Telephony Basics Pt 2

Telephony is definitely not an area for the color blind.  Telephone cables and wires are all color coded to help with pair identification.

Mainly in older installations you will find the Bell Company solid color code which was as follows:

Pair One	Green	Red
Pair Two	Black	Yellow
Pair Three	White	Blue

This scheme did continue for larger numbers of pairs, but it is rare to see any cables with more than three pair left in service.

The modern scheme uses a repeated combination of a group color with a pair color.  The group and pair colors are:

Group	Pair
White	Blue
Red	Orange
Black	Green
Yellow	Brown
Violet	Slate

So using the group and pair colors, the first group of pairs will all have white matched with a color.  Usually the white wire has a tracer of the pair color to help with identification in case the cables become unwound.  Using these colors, you can uniquely identify 25 pairs.  Because the 25 pair cable and related termination on punch down blocks and other terminations is quite common, I have listed out the entire cable pair color chart below.

25 Pair Color Code from Wikipedia

Pair #	First wire	Second wire
1	White	Blue
2		Orange
3		Green
4		Brown
5		Slate
6	Red	Blue
7		Orange
8		Green
9		Brown
10		Slate
11	Black	Blue
12		Orange
13		Green
14		Brown
15		Slate
16	Yellow	Blue
17		Orange
18		Green
19		Brown
20		Slate
21	Violet	Blue
22		Orange
23		Green
24		Brown
25		Slate

Once you go past 25 pairs, the pattern repeats by using colored ribbons called binders to wrap each set of 25 pairs.  So the first set would be wrapped in white and blue ribbons, the next white and orange and so on.  

In networking, we've adopted the same color code for Ethernet cabling, but with only 4 pairs we only use part of the color scheme.  The Ethernet TIA586A and TIA586B standards define two different ways to terminate an Ethernet cable into a RJ-45 or an 8p8c connector.  Most use the B standard which places pair one (white/blue) in pins 4 and 5 which corresponds to line one in telephony.  Line two which is pins 3 and 6 is pair 3 (white/green).  TIA586A on the other hand puts pair 2(white/orange) in the pins 3 and 6.  This allows the termination to correspond to telephony line 2.  Mostly this is just knowledge to have for reference, but you may run across TIA586A in the wild.