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. ;)