Understanding your insulation tester: Safety standards and testing alerts

18 July 2018

Your insulation tester beeps and flashes while trying to perform a test.

What’s wrong?


This is a redundant safety feature, to get the operator’s attention, because working on “auto pilot” is not recommended when dealing with electrical circuitry. Insulation testers, when set to 1 kV, typically will alert the operator.

Complying with standards

While redundancy is generally thought of negatively, in the case of safety features, redundancy can mean saving a piece of equipment or even a life. In this situation, know that everything is operating according to the latest safety standards and just keep testing!

After alerting the operator that 1,000 volts are being applied, the test will proceed, just at lower voltages. Although Megger insulation testers are NOT inherently dangerous, safety officers and safety S.O.P.s often call for added diligence above 500 V.

Time is important

Time is an important test variable in insulation testing, much more so than in many familiar electrical tests. And so, in this case, the operator depresses and holds the TEST button, the tester flashes and sounds its alert, and then proceeds into the test.

This provides the double safety of alerting the operator that the highest test voltage is being applied, while also adding protection against inadvertent application of voltage, such as if connected test leads were lying loose on a bench or test item and the TEST button were accidentally bumped as the instrument was being brought into play. Accidental situations like that can cause serious damage and injury that can be avoided with safety alerts such as these.

This brief delay can be important. As already stated, the testers themselves are NOT inherently dangerous, despite having up to a thousand volts (and a lot more in medium voltage models) output. This is because, while they can deliver a lot of voltage, they are extremely limited in power.

Power is the product of voltage and current

Insulation testers are limited to no more than a few milli-Amps of test current. If insulation were to pass any more than that, it could no longer be considered insulation. Remember, 5 milli-Amps will shock you, and 50 milli-Amps can kill you.

So the next time you’re taking a quality control measurement with your insulation tester and it begins to beep, know that it is simply a safety feature and the tester is alerting you that the voltage being applied is up to 1,000 volts.

IEEE is continually updating testing standards and since at least March 2000 has emphasized the value of higher voltage testing that reveals otherwise hidden flaws. Read more about diagnostic insulation testing above 1 kV to stay ahead of the latest technology and standards, like 10 kV and 15 kV testers.