Houses that have been wired or rewired in Britain since 1947 will be fitted with ring main circuits. These are continuous loops of cable linking all wall sockets. The sockets are uniform 13amp outlets with rectangular holes to take the three flat pins of 13amp plugs. This type of plug is supplied with a 3 or 13amp cartridge fuse (colour coded red and brown respectively). Always fit the fuse recommended by the manufacturer; as a general guide 3amp fuses are used with appliances rated up to 720 watts (for example table lamps) and l3amp fuses are used with larger appliances rated above 720 watts and up to 3000 watts (including kettles, irons and heaters). Some appliances (such as colour televisions, vacuum cleaners and spin dryers) although rated at less than 720 watts require a high starting current and should be used with 13amp fuses. In every case check first with maker’s instructions. Older houses will have radial wiring where separate cables radiate from the fuse board to each socket. These sockets are usually round pin in three sizes. The largest takes a 15amp plug used with larger appliances (such as heaters) while the other sizes take 5 and 3amp plugs used with smaller appliances (drills and table lamps respectively). The outlets may have two or three holes. The two pin sockets are not earthed and should only be used for light fixings with no exposed metal parts or for small double insulated appliances designed to operate without an earth connection and which are supplied only with two core flex. Where possible it is safer to have radial wiring replaced (by your Electricity Board or a registered electrical contractor) with the properly earthed – and safer – ring main circuit. Most plugs are made of tough, hard plastic but special rubberized types are available for equipment likely to be subjected to rough treatment, such as electric drills. Always buy a reputable make of plug because on poorer quality types the pins may move and cause a bad connection.
To fit a plug
First familiarize yourself with the colour code of the flex as it is most important the right core goes with the right terminal. With the new code blue is neutral, brown live and yellow/green earth. On older flex black is neutral, red live and green earth. Remove the cover of the plug by undoing the large screw between the pins. When you look at the plug, with the largest pin (the earth) at the top and the flex outlet at the bottom, the live terminal is on the right (marked L) and the neutral terminal is on the left (marked N). Prepare the flex by removing about 38mm of the outer covering with a knife and fit the flex through the flex grip. This will be either a clamp type secured with two small screws (in which case loosen the screws, thread the flex through the grip and tighten the screws) or a V-shaped grip which holds about 6mm of the flex covering inside the plug. Make sure each core of the flex will reach its terminal, then cut l2mm beyond this for joining to the terminals. With wire strippers carefully remove about l2mm of the insulation at the end of each core and twist the loose strands neatly together. Check which type of terminals the plug has. If it has screw holes double back the wires, insert them into the terminal holes and tighten the terminal screws with a small screwdriver to secure the wires. If the terminals are of the clamp type remove the screws, wrap the wires around the terminal posts in a clockwise direction, replace the screws and tighten them. On some plugs the live terminal is under the fuse housing, in which case you will have to remove the fuse before wiring that terminal. Make sure the plug is neatly wired: the insulation must go right up to the terminals and there must not be any straggling wires. If a fuse is required simply snap the cartridge into the holding clips. Finally double check wires are connected to correct terminals before refitting cover.
If a plug gets hot the terminal screws may have worked loose and need to be tightened. Always replace a cracked plug immediately; never repair it, even temporarily, with insulating tape since there is a considerable risk the casing will come apart as the plug is put into or removed from the socket and you could get an electric shock. It is important to check the flex regularly since the point where it joins the plug is particularly susceptible to breaking and fraying (especially on irons and vacuum cleaners). At first sign of wear cut frayed piece to make new end and rewire plug.
When rewiring a plug make absolutely sure the earth wire (yellow/green or green) is properly connected. If it is not you run the risk of an electric shock should the metal casing of an appliance become accidentally live. The only appliances which do not need earthing are double insulated ones supplied with two core flex and mains operated shavers which are intended for use with special shaver sockets.