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How Complicated Is Telephone Socket Wiring?

Valerie Clark
Valerie Clark

Wiring a phone with a new socket and phone line can be as simple as calling the local phone company to install a network interface device and then running the wires independently. A network interface device is a small box that is mounted to the outside of a building to house telephone connections. Connecting a new telephone line entails running a phone wire from the telephone to the box. A phone socket creates an outlet where one can plug the wire into a wall somewhere between the indoor phone and the outdoor box.

There are several types of phone sockets, or telephone jacks, and the terminology can get confusing. The type of phone socket needed will depend on the type of phone wiring used. The Registered Jack (RJ) 11 is the most commonly used modular telephone jack, even in areas outside the U.S. Some other types of registered jacks are the RJ14, RJ21 and RJ48. An RJ11 jack specifies a two-wire connection, while RJ14, RJ21 and RJ48 jacks refer to four-, six-, and eight-wire connections, respectively.

A telephone.
A telephone.

Telephone socket wiring works with registered jacks to specify a consistent type of wiring pattern. For residential telephone sockets, the phone wire consists of either four wires or two sets of two wires. Each set of two wires corresponds to one phone line. In other words, a single-line configuration will require two of the four wires to be connected. This process is simplified by color-coded wires, with the red and green wires representing the primary phone line.

When completing a telephone socket wiring connection at the network interface device or box, the connections are color coded for easy hook-up. The green and red primary phone lines will be connected to the green and red screws, respectively. For connecting a secondary line, the black and yellow wires should be connected to the green and red screws, respectively. Phone socket diagrams are available to help clarify the color codes and conversions between various types of cables.

British telephone socket wiring is similar to that in the U.S. in that RJ11 is the most common type of phone wiring. The actual connector on the end of the RJ11 cable is different in Britain than the U.S. version, rendering them incompatible. Telephone socket wiring in other parts of the world also may be similar to the U.S. in terms of wiring, but the design of the actual plugs and outlets varies greatly.

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Discussion Comments


@allenJo - Well, you got it right the first time when you said that they were filters. They are both filters and splitters.

You may not need to split the home telephone wiring everywhere, but every phone plug needs the filter’s functionality.

What the filter does is eliminate a lot of the high frequency noise. You need to do this everywhere you have a phone jack; otherwise it will affect the quality of your DSL signal as well as the quality of your phone calls.

Yes, it seems a little counter-intuitive to have these filters sticking out of your phone jacks with nothing attached to them, but that’s just what you have to do. I don’t claim to understand the technology completely myself either.


I think that phone plug wiring is rather simple. What I wonder about is the other stuff that I have to attach to my phone plug sometimes.

Recently I got a DSL modem. I had to attach a DSL filter to the phone plug. It essentially split the wiring so that I could hook up one part of the phone plug to the modem and the other part to the phone. That much I understood.

What I didn’t understand is why I had to attach other filters (they shipped me about four of them) to other phone jacks in the house. These were jacks that didn’t have a modem or a phone attached to them. They were not in use, so why did I need to attach a splitter?

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      By: Michael Flippo
      A telephone.