Cartridge fuses are available in several sizes and Ampages, and are designed for several different applications. It is important to always use the correct fuse for a specific electrical circuit to avoid damage to the circuit or worse. Here is a guide to some of the different electrical fuses and their main uses in your home.
Why do we need fuses?
Fuses are simply a length of wire attached between two terminals and covered in a non-combustible material sleeve. They are a safety feature required in all modern electrical devices. The main purpose of a fuse is to fail, but only when too much electrical current is passed through the wire. When the wire in the fuse has too much current passed through it, it will melt and break the circuit, hopefully preventing damage to the electrical circuit it is fitted into. Common ways to cause too much electrical current to pass through the fuse are overloading, short-circuit, mismatched loads or a faulty device.
The fuses shown below are all fitted into electrical circuits (cooker circuit, shower circuit, etc) rather than the type of fuse you would fit into the plug on your toaster. You can read more about plug fuses further down the page.
Used mainly for lighting circuits.
Generally used in a Storage Heater or Immersion Heater circuit.
Used in a 20 amp radial power circuit and sometimes in storage heater circuits.
A 30 amp fuse will be used in a ring main circuit and sometimes in a radial power circuit (30 amp).
These large fuses are sometimes used in cooker circuits and shower circuits (circuits of more than 13kw). It is unlikely that you will encounter them anywhere else in the home.
Remember that fuses are a safety device, designed to blow out and cut off an electrical circuit in the event of a power surge or electrical malfunction. Replacing fuses with any other metal object just to get the circuit running again (I have seen this done more than once!) is very dangerous and should be avoided. It could not only cause damage to the electrical circuit or appliance, but could also cause a fire or serious injury.
Fuses in Electrical Appliances
Fuses found in the plugs of your electrical products (lamps, toasters, washing machines, etc) are either 3 amp or 13 amp. These ampages have been standardised for several years in the UK, so if you find a fuse of a different ampage (5A for example) in an electrical product, it is probably quite old. You can still buy replacement 5A fuses, alongside 3A and 13A.
In electrical appliances up to 700w, you need to use a 3A fuse. And for appliances over 700w, you need to use a 13A fuse. Typical examples of products under 700w are lamps, televisions, dvd player, computers, food mixers, power tools, fridges and freezers. Appliances that should have a 13A fuse in their plug include washing machines, microwaves, kettles, toasters and irons.
The easiest way to test if a fuse is blown is to use a handheld fuse tester. You can buy these devices very cheaply and most types include the ability to test light bulb and batteries as well as cartridge fuses.
Some circuits in older houses might contain Fuse Wire instead of Fuses. If this is the case in your house, you should use 5 amp wire for a lighting circuit, 15 amp for an immersion heater circuit, 30 amp wire for a ring main or cooker circuit (for cookers up to 12 kw).