TYPES OF TEST

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.

In recent years it has become common for PAT Testers to be small and sometimes a lot lighter as they have less inside! Many PAT Testers nowadays do not have the ability to test an Earth by applying 10 Amps or 25 Amps through the protective earth conductor – it is our belief that this is a step backwards as far at PAT Testers, and safety, are concerned.

Size and price versus functionality is what the compromise has become.

There are still many (usually, but not always) more expensive PAT Tester that are able to do the 10/25 Amp Earth Bond Test – these we would define as electrical safety testers compared to electrical compliance testers. Both can meet the requirements of AS/NZS3760, but one goes a step further and is more likely to fail appliances with faulty earths.

Doing safety testing 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 ie the operator becomes the means by which the active 230 Volts 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 ie an earth bond test shows whether the earth conductor is in a satisfactory condition; whereas an Earth Continuity Test (100 milliamps or less) using Multimeters and the like will possibly only show the earth is connected, not its’ condition.

Insulation Resistance Tests must not be carried out using Ohmmeters or Multimeters because these meters only produce a small battery voltage in the region of 1.5 to 9 volts. This small voltage is insufficient to pressure test the insulation to expose any weakness in it and therefore is totally inappropriate for Insulation Resistance Tests.

Insulation Resistance Testers and PAT Testers on the other hand are specifically designed to produce 500 Volts (or even greater voltage values for some applications) which places the insulation under stress. This test will indicate any weakness that may break down under normal use on the 230 Volt supply. Itis a requirement that the resistance measured by the Insulation Tester in this way should be not less than 1 Megohm (1,000,000 ohms) for an electrical appliance to pass this test.

A practical example showing how a Multimeter or Ohmmeter is inappropriate to test the insulation resistance of an electrical appliance is detailed by the following example:

A 230 Volt floor polisher has a partial insulation breakdown between the motor windings and the earthed metal case. The polisher when in use and at its normal operating temperature, causes the sub-circuit protective fuse to blow as a result of the insulation breaking down to the earthed metal frame.

The polisher, when tested with an Ohmmeter or Multimeter, does not indicate the presence of a fault, as the meter voltages are so low that they do not stress the insulation and therefore do not reproduce the breakdown that occurs when the appliance is in use.

However, testing the same polisher with an Insulation Resistance Tester producing an output of 500 Volts causes the insulation to break down under test, thereby indicating a low insulation resistance value and the presence of a fault path.

NOTE:The importance of a sound low resistance earth continuity conductor is paramount to the safety of any electrical appliance that requires an earth. A test as described above would not achieve anything if the integrity of the earth were not first proven to be in good condition. Should the appliance have an open circuit earth continuity conductor, it would produce a high resistance test result, but in fact when the appliance was plugged in it would enliven the case and expose a potential shock hazard.

This test was first introduced in the 2003 version of the Standard and it can be used to replace the 500 Volt Insulation Test.

The advantage a Leakage Test has over and above the 500 Volt Insulation Test is that the Leakage Test when carried out on an appliance at operating voltage ensures the whole of the appliances’ circuitry is fully tested. The old 500 Volt Insulation Test would not fully test many appliances ie those with internal switching that required operating voltage to activate switches. Hence an appliancemay test safe and not be, when tested with a 500 Volt Insulation Test.

Some fatalities could have been prevented if a Leakage Test had been done instead of the 500 Volt Insulation Test.

NOTE:A 500 Volt insulation test is an adequate test providing all of the appliances’ circuitry can be tested using thismethod.

Unfortunately we can all be careless around electricity -RCDs can give limited protection against a fatal shock

An RCD is specifically designed to minimise the risk of a fatal electric shock when working with electricity. It is an electronicsensing device which constantly monitors the balance of the current flow in the live and neutral conductors to ensure thatshould even a minor leakage occur the RCD will switch off the power within 300 milliseconds (for personal protection RCDs)iein less than the time of a single heartbeat -which could mean the difference between life and death.

You need to remember the following:

1. When properly connected an electric current flows through the live wire on its way to the appliance and returns to ground via a neutral wire
2. If for some reason the current ‘leaks’ (through dampness, frayed wiring, faulty connections etc) the current will take the most direct path to earth – often through a persons’ body. In this situation if the power is not disconnected instantly then there is a strong possibility thatthe person will die.
3. The path taken by the current also contributes to the severity of the electric shock. An electric shock which flows from the hand through the arms and to the chest will affect the breathing and heartbeat.
4. The greatest contributing factor to the severity of an electric shock is the exposure time to the current. An RCD cuts off the power in less than the time of a single heartbeat