< Insulation Resistance  & Leakage Testing

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 PATs 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.

It is 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:

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.

Alternative Leakage Test as required by DRAFT AS/NZS3760:2003

< Leakage Test

This is a new addition to the latest draft Standard.  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 appliance's circuitry is fully tested.

The old 500volt-insulation test would not fully test many appliances i.e. those with internal switching that required operating voltage to activate switches. Hence an appliance may test safe and not be when tested with a 500-volt insulation test.

There have been fatalities that could have been prevented had a leakage test been done rather than the 500-volt insulation test.

PLEASE NOTE A 500-volt insulation test in an adequate test providing all of the appliance's circuitry can be tested using this method