Fuses

Fuses

When electricity passes through a wire it wastes a part of the energy it carries by creating heat.  Electrical wires get hot.  If too much electricity flows then wires can get very hot and melt. If a wire or appliance is supplied with too much electricity its parts may not be able to withstand the power – parts melt and can break or worse cause a fire.

However this heating effect actually provides one of the most basic and important safety features to our domestic power supply – THE FUSE.

Fuse Design

The image below shows a simple fuse with the external label removed so you can see inside. It is a thin wire in a a tiny glass case. The fuse has metal ends that connect to the mains electricity in the plug.

Inside a Fuse
Inside a Fuse

All the electricity has to pass through this fuse wire to reach an appliances power cable. If the wire in the fuse gets too hot and melts the electricity cannot flow into your appliance. This is just like unplugging the item.

If too much power flows through the socket into the appliance ( power surge or mains power fault) the fuse will melt protecting the appliance from damage and making sure it does not start a fire.

If the appliance tries to draw too much power the fuse will also melt. The appliance might do that if it is dropped into a bath or develops a fault or is a toaster that someone has stuck a knife into! In this case the fuse will protect the users from getting a dangerous sock.

A – Amps

Household Fuses
Household Fuses

Fuses have different amp ratings. The amp rating tells you how much electricity they can take before they melt. Typical ratings are shown in the image below.

Each of your appliances will also have a similar rating so you should match the fuse in the plug to the appliance.  You should never put a higher fuse in a plug that the appliance requires – this is unsafe and can result in your appliance breaking.

One Time Use

Burnt Out Fuse
Burnt Out Fuse

Once a fuse has melted it has to be thrown away and replaced by a new one. If one of your appliances has stopped working, unplug it and check the fuse is still intact before you throw it away. The diagram below shows an intact fuse and one that has melted. Notice you can’t see the wire just a lot of soot in the one that has melted.

If you can see any soot inside the glass case then you need to replace the fuse. If the fuse in a particular place keeps melting you should get a professional to check the appliance as it is likely to have a fault.

Fitting A Fuse

Plug Wiring
Plug Wiring

A fuse is fitted to the plug of your applaince. ALWAYS unplug your appliance before you mess about with the plug. Unscrew the underside of the plug and the top will pop off revealing something similar to the picture on the left. Fuses just slot into a small copper bracket in each plug. Gently leaver the old fuse out and then gently press your new fuse into place.

Carefully align the top back ove the plug and then rescrew the base to the top.

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