SWITCH OFF ELECTRICITY AT THE MAINS

To change a fuse in the consumer unit, firstly switch off the main switch on the consumer unit to cut off the supply.

Make sure the consumer unit has fuses inside. Some consumer units have miniature circuit breakers (MCBs) and these are different to fuses, they are not removable and have a button or lever to reset themselves, see Miniature Circuit Breakers for more details.

The fuse blowing is an indication either that the circuit has been overloaded or that a short circuit has occurred somewhere in the circuit. Before replacing the fuse it is important to identify what has caused it to blow. Switch off all the appliances connected to the circuit to ensure it is not overloading. Now see Identifying a faulty circuit for more details on finding the problem.

If you do not know which fuse has blown then remove each one in turn and inspect the fuse wire inside. If the fuse wire is broken then it requires replacement.

There are various different types of fuse carriers in use, but the principle is the same. The three most common are the single bladed and double bladed fuse wire carriers, and the cartridge fuse.
 

 
The picture shows a typical cartridge fuse. First ensure the consumer unit is switched off. The fuse wire is held in place by two screw terminals at the top and bottom of the fuse carrier. Unscrew these terminals but do not remove the screws. Then remove the blown fuse wire from the holder.

Select some fuse wire which is of the correct rating (the rating of the fuse carrier is usually given on the front the case). Take one strand of this wire and pass it through from one terminal to the other and wrap it around the two screws leaving some slack. Finally tighten the screws and replace the fuse.

Fuse	Colour	Typical Uses
5 amp	White	Lighting / small plug circuits
15 amp	Blue	Immersion/storage heaters
30 amp	Red	Ring circuits (sockets), cookers, showers, radial circuits

 

 
A cartridge fuse is similar to those found in plugs only bigger. The cartridge fuse is held by removable carriers similar to above. First ensure the consumer unit is switched off. Then remove the fuse carrier containing the blown fuse. If you do not know which fuse has blown then test each individual fuse using a fuse tester.

The fuses are usually held clamped in place by the surrounding plug and can be prised out using a screwdriver. Some fuse cartridge carriers are held together with a screw that must be removed to gain access to the fuse.

Replace the faulty fuse with an equivalent fuse. Reassemble the carrier if necessary and slot back into the consumer unit. The table below shows the colour fuses and typical uses.

Fuse	Colour	Typical Uses
5 amp	White	Lighting / small plug circuits
15 amp	Blue	Immersion/storage heaters
20 amp	Yellow	Smaller radial circuits / water heaters
30 amp	Red	Ring circuits (sockets), cookers, showers, radial circuits
45 amp	Green	Cookers/showers

 

 
Electrics > Miniature Circuit Breakers
Electrics > Identifying a faulty circuit
 

 
Electricians