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Colour Coding of twisted pairs
Colours play a significant part in identifying pairs
To make it easier for technicians to recognise a pair of wires, there is a standard colour code that makes it easy.
There are five (5) main colours used in twisted pair cables, these are Blue, Orange, Green, Brown and Slate in that order. Each cable [copper or copper-coated aluminum (CCA)] is covered with plastic (or similar insulate) that is pointedly coloured, all coating colours are based on these main colours and each is individually paired and twisted, with a common colour for the second wire such as white.
For Cat5e and RJ21 basic colour coding using White, Red, Black, Yellow & Violet see below
Therefore, the first 5 pairs consist of paired wires that are twisted together, the first pair consists of one Blue wire and one White wire, then the second pair consists of one Orange and one White also twisted together, the wire pairs are collated in groups made up of wires that are paired in colours as follows:
Blue-wire + White-wire
Orange-wire + White-wire
Green-wire + White-wire
Brown-wire + White-wire
Slate-wire + White-wire
The above is merely 5 x pairs and clearly inadequate for many circumstances. Therefore the code is extended by mixing (by using stripes) the same colours in the following order:
Blue-White (blue with white stripes)
Blue-Orange (blue with Orange stripes)
Blue-Green (blue with Green stripes)
Blue-Brown (blue with Brown stripes)
Blue-Slate (blue with Slate stripes)
Therefore the second set of 5 pairs are as follows:
Blue-White + White-wire
Blue-Orange + White-wire
Blue-Green + White-wire
Blue-Brown + White-wire
Blue-Slate + White-wire
Now we can easily identify the first 10 pairs (20 wires) by the above colour coding.
The coding of pairs continues as follows:
Orange-White
Orange-Green
Orange-Brown
Orange-Slate
Green-White
Green-Brown
Green-Slate
Brown-White
Brown-Slate
Slate-White
The resulting number or pairs following this code is as follows:
Blue + White
Orange + White
Green + White
Brown + White
Slate + White
Orange-White + White
Orange-Green + White
Orange-Brown + White
Orange-Slate + White
Green-White + White
Green-Brown + White
Green-Slate + White
Brown-White + White
Brown-Slate + White
Slate-White + White
Cat5e Basic Colour-Coding
RJ45 connection is often used for Cat5e termination, which only uses the first 4 colours of Blue, Orange, Green and Brown. Colours are not twisted with White, Red, Black, Yellow or Violet, but with a white-striped colour of its own pair.
That is, Blue is twisted with a Blue-White cable, Orange with Orange-White etc. Using the first 4 basic colours as shown in the diagram below:
Each of the Solid coloured wires as shown on the left, is twisted with the matching Striped colour wire as shown second from the left. Cat5e only uses four colours, delivering 8 wires to individual pins numbered 1 to 8 counting from left to right when the fixing hook is facing away (on the back). See below for Wire-Pair allocation to Pins.
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The full five (5) basic colours of Blue, Orange, Green, Brown & Slate can be extended dramatically by changing the paired cable from White to: Red, Black, Yellow or Violet and still go through the entire sequence
However, you can more simply achieve a full 25-Pairs of easily identifiable cables without striping the colours and using just the five main basic colours of Blue, Orange, Green, Brown and Slate and changing the colour of the paired wire as follows:
| Blue + White |
Blue + Red |
Blue + Black |
Blue + Yellow |
Blue + Violet |
| Orange + White |
Orange + Red |
Orange + Black |
Orange + Yellow |
Orange + Violet |
| Green + White |
Green + Red |
Green + Black |
Green + Yellow |
Green + Violet |
| Brown + White |
Brown + Red |
Brown + Black |
Brown + Yellow |
Brown + Violet |
| Slate + White |
Slate + Red |
Slate + Black |
Slate + Yellow |
Slate + Violet |
RJ21
Using the above colour coding, the wiring for a RJ21 socket is as shown in this image below:
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For Pin and Pair numbering, please refer to the different RJ45 (Cat5e) & RJ12 configurations in the images below:
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