Numbering and Labelling

Cable Colour Codes

Internal Telephone Cable colour codes are based on the five colours, blue(B), orange(O), green(G), brown(BN) and slate(S).

These colours can be expanded to twenty pairs :
blue, orange, green, brown, slate,
blue/white, blue orange, blue green, blue/brown, blue/slate
orange/white, orange/green/ orange/brown, orange/slate
green/white, green/brown, green/slate
brown/white, brown slate

These single wires are usually twisted with a second wire to form a pair. These second wires take the following colours and take the cable up to 100 pairs :

In an exchange, many circuits are three wire (eg neg, pos and P wires) and so the cable colours above can be further increased by the addition of a turquoise wire to make each pair into a triple.

Small cables are often made up with the following colours :
A wire - blue/white, B wire - white blue
A wire - orange/white, B wire - white/orange
A wire - green/white, B wire - white/green
A wire - brown/white, B wire - white/brown

Current External Quality Cables use the following 30 pair base :
blue/white, orange/white, green/white, brown/white, slate/white
blue/red, orange/red, green/red, brown/red, slate/red
blue/black, orange/black, green/black, brown/black, slate/black
blue/yellow, orange/yellow, green/yellow, brown/yellow, slate/yellow
blue/violet, orange/violet, green/violet, brown/violet, slate/violet
blue/pink, orange/pink, green/pink, brown/pink, slate/pink

where the first pair will be blue/white (B wire) and white/blue (A wire).

To increase the cable size beyond thirty pairs, several 30 (or possibly 15) pair bundles will each be wrapped in its own marker tape.

Railway Provided Cables are usually based upon the blue, orange, green , brown, slate sequence but have unpredictable variations. Some are not constructed with pairs but with quads. In a quad, each pair uses the wire opposite it in the quad to produce the pair and this reduces over hearing etc.

Line Plant

Line plant terminations in cabinets and DPs should be numbered "down". If the terminal strips are horizontal then they should be numbered from "left to right".


MDF lineside 8064 fuse mounting numbering

The MDF line side always numbers "down" within each vertical bar of fuse mountings. This gives each pair a "bar and pair" number, eg: B41.

MDF exchange side heat coils and protectors numbering

The MDF exchange side always numbers "up" within each vertical bar of protectors, heat coils and test jacks. This gives each circuit its individual number.

IDF tag blocks always number "up". However it should be noted that some blocks at Norchard exchange have been provided in the past which do not follow this convention. New work should number "up".

Relay Coil & Contact Numbering

Relay Coil and Contact numbering

U Points

U Point numbering

It is suggested that the following U point allocation be reserved for new work at Parkend Exchange :

1I/C - wire17
2I/C + wire18NU Tone
3Ring Start19
8Dial Tone24
9I/C P wire25
13S Pulse29
14Z Pulse30Int. Ring Tone
15Release Earth31Ring Return Battery
16Busy Tone32Int. Ringing Earth

Unallocated U points can be used as required for other connections eg "line out", "prompt alarm", "deferred alarm" etc.


Page provided by John Bathgate

This page was last updated on
17th June 2010