03:41PM | 12/19/02
Member Since: 10/27/02
5 lifetime posts
I noticed when adding more phone lines in my house that I have a 4 wire phone line but only two wires, the red and green are hooked to the telephones. Where the phone line runs to the house all four are hooked up. The phones all work fine but my question is what is the purpose of the other two wires that are not hooked to the phone?

Jim D

11:03PM | 12/19/02
Member Since: 01/06/01
345 lifetime posts
Hi, the yellow and black wires that you see were used to provide voltage to the lights inside the old style phones, like the Princess phones with the lighted dials. Depending on when the phone company ran the wires to your house, that's why you see all 4 wires connected...the installer was being thorough. I've seen installers in my area (Central VA) simply connect the red and green wires and wrap the yellow & black wires around the line to keep them out of the way.

If you were to add a second line to your house, the installer would probably check and see if you were going to run the second line to every room or just to one of the rooms (like a computer room). I've seen installers use the yellow & black wires to run that second line in, instead of running a separate, new line. They just have to make sure the wall jack is wired properly.

I hope this helps you some. Happy Holidays!

Jim D/Heathsville, VA


09:16AM | 12/27/02
Member Since: 11/18/02
30 lifetime posts
For "plain old telephone service", one pair of wires is sufficient for phones and modems, including power to energize the ringer. Normally this center pair is red and green. I've utilized the "unused" black/yellow pair of an existing cable (already installed in the house) to carry the signal of a second line coming into the house. Needed to separate the individual wires at both ends.

The function of wires in communication cables depends on the utility service.

For example, if your "pots" line has been upgraded to a digital service such as DSL, the wires may be utilized differently. Anybody know this, and any problems using the black/yellow pair as described above?

Years ago, I worked on "four-wire" service communication lines that our company leased from the phone company, to enable data and voice communications from one facility/city to another. A pair of wires (red/green) was used for the Transmit signal; the other pair (black/yellow) for Receive.

Computer LAN (twisted-pair type) cable also has several pairs. If technology hasn't changed, there are four pairs, one for transmit, one for receive, etc..

[This message has been edited by gs99 (edited December 27, 2002).]


01:41PM | 08/26/07
Member Since: 08/25/07
1 lifetime posts
I'm putting in this posting primarily for Jim D., but would appreciate anyone with knowledge of the older land line phone lines, to provide any feedback. I've been in my home about 30 years, and have always used the land line phone lines, with service now supplied by AT&T. Last weekend, whenever someone tried to call me, I would get 1 short chirp, but no ringing, and couldn't receive a call, but I could still call out. I called AT&T, and they sent out a service guy who said the problem was not outside of the house, which is what they cover. To trouble-shoot and repair the problem, it would cost about $200. I told them I would call, when ready to have them do this. I then tried to follow the phone line into the house, and into the phone jacks, to see if anything was obviously bad. All I saw was in my crawl space, where the outside (4-wire) old line comes into the house, it goes into a heavy looking U-Shaped piece, which all the wires connect into different screws on the piece, and these connectors also connect to the wires which then go off to the phones. There was also a rather heavy ground wire which connects to the water piping. There was quite a bit of oxidation and crud on the piece, and I'm wondering - what is this piece?, what does it do?, would cleaning off the leads and re-connecting the wires resolve the problem?, and if I should need another of these pieces, where would I get something like this? Anything that might shed light on my problem would be greatly appreciated.



06:45PM | 08/26/07
Member Since: 04/25/05
1918 lifetime posts
"All I saw was in my crawl space, where the outside (4-wire) old line comes into the house, it goes into a heavy looking U-Shaped piece, which all the wires connect into different screws on the piece, and these connectors also connect to the wires which then go off to the phones. There was also a rather heavy ground wire which connects to the water piping."

That sounds like an old Telephone Circuit Protector.

It is or WAS the telephone companies.

I don't know the teleco's policies are on this, but it should be removed.

And a Demarc should have been installed. That is the point where the Teleco lines end and your wires start.

Also called an NIC (network interface connection) or SNI (system network interface).

There are several different styles. But this is typical. They have a part where the teleco make connections and a customer side with a test jack.

When you unplug the jumper it disconnects the house wiring. Then you can plug is a telephone.

If it works OK there then the teleco lines are OK and the problem is inside.

If you don't have one of these then get them back and have them install one and remove the old protector.


10:29AM | 08/31/07
Member Since: 07/07/06
75 lifetime posts
I agree that the old network interface should been removed years ago. You should call AT&T to install a modern inteface. there should be no charge for this. This may help your problem


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