Is RJ12 downwards compatible with RJ11?

An RJ12 cable will work in an RJ11 connector, but the third pair won't be used. You can use three or four pair cable with an RJ11 connector as long as you follow the relevant standards.

Using an RJ11 cable with an RJ12 jack may not work well as the third pair may be required. Some RJ11 cables have only 1 pair of wires, and won't work with RJ11 devices that expect to use both pairs.

There is lots of documentation on the Internet about telecom wiring and the standards that apply.

BillThor

Posted 2014-11-06T21:52:25.957

Reputation: 9 384

I already thought something like this. That means that if they cables don't exchange some wires (despite the number of wires is correct) it should work (aka follow the standards). You're right there is lots of documentation on this. Mostly it is too much information or they say how the standards work, how they are built up, but they don't mention compatibility. That was the only thing I was looking for. Now I'll buy my RJ12 cable because it has more uses than a pure RJ11 cable. Thanks for your answer! – testing – 2014-11-07T07:07:33.000

2Don't know why people are downvoting this question. It is a legitimate question. I have used Google before and didn't found suitable results with the keywords rj12, rj11, compatible and so on. Try it yourself. Instead of downvoting you could provide an answer if it so easy to find. Happy downvoting! – testing – 2014-11-07T07:02:30.300

Is RJ12 downwards compatible with RJ11?

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