3 Types of cables used in the BSNL Local Subscriber NetworkThe UG cables which are used for the local subscriber network is called a Local Cable.It may bei) LSDC ( Lead sheathed dry core cable)ii) Composite sheathed cableiii) PIJF (Polythene Insulated Jelly Filled cable)
4 Junction workingThese cables are used as the link between two exchanges to take large number of circuits and are called Junction Cables.Previously PCQL (Paper Core Quad Local) cables were used.either PCM (Pulse Code Modulation) cables or OFC (Optical Fibre) cables.
5 Long distance workingThe cable connecting one major town to another town to take more number of channels are called Long Distance Trunk Cables.Coaxial Cables were used for this purpose.Nowadays optical fibre cable is being used.
6 Broad Construction of any Telecommunication cable Core:All the insulated conductors compactly arranged in pairs, units and super units constitute core of the cable. Moisture Barrier :The presence of moisture deteriorates the quality of insulation of the telecom cables.So moisture barrier protects entry of moisture into the core of the cable.Protection :: Telecom cables require Protectionfrom probable mechanical damagesfrom water and chemicals or soil conditionsfrom Induction due to Electrical linesfrom diggings by different agencies and individualsfrom damages while handling
7 Classification of U/G cables wrt design features Place where it is used - Underground/ overhead/ submarineInsulation material used - Paper / polythene cablesThe filling compound - Dry core / jelly filled cablesMechanical protection - Armoured / unarmoured cablesPlace of utilization Primary / Distribution/Junction cable.System for which used Co-axial / PCMType of conductor - Copper cable / Optical fibre cableGauge of the conductor mm/0.50 mm/0.63 mm/ 0.90mm
8 Filling material Dry air / Jelly MECHANICAL PROTECTION 1st pair B Limb3rd pair A Limb2nd pair B Limb1st pair A limbInsulating materialPVC / PAPERAnnealed CopperConductorsSheathPVCCOREFilling material Dry air / JellyMECHANICAL PROTECTION2 LAYERS OF GI STRIPS4/26/2017
11 PURPOSE OF INSULATION IN UNDERGROUND CABLES (1) used to separate the conductors bunched in a unit, so as to prevent short circuit between 2 conductors(2) used as SHEATH to separate the insulated conductors from being corroded. (3) used for marking / identifying the pair or conductor(4) used for preventing the grounding or earthing of the conductors. (5) used for preventing the corrosion of armouring.
12 Pairing and Overlay :Two insulated conductors twisted together with uniform lay to form a pair.The length of the lay of any pair shall be different so as to satisfy the capacitance unbalance requirements and cross-talk requirement.Unit Formation :The pairs are then assembled into units with different length of unit twists assigned to different units.These units are then assembled into a completed cable core.
13 CoreWrappings are applied to the completed cable core to hold the units together.To provide high di-electric strength from core to shield.To protect the conductor insulation from damage, due to the heat of sheathing operation.In PIJF cables, non-hygroscopic and non-wicking polyester tape is used as core wrapping.
14 Filling compoundThe cable should be filled with suitable water resistant compound.Paper insulated cables :: Dry air onlyPolythene insulated cables :: Jelly compound
15 SCREENAn aluminium tape coated with polythene / copolymer on both sides shall be applied over the cable core with a minimum overlap of 6 mm for all sizes of cables.
16 SHEATHThe sheath protects the cable from damage during installation and service.The sheath shall be reasonably circular and free from pinholes and other defects.Paper insulated cables : Lead sheath or Polythene sheathPolythene insulated cables : Polythene sheath only.
17 CONDUCTOR:: ARMOURING :: Each conductor is a solid round wire made of annealed high conductivity copper of diameter 0.32 mm, 0.40 mm, 0.50mm, 0.63mm and 0.90 mm.ARMOURING ::In the armoured cables, bedding and armour are provided over the sheath, to be followed by jacket.If this arrangement is not done, then it is un armoured cables.
18 Jacket Most cables serve their lives with a basic sheath. But for armoured cables, the armouring is to be protected from getting rusty and corrosion.Jacket is the protection which does the job.
19 Identification and Length markings on a Cable Telephone handset emblem Name of the Manufacturer Year of Manufacture Capacity of the cable in pairs Size of the conductor Length markingMarkings at an interval of 1m throughout the length and are visible to the naked eye from a distance of about 1 meter.
20 PIJF (Polythene Insulated Jelly Filled Cables) PIJF cable consists of twisted pairs of polyethylene insulated Copper conductors.Number of PairsThe cables shall be in sizes 5, 10, 20, 50, 100, 200, 400, 800, 1200,1600,2000, 2400, 2800, 3200 and 3600 pairs.ConductorsEach conductor shall be insulated with polyethylene of insulating grade.Different gauges of conductors: 0.32mm, 0.40mm, 0.50mm, 0.63mm, and 0.90 mm.Each conductor shall consist of a solid wire of annealed high conductivity copper smoothly drawn & circular in section, uniform in quality, resistance and free from all defects.
21 Nominal diameter of conductor Resistance per km per conductor at 20 0 Cin mmohms/km0.322230.401350.50860.63580.9028
22 COLOUR CODE FOR WIRE IDENTIFICATION The insulation will have following color for identifying pairs /conductors under normal lighting conditions. Primary colorsSecondary colorsFor 1st wire in a pairFor 2nd wire in a pair and binder tape of unit in 50pr/100pr unitWhiteBlueRedOrangeBlackGreenYellowBrownSlate / Gray
23 UnitA number of twisted pairs laid up to form a group shall constitute the unit. CODE FOR TAPE or BINDER FOR UNIT IDENTIFICATIONUnit number12345Colour of BinderBlueOrangeGreenBrownSlate / Gray
24 Pair No Color First Wire Second Wire 1 White Blue 2 Orange 3 Green 4 COLOUR CODE FOR CONDUCTOR INSULATIONPair NoColorFirst WireSecond Wire1WhiteBlue2Orange3Green4Brown5Slate / gray6Red7891011Black1213141516Yellow1718yellow192021Natural22
25 Note:In 5 pair cable, color code specified for pairs 1 to 5 is used.In 10 pair cable and 10 pair units of 50 pair cables, color code specified for pairs 1 to 10 is used.In 20 pair cables and 20 pairs units of 100 pair cables, color code specified for pairs 1 to 20 shall be used.
26 Stranding A 50 pair cable consists of 5 number of 10 pair units A 50 pair cable consists of 5 number of 10 pair unitsA 100 pair cable consists of 5 number of 20 pair units.These units shall be stranded into a compact and symmetrical cable.The sequence of the units in the cable shall be same throughout the length of the cable.
27 In case of 5, 10, 20 and 50 pair cables, one spare pair will be stranded as the last pair. The color of the spare pair shall be in accordance with pair No. 21 of the table (Natural – Blue).In 100 pair cable, 2 spare pairs shall be provided.The color of the pair shall be pair No. 21 & 22 of the table.The spare pairs in the case of 50 pairs and 100 pairs cables shall be provided within the cable core, but shall not be within any unit.
28 The 200 pair and 400 pair cables ( cables above 100 pr and upto 400 pairs) will be formed by super units of 50 pairs & units stranded in the form of layers.The cable over 400 pairs is formed by the super units of 100 pairs and the units stranded in the form of layers.
29 Note: The numbering of the units will be clock wise at running end. Identification of 50 pair super units in cables of 200 pair and 400 pair & 100 pair super units in cables of over 400 pairs:Position of the unit in the layer Color binderFirst (Marker) RedIntermediate WhiteLast (Reference) BlackNote: The numbering of the units will be clock wise at running end.
30 No of Units / Super units Nominal length in a drum Cable sizeNo of Units / Super unitsNominal length in a drumIn pairsCentre layerMiddle LayerOuter Layer0.50mm0.40mm51x5 (unit)1000-101x10 (unit)201x20(unit)505x10 (SU)1005x20(SU)5002004x50(SU)4002x50(SU)6x50(SU)8002x100 (SU)6x100 (SU)12003x100(SU)9x100(SU)16001x100(SU)5x100(SU)10x100(SU)20006x100(SU)13x100(SU)24002x100(SU)8x100(SU)14x100(SU)
32 Overall Polythene Jacket ArmouringFor armoured cable a close helical lapping of waterproof cotton tape shall be applied over the inner-sheath.The cable shall than be armoured with two applications of galvanized steel tape, each applied helically with a gap of 25% + 10% of the width of the tape, the second tape covering the gap of the first.Overall Polythene JacketA tightly fitting jacket of polythene shall be applied on the armoured cable.
33 USES OF DIFFERENT TYPES OF CABLES Gauges 0.32 mm and 0.44 mm for primary cable.Gauges 0.4 mm and 0.5 mm for secondary cable.Gauge 0.5 mm and 0.63 mm for distribution cable.Gauges 0.63 mm and 0.9 mm for distribution cable.Higher gauges of cable, for distribution side having longer lengths.Armoured jelly filled cable may be laid direct in the ground.Unarmoured jelly filled cable to be laid in Ducts.
34 .As the diameter of the conductor increases, the loop resistance / km will decrease.Hence higher diameter conductor cables are used for long distance subscribers.
35 ADVANTAGES OF PIJF CABLES Counting of pairs is easy and human mistakes are avoided.Jointing is easy, no chamber required.Failure of joints is less.Entry of moisture / water is prevented by Jelly.Cables can be directly terminated on MDF / Cabinet / Pillar and DPs, thus avoiding additional joints.Handling of cable is easy.Life of cable is more.
38 The standard sizes of Cu wires Diameter of wire in mm.Weight in lbs0.4 mm4 lbs / mile0.51 mm6.5 lbs / mile0.63 mm10 lbs / mile0.90 mm20 lbs / mile1.27 mm40 lbs / mile
39 b) Polythene insulation The two purposes of the insulation are Two types of insulation used in cables area) Paper insulationb) Polythene insulationThe two purposes of the insulation area) To prevent metallic contact between the conductors.b) To identify the cable colour code for numbering the cable pairs..
40 CO-AXIAL CABLEThe coaxial cable consists of an inner solid cylindrical conductor placed along the axis of an outer hollow cylindrical conductor.A coaxial cable may consist of two or more cores laid up with suitable lay with proper insulation along with quads laid in the interstices between them and all enclosed in a lead sheath.The cable is recognized withNumber of cores: i.e. either 2 core or 4 coreSize of the inner diameter of tube - i.e type ( large tube – 0.375” ) or type (small tube – 0.174”).The interstice Quads or pairs having diameter of 0.9mm
41 Types and Sizes of Coaxial cables The coaxial cables are divided into two types as follows:(a) Small tube coaxial type - the inner dia of outer tube is 0.174”(b) Large tube coaxial type - the inner dia of outer tube is 0.375”In each of the above type, following sizes are available(a) 2 core coaxial cable with interstice quads/pairs(b) 4 core coaxial cable with interstice Quads/pairs
42 TWO CORE 375 coaxial cable Coaxial core Lead sheath Quads of 0.9 mm Polythene disc
43 PCM Telecom cablesUnder ground PCM telecom cables used for 2mbps digital system. The cables are available in sizes 10+2, 20+4, 48+6, 96+8 and the nominal conductor diameter of 0.63 mm.The core shall be formed in units of 5 pair in the case of 10+2 pair cable, units of 10 pairs in the case of 20+4 cables and units of 12 pairs in the case of and 96+8 pairs.The conductor material and insulating material are same as PIJF cable construction.
44 The colour code for conductor insulation Pair no.123456789101112FIRSTWIREWRSECOND WIREBOGBNSBKColour code for Binder for Unit identificationUnit No.12345678Color of BinderBlueOrangeGreenBrownGreyWhiteRedBlack
45 PCM Cable Lay Up Size of cable No of Units Size of unit No of Extra pairs10+2 pairs25 pairs20+4 pairs10 pairs448+6 pairs12 pairs696+8 pairs8
46 PRIMARY & DISTRIBUTION CABLES For provision of the cable pair along different route the cable sections are classified as Primary, Secondary and Distribution cables.
47 PRIMARY CABLESAre cables laid from the exchange to the cabinets or Direct Pillars.As cost of the primary cable is very high the planning period is kept as 5 years for primary cables.
48 Distribution cablesThe cables from pillar or direct Pillar to various D.Ps are called distribution cables.The planning period is kept as 20 years.For Distribution Cables, 10, 20, 50 & 100 pairs cables are used.gauges- 0.5 mm & 0.63 mm.When the length of D/ cable is longer, higher gauges of cable are used.
49 Construction practice (Cable Laying) Classified in to:-Receipt, Storage, Handling and TransportSurveying and selection of routeTrenching and LayingJointing of Cable & TerminationPreparation of Cable Plan, Cable diagram and other recordsAcceptance Testing.
50 The following points are to be considered while selecting cable route. Principle streets may be avoided even by choosing a slightly longer route.(2) It is cheap to lay cable along foot-path.(3) For Primary & Secondary Cables, side of road is chosen which gives less obstructs and crossings.
51 selecting cable route4) For distribution cable, it is better to run the cable near the building.(5) Corrosive soil should be avoided, if unavoidable cable may be covered with sand or may be drawn through ducts.(6) The consideration should be given for existence, alternation and growth of other services.
52 Selecting cable route(7) Opening of expensive pavements and roads should be avoided.(8) When cables are to be laid close to power cable a minimum separation (both vertical & horizontal) should be 0.6 meters. When not possible telecom cables should be laid in solid (in a trough of bitumen).
53 Selecting cable route(9) When crossing a power cable it should be at right angle and laid in solid for 90 cm on either side of crossing.(10) When ducts are laid for cables, spare length of cable can be provided for future provision.
54 Surveying The route should be as short as possible Normally laid along road and Railway TracksCorrosive soil should be avoidedOpening expensive pavements and roads should be avoidedConsideration given to the existence, alteration and growth of servicesProper co-ordination with other underground services like Water,Electricity, Sewage, Gas etc
55 SELECTION OF ROUTE FOR LAYING CABLE The main points of consideration of cable route are :-a) Shortest possible length.b) Cheapest for laying.But due consideration are given to future requirement and expansions of other services. Normally cable should be laid along road and railway track.
56 Permission for Digging From:- Municipal or Local AuthoritiesTraffic AuthoritiesHighway AuthoritiesRailway DepartmentPort Trust Authorities
57 Co-ordination to be maintained Electric SupplyWater supplyGas PipelineSewage system
58 LAYING METHODS There are three methods normally adopted:- Laying direct in the groundLaying solidDrawing through Duct / Duct laying.
59 TrenchingThe Depth of trench should be 100 cms, and in any case it should not be less than 60 cms.The alignment should be straight at least 50 mts at a stretch.It should be at least 30 cms from the boundary walls.Width should be between 30 to 40 cms.A separation of 60 cms to be maintained while laying parallel to electric cables.Power Parallelism should not exceed 800 mts
60 The minimum bending diameter for armoured cable should be 15 times of diameter of the cable.
61 Road crossing Cable should be laid through G.I Pipes. The depth of pipe from the surface of road should be 1 mtr with a slope to pass water.The number of pipes should cater for 20 yrs.No Joints in the middle of the road.The trench should be reinstated with sand.Along National highways :- Cable should be laid at a distance of 457 cms from the centre of the road.
62 Along over bridge/Culvert/Flyover Culverts should be paved by a concrete channel of 12” depth below the bed of the culvertWhile laying across small bridges Gi pipes to be clamped to and extend beyond piers for safety of cablesIn the case of long bridges/flyovers laison should be kept with authorities for suitable arrangements or can use concrete channel provided with removable covers at a depth of 90 cms
63 Laying cable along Railways The trench should be at a distance more than 5.5 mts from the center of Railway trackExcavation and reinstatement within 3 mtrs should be attended by the Railway staff at the cost of BSNLNo overhead crossing permittedRailway crossing:- Use G.I pipes of 75mm dia, and Minimum depth from rail level should be 1.25 mtrs, and the length of pipe should be sufficiently long and should not extend 4.5 meters from the center of last track
64 Crossing CulvertsUse G.I Pipes cut at the ends in V- Shape on the outer surface and bend downwards so as to lead in the cable end to the trench
65 Cable Jointing Conductor jointing ( Uses UY Connector) Straight Joint & Branch JointJointing technique consists of :-Conductor jointing ( Uses UY Connector)For Cables more than 200 pairs jointing done by 20 pair modules2. Protection against moisture entry3. Protect against corrosion & Mechanical damage
66 Type of Jointing KITs and usage TSF –1 10, 20 Pair (straight joint)TSF – 2 50, 100 PairTSF – PairTSF – PairTSF – PairTSF – PairTSF – & Above
68 MAINTENANCE OF CABLE RECORDS The cable records may be divided into three categories1. Plan2. Line diagram and3. Cards.
69 PLAN OR MAPS Exchange area layout map shows the following details:- Boundaries of existing exchange areaProposed boundaries of future exchanges but liable to alterationsLocation of existing exchangesLocalities where future exchanges may be situated
70 CABINET AND PILLAR AREA LAYOUT MAPS (xge wise) The location of the cabinets, Primary cable routes, Duct lines, Manholes etc. Location of pillar, Secondary cable route, Location of Secondary cable joints, Duct lines, Man-holes etc.Location of DPs ( either internal or external ) the distribution cable route, the location of joint etc.
71 LINE DIAGRAMThese diagrams show the actual orientation of the cable network including the size of the joints, type and size of the DPs etc.Primary line diagram: shows all information of the primary cable, Ducts and Manholes for Primary cables.
72 DISTRIBUTION LINE DIAGRAM This diagram represents the cable orientation for all the distribution cables emerging out of a particular PillarOne diagram is meant for a pillar and all the DPs connected to it.JUNCTION CABLE DIAGRAMThis diagrams show the junction cable network in multi exchange area
73 CARDS SUBSCRIBER INDEX CARD DP CARDS CABINET AND PILLAR CARDS MDF CARDsSUBSCRIBER INDEX CARD
74 CARDSDP CARDSThese cards show the number, size, type (internal or external) and location of the DP and how each terminal of the DP is utilized. One card is required for each 10 or 20 pairs DP.
75 NO OF PAIRS CONNECTED TO PILLAR D.P. INDEX CARDD.P. NO.TYPE & SIZENO OF PAIRS CONNECTED TO PILLARLOCATION OF THE D.P.4700Krone – 10 pair10Market Entrance4701Krone – 20 pair20Market inside
76 THE CABINET AND PILLAR CARDS One set of cards is required for each cabinet or pillar.The set contains one card for each 100 pair CT- box .Each card shows the following particulars:-Number ,size, and type of the CT box, size of shell, location of the cabinet or pillar,Circuits working one each terminal of the CT box,The terminal to which the circuit is jumpered.The distant end code corresponding to each terminal of the CT box and the codes of cable pairs connected to the terminals.These cards must be filled in at the time of installation and subsequent additions or alterations effecting the entries must be incorporated .
78 COMPUTERISATION OF CABLE RECORDS Objective of Cable Records Management System (CRMS) i.e. Digitization of cable records & drawings to facilitate BSNLDesign & maintain a communication network model.To analyze the network model in different ways, distribute information as needed & interact with variety of enterprise systems.To manage the planning , design , construction , operation & maintenance of cable network.Development of centralized telecom database.
79 Drop wire Installation Drop wire used is 2 hard drawn copper cadmium conductor 1.25mm or 0.91 mm diameter laid parallel side by side & covered with black PVC of hard grade insulation.A ridge is provided between 2 conductors so that they can be separated into two fully insulated conductors without any injury to the insulation of individual conductors.
80 Hardware accessories for Installation Drop wire Distribution Clamp:- It is intended for suspending the self supporting drop wires at DP’s and intermediate point on poles
81 Support clamp with U - Back For supporting distribution clampIt is fixed on Channel Iron Bracket using U-Back
83 General layout of an exchange area The exchange area will be divided into two zones - inner zone and outer zone.The inner zone will be made up of DP areas which will be independent units with no flexibility between them.The outer zone is primarily made up of a number of pillar areas.The pillar areas may be either independent units or may be controlled from the cabinet.Each pillar area comprises of DP areas with the pillar providing the flexibility between the DPs.A pillar will be provided in each pillar area.
84 Basic Load and Variable load Any unit of the network - either a cabinet area, a pillar area, or a DP area may be expected to contain a certain minimum number of working lines at any future time.This minimum number below which the working circuits will not fall is termed the basic load for the unit.The range between the basic load and the maximum provision within which the total number of working circuits in the unit would vary, constitutes the variable load.
85 Inner and outer zonesEach existing exchange area has to be divided into inner and outer zones.The inner Zone boundary will be about 500 meters from the exchange.It must be drawn such that the cable feed to the inner zone is made independent, with the least amount of cable re-arrangement and wastage.In an inner zone provision of flexibility is uneconomical and pillars are not installed.The cabling from DPs, is terminated directly on the MDF.
86 Outside the inner zone, the provisions of pillars is justified and the distribution is generally arranged through pillars.Inner zone DPs numbering starts from 00_ _
87 Service LoopThe subscriber loop consists of connection from DP to subscriber premises.May consist of open wire lines or drop wires or buried served wires.
88 Distribution PointsDP area is the smallest territory in the cable system.It is desirable that the number of distribution points should be more and the capacity as small as possible.
89 DPs are given four digit number The first two digits corresponds to the number of pillar from which the DP is fed.In case of Inner zone DP the first two digit will be 00.The last two digits denote the serial number of DP with the pillar area or the inner zone.
90 There are four sizes of DPs which are provided depending upon the requirements :- 20 Pair Dps : These DPs are generally used in case of overhead lines feeding long areas and low populated areas.10 Pair Dps :- These DPs are generally suitable for drop wire type subs loops, where the telephone density is high.5Pair Dps:- Such DPs are normally provided where number of telephones in a building or contiguous building is small.2 Pair Dps :- These are normally provided in subscribers premises where requirement may not be exceeded more than two telephones.
91 Construction & Mtce of DP External DPs are fitted on posts by means of suitable size of U backsInternal DPs are fitted inside buildings on the wall at suitable locationIn cases of Multistoried buildings, where the telephone demand is very high the distribution cable of 20 pair or 10 pair size are taken to different floors or blocks and terminated on 10 or 20 pairs subs DPs.Individual wires are further provided from the subs DPs to the location of the telephone.
92 Leading in Distribution Cable to DP In case of external DPs, the cable is carried to DP box through GI pipe of 2”diameter.The GI pipe is fixed to the post by 2 nos of G.I clamps to hold the GI Pipe firmly. The lower end of the GI pipe should be about 30 cms below the ground surface.In case of internal DPs, the cable is lead into the building through a leading in pipe usually provided by the subscriber.
93 Location of distribution point The DPs should be located at one end of DP area in the direction looking towards the cabinet.In large buildings, which require over 10 pairs, all the pairs that are taken into the building, must be terminated at a convenient point preferably on the ground floor, before they branch off for internal distribution frame, if the number of pairs required is large.
94 Location of Cabinet & Pillar Should be located at obstruction free placeTo be mounted on concrete PlinthEasily accessibleAdequate space for jointing and other worksShould not be in a curve, or a crowded placeShould not obstruct pedestriansAvoid Marshy & Floods area
95 Siting of Cabinets, Pillars & DP Cabinet & Pillars normally 800 and 1000 pair.In Pillars and Cabinets CT-Boxes of terminating capacity of 100 pairs are mounted –which is made up of Krone type modules of 10 numbers.Krone tool is used for terminating wires.( No stripping, No soldering, No screwing required)
96 Location of pillars and demarcation of pillar area The provision of flexibility between DPs, by means of cross connection, requires the cable pairs from the exchange and DP sides to be terminated at the cable terminal point (CT Box), suitably mounted on frames inside steel casing or shell.There will be a number of points in the existing cable network where a pillar can be introduced with an advantage. (the points where a number of distribution cables meet are generally suitable for locating the pillars.)Pillars are numbered from 21 to 99.
97 Each pillar area is distinct, serving the DPs located within its area but not the DPs located in any other pillar area to avoid criss crossing of distribution cables.Each pillar must have a separate distribution network originating from the pillar and there should be no need of teeing in any of the section. The total terminating capacity of pillar are available in the sizes of 400, 800, 1000, 1600 and 2000 pairs.The terminations on distribution side are more than the terminations on the secondary side.
98 Location of PillarThe pillar should be located taking into account the following considerations :-a. The function of the pillar is to provide flexibility. Unless there are 5 to 6 DPs in a block, a separate pillar for the block may not be justified.b. Although the telephone load in a block may not justify a pillar, it is necessary to provide a pillar irrespective of telephone load in the blocks where cabinets are installed. This will avoid back feeding of distribution cables from other pillar areas to meet the demand of the particular block.c. The Pillar areas should be so demarcated that no major road crossings are encountered while laying distribution cables to feed the DPs of the area.d. Primary and Secondary cables being ducted are safer as compared to the distribution cables, which are a weakest element in the system. Therefore, the distribution cables’ length from pillar to the last DP should be minimum possible, by keeping the pillar nearest to the anticipated load centre of the area, to achieve better reliability, minimum fault liability and economy in material and labour.
99 Utilization of underground cable The planning and laying of the cable should have accuracy of maintaining the following utilization standard :-Primary percentSecondary to 85 percentDistribution percent
100 Type of Cable Network Broadly there are two types of networks :- (1) Rigid Network(2) Flexible Network (Cabinet and Pillar system)
101 Flexible networkIn this type of network two cross connection points viz. cabinets and pillars are provided between exchanges and DPs to maintain the flexibility by using a particular cable pair within a number of DPs.(a) Primary cable :- The cable laid between exchange and cabinet is called primary cable. The gauge of such cable is normally 0.32/0.4 mm.(b) Secondary cable :- This cable is linking the cabinet with pillar and the normal gauge of conductor is 0.5mm.(c) Distribution cable :- DPs are connected to the pillar by these type of cable. The gauge varies from 0.5 mm, 0.63mm depending upon the distance of the DPs from the pillar.
102 Numbering schemes of cabinet, pillar and DP Cabinets are given two digits number in the series 01 to 20Pillars are also given two digits numbers but in the series 21 to 99 Once the number is given to a Pillar, it must not be changed unless it is transferred to another exchange area.The verticals are numbered serially commencing from non growing end in two digit 01 to 99
103 Coding of primary ,secondary & Distribution cables Primary cables are given a single letter code A,B,C,D etc. (I and O omitted)Secondary cables are coded with the cabinet number followed by single letter A,B,C,D,......etc. (Example 12 C )The junction cable code consists of two letters denoting the exchanges at which the cable is terminated and digit denotes the serial number ( Eg:-Junction cable between City & Park exchanges are coded as CP 1, CP2, CP3.....etc.)
104 LOCATED AT MARKET PLACE PILLAR NO. 47( 1000 PAIRS KRONE TYPE)LOCATED AT MARKET PLACEA2B1B2C1C2D1D2E1E2A1Primary cable pairsDistribution cable pairs