Insulation resistance testing on a new installation
(i.e. during initial verification)
The object of this test is to verify that the quality of the insulation surrounding the conductors is satisfactory and has not deteriorated or been damaged causing short-circuits and earth faults. It is done at the consumer unit with all the installation switches closed ‘on’. Any neon lamps, capacitors or any electronic components should be disconnected as they are likely to be damaged or create a false reading during the test.
Also, all sockets and switches etc must be screwed onto their back boxes before this test can proceed as in most cases this is when the insulation is damaged and short circuits and earth faults can occur.
There are two tests to be carried out using an insulation resistance tester which must have a test voltage of 500 V d.c. for 230 V and 400 V installations. These are line and neutral conductors to earth and between line conductors (line to neutral).
To complete a line and neutral conductor to earth insulation resistance test…
To test each circuit individually open each circuit breaker switch and test separately between the line conductor and earth and between the neutral bar and earth and record the results on the schedule of test results for each circuit.
To test all of circuits at the same time close all the circuit breaker switches and test between any line conductor and earth and between the neutral bar and earth and record the results on the schedule of test results for each circuit.
Note: Testing all the circuits at the same time will result in a lower insulation resistance value (see multiple resistances in parallel)
To complete a line to neutral insulation resistance test…
To test each circuit individually open each circuit breaker switch and test separately between the each line conductor and the neutral bar and record the results on the schedule of test results for each circuit.
To test all of circuits at the same time close all the circuit breaker switches and test between any line conductor and the neutral bar and record the results on the schedule of test results for each circuit.
Note: Testing all the circuits at the same time will result in a lower insulation resistance value (see multiple resistances in parallel)