TC 1 TELECOM CABLES P V R SAGAR, ILP-2/IRISET 7013 416 426 TELECOM CABLES (COPPER) VER 1.0 1 TC1: Telecom Cables (copper) for POSC - 06hrs Sl No Course Contents 1 Introduction of telecom cables 2 Paired Telephone cables 3 U/G PIJF cables 4 Effects of Railway Electrification on Telecom circuits 5 Telecom Quad cables 6 Cable laying practice CABLES VER cables 10 7TELECOM Jointing of underground (COPPER) 2 Telecom transmission media 1. Aerial Lines (Over Head Lines): GI wires & ACSR (Aluminium Conductor Steel Reinforced). 2. Micro Wave System: Analog & Digital Systems are in use for Radio Patching for Control Communication and long distance Administrative trunk circuits. 3. RE Main Telecom Underground Cable: 0+12+2, 0+17+3, 0+18+2 etc. are in use in RE areas. 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: 24 Fiber Underground OFC Cable is in use for high bit rate Telecom traffic with enormous applications over Indian Railways. TELECOM CABLES (COPPER) VER 10 3 UNDER GROUND CABLES TELECOM CABLES (COPPER) VER 10 4 CLASSIFICATION OF TELECOMCABLES TELECOM CABLES (COPPER) VER 10 6 Special Features of Telecom Cables •PVC insulated •Twin Twisted paired / quad cables •Screened cables •Balanced cables •Loaded Cables and Colour coded TELECOM CABLES (COPPER) VER 10 7 Electrical characteristics of Telecom Cables The four primary elements R = Series Resistance L = Series self inductance C = shunt capacitance G = Shunt conductance [Leakage] TELECOM CABLES (COPPER) VER 10 8 Distortion less condition of a transmission line GL = CR TELECOM CABLES (COPPER) VER 10 9 PAIRED CABLES TELECOM CABLES (COPPER) VER 10 10 TELECOM CABLES (COPPER) VER 10 11 How Cross-talk is Eliminated ? ADJACENT CIRCUIT L1 3v 3v 3v 2v Span-1 L2 2v 2v Span-2 L1=3+2+3+2= 10V span-3 2v Span-4 L2=2+3+2+3= 10V Net induced voltages on L1&L2 are the same, no potential difference, no current flow at telephone and no cross-talk from adjacent Circuits. TELECOM CABLES (COPPER) VER 10 12 ADVENTAGE OF PAIRED CABLE • Paired cables are balanced, by using two closely spaced conductors twisted together, audio is balanced equally on these wires. Since the flow of induced emf on both wires are equal and hence no potential difference, no current flow at telephone and no cross-talk develops from adjacent Circuits. • A ground shield used to prevent high frequency noise and balanced wires also rejects noise coming from ground loops. TELECOM CABLES (COPPER) VER 10 13 TYPE OF PAIRED CABLES • SWITCH BOARD CABLES • UNDER GROUND PIJF CABLES PVC Twin flate-2 core 10 pair-.4/.5mm/.63mm 20 pair-.4/.5mm/.63mm 50 pair-.4/.5mm/.63mm 100 pair-..4/5mm/.63mm DATA COM. CABLES 10 pair-.5mm/.63mm 20 pair-.5mm/.63mm 50 pair-.5mm/.63mm 100 pair-.5mm/.63mm Note: These cables are used for ) UTP (Un shielded twisted pair) b) STP (shielded twisted pair) COAXIAL CABLES RG 58- 180 mtrs, RG 8-500 mtrs These cables are used for Indoor a outdoor wiring, RDSO SPEC. IRS:TC 41/97(Adm. 2) wiring.TEC SPEC.NO:GR/WIR/06/03 OF March 2002 TELECOM CABLES (COPPER) VER 10 14 Colour code of Paired Cables Switch board cable are terminated • • • • • • • • • • • • BLUE - WHITE on krone cable termination box ORANGEWHITE (CTB) GREEN WHITE Under ground PIJF cables BROWN WHITE terminated on CTB SLATE WHITE UNDER ground 6 quad cables are terminated on CTB or wago BLUE RED terminals. ORANGE RED AFTER TERMINATION of cable pairs soldering shell be don other than GREEN RED krone and wago CTB s. BROWN RED AFTER TERMINATION of cable pairs SLATE RED circuit details to be painted. _____________________________________ ALL cables to be tested( end to end) Main colours: Bl, Or, Gr, Br, Sl. once in year. and record the Mate colours: Wh, Rd, Bk, Ye. parameters. TELECOM CABLES (COPPER) VER 10 15 Colour Code of Conductors 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 Gray / Slate 5 10 15 20 5 pairs 10 Pairs 50 pairs 5 number of 10 pair units 100 Pairs 5 number of 20 pair units 20 pairs Each UNIT has it’s own coloured binder : 1. Blue 2. Orange 3.Green 4.Brown 5. Gray TELECOM CABLES (COPPER) VER 10 16 QUAD CABLES • “STAR QUAD” is Four conductor balanced cable, four wires form a tighter, more consistent pack then two wires can and can resist even more noise. TELECOM CABLES (COPPER) VER 10 17 QUAD CABLES TELECOM CABLES (COPPER) VER 10 18 Impedance Vs Frequency. • The impedance, which describes the combined effect of resistance (R), inductive reactance (XL) 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. TELECOM CABLES (COPPER) VER 10 19 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. TELECOM CABLES (COPPER) VER 10 20 RAILWAY ELECTRIFICATION Effects of 25kv 50 cycles AC Traction on Telecommunication. 1.Electromagnetic induction:- 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 fined a path or induces emf in cable sheath and conductors. It is Dangerous to working people and Equipment. 2.Electro static induction:- cable conductor insulated from earth and situated in this filed 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. 3. . TELECOM CABLES (COPPER) VER 10 21 DIRECTIVES OF ITU-T FOR TELECOMM SYSTEM DESIGN ON 25KV AC ELECTRIFED SECTION 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. Psophometric voltage shall not exceed 2mv. During the normal functioning of traction system, the longitudinally induced voltage in telecomm circuit shall not exceed 60 volts. Under conditions of particular difficulty and as far as the telephone working condition permit, the limit of longitudinally induced voltage may raised to 150 v rms subject to spl. precautions being taken. (Tapping Transformers at Derivation point to be used) fault in traction system. To avoid danger to person ,cable and equipment the longitudinally induced voltage in telecomm circuit shall not exceed430 volts. During the time of short circuit TELECOM CABLES (COPPER) VER 10 22 Difference between PIJF underground Paired and Quad Cables Sl.No Telephone Paired Cable Telecom Quad Cable 1 Conductors are available in the form of Pairs. Twin Twisted Conductors are available in the form of Quads. Twin Twisted pairs. 2 3 4 5 • • • • • • • • • • • • • • • • • • • • Used for long distance Signalling and Telecom safety circuits between two Block stations. 7 Loop Resistance of the pair is important criteria. Transmission loss in pair of quad is important criteria. 8 RDSO spec. of Cable: IRS-TC: 41/97 RDSO spec. of Cable: IRS-TC: 30/2005 9 Jointing is in the form of Straight Through Joints. Jointing is in the form of Straight Through/ Derivation/Transformer/Condenser/Loading Coil Joints(as required in the section). 10 (TSF) Thermo Shrink Filled Jointing Kits for different size of cables used as per RDSO spec. no: RDS0/SPN/TC/57/2006 (RTSF) Reinforced Thermo Shrinkable Jointing Kits for 4/6 underground Quad Cable as per RDSO spec. no: IRS:TC:77/2012 11 Terminated in Krone/Wago type modules and terminal strips. Terminated in 10 Pair/20 Pair CTBs and Wago type modules 12 Generally used by all Telecom Service providers. Exclusively designed for Signaling and Telecom applications of Indian Railways. Available in 10/20/50/100 pairs Available in 4/6 quads Dia of conductors : 0.51/0.63 mm Dia of conductors : 0.9/1.4 mm Z o of the pair : 600 Ohms Z o of the pair in the quad: 470 Ohms (0.9 mm dia) / 310 Ohms (1.4mm dia) Induced Voltage reduction in two stages by earthing Al foil & armour Induced Voltage reduction in three stages by earthing Al foil, Aluminum screen & armour. TELECOM CABLES (COPPER) VER 10 23 Difference between PIJF underground Paired and Quad Cables Sl.No Telephone Paired Cable Telecom Quad Cable 6 Used for short distance Telephony/ Data Circuits applications in station area as last mile connectivity. Used for short distance Telephony/ Data Circuits applications in Railway station area as last mile connectivity. 7 Loop Resistance of the pair is important criteria Transmission loss in pair of quad is 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 Joints. Jointing is in the form of Straight Through/derivation Joints TSF Jointing Kits for different size of cables used as per RDSO spec. no: RDS0/SPN/TC/57/2006 RTSF) Jointing Kits for 4/6 u/g Quad Cable as per RDSO spec. no: IRS:TC:77/2012 9 10 TELECOM CABLES (COPPER) VER 10 24 Difference between PIJF underground Paired and Quad Cables Sl.No Telephone Paired Cable Telecom Quad Cable 11 Terminated in Krone/Wago type modules and terminal strips Terminated in 10 Pair/20 Pair CTBs and Wago type modules 12 Generally used by all Telecom Service providers Exclusively designed for Signaling and Telecom applications of Indian Railways TELECOM CABLES (COPPER) VER 10 25 What is 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 psophometric meter. • Psophometric voltage readings, V, in mill volts, are commonly converted to dBm(psoph) . TELECOM CABLES (COPPER) VER 10 26 PSOPH CURVE TELECOM CABLES (COPPER) VER 10 27 Effects of 25kv 50 cycles AC Traction on Telecommunication. It is reduced by the following.. Changing over Overhead system to Under Ground Cables. It is consider that a normal filed strength of 87.5v/km exists in vicinity of telecom cable . This induces a voltage of 8.75 v/km in each wire of cable ,because of its screening factor is 0.1 as cable length increase this voltages also increases proportionately. If this longitudinally induced voltage exceeds 150 v the safety 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-kilometer induced value 8.75/km of the cable, gives 17km of max. permissible length for cable circuits .Hence Isolating circuits physically by providing Isolation Transformers at distance of 17km on each circuit at cable Hut. By doing this accumulation of induced voltage on the cable pairs is brought to Zero. TELECOM CABLES (COPPER) VER 10 28 It is reduced by the following Provision of Earthing and SPD`s for all telecomm Equipments as per RDSO guidelines. By using seethed cables(Al or Pb) having good screening factor. Screening factor is the ratio of induced voltage of cable in presence of cable sheath and induced voltage cable with out cable sheath. TELECOM CABLES (COPPER) VER 10 29 PRECATIONS TO BE TAKEV FOR PROTECTION OF STAFF AND EQUIPMENT IN 25kv 50 cycles AC TRACTION TERRRITORY. Precaution are required on account of the flowing. 1. Proximity of Live Conductor 2. Pressure of return current in rails. 3. Induction in all metallic bodies situated close to overhead equipment. Precautions to be taken:1. Use Insulated Tools. 2. Use Rubber Gloves. 3. Use Rubber Mats. 4. Before cutting the armour or sheath of cables an electrical connectivity to be made between two ends of the cable through an external wire. TELECOM CABLES (COPPER) VER 10 30 SIZE OF RE CABLES (l+m+n) 0 = No of carrier quads 3 = No of pet quads 17 = No of paper insulated quads 0 = No of carrier quads 2 = No of pet quads 18 = No of paper insulated quads TELECOM CABLES (COPPER) VER 10 31 CONSTRUCTION OF 6Q CABLE 1. Conductor 2. Petroleum jelly 3. Dummy tube 4. Binder 5. Polyester tape 6. Poly aluminum tape 7. PVC inner jacket 8. Aluminum wire screen 9. Woven tape(yellow color) 10. PVC intermediate jacket 11. G.I. Steel armour 12. PVC outer jacket TELECOM CABLES (COPPER) VER 10 32 SPECIFICATIONS OF 6Q CABLE RDSO SPN.N0:IRS-TC 30/2005 Version I.W.E.F:1-1-2006 1. 2. 1. 2. 3. 4. 5. 6. 7. 8. 9. Loop resistance : 56Ω/Loop Km Transmission loss : 0.25 dB/Loop Km( When loaded) : 0.63 dB/ L.Km (When not loaded) Impedance : 470 Ω Insulation resistance : >100 MΩ with 100V Megger Conductor diameter : 0.9 mm Thickness of sheath (PVC): 1.8 mm Thickness of G.I. Armour: 4 X 0.8 mm Thickness of inner PVC sheath: 1.8 mm Thickness of Aluminum tape: 0.2mm±10% Aluminum Screen : 36 no. of wires / 13 no. of strips ( depends on dia / thickness) Mutual Capacitance : 0.05 uF/Km TELECOM CABLES (COPPER) VER 10 33 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, TELECOM CABLES (COPPER) VER 10 34 WHAT IS LOADING OF CABLE • For Attenuation free Transmission line. These line parameter should Justify the follow equation. • LG=RC but R C > L G • R and C are very high due to thin and very closely spaced conductors in the cable. It can not be decreased by increasing dia and spacing of the conductors due to limitation of cable size. G- is the conductance (leakage) can not increase due to low insulation of cable. The possibility is only adding the Inductance to the transmission line. It is known as Loading of cable. TELECOM CABLES (COPPER) VER 10 35 LOADING • Connecting the loading coils of value 118mH in series with each conductor to reduce the original attenuation of 0.63 dB to 0.25dB is known as “Loading” for 0.9 mm dia conductor : 88 mH/ 1830 mtrs. ( RE Cable) : 118 mH/ 2Km ( 6 Quad) TELECOM CABLES (COPPER) VER 10 36 LOADING SECTION IN CASE OF 6Q CABLE 1. Loading section – 2000 Mtrs. 2. Normal joint -500 m 3. Condenser joint – 1000 Mtrs. TELECOM CABLES (COPPER) VER 10 37 BALANCING OF CABLE • Bringing down the various capacitance unbalances below the nominated value to reduce the noise & cross talk in known as “Balancing” • Permissible limits of capacitance unbalance for full and half loading are 40 pF and 20 pF respectively. • 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 “Cross-talk Coupling”. • Cross-talk couplings causes cross-talk and Earth couplings cause ‘Noise’ in VF circuits. TELECOM CABLES (COPPER) VER 10 38 COLOUR CODE & QUAD ALLOCATION IN NON-OFC SECTION AS PER RLY.BOARD GUIDE LINES.LTR. NO.2003/TELE/TP/1 DT.8/8/03 Q.No COLOUR OF INSULATION Circuit A-Wire B-Wire C-Wire D-Wire 1 Orange white Red Grey BLOCK 2 Blue White Red Grey SEC.CTO 3 Brown White Red Grey EC 4 Green White Red Grey 4/1-BPAC 4/2GATE PHONE 5 Yellow White Red Grey BPAC 6 Black White Red Grey TAWS TELECOM CABLES (COPPER) VER 10 39 COLOUR CODE & QUAD ALLOCATION IN OFC SECTION Q.No COLOUR OF INSULATION Circuit 1 A-Wire B-Wire C-Wire D-Wire Orange white Red Grey Block 2 Blue White Red Grey Spare for Block 3 Brown White Red Grey E.C CKT 4 Green White Red Grey 4/1-LC GATE 4/2-BPAC 5 Yellow White Red Grey BPAC 6 Black White Red Grey TAWS TELECOM CABLES (COPPER) VER 10 40 LAYING OF TELECOM QUAD CABLE ASPER TELECOM MANUAL CHAPTERX III TELECOM CABLES (COPPER) VER 10 41 Checks on receipt of drum • • • • • • • • • Drum length 1 Km Wt. 2MT approx Drum no. , size of cable & diameter of conductor. Manufacturer’s details Length of cable Address of consignee Year of manufacturer Net & Gross weight Arrow indicating direction of rolling End seal shall be checked & RDSO inspection marks shall be seen TELECOM CABLES (COPPER) VER 10 42 Handling cable drum Use crane / ramp for loading & unloading Use centre bar for carrying Drum shall not be dropped Cable shall not be kept flat Do not stock drums closely TELECOM CABLES (COPPER) VER 10 43 Planning for laying • • • • • • Survey of cable route Mark details on 200m charts – Track – Yard – Buildings – LCs – Bridges – Water bodies – Existing cable paths – Likely track crossings Consider 1 drum length (1 km) to cover 0.96 RKm (the margin take scare of detour, crossing etc.) Joint on either end of bridges Locate ECs rationalizing no. of joints Get approval of Engg. & S&T (Open line) TELECOM CABLES (COPPER) VER 10 44 General precautions while laying • • • • • • • • • Do not drag the cable on ground Cable to be carried using centre bar Drum to be lifted with jack and rotated freely Measure insulation before laying Cable end sealing after laying Drum no. & km no. to be noted Straight line laying Overlap to be left for jointing Extra loop of 5/10 mtrs near bridges/culverts/repeaters TELECOM CABLES (COPPER) VER 10 45 Specific precautions while laying • • • • • • • • Criteria – At least 5.75 mtrs away from centre of track – Beyond embankment – Close to Railway Boundary Normal soil - Trench depth 1 m, width 30 cm (depth shall not be less than 70 cm in any case) Rocky area – at least 30 cm depth & use of DWC/HDPE/RCC pipe & concrete protection Use of MS channels & GI trough on girder bridges RCC / GI pipe protection on RCC culverts /bridges Check for availability of cable duct on RCC bridges LC gate crossing / track crossing – Use of GI pipes Insulation test of drum before laying & jointly signed by Maintenance & Construction representatives TELECOM CABLES (COPPER) VER 10 46 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. TELECOM CABLES (COPPER) VER 10 47 METHODS OF LAYING CABLE Methods of laying underground cables: 1. Laying direct in the ground 2. Drawing through ducts 3. Laying solid 4. Cable laying at road crossing 5. Cable laying on the long bridges 6. Cable laying at a railway track crossing TELECOM CABLES (COPPER) VER 10 48 Laying direct in the ground Digging the trench and putting the cable in it and closing. This method of laying cables is comparatively simple and cheap, and is the one that is widely used. Depth of the trench is 100 cm and width is 30cm. In case of Quad cable and OFC cable laying together in same trench then the depth of the trench is 120 cm with width of 30 cm. TELECOM CABLES (COPPER) VER 10 49 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 of ducts is high. The system is generally used only in difficult location such as crossings, railway bridges, culverts and in such situations where subsequent excavation of a trench is both very expensive and inconvenient. TELECOM CABLES (COPPER) VER 10 50 Laying solid • The places where the chemical soil is there, the cable cannot be laid directly. After making brick structure around it, the bitumen compound to be filled around the cable, and covered by bricks on the above. • Laying solid is higher cost than laying direct. TELECOM CABLES (COPPER) VER 10 51 Cable laying at road crossing At road crossings cables should be laid in pipes. Depth of the trench shall be 100 cm RCC/GI/DWC Pipes should be laid with a slight slope from the centre to the sides of the road to prevent collection of water. Trenching across roadways, for laying cable may be by manual excavation, thrust boring or tunnelling. TELECOM CABLES (COPPER) VER 10 52 Cable laying on culverts and bridges cables should preferably be laid in G.I. troughs / DWC pipes. Joints should be avoided, as far as possible, in the middle of the bridge. At the end of the bridge the cable should be gradually sloped down to normal trench depth through pipes. This is necessary to protect the cable from theft and damage by pedestrians or vehicular traffic. TELECOM CABLES (COPPER) VER 10 53 Cable laying at railway track crossing It should be laid in RCC/ GI / DWC pipes of not less than 75mm diameter at a minimum depth of 1.25 meters below rail level. The pipeline should extend on both sides of the Railway track for sufficient distance to enable repairs to the cable being undertaken without the necessity of disturbing the formation under the Railway track. TELECOM CABLES (COPPER) VER 10 54 STEPS IN LAYING 1. 2. 3. 4. 5. Trenching Cleaning the trench Drawing the cable Putting the bricks over it if necessary. Closing the trench with earth. Wlile closing suitable cable marker to be installed over it. TELECOM CABLES (COPPER) VER 10 55 Length of 6 Quad Cables The Quad cable length is worked out on following basis to arrive at the location of the straight joints. a) Route length as per actual measurement plus contour allowances of 2.5%. b) Extra length for track crossing including 2.5-meter loop on each side etc. c) Extra length on approach crossing of the bridges and 5 meters on measurement in the detailed survey. TELECOM CABLES (COPPER) VER 10 56 d) 10 meter of cable to be kept on either side of major steel bridges and 5 meters on minor bridges. e) At every joint a loop of 10 meters on either side. f) At Station a loop of 10 meters in the cable pit. TELECOM CABLES (COPPER) VER 10 57 TESTING OF CABLE TELECOM CABLES (COPPER) VER 10 58 TESTING OF CABLE TYPES OF TESTING: 1. Testing before laying of cable. 2. Testing after laying of cable. 3. Fault localization tests. 4. Testing of cable before commissioning of BPAC/SSDAC/MSDAC( as per RDSO lr. no.sts/e/ssdac/spn/177 dtd.28/30-8-6) 5. Routine Testing (as per Telecomm Manual) TELECOM CABLES (COPPER) VER 10 59 TESTING BEFORE LAYING a) Test the cable for proper end sealing. b) Checking for any physical/Mechanical damages during transportation, and during manufacturing. Etc., TELECOM CABLES (COPPER) VER 10 60 TESTS AFTER COMPLETION OF CABLE LAYING a) Continuity test – Ohm-meter / Multi meter b) Absence of crosses – Ohm-meter / Multi meter c) Absence of contacts – Volt-meter/Ohm meter / Multi meter d) Insulation testing – Insulation tester / Insulation Megger. TELECOM CABLES (COPPER) VER 10 61 ROUTINE TESTS in QUAD CABLE AS PER TELECOMM MANUAL CHAPTER VIII a) b) c) d) e) Conduction test.- Monthly Transmission loss test.- Monthly Crosstalk (near end far end)- Quarterly Psophometric Noise- Quarterly Insulation test – Yearly TELECOM CABLES (COPPER) VER 10 62 Mandatory Check &Tests to be don before commissioning of BPAC/SSDAC/MSDAC Applications on Quad/PIJF cables. a) b) c) d) e) f) g) h) i) j) • • Conduction test.-56 ohms/loop km Insulation Resistance – 10 M Ohms. Transmission loss test.-At 2khz/600ohms Transmission loss should not be more than 30 db for full length of quad cable. Near end Crosstalk- Should be better than -55 dbm at 155khz &-61 dBm at 1KHz Far End Crosstalk- Should be better than -55 dbm at 155khz & -65 dBm at 1KHz Psophpmetric Noise- should not be more than 2mv. Continuity of Armour - Should be Ensured Earth Resistance at Armour-Should be Ensured less than 1 Ohm. Position of one quad in quad cable x(A) x (C) x (D) 1st PAIR-AB x (B) 2ed PAIR-CD Each Quad is binded by respective quad colour binder TELECOM CABLES (COPPER) VER 10 63 Precautions to be taken while using quad cable • Designated pair of wire of same quad should be used. • Do not use one wire of one quad and another wire from other quad. • If any wire of a pair of the quad is broken then use fresh pair of wire should be used. • No wire should be paralleled for reducing the conductor resistance. TELECOM CABLES (COPPER) VER 10 64 CONDUCTION TEST a) Purpose of this test is to measure the loop resitance of conductors which indicates the condition of joints. b) Measuring instrument used: Ohm meter or Bridge Megger. c) Time of measurment: Hotest period of the day in case of Over Head lines / at any time in cable. d) Acceptance value: 5% more than standard values. +-- TELECOM CABLES (COPPER) VER 10 65 TRANSMISSION LOSS TEST a) Purpose of this test is to measure the dB loss of the system (cable). It also indicates the insertion loss of way station equipments. b) Time of measurement: coldest period of night i.e. 4 AM to 5AM in case of over head lines / any time in case of cables. c) Instrument used: TMS Kit. TELECOM CABLES (COPPER) VER 10 66 INSULATION RESISTANCE a) Purpose of this test is to know the proper insulation of the conductor. b) Time of measurment: Any time of the day. c) Instrument used: Insulation Megger. TELECOM CABLES (COPPER) VER 10 67 STANDARD VALUES Sl No Description 1 Loop Resistance in Ω 2 3 Insulation in MΩ 25.4 Ω /L.Km a) G.I wire of 3.55mm dia 5.62 Ω / L.Km b) ACSR wire of6/1/1.5 mm c) cable conductor of dia 0.9mm 56 Ω / L.Km 2 mill volts a) Psophpmetric Noisea) b) 4 Value 100 MΩ >1000 MΩ > With 100V Megger With 500V Megger Transmission loss in Db a) b) c) Cable conductor of dia 0.51 mm Cable conductor of dia 0.63 mm Cable conductor of dia 0.9 mm TELECOM CABLES (COPPER) VER 10 1.379 1.107 o.63 (UN-LOADED) 0.25 (LOADED} 68 JOINTING OF TELECOM CABLE(6Q) • Now a days to make any telecom cable joint Thermo Shrinkable Jointing Kit is used (TSF kit). • To make 6quad cable joints universal TSF kit under RDSO Specification IRS-TC-77/2012 is used. • To make cable joints for PIJF Under Ground telephone cable universal TSF kit under RDSO Specification IRS-TC-57/2006 is used. •TELECOM CABLES (COPPER) VER 10 69 CABLE JOINTS 6 QUAD CABLE TELECOM CABLES (COPPER) VER 10 70 JOINTS IN 6-QUAD CABLE 1. Normal joint: To join two lengths of cable. 2. Transformer joint / Derivation joint: This is made whenever we want to extend the control/block to any place. 3. Loading coil joint: To reduce the original attenuation of the cable to a lower value. 4. Condenser joint: To minimize the noise and cross talk in the cable. TELECOM CABLES (COPPER) VER 10 71 JOINTING OF TELECOM CABLE(6Q) Now a days to make any telecom cable joint Thermo Shrinkable Jointing Kit is used (TSF kit). To make 6quad cable joints universal TSF kit under RDSO Specification is used. IRS-TC-77/2012. is the specification number of the RTSF kit. IRS-TC-57/2012 TSF JOINTING KIT FOR PJF CABLES OF DIFRENT SIZES. TELECOM CABLES (COPPER) VER 10 72 JOINTS IN LOADING SECTION TELECOM CABLES (COPPER) VER 10 73 JOINTING PRECAUTIONS 1. The mud around the tent should protect the pit from entry of water. 2. The joint should be kept at the same horizontal level. 3. The end of the cable should meet the other end of the subsequent cable length with appropriate loops. 4. A heap of mud is to be placed over the buried joint so that the water flows away from the joint. TELECOM CABLES (COPPER) VER 10 74 Causes for cable failures & precautions Manufacturing defects – Test the cable before laying. Laying of cable at lower depth – Check the depth of trench before closing the cable trench. Joint failure due to sub stranded/ expired jointing kit used or jointing done by un skilled jointer- Use RDSO approved RTSF jointing kit and ensure skilled jointer before starting the work. Cable joint burnt due to Lightning - Ensure the proper continuity of metallic protection mechanism before closing the joint and Earth Resistance shall be less than 1 ohm at both ends of cable termination. TELECOM CABLES (COPPER) VER 10 75 • Using of Quad cable without jelly – Water enters into the joint along with cable core when there is any cable damage(crow bar hit) in between two joints- Use the PIJF 6 quad cable as per RDSO spec no. IRS:TC 30-2005 ver.1. • Exposing of cables on Bridges/ Culverts/Rocky areas- Regular Cable route inspection shall be done by section Technician/JE/SSE and strengthening of cable route shall be carried out as per Railway Board Telecom Action plan. TELECOM CABLES (COPPER) VER 10 76 Cable cuts and thefts- Ensure the cable is with in Railway Boundary, avoid the exposing of cable, implement the Railway Board JPO, Update the cable route diagrams and upload to web page for easy access to concerned dept. Codal life of Cable- Plan for replacement of cable with in codal life (20 / 25 years). TELECOM CABLES (COPPER) VER 10 77 Typical 6 Quad cable failures & their causes 1. Cable burnt at joint due to lightning and all circuits failed- Armour connectivity at joint is given up. 2. Cable is noisy while train passing in the section BPAC circuit frequently failingimproper earthing of cable armour/ screen/ Al. moisture barrier. TELECOM CABLES (COPPER) VER 10 78 Typical 6 Quad cable failure contd. • Abnormal delay (48 hrs) in restoring of 6 quad cable fault: Cable not traceable because cable is laid outside Railway Boundary and the Colony people constructed culvert on the cable route for about 10mts. The drainage water was over flowing and spread over the area and got covered with thick bushes also. Staff not able to walk on the cable route with cable route locater and could not locate the cable the fault. Later, found Cable was in damaged condition in the culvert. TELECOM CABLES (COPPER) VER 10 79 Thank you TELECOM CABLES (COPPER) VER 10 80