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Visual Inspections

Many problems are obvious to the trained eye. Look at all the leads to appliances. These should only have the outer insulation showing. If this is damaged, the lead should either be shortened, cutting out the damaged piece, or replaced altogether Wire Crimp Pull Tester. Damage usually occurs at either end of the lead. If the lead does not go into the plug properly, the plug should be rewired (see plugs); similarly at the other end. If the lead has been damaged in the middle (a common occurrence with vacuum cleaners, hedge trimmers, lawn mowers, etc.), the lead should either be replaced or reconnected with a proper lead connector (2 or 3 core depending on whether the lead is earthed or not), which has proper cable grips for the lead going in and out. Using ‘choc. blocks’ and/or insulation tape for reconnecting leads is not advised.

Wire Pull Tester - WT3-201 Measure Wire Crimp Strength, alternative to  Daniels PT-150H

Any damage to the casing of appliances should be repaired. Live parts should be well protected from the outside casing, and if this contains any metal, in most cases the appliance should be earthed. (Many old table and floor lamps, particularly home made ones, are not earthed even when they have metal parts. These should be re-wired with 3 core cable.) It is permitted for ‘double insulated’ products not to have an earth (even some with metal outside parts). In this case there must be at least two layers of insulation between live parts and the outside. If the product has been bought from a reputable dealer in the last few years, and is not earthed, it is probably OK.

Any signs of overheating (black or burning marks etc.) indicate a problem (see later).

Many people think seeing sparks at switches (more commonly in the dark) indicates a problem, but this is normal in most cases. Special switches are available which do not spark, but these are expensive and only necessary in environments where there are inflammable materials around.

Feeling and Listening

Anything that feels hot to the touch (often accompanied by signs of burning) indicates a bad connection, except of course in heaters themselves. So does a crackling sound. This often occurs between plug and socket and could indicate a bad contact between these two. In this case one or the other, or often both, should be replaced. If say a plug has become worn, continued use of it will often cause the socket it is plugged into, to become worn as well, and in this case both should be replaced. A simple way to tell if the socket is worn, is to plug something else into it with a good looking plug, and see if it overheats with this.

Bad contacts can occur at other places too. They can often be cured by rewiring so that all connections are tight and well insulated.

If an otherwise seemingly good lead seems to be getting hot, it usually indicates it is not up to the job, and needs to be replaced by a thicker one. This is particularly true of extension leads (see later).

If a ‘tingle’ is felt when touching an appliance, it indicates a serious fault, and the appliance should not be used until this has been rectified.


All sockets can be tested with a relatively cheap (around £5) socket tester. For a UK version, see the link below, but these are also available in other countries for their particular type of socket. They usually have three lights and when plugged into a socket, if all three lights come on, the socket is wired correctly. If only two, one or no lights come on, there is a fault and the combination of lights tells you what that fault is. Sockets should preferably be switched so that the supply to any appliance can be turned off in an emergency.


This applies to UK square 3 pin plugs, but the same principles apply to other types.
If the plug is not of the moulded type (these cannot be repaired – they must be cut off, discarded and replaced if faulty) unscrew the cover and inspect the plug. The cable grip must grip the outer insulation of the lead. The international colour code is: brown to live terminal (the one with the fuse connected to it), blue to neutral (opposite to the live) and green or green/yellow to the top earth terminal. Each contact should be secure, with little or no uninsulated wire showing outside the terminal. There should be little slack on the live and neutral; the earth lead can be left slacker, so that if the lead is pulled out, the earth is the last one to come out. The correct fuse for the appliance should be fitted in the plug. The most common values are 3A, 5A and 13A. Use 3A for appliances up to 700 watts (e.g. lamps, much electronic equipment, etc.), 5A up to 1200 watts (some drills, hair dryers, etc) and 13A up to 3000 watts (most heaters, kettles, washing machines, tumble driers etc.). A rating plate somewhere on the appliance should tell you the wattage. If it gives the current (in amps.) instead, this can be easily converted to watts by multiplying be the mains voltage (e.g. a 2A appliance running off a 240V mains would have a wattage of 480).

The old plugs with uninsulated live and neutral pins should be replaced, so that a plug half pulled out of a socket is safe, even if someone pokes a metal object between plug and socket.
Pins on plugs should be shiny brass (brass is used because it contains copper, a good conductor, but is stronger than copper). If they are dull or dirty, they should be cleaned with emery cloth or replaced.

Increasing the no. of sockets

In these days of a profligacy of computer and other electronic equipment, there are often not enough sockets available and there are various ways of increasing these. The best way is to use a suitable extension lead, which can have 2, 4, 6, 8 or 10 separate sockets and each socket can be switched individually or not. Alternatively, socket converters can be used. These plug into a socket and 4 or 3 switched new sockets are then available. There is no lead associated with these. Mains adaptors (certainly unswitched and unfused ones) should be avoided.

Extension leads have a plug on them, fused at the maximum current the lead will take, usually governed by the thickness and length of cable used on the lead. It is probably better to use a 13A lead in all cases (this is the maximum that should be drawn from a single socket). If the total power plugged into the lead exceeds what it is fused at, the fuse will blow. Very long leads should have a thicker cable, and those on a reel should be unwound fully to aid heat dissipation, if a current approaching their maximum is being used. If the lead gets warm (see earlier) it is a sign that it is reaching its maximum capacity.

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