Although most IR testers have a variable output voltage, the hipot tester is usually specified at 500 or 1000 volts. The IR test is sometimes required by safety agencies to be performed subsequent to the hipot tester in order to make sure that the DUT’s insulation was not damaged as a result of the high voltage applied to it.
Insulation resistance test considerations
There are a few things to keep in mind when running an IR test:
Since most products are capacitive in nature, it is important to allow the hipot tester to run for an adequate period of time before recording any measurements. Test times can vary, but a 1-10 min test should supply a stable reading.
It is always a good idea to ramp up the voltage over a period of time. This ensures the DUT is not subjected to a voltage surge that could damage it. This will also help avoid false failures due to inrush current (as with the DC hipot tester).
The most important parameter for the IR test is the resistance low limit. If the resistance is too low, more current will flow and the test will fail. Remember, the higher the resistance, the better the insulation. If no IR value is specified by and agency specification, the insulation resistance for an IR test at 1000 V or less should be at least 1 MΩ.