< Earth Testing

Legally it is a requirement – but is it really necessary?

Potentially the most dangerous appliances are Class I appliances (earthed appliances) eg floor polishers and the like, but also in this category are extension leads.

Class I appliances are designed to have an earth – this means that in the example of the floor polisher the body of the polisher is connected to earth - literally to the ground via an earth conductor which goes right back to the building switchboard and then into the ground the building is sitting on.

If this conductor is damaged anywhere then the consequences can be fatal – I will explain this point in greater detail shortly. It is obvious therefore that the conductor needs to be tested.
                 How can this be done properly?
Unfortunately, most people believe they are carrying out the testing properly if they are using a Multimeter or an Insulation Tester, but these types of instruments will not usually pick up an earth fault unless there is a complete break in the conductor.

There is another type of tester available which is relatively new on the market that people, including many electricians, are not aware of – it is called a Portable Appliance Tester or “PAT” for short. The PAT is specifically designed to test electrical safety and does all the different tests necessary to ensure the electrical safety of the appliance and makes testing easy.

The difference between using a Multimeter and a PAT is that a Multimeter does a Continuity Test where as a PAT does an Earth Bond or Earth Integrity Test.

There is a VERY BIG DIFFERENCE between the two tests.

To see the difference between testing with a Multimeter or an Insulation Tester compared with a Portable Appliance Tester (PAT), try doing this simple test:

In these two diagrams the battery charger represents a PAT Tester, something that produces a low voltage high current electrical supply. The 10 amp fuse in both cases represents the last remaining strand of a multi-core earth wire.

If you test with a Multimeter or any type of Continuity Meter/buzzer or Insulation Tester you will see that the meter indicates that the earth conductor is OK and therefore the earth conductor is presumed to be safe – however sadly this is not the case. Now try the same test with a battery charger – the fuse will blow. Now you know that your earth is faulty and you can fix it.

Doing safety tests with just a Multimeter or similar type of instrument is like carrying an umbrella around in case it rains; only to find when it does rain that the umbrella leaks!! An earth conductor substantially damaged or not there means that in a situation where a fault occurs the operator becomes the earth i.e. the operator becomes the means by which the active 230Volts supply returns to earth – likely killing the person in the process!! It is essential that when an earth conductor is needed that it is able to pass the earth current required otherwise you or someone else will become the earth.

You should by now be able to see the difference between an Earth Bond and Earth Continuity Test i.e. an earth bond test shows whether the earth conductor is in a satisfactory condition; whereas an Earth Continuity Test using multimeters and the like will possibly only show the earth is connected, not its condition.