T8 B Telecom Cables

 Size of Cable-

The various size of conductors used in Cable are - 0.4 mm,0.51 mm,0.63 mm,0.9 mm and 1.2 mm.

Twisting is done to avoid crosstalk.

Distortionless condition-

If there is no phase Distortion, the velocity of propogation must be same for different Frequency components and should be independent of Frequency.

GL=RC is distortionless condition 

Loading of Underground cable -

When diameter of conductor increases,  value of R decreases . This is not possible due to its increased cost.

If the value of G increases, transmission loss will increase which is also not acceptable.

Therefore there is only one way to increase the value of GL by increasing L.This is achieved by using the coils of suitable inductance value wound on dust cores are placed in series with line on suitable intervals.

This is called coil loading or lump loading.Value of each coil connected in each limb of a quad cable is 59 mh.

V.F.balancing of underground cable-

V. F balancing of underground cable is done to reduce noise and crosstalk in cables.

This is necessary in RE cables because the cables carry important circuits and they are having repeaters at every 40-50 km.

The process of measuring the capacitance unbalances between various quads and earth,within the quad and with adjacent quads and minimising the unbalances by connecting condensor is called V.F balancing .

6 Quad Colour and Allocation 

Quad 1- Orange,White,Red,Slate - Section control

Quad 2- Blue,White,Red,Slate - Emergency Control 

Quad 3- Brown,White,Red,Slate - Dy Control

Quad 4 - Green ,White,Red,Slate - Test Quad

Quad 5-  Yellow,White,Red,Slate - Block

Quad 6 - Black ,White,Red,Slate - Pair 1- LC gate

                                                             Pair 2 - Spare 


PIJF Cable-

Widely used for local loop and other networks.

IRS Specification - IRSTC - 41/97.

NO of pairs -

Vary from 10 to  200 pair.

Conductor Diameter-

0.5 mm,0.63 mm,0.9 mm

4/6 Quads -

Characteristics impedance- 470 Ohms ( unloaded)

                                                  1120 ohms ( loaded)

Cross sectional diameter  - 0.9 mm

Transmission loss - 0.25 dB ( loaded)

                                    0.63 dB ( Unloaded)

Permitted transmission loss per km for BPAC/SSDAC/MSDAC application - 1.2 dB

Attenuation in PIJF Cable is greater than Quad cable in dB/Km.

RDSO Specification of 4/6 Quad cable of 0.9 mm dia is IRS: TC 30/2005 ver.2

6 Quad cable ( Non RE)-

Quad 1 - Section controller

Quad 2- Emergency control 

Quad 3- Dy control

Quad 4- Test Quad

Quad 5- Block

Quad 6 - Lc gate and Spare.

Data Communication Cables-

For data communication,two types of cables are used for LAN.

UTP - Unshielded twisted pair

STP - Shielded Twisted pair

UTP-

Less expensive than STP.

Economical alternative of Eathernet.

Each conductor is made up of annealed copper of dia 0.9 mm.

Connected with RJ 45 connector.

STP - 

For high speed data,STP cables are used.

Each conductor is made up of annealed copper of dia 0.9 mm or 0.6 mm.

Size and Length of main cable length-

Contour Allowance- 2.5%

Jointing Allowance- 1%

At level crossing gates minimum 3 m of loose cable should be coiled to meet future need.

In Non RE Area distance of distance of 2.75 m and in RE Area distance of 5.75 m from centre of track to be maintained while laying the cable.

Cable route markers to be provided at every 20 m in straight and at joints with proper marking.

PIJF cable Jointing -

Available in 20,50 and 100 pairs of 500m drum length.

For straight jointing of PIJF cables, TSF-1,TSF-2,TSF-3 and TSF-4 jointing kits are used.Same kits are used for branch joint also.

Jointing of Quad Cable -

A) Straight Jointing 

TSF 1 - Used for 4 Quad 0.9 mm

TSF 2-  Used for 6 Quad 0.9 mm.

As per latest RDSO Specification RTSF Jointing kit is used for quad cable.

In the RTSF Jointing kit- 

Tinned copper braid is used to provide continuity between Aluminum Screening of both the cables.

Sealant tap in RTSF kit is used to cover metallic projections.

B) Derivation Joint-

This kit is used where Derivation cable is connected with Emergency Socket.

On steel girder bridge 10 m of cable is to be left on both sides while laying.

Laying of telecom cables outside the station limit-

Laid 10 m from centre of track.


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