How an Insulation Test Works

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When repairing, replacing, or working around electrical systems it’s of the utmost importance that you test the insulation within the wires and cables that you’re working with. A testing device such as a Megger meter can perform an insulation test for you and ensure that the wires and safe and do not need to be replaced. But, just how do they work?


Once the tester is connected to the wire it will apply direct current (DC) voltage directly on the wire or cable. This DC voltage will interact with the wire to produce a current, and the tester will then measure that current. If the current is contained within the wire, the tester will show that the insulation is in proper working condition and that no repair is needed. However, the tester will also indicate whether or not there is any current leaking from the wire. If so, that wire will typically need to be replaced.

Because testers use DC voltage to perform their tests, it’s extremely important that you choose a model compatible with the voltage within the current electrical system. A low-voltage system, such as those found in homes, will only require a small, compact low-voltage tester of maybe 100 or 250 volts. A high-voltage system on the other hand, such as commercial systems, motors, and transformers, will need a high-voltage tester with 500 or 1000 volts. Using the improper voltage within the tester can either render the test ineffective, or it could even do damage to the wires.

When it’s time to test the insulation in your electrical system, contact us at Protec Equipment. We have the best names such as the Megger Insulation Test, and we’ll explain how to use them too, if you’re new to these kits.