It's annoying if an electrical socket or appliance doesn't work. But with a bit of logical detective work, you should be able to find the cause of the problem - and, in many cases, correct the fault yourself. Before you begin any kind of electrical work, though, you'll need to know how to isolate a circuit and double-check that it's dead.
For your safety, electrical products must be installed in accordance with local Building Regulations. If in any doubt, or where required by the law, consult a competent person who is registered with an electrical self-certification scheme. Further information is available online or from your Local Authority.
Never take risks with electrical safety. Before you start any type of electrical work, you must follow these following safety precautions:
Follow these steps to find the cause of your electrical problem.
Each of the electrical circuits in your home is provided with a fuse or a circuit breaker. They can be either an MCB (miniature circuit breaker) or RCBO (residual current breaker with overload protection).
These devices protect the circuit against overloading, which could generate heat within the wiring that melts the insulation and causes a fire.
They also react to short circuits that are caused when the current-carrying cores of cables come into contact with each other. This can happen if the cores become loose inside an electrical accessory, or if the cable is pierced accidentally by a drill or nail.
Fuses contain a special wire that melts, separates and cuts off the flow of electricity if the circuit draws too much current or a short circuit occurs.
The wire might be exposed within the carrier, or it can be contained within a special cartridge. Circuit breakers are trip switches that turn themselves off under the same circumstances, and can be reset by pushing a button or operating the switch.
The demand placed on circuits varies (light fittings consume less electricity than most plug-in appliances, for example). So as well as having different sized cable, the circuits are protected by fuses or circuit breakers with different ratings.
Lighting circuits are protected by 5 or 6 amp fuses, socket circuits by 30 or 32 amp fuses, an immersion heater by a 15 or 16 amp fuse, and so on. It's very important that you use fuses of the correct rating. One with too low a rating will keep blowing, while one with a rating that's too high might not protect the circuit against overloading - with potentially fatal consequences.
To prevent your RCD-protected systems from tripping, you should work with the whole power supply switched off. Switching off a circuit breaker or removing a circuit fuse only isolates the L (live) side of the circuit, while the N (neutral) stays connected to the mains. This is quite safe for working on the circuit, but it means that any contact with the N wire will cause the RCD to trip and switch off the entire house supply. This is not only irritating, but can also be dangerous when you're in the middle of a repair.
Cartridge fuses are easy to replace - but make sure you use the correct fuse rating for the circuit, as fuses vary in size and colour coding according to their rating.
Switch off the power and remove the cartridge fuse. Some are simply held in spring clips and can be prised out, while on others you'll need to open the fuse carrier by releasing a screw.
Press a new fuse of the correct rating into the spring clips, or insert it into the open ends of the carrier's pins. Then, if necessary, reassemble the fuse carrier. Check the main power switch is off and replace the fuse - usually, the pins are offset to one side so it'll only fit one way round. After that, you can restore the power.
Watch our how to video below which shows you how to change a plug and fuse.
If a rewirable fuse has blown, you should be able to see that the fuse wire has melted. You should replace it with new fuse wire of the correct amperage.
Fixed appliances are permanently wired to a connection unit that has an on/off wall switch and a cartridge fuse. To replace a connection unit fuse, first switch off the connection unit switch. Then unscrew or prise out the fuse holder. Remove the fuse and insert a new one of the correct rating. Make sure you push or screw the holder back fully before you restore the power.
Turn off the power, lift the fuse cover on the consumer unit and remove the blown fuse. Release the terminal screws and remove the fuse wire.
Take a length of fuse wire of the correct rating and insert it in the carrier. Wind the ends of the wire around the terminals, but don't pull it taut. Cut off the excess, then tighten the screws. Check the main power switch is off, then refit your fuse. Replace the cover and turn the power back on.