When the lights go out or an electrical appliance won’t work, the reason is often obvious. But when it isn’t, it helps to know how to locate the fault and put it right.
Most people’s immediate reaction to something going wrong with their elecricity supply is to head for the meter cupboard, muttering darkly about another blown fuse. Fuses do blow occasionally for no immediately obvious reason, but usually there is a problem that needs to be pin-pointed and put right before the power can be restored. It’s no use mending a blown fuse, only to find that when the power is restored the fuse blows again because the fault is still present. Tracing everyday electrical faults is not particularly difficult.
You simply have to be methodical in checking the various possible causes, and eliminating options until you find the culprit. More serious faults on the house’s fixed wiring system can be more difficult to track down, but again some careful investigation can often locate the source of the trouble, even if professional help has to be called in to put it right.
Before you start investigating any electrical faults, remember the cardinal rule and switch off the power at the main switch. When fuses blow, it is all too easy to forget that other parts of the system may still be live and therefore dangerous, and even if you know precisely how your house has been wired up it is foolish to take risks. If the fault appears to be on an electrical appliance, the same rules apply: always switch off the appliance and pull out the plug before attempting to investigate.
Don’t rely on the switch to isolate it; the fault may be in the switch itself. It’s also important to be prepared for things to go wrong with your electrics; even new systems can develop faults, and in fact a modern installation using circuit breakers will detect faults more readily than one with rewireable or cartridge fuses, so giving more regular cause for investigation. Make sure that you keep a small emergency electrical tool kit in an accessible place where it won’t get raided for other jobs; it should include one or two screwdrivers, a pair of pliers, a handyman’s knife, spare fuses and fuse wire, and above all a working torch. There is nothing more annoying when the lights go out than finding the torch does not work.
Check the obvious
When something electrical fails to operate, always check the obvious first – replace the bulb when a light doesn’t work, or glance outside to see if everyone in the street has been blacked out by a power cut before panicking that all your fuses have blown. Having satisfied yourself that you may have a genuine fault, start a methodical check of all the possibilities.
A fault can occur in a number of places. It may be on an appliance, within the flex or plug linking it to the mains, on the main circuitry itself or at the fuseboard. Let’s start at the appliance end of things. If something went bang as you switched the appliance on, unplug it immediately; the fault is probably on the appliance itself. If it simply stopped working, try plugging it in at another socket; if it goes, there’s a fault on the circuit feeding the original socket. If it doesn’t go, either the second socket is on the same faulty circuit as the first one (which we’ll come to later) or there may be a fault in the link between the appliance and the socket – loose connections where the cores are connected to either the plug or the appliance itself, damaged flex (both these problems are caused by abuse of the flex in use), or a blown fuse in the plug if one is fitted.
Plug and flex connections
The next step is to check the flex connections within the plug and the appliance.
The connections at plug terminals are particularly prone to damage if the plug’s cord grip or flex anchorage is not doing its job; a tug on the flex can then break the cores, cutting the power and possibly causing a short circuit. If the connections are weak or damaged, disconnect them, cut back the sheathing and insulation and remake the connections. Make sure that the flex is correctly anchored within the body of the plug before replacing the cover. If the plug contains a fuse, test that it has not blown by using a continuity tester, or by holding it across the open end of a switchedon metal-cased torch.
Replace a blown fuse with a new one of the correct current rating; 3A for appliances rated at 720Wor below, 13A for higher-rated appliances (including televisions sets). Next, check the flex connections within the appliance itself. Always unplug an appliance before opening it up to gain access to the terminal block, and then remake any doubtfullooking connections by cutting off the end of the flex and stripping back the outer and inner insulation carefully to expose fresh conductor strands. If the flex itself is worn or damaged, take this opportunity to fit new flex >f the correct type and current rating.
Make sure ‘ou re-use any grommets, heat-resistant shelving, special captive washers were fitted to the appliance. Lastly, check the flex continuity; it is possible that damage to the flex itself has broken of the cores within the outer sheathing.
use a continuity tester for this, holding he two probes against opposite ends of each core in turn, or use your metal-cased again, touching one core to the case ind the other to the battery. Replace the flex, any core fails the test; the appliance may work if the earth core is damaged, but he earthing will be lost and the appliance would become live and dangerous to anyone.
Similar problems to these can also occur on lighting circuits, where the pendant flex linking ceiling roses to lampholders can become disconnected or ‘faulty through accidental damage or old age. If replacing the bulb doesn’t work, switch off the power at the mains and examine the condition of the flex. Look especially for bad or broken connections at the ceiling rose and within the lampholder. Replace the flex if the core insulation has become brittle, and fit a new lampholder if the plastic is discoloured (both these problems are caused by heat from the light bulb). If the lampshade ring will not turn you will have to cut this with a hacksaw.
Mending old blown fuses
A circuit fuse will blow for two main reasons, overloading and short circuits . Too many appliances connected and this will melt an old fuse. Similarly, a short circuit – where, for example, bare live and neutral flex cores touch – causes a current surge that blows the fuse. If overloading caused the fuse to blow, the remedy is simple: disconnect all the equipment on the circuit, mend the fuse and avoid using too many high-wattage appliances at the same time in future. If a short circuit was to blame, you will have to hunt for the cause and rectify it before mending the fuse – see photographs on the next page. When a circuit fuse blows, turn off the main switch and remove fuseholders until you find the one that has blown.
Then clean out the remains of the old fuse wire, and fit a new piece of the correct rating for the circuit-5A for lighting circuits, 15A for circuits to immersion heaters and the like, and 30A for ring circuits. Cut the wire over-long, thread it loosely across or through the ceramic holder and connect it carefully to the terminals. Trim the ends off neatly, replace the fuseholder in the consumer unit and turn on the power again. If the fuse blows again, and you have already checked for possible causes on appliances, flexes and lighting pendants, suspect a circuit fault – see below. If you have cartridge fuses, all you have to do is find which cartridge has blown by removing the fuseholder and-testing the cartridge with a continuity tester or metalcased torch.
A blown cartridge fuse should be replaced by a new one of the same current rating. Again, if the new fuse blows immediately, suspect a circuit fault. If you have miniature circuit breakers (MCBs) you will not be able to switch the MCB on again if the fault that tripped it off is still present. Otherwise, simply reset it by switching it to ON or pressing in the centre button.
Earth leakage circuit breakers (ELCBs)
If your installation has an ELCB, it will trip off if an earthing fault occurs – for example, if a live wire or connection comes into contact with earthed metal. Like an MCB, it cannot be switched on again until the fault is rectified – a useful safety point. However, it will not trip off in the event of a short circuit between live and neutral, or when overloading occurs. The high-sensitivity current-operated ELCB, in addition to detecting earth faults, also protects against the danger of electric shocks by tripping off if it detects current flowing to earth through the human body. It can do this quickly enough to prevent the shock from causing death.
Tracing circuit faults
If you have checked appliances, flexes, plug connections and pendant lights, and a fault is still present, it is likely to be in the fixed wiring. Here, it is possible to track down one or two faults, but you may in the end have to call in a professional electrician.
The likeliest causes of circuit faults are damage to cables (perhaps caused by drilling holes in walls or by nailing down floorboards where cables run), ageing of cables (leading to insulation breakdown, and overheating) and faults at wiring accessories (light switches, socket outlets and so on). Let’s look at the last one first, simply because such items are at least easily accessible.
If the cable cores are not properly stripped and connected within the accessory, short circuits or earth faults can develop. To check a suspect accessory such as a socket outlet, isolate the circuit, unscrew the faceplate and examine the terminal connections and the insulation. Ensure that each core is firmly held in its correct terminal, and that each core has insulation right up to the terminal, so that it cannot touch another core or any bare metal. There is usually enough slack on the mains cable to allow you to trim over-long cores back slightly.
Check that the earth core is sleeved in green/yellow PVC, and try not to double over the cable as you ease the faceplate back into position; over-full boxes can lead to short circuits and damage to cable and core insulation and more trouble. You can carry out similar checks at light switches and ceiling roses. Any damaged accessories you find should be replaced immediately with new ones.
Damage to cables is relatively easy to cure provided that you can find where the damage is. If you drilled or nailed through a cable, you will of course be able to pin-point it immediately. Cable beneath floorboards can be repaired simply by isolating the circuit, cutting the cable completely at the point of damage and using a three-terminal junction box to link the cut ends.
Cable buried in plaster must be cut out and a new length of cable inserted between adjacent accessories to replace the damaged length. Where this would involve a long length of cable (on a run to a remote socket, for example) it is acceptable to use junction boxes in nearby floor or ceiling voids to connect in the new length of cable. You will then have to make good the cutting-out.
Tracking down a break in the cable elsewhere in the installation is a difficult job best left to a qualified electrician. If, however, you find that your house is wired in rubbersheathed cable and faults are beginning to occur, don’t waste time and effort trying to track them down; you need a rewire. Unless you know what you are doing, this is certainly a job for the electrician. If you are unable to trace an electrical fault after checking all the points already described, call in a professional electrician who will be able to use specialist test equipment to locate the fault. Do not attempt to bypass a fault with a makeshift wiring arrangement, and NEVER use any conducting foreign body such as a nail to restore power to a circuit whose fuse keeps blowing. Such tricks can kill.
You will find that a little common-sense maintenance work will help to prevent a lot of minor electrical faults from occurring at all. For example, it’s well worth spending a couple of hours every so often checking the condition of the flex on portable appliances (especially those heavily used, such as kettles, irons, hair driers and the like) and the connections within plugs. Also, make a point of replacing immediately any electrical accessory that is in any way damaged.