CAT5E Wiring – 568A or 568B?


This is a question that we get frequently. Which is the best standard for terminating CAT5E cables, 568A or 568B?

Well there really is no correct answer. As long as the cable has the same standard on both ends it will work properly. The only difference between A & B is that the green wires are swapped with the orange.

Our installers all use the 568B standard for any cables we have to terminate. That way there is never any confusion on which standard was used.

Most contractor’s (including us) use standard 4-pair CAT5E wires for telephone lines as well. While this may be overkill, it allows for much easier upgrading to VOIP as well as allowing for up to 4 individual phone lines. By using the 568B standard for these lines as well, the 1st phone line is on the blue & blue/white pair of wires (which is also centered in the jack and does not require a special phone cord). The 2nd line would then be the green & green/white pair and is also positioned correctly in the jack for a standard 4-wire phone cord. Generally when we get above 2 lines we would use a phone system, either VOIP or analog. WOIP phone use a standard TCP/IP network to communicate and would use all 4 pairs in a standard 568B configuration. The analog systems traditionally use the 2-pair model for lines 1 & 2.

Here is a diagram for the 2 different terminating standards:

If you would like any further information on this subject, please don’t hesitate to contact us. Thanks!

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