Telephone Basic Question

[D-Con]

As I was troubleshooting a problem with a dead phone jack at a house I'm remodeling, the voltage I measured at each working phone jack was only about 2.4 VDC. I thought the voltage should have been higher than that (6 to 12 volts DC.) I found the problem (broken wire), and the phone jacks in the house all seem to work fine. What should the supply voltage be? Does anyone know of any good FAQ's for telephone wiring?

Thanks, Dan

[Mr T]

Phone voltage varies. It is also AC voltage riding on DC voltage. When it rings it can be 70V and higher, (for those old mechanical bells), I think there is a 5V and a 9V componet (forget what is ac and what is DC) at idle time.

Easiest way to troubleshoot is to verify your reds and greens are correct. Reverse polarity will cause weird crap to happen. If you get a dial tone, can call out and can get it to ring, chances are you are ok.

Best place to start is at your network interface, you can test your phoneline while having the house totally disconnected. If it works here, hook up your lines at the box one at a time till you find a problem, or they are all good.

If the wiring has age to it, I'd just run new wire. Its cheaper, and if you can update for modern technology (star pattern/home runs with cat 5 wire)

Good luck.

[mdshunk]

I dunno, I've never checked the voltage on a phone line. I troubleshoot phones by checking for dial tone with a butt set. You can make one by putting alligator clips on the cord of an old phone.

[dznewz]

IIRC, on hook is 48vdc, off hook is 6.5 vdc. ring is 90-120 vac at 20Hz.

[Mr T]

http://www.homephonewiring.com/nid.html

This site talks about the network interface box, what it looks like, how to use it for troubleshooting, ect.

Go to the top level site http://www.homephonewiring.com and it will tell you all you want and more about phone wiring, including punchdown blocks
(There has been several inquiries on this board about them latley). Looks like a pretty good site.