An IR tester, also known as a Megger insulation resistance tester, can be particularly useful when carrying out electrical work. It is important to ensure that you have not made any wiring mistakes or caused any damage to the insulation.
The first step
The first step is to turn off the power to the circuits you intend to test. Suppose there is any uncertainty as to which breakers or fuses are responsible for controlling the circuits. In that case, the main breaker should be switched off, and a note placed on the breaker panel to advise others not to switch the power back on while you are working on the circuits. If it is at all possible, it would be a good idea for you to lock the switch closed.
The second step
The next step is to prepare a table in which the insulation values from your tests can be recorded. When dealing with a 110 volt circuit, spaces should be left for the insulation test results between the white wire and the black wire and the insulation between the ground and each wire.
When dealing with a 220 volt circuit spaces should be left for the results of the insulation tests between all of the three wires in addition to the other two and also between all of the three wires and the ground. For equipment like an appliance or circuit breaker space should be left for insulation values between all the terminals as well as every terminal and ground.
The third step
The third step is to choose 500 or 1000 volts DC as the test voltage setting on your IR tester, depending on the particular model you intend to use. It is important to check if the model being used comes with an integrated voltage tester for use with live circuits. If this is not the case, the tested circuits should be checked with a voltage tester to ensure they are not live.
The positive and negative probes of IR testers should be placed between the two terminals or conductors the insulation resistance of are being tested. When testing insulation resistance to ground, the positive probe should be placed on the grounded metal junction box or the ground wire, with the negative probe placed on the terminal or conductor. The IR tester should be energised for sixty seconds and at the end of the minute test the value of the resistance read and noted in your table. This testing procedure should be continued until values have been placed in all your table’s spaces.
The final step
The final step is to examine the resistance values in your table, all of which should be over 25 megohm. If one value is substantially different from others check connections and do the test again. If a value is less than 25 megohms, check the circuit.
A wide variety of IR testers are available and using them to test insulation resistance can help to reduce dangers caused by failed or damaged insulation, such as tripping circuit breakers, blowing fuses, and even electric shocks to people who come into contact with wire that is poorly insulated or the metal surrounding it.