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External Plant.

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Presentation on theme: "External Plant."— Presentation transcript:

1 External Plant

2 Nomenclature of the cables based on their use

3 Types of cables used in the BSNL
Local Subscriber Network The UG cables which are used for the local subscriber network is called a Local Cable. It may be i) LSDC ( Lead sheathed dry core cable) ii) Composite sheathed cable iii) PIJF (Polythene Insulated Jelly Filled cable)

4 Junction working These 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 working The 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 Protection from probable mechanical damages from water and chemicals or soil conditions from Induction due to Electrical lines from diggings by different agencies and individuals from damages while handling

7 Classification of U/G cables wrt design features
Place where it is used - Underground/ overhead/ submarine Insulation material used - Paper / polythene cables The filling compound - Dry core / jelly filled cables Mechanical protection - Armoured / unarmoured cables Place of utilization Primary / Distribution/Junction cable. System for which used Co-axial / PCM Type of conductor - Copper cable / Optical fibre cable Gauge of the conductor mm/0.50 mm/0.63 mm/ 0.90mm

8 Filling material Dry air / Jelly MECHANICAL PROTECTION
1st pair B Limb 3rd pair A Limb 2nd pair B Limb 1st pair A limb Insulating material PVC / PAPER Annealed Copper Conductors Sheath PVC C O R E Filling material Dry air / Jelly MECHANICAL PROTECTION 2 LAYERS OF GI STRIPS 4/26/2017

9 Design of Cable Conductors Core Moisture Barrier Screen Sheath ( PVC )
Bedding Armouring Jacket 4/26/2017

10 Unarmoured & Armoured Cable
Jacket (PVC) Armouring (G.I) Bedding (Polythene) Screening (Al) Core Wrapping (PVC) Conductor (Cu) Sheath (PVC) Screening (Al) Core Wrapping (PVC) Conductor (Cu) 4/26/2017

(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 Core Wrappings 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 compound The cable should be filled with suitable water resistant compound. Paper insulated cables :: Dry air only Polythene insulated cables :: Jelly compound

15 SCREEN An 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 SHEATH The 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 sheath Polythene insulated cables : Polythene sheath only.

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 marking Markings 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 Pairs The cables shall be in sizes 5, 10, 20, 50, 100, 200, 400, 800, 1200,1600,2000, 2400, 2800, 3200 and 3600 pairs. Conductors Each 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 C in mm ohms/km 0.32 223 0.40 135 0.50 86 0.63 58 0.90 28

The insulation will have following color for identifying pairs /conductors under normal lighting conditions.  Primary colors Secondary colors For 1st wire in a pair For 2nd wire in a pair and binder tape of unit in 50pr/100pr unit White Blue Red Orange Black Green Yellow Brown Slate / Gray

23 Unit A number of twisted pairs laid up to form a group shall constitute the unit.  CODE FOR TAPE or BINDER FOR UNIT IDENTIFICATION Unit number 1 2 3 4 5 Colour of Binder Blue Orange Green Brown Slate / Gray

24 Pair No Color First Wire Second Wire 1 White Blue 2 Orange 3 Green 4
COLOUR CODE FOR CONDUCTOR INSULATION Pair No Color First Wire Second Wire 1 White Blue 2 Orange 3 Green 4 Brown 5 Slate / gray 6 Red 7 8 9 10 11 Black 12 13 14 15 16 Yellow 17 18 yellow 19 20 21 Natural 22

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 units A 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 binder First (Marker) Red Intermediate White Last (Reference) Black Note: The numbering of the units will be clock wise at running end.

30 No of Units / Super units Nominal length in a drum
Cable size No of Units / Super units Nominal length in a drum In pairs Centre layer Middle Layer Outer Layer 0.50mm 0.40mm 5 1x5 (unit) 1000 - 10 1x10 (unit) 20 1x20(unit) 50 5x10 (SU) 100 5x20(SU) 500 200 4x50(SU) 400 2x50(SU) 6x50(SU) 800 2x100 (SU) 6x100 (SU) 1200 3x100(SU) 9x100(SU) 1600 1x100(SU) 5x100(SU) 10x100(SU) 2000 6x100(SU) 13x100(SU) 2400 2x100(SU) 8x100(SU) 14x100(SU)

31 1x100 +5x x100prs

32 Overall Polythene Jacket
Armouring For 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 Jacket A tightly fitting jacket of polythene shall be applied on the armoured cable.

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.

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 lbs 0.4 mm 4 lbs / mile 0.51 mm 6.5 lbs / mile 0.63 mm 10 lbs / mile 0.90 mm 20 lbs / mile 1.27 mm 40 lbs / mile

39 b) Polythene insulation The two purposes of the insulation are
Two types of insulation used in cables are a) Paper insulation b) Polythene insulation The two purposes of the insulation are a) To prevent metallic contact between the conductors. b) To identify the cable colour code for numbering the cable pairs. .

40  CO-AXIAL CABLE The 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 with Number of cores: i.e. either 2 core or 4 core Size 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 cables Under 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. 1 2 3 4 5 6 7 8 9 10 11 12 FIRST WIRE W R SECOND WIRE B O G BN S BK Colour code for Binder for Unit identification Unit No. 1 2 3 4 5 6 7 8 Color of Binder Blue Orange Green Brown Grey White Red Black

45 PCM Cable Lay Up Size of cable No of Units Size of unit
No of Extra pairs 10+2 pairs 2 5 pairs 20+4 pairs 10 pairs 4 48+6 pairs 12 pairs 6 96+8 pairs 8

For provision of the cable pair along different route the cable sections are classified as Primary, Secondary and Distribution cables.

47 PRIMARY CABLES Are 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 cables The 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 Transport Surveying and selection of route Trenching and Laying Jointing of Cable & Termination Preparation of Cable Plan, Cable diagram and other records Acceptance 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 route 4) 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 Tracks Corrosive soil should be avoided Opening expensive pavements and roads should be avoided Consideration given to the existence, alteration and growth of services Proper co-ordination with other underground services like Water,Electricity, Sewage, Gas etc

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 Authorities Traffic Authorities Highway Authorities Railway Department Port Trust Authorities

57 Co-ordination to be maintained
Electric Supply Water supply Gas Pipeline Sewage system

58 LAYING METHODS There are three methods normally adopted:-
Laying direct in the ground Laying solid Drawing through Duct / Duct laying.

59 Trenching The 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 culvert While laying across small bridges Gi pipes to be clamped to and extend beyond piers for safety of cables In 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 track Excavation and reinstatement within 3 mtrs should be attended by the Railway staff at the cost of BSNL No overhead crossing permitted Railway 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 Culverts Use 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 Joint Jointing technique consists of :- Conductor jointing ( Uses UY Connector) For Cables more than 200 pairs jointing done by 20 pair modules 2. Protection against moisture entry 3. Protect against corrosion & Mechanical damage

66 Type of Jointing KITs and usage
TSF –1 10, 20 Pair (straight joint) TSF – 2 50, 100 Pair TSF – Pair TSF – Pair TSF – Pair TSF – Pair TSF – & Above

67 Sequence of Joint closure
Cable Marking Armour continuity Conductor jointing Sheath continuity Filling compound Metal canister Cable preparation Install sleeve Thermo shrinking Armour continuity completed

The cable records may be divided into three categories 1. Plan 2. Line diagram and 3. Cards.

69 PLAN OR MAPS Exchange area layout map shows the following details:-
Boundaries of existing exchange area Proposed boundaries of future exchanges but liable to alterations Location of existing exchanges Localities where future exchanges may be situated

  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 DIAGRAM These 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.

This diagram represents the cable orientation for all the distribution cables emerging out of a particular Pillar One diagram is meant for a pillar and all the DPs connected to it. JUNCTION CABLE DIAGRAM This diagrams show the junction cable network in multi exchange area


74 CARDS DP CARDS These 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.

D.P. INDEX CARD D.P. NO. TYPE & SIZE NO OF PAIRS CONNECTED TO PILLAR LOCATION OF THE D.P. 4700 Krone – 10 pair 10 Market Entrance 4701 Krone – 20 pair 20 Market inside

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 .


Objective of Cable Records Management System (CRMS) i.e. Digitization of cable records & drawings to facilitate BSNL Design & 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 clamp It is fixed on Channel Iron Bracket using U-Back

82 Cabinet, Pillar & DP

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 zones Each 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 Loop The 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 Points DP 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 backs Internal DPs are fitted inside buildings on the wall at suitable location In 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 place To be mounted on concrete Plinth Easily accessible Adequate space for jointing and other works Should not be in a curve, or a crowded place Should not obstruct pedestrians Avoid 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 Pillar The 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 percent Secondary to 85 percent Distribution 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 network In 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 20 Pillars 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.)

PILLAR NO. 47 ( 1000 PAIRS KRONE TYPE) LOCATED AT MARKET PLACE A2 B1 B2 C1 C2 D1 D2 E1 E2 A1 Primary cable pairs Distribution cable pairs

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