Telephone over Cat5: Is it possible without voip?
June 21, 2005 1:57 PM   Subscribe

I'm setting up some telephone lines, and well, I really don't want to lay more wires than I have to. So this is the deal, I've got five telephone lines, and three telephone (rj11) jacks. We've just installed wifi, and so a number of unused ethernet cables. Is it possible to buy an adaptor that will allow me to use a cat5 cable to send plain old telephone over them?

We have a room in the back where we have out ethernet switch and patch cables, as well as where verizon brings our telephone lines in. I want to be able to put in a jack, and then connect a patch cable from the rj11 telephone jack to the rj45 ethernet jack that goes from that location to the desk, then connect that cable(going from rj45 back to rj11) to a telephone, or fax machine.

I imagine there might be issues with electrical incompatibilities, or wiring incompatibilities, etc. If anyone has any ideas about other ways to do this without rewiring, I'd love to hear them.

posted by Freen to Technology (11 answers total)
I'd think your local radio shack or analog should have rj11 cable ends and a crimper. You could just cut the rj45 ends off and reterminate the cables. Just make sure the wire layout on the ends match.
posted by squant at 2:09 PM on June 21, 2005

I think CAT5 would work fine for telephone. What is it, 4 pair? I forget.

Just take the jacks off the ethernet and put phone jacks on, paying attention that you have the same color pairs in the jack on both ends.

It's a waste of pairs, but then again all phone lines are. They all (reasonably recent) have at least 2 pairs, and sometimes more, only one of which is used at any time. But that way a house can be retrofitted for multiple lines without rewiring

You'd have to pay attention to what you did your switch room. (I.e, splice blue and green ethernet onto the incoming phone lines from the telco, make sure you splice blue and green on the phone jack).

A volt meter could help. Telephone line voltage is supposed 49 volts DC (or something around there) to find out which color lines are hot from the telco.

I could be wrong. Or I could be right.
posted by teece at 2:10 PM on June 21, 2005

Here's the skinny on cat. 5.
And here's more info.

I think teece has got it, sounds like it should work just fine.
posted by Floydd at 2:19 PM on June 21, 2005

You mentioned that you have five telephone lines but only three RJ11 jacks plus some ethernet cables. Are the three RJ11 jacks near all the locations you want phone service, or do you want to deliver phone service to locations serviced only by the ethernet cables?

The reason I ask is that most phone cables and jacks can be wired to carry two phone lines. So it is likely that the existing three RJ11 jacks could deliver phone service for up to six lines, assuming they are in the correct locations. If the three RJ11 jacks are in the correct locations, just install three line 1/line 2 phone splitters in the back room and one at each of the three destination jacks.
posted by RichardP at 2:24 PM on June 21, 2005

Groovy. Is there anywhere I can buy a dongle that i just plug the rj45 cable into, and then get two rj11 jacks? Or is that a pipe dream, and I better get to cutting, crimping, and re-terminating.
posted by Freen at 2:24 PM on June 21, 2005

Not only will it work, it's why 10-Base-T ethernet leaves two pairs empty.

I don't know of any dongles -- the best way to do it is with a double keystone jack. You plug in an RJ-45 and RJ-11 jack, terminate the Orange and Blue pairs to the RJ-45, and the brown to the RJ-11 for the phone.

If you need two phones, you might find a 3-hole faceplate, but those are rare -- so you get a four way plate, plug in an RJ-45, two RJ-11s, and a blank. Orange and Blue pairs to the RJ-45, Green to one RJ-11, brown to the other.

Neat and sweet. You can find the faceplates and jacks at your local HomeDepot/Lowes/Whatever. There are lots of other jacks -- video, audo, coax, so you could use that 4th space for something, if you wish.
posted by eriko at 2:44 PM on June 21, 2005

I've used these to do basically what you're asking for. They're a little expensive, but its a clean solution. It gives you 4 combinations of 4 lines--2 lines per telephone jack.
posted by joelr at 2:44 PM on June 21, 2005

My rj11 jacks seem to have 2 wires each. I think that means they can only handle one line each, although I could be very wrong.And yes, the jacks are all located right where we want phones, I just want two more phones than I have rj11 jacks.

on preview: Joelr, that's just what I'm looking for.

Thanks, for all your help.
posted by Freen at 3:01 PM on June 21, 2005

For what it's worth, I run only cat5e at work. I don't run cat3 (POTS). Oh, and you just take the two center wires of your cat5 jack and connect those to the two phone wires, then plug your phone right into the jack. Be gentle and you won't have any trouble.
posted by kc0dxh at 3:34 PM on June 21, 2005


Some phone cable has two wires (one line), some has four (two lines). I believe six wires is also possible, but I don't think I've ever seen it.

Two-line phones deal with the four-wire stuff transparently. If you want two one-line phones hooked into one of these, you can get a splitter at Radio Shack for just a few bucks, which will typically have three jacks: L1, L2, L1+L2.

Dealing with Cat-3 and Cat-5 is dead simple with the right tools (which are cheap), and hard to mess up.
posted by adamrice at 7:48 AM on June 22, 2005

My home POTS (that's "Plain Old Telephone Service" for you non-techies) runs through Cat5e, and it's all good. Just make sure you pin all of your terminations identically, and everything will be dandy.

POTS is really just copper two conductor at 48 volts, so you don't need to worry about a big wire gauge for high voltage, and UTP can only help your signal quality...POTS has standards, but they're not anywhere near as stringent as Cat5.
posted by SlyBevel at 8:46 AM on June 22, 2005

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