Radial Circuits - Socket Outlets

Example of a radial circuit A single cable (containing live, neutral and earth wires) starts from the consumer unit or fusebox, and connects to each socket outlet in turn. Each socket outlet is supplied with power by the previous one.

The final socket outlet can be identified easily, as it will only have one cable connected to it.

Faults on radial circuits are easy to locate. If there is a break anywhere along the cable, all of the socket outlets after the break will no longer work.

Radial socket outlet circuits are less common in UK dwellings, as until recently, the usual method was the ring circuit.

Socket Wiring

Socket outlet wiring, radial circuit, new colours As described above, a radial circuit starts at the consumer unit, connects to each socket outlet in turn, and ends at the final socket outlet.

All of the socket outlets (except the final one) will have two cables, one coming in from the previous socket or consumer unit, and another going out to the next socket.

Both brown wires connect to the Live or L terminal. Both blue wires connect to the Neutral or N terminal. The earth wires will be bare copper, and should have some green/yellow stripe sleeving placed over them. Both earth wires connect to the Earth or E terminal.

This socket outlet shows two earth terminals. These are used on some circuits where high integrity earthing is required. For most domestic situations, either terminal can be used.
Also note that both of the earth terminals are connected together with a metal strip, and this strip also surrounds the two fixing holes, so that when fitted to the wall, both of the fixing screws are earthed.

If the socket outlet is fitted to a metal backbox, this will also be earthed via the fixing screws. You may find a short length of wire connecting from the socket earth terminal to the metal backbox. This is only needed if the backbox has two adjustable fixing lugs - most have one permanently fixed.

Old colour socket wiring

Socket outlet wiring, radial circuit, old colours Older circuits will have wires to the previous colour code. An example is shown below. Red is Live, Black is Neutral; the earth is still yellow/green stripe. Some very old installations may have a solid green earth. If this is found, or the black and red wires have stranded cores, it is probably time to replace the cables as they will be over 30 years old.

Wiring for the final socket outlet

Socket outlet wiring, radial circuit end, new colours Socket outlet wiring, radial circuit end, old colours The last socket outlet on a radial circuit will have a single cable. Connections are as before. Examples are shown below in the new and old colour codes.


There is no standard arrangement for the terminals on the back of socket outlets. Different brands of socket will probably have the terminals in different places. Always check carefully that you have connected the wires to the right terminals.
If replacing a damaged socket outlet, it is desirable to obtain a replacement from the same manufacturer, otherwise you may find the wires are too short to reach the terminals.