Ever wondered how the guys and gals at the telephone company can tell which wires go to which house when they're working on a cable that could have hundreds or even thousands of telephone lines running through it? The answer is simple: the wires are colour coded!

A telephone line consists of two wires, designated tip and ring. The colour code specifies the insulation colouring for up to 25 tip/ring pairs. Every wire has a dominant colour and a tracer. The dominant colour can be used to determine if an individual wire is a tip or a ring. The colours for the tip are white, red, black, yellow, and violet. The colours for the ring are blue, orange, green, brown, and slate. The colour of a wire's tracer indicates the dominant colour of that wire's companion. When referring to a wire, either the number is given or the dominant colour of that wire is named first and followed by the colour of its tracer.

And now, a table to demonstrate how all this works:

Pair    Tip          Ring
 No.  Colours       Colours
   1  White/Blue    Blue/White
   2  White/Orange  Orange/White
   3  White/Green   Green/White
   4  White/Brown   Brown/White
   5  White/Slate   Slate/White
   6  Red/Blue      Blue/Red
   7  Red/Orange    Orange/Red
   8  Red/Green     Green/Red
   9  Red/Brown     Brown/Red
  10  Red/Slate     Slate/Red
  11  Black/Blue    Blue/Black
  12  Black/Orange  Orange/Black
  13  Black/Green   Green/Black
  14  Black/Brown   Brown/Black
  15  Black/Slate   Slate/Black
  16  Yellow/Blue   Blue/Yellow
  17  Yellow/Orange Orange/Yellow
  18  Yellow/Green  Green/Yellow
  19  Yellow/Brown  Brown/Yellow
  20  Yellow/Slate  Slate/Yellow
  21  Violet/Blue   Blue/Violet
  22  Violet/Orange Orange/Violet
  23  Violet/Green  Green/Violet
  24  Violet/Brown  Brown/Violet
  25  Violet/Slate  Slate/Violet

This scheme is sufficient for only up to the 25th pair before it has to repeat. So what of those hundreds and thousands of pairs I mentioned? To differentiate larger groups of wires, ribbons known as binders are used. 25 binders are allowed for, coloured and numbered as tip wires would be. So, the first 25 pairs have a white/blue binder, the second have a white/orange binder, and so on. This will allow for 625 wire pairs in a cable.

625 pair cable is thicker than my arm, and probably a good deal heavier. A large telephone exchange can have dozens of these cables coming into it

A single telephone exchange can have thousands of subscribers connected to it. 625 codes won't be able to tell this many wires apart! To deal with this, 'super groups' are used. Super groups have a single-colour binder wrapped around them. Super groups go through the tip colours first, then the ring colours, and are numbered in the order listed at the top of this node. With super groups, 6250 wire pairs can be distinguished.

Using the cyborg name generator at the the Brunching Shuttlecocks site, I've got a couple of silly mnemonics for these:
Being Optimized for Galactic Battle and Sabotage
Wireless Robotic Being Yearning for Violence
Of course, there are some easier ones that I used in school:
Bring Our Gin Back, Sir
Whiskey, Rye, Bring Your Vodka

muted says red ring right, green tip left was how we used to remember it, back in our 7/16"-hex-driver-carrying days. ;)

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