There are three main types of circuit fuse: wire fuses, cartridge fuses and circuit breakers. It is important to know.which type you have and to keep a supply of spare fuse wire or cartridges. Circuit breakers need no spares as they are switches which automatically shut off if the circuit is overloaded at any time.
Most fuse boxes are covered by a plate which either clips on or screws into place. Always turn off the mains switch before removing the plate or touching any fuse.
With the plate removed you will see a row of fuse carriers made of porcelain or moulded plastic. Some are colour coded on the back: white for 5 amp lighting circuits, blue for 15 amp heating circuits and red for 30 amp power socket circuits. Alternatively, the amperage may be stamped on the back of the holder.
As a further guide it is a good idea to mark the fuse holders with the purpose of the circuit they protect— ‘1st floor sockets’, ‘Ground floor lights’ and so on.
Take out the first fuse—the holders simply pull out and clip back into place—then replace the cover and turn the mains switch back on.
Check each circuit until you find the one that has stopped working. Turn off the mains again, remove the cover and mark the fuse holder accordingly. Afterwards, clip it back into place and repeat the operation for the other fuses in the box.
When a fuse blows, the first thing to. do is to discover the cause and rectify it. If you suspect that the failure is due to a faulty appliance, unplug it and do not use it again until it has been mended.
Sometimes fuses blow for no obvious reason. It may be that the fuse has just worn out in which case when it is replaced, the current will flow as before. But if a fuse keeps blowing each time it is replaced, there may well be a serious fault somewhere in the wiring and you should contact an electrician.
Once the fault that caused the fuse to blow has been put right, locate the blown fuse. On bridge wire fuse holders , the fuse wire is held in position by a screw at either end. The wire runs over the surface of the holder, so a broken fuse can be clearly seen. In protected wire fuse holders, the wire runs through a tube inside the holder. To check it, gently try to prise the wire out of the tube with a small screwdriver. If the fuse is blown, half of the wire will come away.
To mend a wire fuse, loosen the screws and discard the broken wire.
Replacement fuse wire is sold ready for use, mounted on a card. Use wire-cutters to cut a new length of wire of the correct amperage rating. Wrap the ends of the wire around the screws in a clockwise direction so that when you retighten the screws the wire is not dislodged. Finally, replace the holder and fuse box cover and switch the power back on.
In cartridge fuses, the wire is encased in the cartridge and can only be checked, at this stage, by replacement. Unclip the old cartridge and fit a replacement of the same amperage rating as the original.
When a circuit breaker shuts off, locate the fault that has caused it to do so, then reset the switch or button on the affected circuit.
When mending fuses, on no account be tempted to use a fuse of too high an amperage rating—you will be putting your entire electrical system at risk.
All the equipment you need for mending fuses—screwdriver, torch, wire cutters and different sizes of fuse wire or cartridges—should be electrically insulated.
How to Wire a plug
Cheap accessories invariably heat up in use—producing a fire risk—so it is important to use high quality plugs. Furthermore, it is essential to wire plugs correctly—incorrect wiring can be dangerous.
Remove the cover of the plug, by unscrewing the large screw between the pins, to reveal the three terminals which are attached to the pins of the plug. As you look at the plug, the terminal at the top connects to the green and yellow earth wire. The brown live wire connects via the fuse to the live pin on the right, and the blue neutral wire to the neutral terminal on the left.
Some older appliances have differently coloured wires; green for earth, red for live and black for neutral.
Appliances that are double insulated—such as television sets—do not have an earth wire so the earthing terminal should be left unconnected.
Loosen the cord grip which is secured by two screws at the base of the plug. The cord grip is to clamp the sheathing of the flex to the plug to prevent it from being pulled out accidentally. Some modern plugs are fitted with a fixed plastic gate in place of a conventional cord grip.
The sheathing of the flex must now be removed to a distance of about 60mm to allow the earthing wire to reach its terminal. Slit ‘the outer sheath of the flex with a sharp knife taking care not to damage the wires. Wires with damaged insulation should never be used.
Put the flex under the cord grip and firmly tighten the fixing screws so that the grip clamps the sheathing firmly in place. On plugs with a plastic gate, the sheathing should be pressed into position between the two halves of the gate.
Cut the three wires with wire clippers so that each can wrap round or pass through its terminal, then use a wire stripper to remove the insulation from the ends. Bare enough wire to fit around the terminal. Twist the strands making up each wire together then fasten the wires to their terminals making sure that there are no loose strands left free.
Remove the terminal nut and washer and form the wire into a closed, clockwise loop around the terminal so that it will not unravel it when the wire is being retightened. Replace the washer and nut and tighten.
In some plugs, the wire passes through a hole and is secured by a small screw at the top of the terminal. Here, the wire should be bent double before being inserted.
Finish off by clipping a working fuse into the fuseholder, making sure it is of the right amp rating for the appliance. Screw on the cover of the plug and it is ready for use.
Round pin plugs should be wired up in the same way as 13 amp plugs but, as they have no fuse, make sure that the current rating of the plug is adequate for the connected load.