Electrical equipment is now used more and more in the home, so an extra power socket is always useful. Here’s how to fit one
There’s nothing really difficult about installing a new power point. It’s easier than putting in a new light as you don’t have to worry about a switch cable.
Ever since the early 1950s, the power supply to the sockets has almost always been wired as a ring circuit. And any house rewired since then will almost certainly have had this system installed. This means that once you’ve decided where you want the new outlet point -by a shelf in the living room for a hi-fi system, or over a worktop in the kitchen, for example -all you then have to do is to run a ‘branch’ or ‘spur’ to it from a convenient point on a nearby ring circuit.
The connection could be made at any socket on the ring (unless it already has a spur coming from it), or by using a three-terminal junction box inserted into the cable run. Each spur can have either two singles or one double socket fitted to it, or else a fused connection unit. But new regulations will come into force from the beginning of 1983 and then you’ll only be able to install one single or one double socket on the spur.
Checking your circuits
Although it’s very likely that your house has ring circuits for the power supply, it’s important to make sure. A ring circuit serves a number of 13A power outlets, and the sockets themselves take the familiar three-pin plugs with flat pins. But having this type of socket doesn’t necessarily mean you’ve got a ring circuit – a new radial circuit may have been installed with these fittings, or an old radial circuit may simply have been modernised with new socket outlets. 1 explains the distinction.
First you’ve got to check whether you’ve got a modern consumer unit or separate fuse boxes for each of the circuits. Having a consumer unit is a fair indication that you’ve got ring circuit wiring, and if two cables are connected to each individual 30A fuseway in the unit this will confirm it. Normally each floor of the house will have a separate ring circuit, protected by a 30A fuse or MCB.
If you have separate fuse boxes, look for the ones with 30A fuses. If they have one supply cable going into them and two circuit cables coming out, this indicates a ring circuit.
It’s easy to identify the sockets on any particular circuit simply by plugging in electrical appliances, such as table lamps, turning off the power and then removing a 30A fuse from the fuse box or consumer unit, or switching off a 30A MCB. When you restore the supply, the equipment that remains off will indicate which sockets are on the circuit.
Dealing with radial circuits
Where a house hasn’t got ring circuits, then the power sockets will be supplied by some form of radial circuit. Because there are different types of radial circuit, each governed by separate regulations controlling the number and location of sockets on the circuit, the size of cable to be used and the size of fuse protecting it, it’s not possible to connect a spur to a nearby radial circuit. In all probability you’ll have to install a new circuit starting at a new, separate fuse box or else at a spare fuseway in a consumer unit.
If you’ve still got unfused 15A, 5A and 2A round-pin plugs, then this is a sure sign of very old radial circuits, which were installed more than 30 years ago. Rather than extending the system you should seriously consider taking these circuits out and replacing them with ring circuits, as the wiring will almost certainly be nearing the end of its life. You’ll then be able to position the new sockets exactly where you want them. If you’re in any doubt about the circuitry in your house you should contact your local electricity authority or a qualified electrician before carrying out any work.
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 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 with clips, then plaster over it. But the best method of all is to run the cable 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
The power supply to the sockets will probably be wired as a ring circuit. You can add a spur to this provided the number of spurs doesn’t exceed the number of sockets on the ring.
New spurs should be in 2.5mm2 cable
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.
AT A SINGLE SOCKET One cable entering
Socket is on the end of a spur. There could be another single socket on the branch. Action: trace cable. If it goes to another single socket and this socket has only two cables going to it, then you have found an intermediate socket on the spur. It it goes to a double socket where there are three cables, then the single socket is the only socket on the spur. It’s the same if the cable goes to a junction box.
Two cables entering
Socket could be on the ring, or it could be the intermediate socket on a spur. Action: You’ll need to trace the cable runs. If the cable is the only one going to another single socket, then the socket is on a spur. If the cable makes up one of two cables in another socket then it’s on the ring.
Three cables entering
Socket is on the ring with a spur leading from it.
Action: to check which cable is which you’ll need to trace the cable runs.
AT A DOUBLE SOCKET One cable entering
Socket is on a spur. You can’t connect a new socket from this.
Two cables entering
Socket is on the ring. You can connect a spur into this.
Three cables entering
Socket is on the ring with a spur leading from it. Checking to see which cable is which is the same as for a single socket with three cables. You can’t connect a spur from this socket.
The back you can use a long steel cold chisel 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. Cable in the ceiling void can rest on the surface.
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. Sleeve the earth wires in green/ yellow PVC first.
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.
Metal boxes are recessed into the wall and provide a fixing for the socket itself. Knockouts are provided in the back, sides and ends to allow the cable to enter the box. Rubber grommets are fitted round the hole so the cable doesn’t chafe against the metal edges.
Elongated screw slots allow box to be levelled when fixed to wall.
Adjustable lugs enable final adjustments to level of faceplate on wall.
Boxes are usually 35mm deep, but with single-brick walls boxes 25mm deep should be used, along with accessories having deeper-than-usual faceplates.
Lugs can be fitted to a metal box so that it can be fitted into stud partition walls.
Surface-mounted boxes (usually white plastic) are 35mm deep, and are simply screwed to the wall surface where required.
TIP: FIT SAFETY PLATES
Safety plates can be fitted to sockets to prevent young children playing with them.
– Crumbly plaster There’s little that can be done other than cutting back to sound area. Position box and socket as required then make good surrounding area.
– Poor bricks Because of soft bricks you can quite easily chop out too big a recess for the box. Pack the recess with dabs of mortar or plaster.
– Cavity Walls To prevent breaking through into the cavity only chop out a recess big enough to take a shallow box, about 25mm (1 in).
Installing a plug socket
The ordinary three-pin socket outlet gives great flexibility as to where you can use electrical equipment round the home. From the same point, for example, you can use an iron, a food mixer or an electric drill – it’s simply a matter of unplugging one and plugging in another. Such equipment can be classed as portable, and ideally, if the socket is not the switched type, it should be unplugged when not in use.
But there are situations when you might want to use a power point for a specific purpose, particularly if the appliance being run from it is fixed in position. Freezers, refrigerators, washing machines, water heaters and extractor fans all come into this category, and it could prove very inconvenient if any of these were unplugged by mistake. So in order that the outlet can’t be used for any other purpose, you can fit a fused connection unit. This is a switched connector that usually takes the place of a single socket outlet, and the flex of the appliance is wired directly into the unit, rather than via a fused plug.
There are additional advantages of fused connection units, especially those with an on/off neon light to indicate when power is flowing to the appliance. With some water heaters, for example, this may be the only way of telling whether they are on or off.
You’ll also have to use one of these units when you are installing an additional lighting circuit (say, to an outside light) as a spur from a ring circuit; such a spur has to be protected by a fuse of lower amperage than that used to protect the main ring.
The rating of the fuse within the unit must be selected according to the wattage of the appliance – a 3A (red) fuse is used for those up to 720 watts and a 13A fuse (brown) for those between 720 and 3,120 watts.
How to install a connection unit
You can install one of these units in exactly the same way as you would a single socket outlet. You have to remove the existing faceplate, detach the cores and insert them into the appropriate terminals of the unit. The flex of the appliance also has to be wired in at this time and the cord grip secured before the unit is screwed into place. However, if you have a double socket, you can fit a special double mounting box, which is slightly wider, and allows you to fit a connection unit and a single socket side-by-side.
If you are installing the unit on a spur, remember that you can only have one unit and no other sockets on that particular branch. But if you want to connect from an outlet socket which is already on a spur, you can blank off the socket and use it as a junction box, laying in the cable to the position of the connection unit above the work surface. The unit can be surface-mounted or set flush with the wall and, depending on the type, the flex can enter through the front or from below. The latter is useful if you want to run the flex in conduit, chased into the wall (out of sight), so that, for example, it can be taken behind a work surface and then to a washing machine, refrigerator or waste disposal unit.