External Plant

Nomenclature of the cables based on their use

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)

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.

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.

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

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 - 0.40 mm/0.50 mm/0.63 mm/ 0.90mm

04/21/23 8

1st pair B Limb

3rd pair A Limb

2nd pair B Limb

1st pair A limb

Insulating material PVC / PAPER

Annealed CopperConductors

Sheath PVC

C

O

R

E

Filling material Dry air / Jelly

MECHANICAL PROTECTION2 LAYERS OF GI STRIPS

Design of Cable

• Conductors

• Core

• Moisture Barrier

• Screen

• Sheath ( PVC )

• Bedding

• Armouring

• Jacket04/21/23 9

Unarmoured & Armoured Cable

04/21/23 10

Sheath (PVC)Screening (Al)

Core Wrapping (PVC)Conductor (Cu)

Core Wrapping (PVC)Screening (Al)Sheath (PVC)

Jacket (PVC)Armouring (G.I)

Bedding (Polythene)Screening (Al)

Core Wrapping (PVC)Conductor (Cu)

Core Wrapping (PVC)Screening (Al)

Bedding (Polythene)Armouring (G.I)

Jacket (PVC)

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.

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.

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.

Filling compound

• The cable should be filled with suitable water resistant compound.

• Paper insulated cables :: Dry air only• Polythene insulated cables :: Jelly compound

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.

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.

CONDUCTOR::

• 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.

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.

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.

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.

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

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

COLOUR CODE FOR WIRE IDENTIFICATION

The insulation will have following color for identifying pairs /conductors under normal lighting conditions. 

Unit number 1 2 3 4 5

Colour of Binder

Blue Orange Green BrownSlate /

Gray

UnitA number of twisted pairs laid up to form a group shall constitute the unit.

 CODE FOR TAPE or BINDER FOR UNIT IDENTIFICATION

Pair No ColorFirst Wire Second Wire

1 White Blue 2 White Orange3 White Green4 White Brown5 White Slate / gray6 Red Blue7 Red Orange8 Red Green9 Red Brown10 Red Slate / gray 11 Black Blue12 Black Orange13 Black Green14 Black Brown15 Black Slate / gray16 Yellow Blue 17 Yellow Orange18 yellow Green19 Yellow Brown20 Yellow Slate / gray21 Natural Blue22 Natural Orange

COLOUR CODE FOR CONDUCTOR INSULATION

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.

Stranding • 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.

• 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.

• 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.

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.

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) 1000 -

20 1x20(unit) 1000 -

50 5x10 (SU) 1000 -

100 5x20(SU) 500 -

200 4x50(SU) 400 -

400 2x50(SU) 6x50(SU) 400 -

800 2x100 (SU) 6x100 (SU) 200 200

1200 3x100(SU) 9x100(SU) 200 200

1600 1x100(SU) 5x100(SU) 10x100(SU) - 200

2000 1x100(SU) 6x100(SU) 13x100(SU) - 200

2400 2x100(SU) 8x100(SU) 14x100(SU) - 200

1x100 +5x100 +10x100prs

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.

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.

.

• As the diameter of the conductor increases, the loop resistance / km will decrease.

• Hence higher diameter conductor cables are used for long distance subscribers.

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.

 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. 0.375 type ( large

tube – 0.375” ) or 0.174 type (small tube – 0.174”).• The interstice Quads or pairs having diameter of 0.9mm

Types and Sizes of Coaxial cables

The coaxial cables are divided into two types as follows:

(a) Small tube coaxial - 174 type - the inner dia of outer tube is 0.174”

(b) Large tube coaxial - 375 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

Coaxial core

Lead sheath

Quads of 0.9 mm

Polythene disc

TWO CORE 375 coaxial cable

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 48+6 and 96+8 pairs.

• The conductor material and insulating material are same as PIJF cable construction.

PCM Cable Lay Up

Size of cable

No of Units

Size of unit

No of Extra pairs

10+2 pairs

2 5 pairs 2

20+4 pairs

2 10 pairs 4

48+6 pairs

4 12 pairs 6

96+8 pairs

8 12 pairs 8

PRIMARY & DISTRIBUTION CABLES

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

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.

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.

Construction practice (Cable Laying)

• Classified in toClassified in to:-:-• Receipt, Storage, Handling and TransportReceipt, Storage, Handling and Transport• Surveying and selection of routeSurveying and selection of route• Trenching and LayingTrenching and Laying• Jointing of Cable & TerminationJointing of Cable & Termination• Preparation of Cable Plan, Cable diagram and Preparation of Cable Plan, Cable diagram and

other recordsother records• Acceptance Testing.Acceptance Testing.

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

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.

Permission for Digging Permission for Digging From:-From:-

• Municipal or Local AuthoritiesMunicipal or Local Authorities

• Traffic AuthoritiesTraffic Authorities

• Highway AuthoritiesHighway Authorities

• Railway DepartmentRailway Department

• Port Trust AuthoritiesPort Trust Authorities

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

• The minimum bending diameter for armoured cable should be 15 times of diameter of the cable.

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.

Cable Jointing

Straight Joint & Branch Joint

Jointing technique consists of :-1. Conductor jointing ( Uses UY Connector)

For Cables more than 200 pairs jointing done by 20 pair modules

2. Protection against moisture entry3. Protect against corrosion & Mechanical

damage

Type of Jointing KITs and Type of Jointing KITs and usageusage

• TSF –1TSF –1 10, 20 Pair (straight 10, 20 Pair (straight joint)joint)

• TSF – 2TSF – 2 50, 100 Pair50, 100 Pair

• TSF – 3TSF – 3 200 Pair200 Pair

• TSF – 4TSF – 4 400 Pair400 Pair

• TSF – 5TSF – 5 800 Pair800 Pair

• TSF – 6TSF – 6 1000 Pair1000 Pair

• TSF – 7TSF – 7 1200 & Above1200 & Above

Sequence of Joint closure

1) Cable Marking

2) Armour continuity

3) Conductor jointing

4) Sheath continuity

5) Filling compound

6) Metal canister

7) Cable preparation

8) Install sleeve

9) Thermo shrinking

10) Armour continuity completed

MAINTENANCE OF CABLE RECORDS

The cable records may be divided into three categories

1. Plan

2. Line diagram and

3. Cards.

PLAN OR MAPS

Exchange area layout map shows the following details:-

a) Boundaries of existing exchange area b) Proposed boundaries of future exchanges

but liable to alterations c) Location of existing exchanges d) Localities where future exchanges may be

situated

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.

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.

DISTRIBUTION LINE DIAGRAM

• 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

CARDS

DP CARDS

CABINET AND PILLAR CARDS

MDF CARDs

SUBSCRIBER INDEX CARD

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

10Market

Entrance

 4701

 

Krone – 20 pair

20 Market inside

   

     

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:-1) Number ,size, and type of the CT box, size of shell,

location of the cabinet or pillar,2) Circuits working one each terminal of the CT box,3) The terminal to which the circuit is jumpered.4) The distant end code corresponding to each terminal of

the CT box and the codes of cable pairs connected to the terminals.

5) These cards must be filled in at the time of installation and subsequent additions or alterations effecting the entries must be incorporated .

SUBSCRIBER INDEX CARD

COMPUTERISATION OF CABLE RECORDS

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.

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.

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

Support clamp with U - Back

• For supporting distribution clamp

• It is fixed on Channel Iron Bracket using U-Back

Cabinet, Pillar & DP

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.

• 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_ _

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.

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.

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.

• 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.

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.

Location of Cabinet & PillarLocation 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

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)

Location of pillars and demarcation of pillar area

• 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.

• 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.

Utilization of underground cable

• The planning and laying of the cable should have accuracy of maintaining the following utilization standard :-

• Primary - 90 percent

• Secondary - 80 to 85 percent

• Distribution - 75 percent

Type of Cable Network

Broadly there are two types of networks :-

(1) Rigid Network

(2) Flexible Network (Cabinet and Pillar system)

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.

 

PILLAR NO. 47( 1000 PAIRS KRONE TYPE)

LOCATED AT MARKET PLACE

Primary cable pairs

Distribution cable pairs

A1   A2

B1 B2

C1 C2

D1 

D2

E1 

E2