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Connecting a new socket to the mains

There are three basic ways in which you can add a socket to a room: by running a spur from another socket; by adding a junction box into the ring circuit; or by splicing it into the ring circuit directly.

Whichever way you’re doing it, you’ll need to be aware of the correct colour coding for the cables when connecting up the socket. You can find out about that on our Electricity cable colour coding page.

Running a spur from another socket

This is a handy solution if all you need to do is run a cable along the surface of the wall or worktop, for instance in a shed or garage or anywhere else where you’re not that bothered about appearances.

First, turn off the power to the ring circuit at the consumer unit!

Next, remove the screws securing the faceplate of the socket you’re proposing to run the spur from, and have a look at the back of the socket to see how many cables it’s connected to. If there are two cables running to the socket, then you’re in business. (If there’s only one, then the socket is probably already at the end of a spur; if there are three, then the socket’s already providing a spur connection.) Undo the terminal screws and remove the wires from the socket.

Having fitted your new socket, wire it up in the usual way and run the cable to the existing socket. You may find that you need to make the existing cable entry hole larger to accommodate the spur cable, or else that you need to knock out another hole. Once you’ve done that, feed the cable into the socket box, strip off the ends of the neutral and live conductors, slip a length of green-and-yellow insulation onto the earth wire, and then twist the ends together with the ends of the existing cables. Insert the wires into the appropriate terminals (again, see our Electricity cable colour coding page if you’re in any doubt) and tighten the screws. Then refix the socket to the socket box, turn the power back on at the consumer unit, and test the new socket.

Connecting a socket to the ring circuit via a junction box

This is probably the best option if there are no handy sockets nearby to run a spur from, or if adding a spur would mean disturbing plaster or having an exposed cable run where you’d rather have it concealed.

You’ll need a junction box with at least three cable entry holes (two for the ring circuit cable, one for the spur to the socket); depending on the type of box you have, you can either rotate the cover so that exactly three holes are available, or knock three blanks out of the knock-out holes in the moulding. Lift a floorboard up near where you want the socket to be, and where you can run the ring circuit cable into the box without putting it under strain. Fix the junction box securely, either directly to one of the joists or by adding a fixing platform between two of them. (If you’re using a fixing platform, it’s better to put the cable over the platform beforehand so that you don’t have to cut the conductor wires.)

Turn the power off at the fuse box or consumer unit!

Put the cable across the junction box and mark off how much cable sheath you need to remove (ensuring that you don’t remove so much that the conductor wires are exposed. Then slit it down the middle, taking care not to cut into the insulation for the live and neutral wires, and peel it back. Strip off just enough insulation from the live (red, or brown in modern installations) and neutral (black, or blue in modern installations) wires to fit the exposed wires into their respective terminals. Cut the bare earth wire and put lengths of insulating sleeve (green-and-yellow) onto each end.

Take out the screws from all three terminals and lay the wires across them. The earth wire should go into the middle terminal. Then, having fitted your new socket, wire it up in the usual way and run the cable to the junction box. Feed the cable into the box, strip off the ends of the neutral and live conductors, slip a length of green-and-yellow insulation onto the earth wire, and then insert the ends into the appropriate terminals (again, see our Electricity cable colour coding page if you’re in any doubt). Tighten the screws. Then replace the junction box lid. Clip the cables to joists to reduce strain on the terminals, and replace the floorboards. Turn the power back on at the consumer unit and test the new socket.

Adding a socket directly into an existing ring circuit

This is only really an option if your existing wiring has plenty of slack. Given that it’s undesirable to leave cable under strain – as is likely to be the case if you pull up all the slack – we wouldn’t normally recommend this one.

Turn the power off at the fuse box or consumer unit!

Pull a loop of the ring main cable up to the new socket and feed it into the socket box through an entry hole. Cut it. Strip back the sheathing of both ends and the insulation of the live and neutral wires. Fit insulation sleeves onto the earth wires.

Do not twist the matching wires together (see comments below). Fit each of the ends of the wires into the appropriate terminals on the socket (again, see our Electricity cable colour coding page if you’re in any doubt). Tighten the terminals.

Replace the socket faceplate and screw it tight. Turn the power back on at the consumer unit and test the new socket.

4 Responses to “Connecting a new socket to the mains”

  1. E Pocock

    You state that when connecting socket appropriate cable ends should be twisted together. I understood that manufacturers of sockets do not recommend twisting cable ends together before connecting to socket.

  2. HouseWiz

    Thanks. This is something I hadn’t heard before – my understanding was that twisting the wires together is advisable as it reduces the possibility of one of the wires working its way free and slipping out of the terminal. The majority of opinions I’ve been able to find online and in print recommend twisting.

    Where did your information come from?

  3. Rich

    Never twist wires together, it’s against BS7671 IEE Wiring Regulations. Double over the ends of the cables to give a bigger CSA in the terminal but NEVER twist! The same goes for the earth wires.. despite the fact that they are probably twisted together in the existing sockets, un-twist them.

    And ALWAYS consult with an approved qualified electrician, there may be tests that are required. Part P has been in for some years now yet it still surprises me how many DIY buffs still illegally play with their electrics and probably make them dangerous.

  4. HouseWiz

    Thanks. I’ve updated the page accordingly – opinion seems to be that (a) manufacturers don’t call for it, and therefore it shouldn’t be done; (b) twisting the solid cores together weakens them and can lead to them breaking.

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