Frequently asked questions
Insulation resistance testing

Insulation resistance testing

  • How do I null my leads?

    Short the 2 test leads together and push the test button.

  • Why do I read a continuity value of 0.00 Ohms or a negative value?
    The test leads may have been nulled incorrectly. Try and null them again. If this continues to occur, replace your test leads.
  • Why I am reading > 199 MOhms?
    Some insulation testers have a maximum reading of 99, 199 or 299 MOhms for different test voltages so good insulation may be shown as greater than (>) the maximum reading.
  • What is PI?
    Polarisation Index is the ratio of insulation resistance at 1 minute to 10 minutes. It shows how the insulation is charging up and can identify if insulation is clean and dry.
  • Why does the battery symbol show on the continuity range?
    The continuity range uses most battery power so may cause the battery symbol to show before other ranges.
  • What test voltage do I use?
    This would depend on the application. Usually 500 V is used on standard electrical installations. Lower voltages are used for control circuits and for quick checks that nothing is left in circuit.
  • Why does the accuracy decrease at high levels of insulation resistance?
    As the insulation value increases, the test current decreases and becomes harder to measure with the same level of accuracy.
  • What difference does the continuity test current have?
    Certification usually requires a test current of 200 mA. Changing to a lower test current, such as 20 mA, when not certifying will give a better battery life.
  • Why does my insulation tester just show a voltage reading?

    Most insulation testers will not operate if they detect a voltage on the circuit under test and will display the voltage that has been identified.

  • Why does a fuse symbol appear at the top of the display?
    This symbol indicates that the instrument has experienced an overcurrent causing the fuse to blow. The fuse is located in the battery compartment and can be replaced with the spare fuse.