DIY Tips: #2 Change a fuse

Fuses are a deliberate weak link in a circuit. The strands of wire used in fuses are thinner than those used in the rest of the wiring circuit. When a fault occurs in your wiring or a piece of equipment, either through overloading, through a short or ‘earthing out’, there will be a significant increase in power through the cables. This causes the thinner fuse wire to rapidly heat and melt, quickly breaks the circuit, switching off the power.

The limit at which a fuse ‘blows’ is determined by the thickness of the wire running through it. Different thickness fuse wires blow at different levels of power. Exceeding the maximum rated for that fuse wire will cause the wire to break. Modern installations make use of ‘circuit breakers’ instead of the old style fuse wires. These devices will detect an increase in the current and automatically switch off the power. The advantage of these devices is that they can simply be reset by pressing a button.

Incorrect value fuses are a hazard, not only to the equipment they are protecting but also to your health. This socket will have to be replaced and the wiring checked – the equipment which was plugged into it is most probably no good now unless it had an extra internal protection fuse which may have saved it.

Handy Fuse Chart for 3 pin plugs:

Power Consumption				Fuse
<230W (e.g. bedside lamp)				1 Amp
231w – 690w (e.g. stereo)				3 Amp
691 – 1150w (e.g. Vacuum)				5 Amp
>1151w (e.g. heater, bread maker)				13 Amp

It is very sensible to keep a selection of fuses somewhere handy – somewhere you can find in the dark is good. A packet of common fuses doesn't cost much and one day you'll be glad you got them – I promise. Oh and a torch – a working torch.

Now, to replace the fuse in a plug – Loosen the centre screw from the pin side of the plug (do not loosen the two (if there are any) close to the point where the cable goes into the plug). Remove the plug back to expose the wire connections and the fuse.

Take a small screwdriver and lever out the fuse from its grips – if a terminal comes up with the fuse, just push it back into place. Always replace fuses with the correct rating/value fuse and certainly don't ever be tempted to use a higher rated fuse to “stop the thing keep blowing”. If the fuse does keep blowing, this is telling you there is something wrong – either with the equipment or with the wiring – you really must get them checked. Before you screw the top back onto the plug just check the terminals holding the wires are correct to the diagram above and there are no stray strands of wire and that the terminal screws are tight. Once the back is on – plug it back in, turn the kettle on, have a cuppa and a custard cream – job well done. Oh one last thing on plug fuses – the plug will probably say on it “13A” this is what the plug is rated to – not what fuse should go in it – always use the correct rating fuse for your equipment.

Sadly I have run out of space to cover fusebox / consumer unit fuses this week.

Next week we shall repair a blown fuse in a fusebox.

Keep safe.

Dave