How to Calculate Insulation Resistance

Updated July 20, 2017

Insulation resistance is an important characteristic to test for in electronics. If the item you are testing has a low insulation resistance, the result could be a drop in power reliability or, worse, a safety risk to personnel around the item. As the insulation resistance of any material deteriorates over time and because of harsh weather conditions, regular testing is of great importance.

Plug the crocodile clips into the megohmmeter (an instrument that measures very high electric resistance --- above 10s ohms --- particularly that of insulation on wires, cables, connectors, transformers and windings of electric motors).

Turn on the megohmmeter. Make sure the device is set to "Insulation Resistance."

Change the test voltage to an appropriate setting for the electronic device. If unsure of what test voltage to use, start with the lowest setting and adjust as necessary. It is best to start with a lower voltage as high voltages can damage certain equipment.

Turn the megohmmeter off. Connect the other ends of the crocodile clips to the positive and negative leads on the electronic device you are testing.

Turn the megohmmeter on and press the "Test" button. If there is little to no change from the test voltage, the device is in good condition. If the change is drastic, the device may have a low insulation resistance.


Check that the megohmmeter is in working condition before you use it.


Be careful when working with electronics, as there is always the possibility you may shock yourself.

Things You'll Need

  • Crocodile clips
  • Megohmmeter
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About the Author

Daniel Valladares began his career as a medical writer in 2008. He has written patient education brochures for several pharmaceutical companies and has worked as an auto mechanic at Kim's Speedy Auto Service since 2007. Valladares holds a Bachelor of Arts in English from Rice University and is currently studying to become a personal trainer.