Home Electrical circuit testing

Throughout this post, references are made to meters and their use in continuity testing of individual parts of the appliances and their connecting wires. All testing and checking for ‘open’ (not allowing for current flow) or `closed’ circuit (allowing current to flow) must be carried out using a battery-powered multimeter or test meter. Testing should never be carried out on live items under any circumstances. Appliances must be disconnected from the mains supply.

Although some meters or testers have the facility to check mains voltages, these are not recommended for use in repairs to domestic appliances. Faults can be easily traced by simple low-voltage (battery power) continuity testing, proving that the simplest of meters or even a home-made one like that described below are perfectly adequate. Remember that safety is paramount and in no circumstances should it be compromised. Always double- check that the appliance is unplugged — a good tip is to keep the plug in view so that no-one else can plug it in unbeknown to you.

Choosing a meter

If you decide to buy a test meter, do not be tempted by an over complicated one as it could end up confusing and misleading you. Read the manufacturer’s instructions thoroughly and make sure that you fully understand them. The meter shown here is simple to use when continuity testing and has a scale that reads ‘open’ circuit or ‘closed’ circuit. It was purchased at a reasonable price from a local D-I-Y shop. The meter will also help locate faults with car electrics, but it should never be used on live mains circuits.

Some multimeters show the resistance value of the item being tested as well as indicating continuity. This can be extremely useful if the correct value of the item being tested is known, although this is by no means essential. Details of how to use the multimeter for this function will be found in the manufacturer’s accompanying instruction leaflet. Meters are also available with buzzers or lights which make testing in dark corners easier.

A simple continuity tester

This simple device can be used to trace faults in most appliances and is very easy to make. It uses the lack of continuity to its full advantage. You will need a dry torch battery, a bulb of the same voltage and three wires (1 x 5 inch and 2 x 10 inch). Connect the short wire to the positive terminal of the battery and the other end of that wire to the centre terminal of the torch bulb. Attach one of the longer wires to the negative terminal of the battery and leave the other end free. Attach the third wire to the body of the bulb and leave the end free.

The two loose ends now act as the test wires on the tester. Press the two ends of the wire together and the bulb will light. When testing an open circuit the light will stay off, and when testing a closed circuit the light will be on.

Ensure that the appliance is isolated from the mains supply before attempting to use a meter. Low voltage bulb type testers of 112 volts or 3 volts are unable to test the continuity of many components and should be used mainly for wiring fault finding. A test meter like the one shown is needed to test components, such as motors and heaters.

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