Fuses are an essential part of any electrical installation. There are hundreds of different types of fuse but they all provide a weak link in a circuit that should cut out before causing damage to the circuit itself. In many situations today fuses have been replaced with modern circuit breakers, which are slightly more sensitive. Fuses are still regularly used and are an integral part of most electrical installations.
| Before working on any electrical circuit you must ensure that it is isolated correctly and cannot accidentally be switched back on. Please read the article on safe isolation procedures before doing any electrical work. If you are not 100% certain what you are doing call a qualified electrician. Building regulations are changing all the time and modifying your home electrics could be against new rules and could invalidate your home insurance, if in doubt check first! |
For a electrical installation to be as safe as possible it needs the correct thickness of wire to be used and the correct amperage fuse to be used. If you use a fuse of higher amperage than the circuit is designed for, then the wire could melt and set on fire or the appliance can be seriously damaged Fuses are rated in Amperes or Amps as they are more commonly known, a fuse is a deliberate weak link in a circuit and will melt if too much current passes through the fuse. There are several different types of fuse but they all do the same thing which is protect the circuit. A fuse will not stop you from being electrocuted! but a fuse can help prevent electrical fires. As a general rule of thumb fuses are rated by how many watts that circuit is using, 1000 watts is equal to 4 amps so therefore the maximum single appliance size that can be plugged into a socket is 3000 watts, this would be protected by a 13 amp fuse.
Cartridge fuses are the commonest type of fuse, these are often found in consumer units and domestic electrical plugs.
Here a industrial type cartridge fuse is contained in a fuse carrier, this is then inserted into the fuse holder on the distribution board.
Here three cartridge fuses can be seen protecting a three phase supply for a large industrial motor.
This is a picture of the Main fuse in a house, this is owned by the electricity company and cannot be removed without their permission. These fuses often have an anti-tamper seal so that the fuse cannot be removed without cutting off the anti-tamper seal. If you suspect the main fuse has blown then you must contact your electricity provider to have it replaced.
Fuse Wire
Some fuses especially in consumer units do not use cartridge fuses but instead use fuse wire. This is normally held in place at each end of the fuse with a screw. The fuse ratings for cartridge fuses and fuse wire are the same.
Fuse ratings
| 45 AMP | For circuits of more than 13kw (13000 w) |
| 30 AMP | For socket ring mains, some cooker and shower circuits up to 7kw (7000 w) |
| 20 AMP | For storage and water heater circuits |
| 15 AMP | For single appliance circuits up to 3kw (3000 w) |
| 13 AMP | For appliances between 700 and 3000w (3kw) |
| 5 AMP | For lighting circuits. The maximum permissible load of a lighting circuit is 1200w or 12* 100 watt lamps |
| 3 AMP | For appliances up to 700 watts, such as table lamps and alarm clocks |
