When a circuit fuse blows, turn off the main switch, remove the fuse in the consumer unit and try to find out what made it blow. It could be over-loading. If it is a lighting circuit fuse, examine the flex of the light which blew the fuse when it was switched on. Also examine all pendant flexes. A bulb that fails when switched on sometimes blows the circuit fuse. If a fuse blows for no apparent reason, it is probably because the fuse wire has deteriorated with age. A cartridge-type fuse does not usually deteriorate. When a fuse blows with a “bang” the reason is almost always a short circuit; the fuse wire disintegrates, leaving a blob of metal and a blackened fuse- holder.
Replacing a re-wirable fuse.
1. Remove the bits of fuse wire and any blobs of metal and any deposit.
2. Insert a new piece of fuse wire of the correct rating into the tube. Secure the end, clockwise under the terminal washer or in the terminal hole according to type, and tighten the screw.
3. Do likewise at the other terminal, taking care not to stretch or strain the fuse wire
4. Strip the ends of the wire, insert the fuse and turn on the main switch. Replacing a cartridge fuse.
1. Remove the old cartridge from the fuse-holder and discard it.
2. Select a new fuse of the same current rating and colour.
3. Fit the new fuse in the holder.
4. Replace the holder in the fuseway of the consumer unit. Precautions. After a fault, never insert a rewirable fuse with the main switch on. If after replacement, a fuse blows again immediately, do not insert another but have the installation tested by an expert Never put in a larger fuse wire than the current rating of the circuit or you may overload and damage the wiring. Never attempt to re-wire a cartridge fuse with fuse wire or it may disintegrate as a “bomb’ under short circuit conditions. Never use a substitute for a cartridge fuse when you have no spare.
Re-flexing a pendant
A simple “plain- pendant consists of a ceiling rose, flex and lampholder. Most old pendants are fitted with twisted twin flex. Modern pendants have sheathed flex, usually two-core but sometimes three-core.
1. Remove the old flex.
2. If twisted twin flex, strip off about in. (12 mm) of insulation from one end of both cores and connect the bared ends to the terminals from which the old flex was removed. If sheathed flex, first strip off about 3 in. (7.5 cm) of sheath and in. (12 mm) of insulation from each core. Connect the bared ends to the terminals.
3. Fit the cores under the anchorage.
4. Cut the flex to length and screw on the ceiling rose cover.
5. Prepare the cut end of the flex in the same way and connect the bared ends to the lampholder.
Re-wiring a light fitting
Remove the old flex from the fitting and replace it with parallel twin flex, leaving about 6 in. (15 cm) in the ceiling plate for connecting to the circuit within the ceiling box. The flexes are jointed to the circuit wires by means of a two-way insulated connector. If the fitting has exposed metal and there is no earth conductor at the point, it is necessary to run a length of green PVC insulated cable from the lighting point to the consumer unit earth terminal.
Renewing flexes on appliances
1. Buy a length of flex of the correct type and size.
2. Remove the old flex and disconnect the plug.
3. Prepare one end of the flex by removing sufficient sheath to reach the terminals within the appliance. If circular braided flex, fit a rubber ‘grommet over the end of the braid. The cable entry of a metal appliance must also have a grommet to protect the flex covering.
4. Strip about 1 in. (2.5 cm) of insulation from each of the cores and connect them to the appropriate terminals. The brown core to the “L” terminal is sometimes marked with a red blob: the blue core to the “N” terminal with a black blob; and the green-yellow conductor to the “E” with a green blob. Check the terminals for identification before removing the old flex, remembering that this will probably be in the old colours: red, black and green.
5. Now fit the plug (L=live, N=neutral; E=earth).
Renewing a kettle flex
The flex of an electric kettle and some other appliances is not connected direct to the appliance but has a removable flex connector. When renewing the flex, carefully dismantle the adaptor and note how the old flex is connected. Fit the new flex likewise.
Wiring a plug
Most plugs used today are 13 A fused plugs.
1. Remove the cover.
2. Strip about 2 in. (5 cm) off the end of the flex sheath or braid and about in. (1.2 cm) of the insulation from the ends of the cores.
3. Place the end of the sheath over the flex clamp and check each core for length. Trim the ends if necessary.
4. Insert the bared portion of each core into its respective terminal. First connect the green-yellow core to the “E” terminal, which is the centre pin near the top. Next connect the brown core to the right-hand terminal marked “L”. To do this with some plugs you may have to lift out the plug fuse. Next connect the blue core to the left terminal marked “N”.
5. Position the cores in the grooves so that the cover will not “ride”, and secure the end of the sheath in the flex clamp.
6. Double-check that the fuse is of the correct rating: 3-amp
(red or blue) for lamps and appliances up to 720 watts; 13-amp (brown) for all appliances from 720W to 3000W.
7. Insert the fuse and replace the plug cover.
Fixing a wall light
Circuit wires of most wall lights must terminate in a metal flush box which will house the flex connector and provide the necessary non-combustible chamber. Spotlights have circular base plates with 2 in. (50 mm) fixing centres and can be mounted on a circular conduit box fixed on the wall surface or sunk flush with the plaster. Metal wall lights must be connected to an earth wire.
Replacing a switch
An old-type circular tumbler switch mounted on a wood block or pattress can be easily replaced by a modern “square” switch. Remove the old switch and its block and fit a new box in its place. This can be a plastic box fixed to the wall surface or a plaster-depth metal box sunk flush with the wall surface.
For a flush box
1. Chop out the plaster to fit the box and some of the wall if the plaster is thin.
2. Thread the cable through the PVC grommet in the top edge of the box.
3. Fix the box in the chase, using wood screws in plugged holes.
4. Connect the wires to the switch and fix the switch with the screws provided.
For a surface box
Remove a section of thin plaster for the cable entry. Pass the cable through, fix the box to the wall, connect and fix the switch.
Before you replace a switch examine the conductors. If the rubber insulation is brittle and hard at the ends, slip red PVC sleeving over the ends as a temporary measure until the circuit is re-wired. This is particularly important with a metal box, which also needs earthing if no earth conductor is in the circuit.
Replacing a socket outlet
Most modern patterns of 13A socket outlet are of the plate type mounted on a rectangular surface or flush box. To replace a faulty socket, release the existing socket outlet from its box, disconnect the wires, examine the insulation for damage and connect and fix the new socket. Make certain that the red insulated wires go to the “L” terminal, the blacks to the “N” terminal and the earth wires, enclosed in green PVC sleeving, to the earth “E” terminal. You can also convert single socket outlets to doubles with specially designed inexpensive conversion kits.
Electricity supply to a detached building — garage, greenhouse, shed or sun house — must be independent of the house circuits. The outdoor section of a circuit cable from the house may be run overhead, underground or along a wall but never along a fence. The cable must originate at a separate fuseway in the consumer unit. In the outbuilding it must terminate at a mainswitch and fuse unit or a small consumer unit to control lighting and power in the building, even if only a small shed. Switches and accessories in the outbuilding must be metal clad and outdoor socket-outlets, switches, light fittings and apparatus must be of weatherproof pattern.
Installing bells and doorchimes
A simple bell (or buzzer) circuit requires a bell (or buzzer), a bell-push, some twin bell wire, insulated staples and a source of power which may be a battery or a mains transformer. For an illuminated push a transformer is essential. Some bells house the battery. In such cases it is necessary only to run a length of twin bell wire to the push.
The circuit and wiring for door chimes is the same as for a bell or buzzer but some models allow for both front door and back door pushes, each giving different notes or chimes.
The mains transformer for bells and chimes is purpose-made, as it must be double wound and have an earthed secondary winding. The input is mains voltage and can be supplied from a lighting circuit or from a fused outlet on a ring circuit. The output gives a choice of these voltages: 3V, 5V or 8V for bells: 4V, 8V or 12V for chimes. Small bells and buzzers require 3V, larger bells 5V and two bells operating together 8V. Chimes usually need 12V.
Simple burglar alarms
You can protect your home to a limited extent from house-breakers by installing one of a number of simple systems — mainly do-it-yourself kits that include door and window contacts and doormat pressure contacts. They operate from batteries and therefore remain working when the electricity supply is cut off, for example during a power failure. Full instructions are supplied with the kits.