cable, when laid along with OFC or without OFC is as under: a) 6 quad cable with OFC b) 6 quad cable without OFC Quad No Name of the circuit Quad No Name of the circuit 1 Block Circuit 1 Block Circuit 2 Spare 2 Section Control 3 Emergency Control 3 Emergency Control 4/1 LC gate telephone 4/1 BPAC 4/2 BPAC 4/2 LC gate telephone 5 BPAC 5 BPAC 6 TAWS 6 TAWS Quad allocation of 6 quad cables 5.9 Difference between PIJF underground Paired and Quad Cables: Sl.No PIJF Telephone Paired Cable PIJF Telecom Quad Cable Conductors are available in the form of Pairs. Conductors are available in the form of Quads. 1 Twin Twisted. Twin Twisted pairs. 2 Available in 10/20/50/100 pairs Available in 4/6 quads 3 Dia of conductors : 0.51/0.63 mm Dia of conductors : 0.9/1.4 mm Characteristic Impedance of the pair : 600 Characteristic Impedance of the pair in the quad: 4 Ohms 470 Ohms (0.9 mm dia) / 310 Ohms (1.4mm dia) Induced Voltage reduction done in two stages Induced Voltage reduction done in three stages 5 by earthing Al foil & armour by earthing Al foil, Aluminium screen & armour. Used for short distance Telephony/ Data Used for long distance Signalling and Telecom 6 Circuits applications in the Railway station area safety circuits between two Block stations. as last mile connectivity. Loop Resistance of the pair is an important Transmission loss in pairs of quad is an 7 criteria. important criteria. 8 RDSO spec. of Cable: IRS-TC: 41/97 RDSO spec. of Cable: IRS-TC: 30/2005 Jointing is in the form of Straight Through/ Jointing is in the form of Straight Through 9 Derivation/Transformer Joints(as required in the Joints. section). Thermo Shrinkable Jointing Kits for different Thermo Shrinkable Jointing Kits for 4/6 10 sizes of cables used as per RDSO spec. no: underground Quad Cable as per RDSO spec. RDS0/SPN/TC/57/2006 no: IRS:TC:77/2012 Terminated in Krone/Wago type modules and Terminated in 10 Pair/20 Pair CTBs and Wago 11 terminal strips. type modules Generally used by all Telecom Service Exclusively designed for Signaling and Telecom 12 providers. applications of Indian Railways. IRISET 31 TC1 - Telecom Cables (Copper) Cable Laying Practices CHAPTER-6 CABLE LAYING PRACTICES 6.1 Introduction: This Chapter deals with the Specifications under which the various works for trenching and laying of underground telecommunication cables. The OFC HDPE duct and 6quad underground communication cable are to be laid in the same trench. Basically the HDPE duct for OFC cable is to be laid into the ground in a depth of 1200 mm or at the bottom of the trench. 6 quad cable shall be laid after 200 mm backfilling i.e. at a depth of 1000mm, followed by bricks protection wherever requires and also between station area ( home signal to home signal). OFC and 6 quad cable with warning brick in a cable trench 6.2 Important stages in Telecom Cable laying a. Cable route survey b. Obtaining permission from Engineering department c. Trial pits to identify soil condition d. Trenching e. Shifting of material and cable drum placement f. Laying of various types of pipes in trenches wherever required g. laying the Cable h. Bedding and tiling to protect the cable i. Backfilling of trench j. Placing of Cable route markers IRISET 32 TC1 - Telecom Cables (Copper) Cable Laying Practices 6.3 Survey Work a. Surveying of the route and submission of proposed cable route plan b. Preparation of soil strata report and data collection. c. Submission of Cable route plan. 6.3.1 Route Survey: Cable route surveys are two types a) Preliminary Cable Route Survey b) Detailed Cable Route Survey After allocation of work, foot inspection has to be carried out to arrive at the approximate and exact route plan of the alignment of cable route. While carrying out the survey, Railway boundaries, availability of other Signal, Electrical cables, water pipes etc. are shall be identified and certified by the P. Way, Signal & Electrical authorities of Railways. In case of obstruction or availability of other cables, alternative routes have to be selected. On approval of the same, the detailed survey of the section has to be started. 6.3.2 Soil strata report: After getting the clearance, carry out the soil strata analysis. To identify soil condition, at every 500mtrs the pits have to be excavated and soil condition has to be analysed. The analysis readings are to be recorded and incorporated in the report as well as in the drawings. 6.3.3 Submission of cable route plan: Based on the above survey the cable route plan should be prepared. 6.4 Points to be covered under the survey for cable route 1. Avoiding underground structures, signalling cable, power cables and pipelines etc. 2. Avoid rodent/termite infested or infected side of the alignment. 3. Off set of the cable trench from the central line of the track such as having burrows. 4. Avoiding proximity to chemical, paper and such other industries, which discharge Chemically active affluent. 5. Avoiding areas prone to water logging. 6. Avoiding large rock cutting thick jungles and areas difficult to approach etc. 7. Avoid the side of the alignment which is likely to be affected due to addition/alteration of earth work, super structures such as doubling, shifting of alignment of the existing track etc., For this, cable route should be discussed with construction and doubling organization. 8. The orientation of the route i.e. left or right side of the track in the sections to be decided on following: - a. That side of the main line, which is away from other cables such as signalling and power. b. Side which is likely to involve least track crossings and likely to be more convenient for crossing the track, bridges culverts etc. 9. Figure out and scale crossing of roads, tracks etc. 10. Scale out proposed arrangements of crossing bridges, culverts etc. out of the many alternatives available. 11. Assess special problems if any in the section such as undulating surfaces, long cuttings, tunnels etc. 12. Scale out the cable entry or exit arrangement at the cable huts of drop insert locations. Avoid built up areas including those areas where buildings etc. are likely to come up in future. IRISET 33 TC1 - Telecom Cables (Copper) Cable Laying Practices 13. With engineering drawing already in hand, verify pathways/pedestrian crossing and other lateral clearances. 14. Scale out the special work required if any and the manner of the cable route in approach of the existing bridges locations. 15. Identify, if any special lengths of cable is required to avoid joints on bridges/culverts etc., 16. For the straight runs as far as possible a separation of 10 Meter should be kept from the nearest track. 17. No OFC or Quad Cables shall be laid close to the existing track. It shall be laid close to the Railway boundary on one side of the Railway track to the extent possible to avoid any interference with the future works. 18. As a rule a minimum distance of 5.75 M should be maintained between the OHE masts and the cable. In Yards etc., where observance of this rule may be difficult, a minimum distance of 3 Meter should be maintained. In exceptional cases where the cable trench depth is less than 0.5 Meter the lateral distance may be reduced to 1Meter. In such trenches, which are in close proximity to OHE masts, the cable should be laid in PVC/RCC Pipe. 19. Location of traction substations / feeding posts and other OHE switching posts. 6.5 Information in Cable Route Plan The cable route plan shall contain following information: 1. Whether the cable route is on the up or down side of the Railway Tracks. 2. Approximate location and length where the cable shall be laid in GI pipes and GI troughs and under the bed on culverts. 3. Locations of sections where the cable shall be covered by burnt bricks positioned breadth wise @ nine bricks/meter (average). 4. Location of track crossing and the number of tracks to be crossed. 5. Location of road crossing and the number of RCC pipes to be provided. 6. Locations and length for protection of cable in rocky area and platform cutting etc. 7. Approximate locations of derivation Joints for L.C. Gate or emergency socket posts will be provided on 6-Quad cable. EC posts will be installed exactly at KM Zero markings. 8. The size, length and route of PIJF derivation cables from OFC cable hut to various subscriber points. 9. Furnish the final cable route plan showing the distance of cable from the nearest track centre at every 30 M and location of EC posts and joint locations. 6.6 Detailed Cable Route Survey The purpose of the detailed survey is to undertake the closer study of the various existing telecommunication facilities, to work out the exact requirement of the 6 Quad and Derivation /PIJF Cables and materials required for different items of work, finalise all the drawings and site plans required for the execution of work as also to examine the details collected during preliminary survey and to effect necessary changes/modification if any. 6.7 Length of 6 Quad Cables The Quad cable length is to be worked out on the following basis to arrive at the location of the straight joints. IRISET 34 TC1 - Telecom Cables (Copper) Cable Laying Practices Cable location Cable reserve / loop required Route length distance between two stations Contour allowance 2.5% of route length Track crossing / Road crossing 2.5 meters on each side Major bridges 10 meters on each side Minor bridges 5 meters Cable joint 10 meters from both ends LC gates / other derivation locations 3 meters Station / OFC hut 10 meters 6.8 A typical cable requirement calculation for a block section having length of 10 km with 3 LC gates, one major bridge and two minor bridges/culverts Sl.no. Cable requirement length in Km. 1 Block section route length 10.00 2 Contour allowance length @ 2.5% x 10 km 00.25 3 Cable loop at 3 LC gates: 3x3 mtrs 00.01 4 Cable approach towards either side of bridge : 10+10 mtrs 00.02 5 Cable loop at either side of major bridge : 10+10 mtrs 00.02 6 Cable loop at 2 minor bridges/culvers: 5+5 mtrs 00.01 7 Cable loop at joints ( joints in the section are 10):10x 20 mtrs 00.20 8 Cable approach towards station buildings: 10+10 mtrs 00.02 9 Cable loop at both the station ends: 10+10 mtrs 00.02 10 Total length of cable 10.55 = 10.6 6.9 Telecom cable laying / arrangement in major yards and stations In big yards and major stations involving large numbers of Cabins/Depot/Tapping points, it may not be practicable to lay independent derivation cables for various locations. Therefore one main cable shall be laid to transverse in a zigzag way through the yard involving frequent tapping points. 6 Quad and/or higher size PIJF paired cable may be laid for this purpose. The circuits shall be preferably be tapped through V.F. Transformers. If the depth of the trench is not feasible to standard depth of one meter in yards and station areas, the lesser depth of cable trench shall be protected with warning bricks. IRISET 35 TC1 - Telecom Cables (Copper) Cable Laying Practices 6.10 Storage of Cable drums a. The cable drums shall be stored on a well drained, hard surface, so that the drums do not sink in the ground causing rot and damage to the cable drums. Paved surface is preferred, particularly for long term storage. b. The drums shall always be stored on their flanges, and not on their flat sides. c. Both ends of the cables should be properly sealed to prevent ingress/ absorption of moisture by the insulation during storage. d. Protection from rain and sun is preferable for long term storage for all types of cables. There should also be ventilation between cable drums. e. Damaged battens of drums etc. should be replaced as may be necessary 6.11 Basic methods of laying underground cables a) Laying direct in the ground b) Drawing through ducts c) Laying solid 6.11.1 Laying direct in the ground This method of laying cables is comparatively simple and cheap, and is the one that is widely used. It involves digging a trench in the ground and directly laying the cable on a bedding of soft earth free from corrosive elements at the bottom of the trench, covering the cable with a layer of soft earth, placing warning bricks centrally over the soft earth covering and finally filling up the trench. When the soil contains appreciable quantities of stones or pieces of rock 1.25 mm layer of sand may be used for the bedding and covering below the layer of bricks. 6.11.2 Drawing through ducts In this system, also known as the draw in system, one or more ducts are laid together, according to anticipated requirements and a single or more cables according to size are drawn through each pipe or duct. Manholes are provided at definite intervals. The initial cost of laying ducts is high. The system is generally used only in difficult locations such as crossings, railway bridges, culverts and in such situations where subsequent excavation of a trench is both very expensive and inconvenient. 6.11.3 Laying solid This method involves laying a cable in trough made in the excavated trench, filling the trough completely with molten bituminous compound/ cement concrete, providing warning bricks on top and then back filling with earth. Laying solid is higher cost than laying direct. 6.12 Special cable laying practices 6.12.1 Track Crossings a. All cable crossings across the Railway track in station yards shall be done in DWC pipes, threading the cable through these pipes. The Contractor shall do the trenching to the required depth wherever necessary, such as approaches to track crossing and the length in between the adjacent tracks. Two G.I Wires of 10SWG size shall be threaded through DWC pipes, one to pull the cable and one for future use. The arrangement of cable and DWC pipe trunking under track crossings has been shown in Drg. No. RDSO/TCDO/COP/19. b. At locations other than specified above, as directed by site engineer, Track crossing shall be done by horizontal boring for DWC pipe provision. IRISET 36 TC1 - Telecom Cables (Copper) Cable Laying Practices 6.12.2 Road Crossings a. Metalled, macadamised, concrete and stone paved roads shall also be cut to a depth of 1 metre. The cable shall be laid through RCC or DWC or GI pipes as applicable as per Drawing No. RDSO/TCDO/COP/20. The road surface shall be restored to original. b. When crossing Roadways, it is necessary to lay the cable in such a manner as to avoid the necessity of handling the cable sharply and minimize the excavation of road surface as far as possible. Where cable is laid on the surface, trunking, trunking aligning should be curved down to the pipes and proper brick or concrete joint should be made between trunking and pipe. c. The crossing of main roads often involves difficulties especially if traffic is heavy. Precautions to avoid accidents to workmen, pedestrians and the vehicles should be taken. On minor roads, which can be temporarily closed to traffic, it is possible to open up and cross the entire width of the road. Pipes should be installed quickly in the cutting, which is then filled in thereby reducing to a minimum time for which the road is closed. d. Some roadways, which are broad, may be opened for half the width first allowing the other half for use by Road traffic. Pipes are laid in the opened half. After the backfilling the opened portion, the other half is opened and the first half will be used by the road traffic. After the pipes have been laid in the second half, they must be linked with those laid in the first half. DWC pipes shall be used for road crossings. In all cases, pipes shall be laid at a depth of one meter below the formation level or lower as may be required. e. Wherever a cable is laid across an important road particularly one with a special surface it is good investment to provide for future expansion. The following methods may be adopted. f. The size of the pipe shall be so chosen that other cables may be drawn subsequently. Two lengths of G.I. wire 10 SWG shall be used as lead wire. Two such lengths of G.I. wire shall be laid through the pipe. One wire shall be used for leading in the cable and the other shall be kept with suitable overlay to enable cable pulled out at later stages if required. At road crossings, RCC or DWC pipes of specified dia shall be used. 6.12.3 Culverts and Bridges a. Wherever possible, the cable shall be laid under the bed of the culvert through RCC pipes as applicable at site. Similar arrangement shall be provided for taking the cable in water logged areas and drains. b. In case of wet culverts or unfriendly terrains where it is not possible to lay cables under the bed of culverts, the cable may be laid over the culverts and GI pipes as per the Drawing No. RDSO/TCDO/COP/13 &14. c. When laying cable on long bridges, the question of longitudinal expansion caused by temperature differences should be taken into consideration and suitable cable loops should be provided at the pillars of the Bridges. The cable should also be laid sinuously inside the GI pipe. d. The laying of the cable on the bridges is to be done with much care and planning. It is necessary that the cable drum to be laid on the bridge is inspected and tested thoroughly so that damaged cable cannot be installed. e. As laying involves movement of a large number of staff over the bridge, the line should be blocked if necessary and flagman posted on the other side. IRISET 37 TC1 - Telecom Cables (Copper) Cable Laying Practices 6.12.4 Laying of Cable in Solid & Rocky soils and Residential & Marshy areas a. If the terrain is rocky normal dimensions of the trench cannot be ensured. In such cases trenching to be done as per Railtel diagrams enclosed. b. In marshy areas, where it is not possible to divert the cable route, the cable should be suitably laid and protected as per the decision of the Railway c. Representative depending on site condition, like laying cables in RCC pipes of suitable dia concreted at every Meter. d. The cable will have to be led inside any masonry buildings such as ASM’s Room at a depth of 0.75 m by cutting the Masonry structure of the wall. After the cable has been led inside the masonry wall, the floor inside shall be duly repaired and Plastered. e. Laying of Cable near Power cable: When the contractor comes across any other cable already laid, he shall first report the fact to the engineer. Should the cable be identified by the Engineer as a Power cable (LT / HT), the trench shall be dug as far away from the route of the power cable as practicable. f. Crossing of Telecommunication cable with another cable shall be avoided wherever possible. Where, however, this is not possible the telecommunication cable shall be laid in RCC pipe. The length of the RCC Pipe to be provided on either side of the crossing shall be at least one meter. g. The cable shall be laid through GI pipes at the location marked on the tapping and route plan and as required by SSE/JE.. h. Laying the cable through pipes, galvanized steel wires of a cross section not less than 10 SWG shall be used as a lead wire. Two such lengths of wires shall be laid through the pipes so that after the cable is threaded through the pipe one led wire is permanently left in the pipe with a suitable overlay at two ends to enable the cable to be pulled out at a later stage if required to do so. i. On arch bridges and culvert bridges, the cables will be threaded through the GI pipes etc. j. Damages to cables is likely if care is not taken in laying cables where the bed changes from solid support such as the foundation pipe or bridge to soft support such as soft soil. The cable must not press against the edge of the solid support. The soft soil near the edge must be tamped and the cable raised slightly. k. Special Soil Condition: Cable should not be run through high acidic or alkaline soil or through sewage. If this is unavoidable, special measures should be taken against Corrosion. l. Laying of 6 quad Cable near Feeding Posts/TSS: In the vicinity of feeding posts as far as possible the cable shall laid be on the side of the track opposite to the feeding post. Further the cable shall be at least one meter away from any metallic part of the OHE and other equipments at the substation, which is fixed on the ground and at least one meter away from substation earthing. In addition the cable shall be laid in RCC pipes for a length of 300 meters on either side of the feeding point. 6.13 Cable Markers RCC cable markers shall normally be provided at a distance of every 50 meters on the cable route, at derivations and also to be provided at all types of cable joints. They should be of standard RCC with letters “IR / 6 QUAD CABLE “and logo engraved and painted. They shall be painted with Green when placed at joint locations and painted with Red/ Orange for normal indication. IRISET 38 TC1 - Telecom Cables (Copper) Cable Laying Practices Joint Inspection shall be carried out by SSE/JEs of Open Line and SSE/JEs of Concerned Organisation (Ex: Projects/Con.) after completion of cable laying works. 6.14 Power Crossing 11KV and above Power and telecom cables should have the shortest length of parallelism. When high voltage power cable 11 KV and above, has a parallelism exceeding 0.8 Km, appropriate safety measures have to be taken. Whenever laying of new telecom cables across or parallel to the existing 11KV and above power crossing, PTTC (Power Telecom Co-ordination Committee) approval is mandatory to protect Railway Telecom network from induced voltage effects from power lines and vice versa. As per the PTTC guideline the protection devices such as surge protection devices shall be provided. As per PTTC, it is advisable to take the telecom cable with maximum horizontal clearance as far as practicable but not less than 0.6 meters, so that the intensity of inductive interference can be minimized. Absence of sheath continuity and armour continuity in Telecom cable and it’s improper earthing in the vicinity of power cable will result in AC induction and consequen

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