Adding a spur socket to a ring electrical circuit
CHECKING OUT A RING CIRCUIT These instructions assume that your installation conforms to the Wiring Regulations. If it seems to have been modified in an unauthorised way, get a qualified electrician to check it.
TURN OFF THE POWER SUPPLY.
Start by undoing a socket near where you want to install the new socket.
Adding a spur to a ring
Once you’ve established you’re dealing with a ring circuit and what sockets are on it, you’ll need to find out if any spurs have already been added. You can’t have more spurs than there are socket outlets on the ring itself. But unless the circuit has been heavily modified, it’s unlikely that this situation will arise. You’ll also need to know where any spurs are located – you don’t want to overload an existing branch by mistake. You can distinguish the sockets on the ring from those on a spur by a combination of inspecting the back of the sockets and tracing some cable runs. But remember to turn off the power first. When you’ve got this information, you can work out whether it’s feasible to add to the ring circuit. And you’ll have a good idea where the cable runs.
Installing the socket
It’s best to install the socket and lay in the cable before making the final join into the ring, since by doing this you reduce the amount of time that the power to the circuit is off. You can either set the socket flush with the wall or mount it on the surface. The latter is the less messy method, but the fitting stands proud of the wall and so is more conspicuous.
Flush-fixing a socket on a plasterboard wall is a little more involved. If you choose to surface-mount the socket, all you have to do is to fix a PVC or metal box directly to the wall after you’ve removed the knockout (and, if metal, useagrommet) where you want the cable to enter. The socket can then be screwed directly to this.
Laying in the cable
Because cable is expensive, it’s best to plan the spur so that it uses as little cable as possible. When you channel cable into a wall you’ll need to chase out a shallow run, fix the cable in position in oval PVC conduiting. It won’t give any more protection against an electric drill, but it’ll prevent any possible reaction between the plaster making good and the cable sheathing.
Always channel horizontally or vertically, and never diagonally, so it’s easier to trace the wiring run when you’ve completed decorating. You can then avoid the cable when fixing something to the wall. Normally the cable will drop down to below floor level to connect into the circuit. Rather than remove the skirting to get the cable down to chip out a groove.
You’ll then have to drill down through the end of the floorboard with a wood bit. Alternatively, you can use a long masonry bit with an electric drill to complete the task. But if the floor is solid, the ring is usually in the ceiling void above, in which case the branch will drop down from the ceiling. And this will involve a considerable amount of channelling out if you want to install the new socket near floor level. Stud partition walls also present a few problems. If the socket is near the floor, you should be able to get a long drill bit through the hole you cut for the socket to drill through the baseplate and floorboard. You can then thread the cable through. But if the socket is to be placed higher up the wall, noggings and sound insulation material may prevent the cable being drawn through the cavity. In this case you will probably have to surface-mount the cable. In fact, surface-mounting is the easiest method of running the cable.
All you do is fix special plastic conduit to the wall and lay the cable inside before clipping on the lid. But many people regard this as an ugly solution. When laying cable under ground floor floorboards you should clip it to the sides of the joists about 50mm (2in) below the surface so that it doesn’t droop on the ground.
When you have to cross joists, you’ll need to drill 16mm (5/sin) holes about 50mm (2in) below the level of the floorboards. The cable is threaded through them and so is well clear of any floorboard fixing nails. Connecting into the circuit If you use a junction box, you’ll need one with three terminals inside. You have to connect the live conductors (those with red insulation) of the circuit cable and the spur to one terminal, the neutral conductors (black insulation) to another, and the earth wires to the third.
You might decide that it’s easier to connect into the back of an existing socket rather than use a junction box, although this will probably mean some extra channelling on the wall. Space is limited at the back of a socket so it may be difficult to fit the conductors to the relevant terminals. However, this method is ideal if the new socket that you’re fitting on one wall is back-to-back with an existing fitting. By carefully drilling through the wall a length of cable can be linked from the old socket into the new.
