One aspect of electrical appliances that tends to cause a lot of confusion is the question “What fuse should this appliance have?” In this article, we look at fuses in detail and give guidelines on how to work out the correct fuse for the appliance.
What are fuses?
A fuse is an electrical component that is designed to prevent the flow of current that is higher than the value of the fuse. Eg a 3A fuse will “blow” if the current through it exceeds 3A.
Fuses are used in circuits to prevent excessive currents flowing under fault conditions and causing a fire. All mains plugs used in the UK are fitted with 3A, 5A or 13A fuses. The primary purpose of the fuse is to protect the mains cable and prevent it melting and/or catching fire under fault conditions.
The value of fuse used is based on the power of the appliance. A higher powered appliance, such as an electric heater will take more current and will typically require a 13A fuse along with a cable that can carry this level of current.
Fuses are colour coded for easy identification as shown below.
3A – Red
5A – Black
13A – Brown
Fuses in moulded mains plugs
As these plugs are moulded to the cable the fuse in these can be fixed by the manufacturer. They know what the maximum current that the cable can carry and the fuse is selected to protect the cable and “blow” if the current exceeds the capacity of the cable.
The value of the fuse that is fitted inside the moulded plug is marked on the outside. This makes the job of checking the fuse in a moulded plug very easy. Just lever out the fuse and check that the value is the same as that marked on the plug.
Fuses in rewireable mains plugs
These are plugs which the user can wire. These plugs can handle a maximum of 13A of current and are marked as such. Many people assume that this means a 13A fuse should be used in this appliance which is a mistake.
The fuse used in rewireable mains plug is sometimes marked on a paper label fixed to the plug or is referred to in the user manual. But in many cases, the person inspecting the appliance has to work out the value of the correct fuse.
First of all one needs to find out what the power consumption of the appliance is. This is usually indicated in Watts on the rating plate.
An iron is fitted with a 13A fuse and the power consumption of the appliance is 1900W. As this is greater than 700W, this is the correct fuse for the appliance.
If the cable on this iron is being changed, then it is important to replace it with an identical type, capable of carrying 13A.
The advice on the rating plate of this lamp says that the maximum lamp that can be fitted is a 40W one. The plug is fitted with a 13A fuse.
As the power rating is so low, we can quickly see that the fuse is too high and has to be changed to a 3A one.
This sandwich toaster has a plug fitted with a 13A fuse and according to its rating plate has a power consumption of 700W. As this is right on the decision threshold, what should we do?
In general, heating appliances are fitted with a 13A fuse. If in doubt, check the cable used for this sandwich toaster. If it is capable of taking 13A, then a 13A fuse is the correct choice.