Brandon's Notepad

August 13, 2011

Phone & Network Wiring

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Once upon a time, I had the need to make ethernet cables as a part of my job, crimping the little plastic connectors on the ends of bulk Cat 5 cable. I no longer work in this area of information technology, but I’ve recently found it necessary to renew and extend my knowledge if network cabling for other reasons. Here are some handy resources and notes.


Registered Jacks

RJ stands for “Registered Jack” and the succeeding number designates the standard wiring pattern used (a.k.a. pinout). Despite popular demand, this designation does not refer to the physical jack or connector. The connectors are actually named for the number of positions and conductors. For example, RJ-45 cables used for data networking use an 8P8C connector, whereas RJ-45 cables once used for telephony used an 8P2C connector. Similarly, wall-to-phone cables are either RJ-11 or RJ-14, which use 6P2C and 6P4C connectors respectively; the former has only one pair of wires to support one phone line and the other has two pair to support two lines.

Cable Categories

Unshielded, twisted-pair (UTP) cable is categorized based on its physical properties. The main practical difference is speed. Cat 3 is used for telephony and 10BASE-T networking, Cat 5 can support 100BASE-T, 5e can support 1000BASE-T (Gigabit), and Cat 6 supports 10GBASE-T.

Cat 6 may include a better grade of wire than Cat 5, but the performance increase results primarily from improved insulation; thus, the connectors must accomodate the larger jackets or performance may be degraded due to poor assembly.

Pinouts

I’m not going to memorize these, so a good reference is always welcome.

Telephony. The colors of the wires for positions 1-6 are W/G,W/O,Bl,W/Bl,O,G. RJ-11 uses only conductors on positions 3 & 4, RJ-14 add positions 2 & 5, and RJ-25 use all six. The old colors are W,Bk,R,G,Y,Bl. Wikipedia has a very good table detailing these pinouts.

Ethernet. Ethernet follows the TIA/EIA-568 standards, either “A” or “B”. The order of the colors is different, but the order of the pairs is identical. [I’ve always seen T568A, but then, it’s not like I look at the pinouts on network cables every day.] For T568A, the colors for positions 1-8 are W/G,G,W/O,Bl,W/Bl,O,W/Br,Br; for T568B, swap all of the greens for oranges in the list above. Again, Wikipedia has a very good table for detailing these pinouts.

The Best Wiring Diagrams

Good pictures are always better – or at least quicker – to use than to have to decipher the orders of wires above. The best wiring diagrams I’ve found for wiring the more popular male connectors are published by Huffman Reference Materials. They even offer free PDF downloads showing the pinouts for several RJs on 6PXC and 8P8C connectors.

The diagrams on Project Resource Solution’s website are also very clear.

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