Made 2 Measure: Safe isolation

Made 2 Measure: Safe isolation

The Megger team answer your questions about safe isolation.


I’ve had one or two nasty “belts” over the years, when I thought a circuit was dead and it wasn’t.

What do I need to do to make sure that circuits are properly isolated so that this never happens again?


You need to use the right equipment and the correct procedure for proving that the circuit is dead.

The equipment you need is a two-pole tester, such as the Megger TPT320, and a proving unit like the Megger MPU690.

Don’t be tempted to use a voltfinder – they’re handy little tools, but they’re not suitable for proving circuits are dead. With the two-pole tester and proving unit, the procedure is simple.

First, check the output of the proving unit with the two-pole tester, which must verify that the output voltage is present.

Then, use the two-pole tester to check the circuit that you want to prove is dead. The tester must show that there’s no voltage present.

Finally, you need to check that the tester hasn’t failed during the test, which you do by simply reconnecting it to the proving unit when, once again, it must show voltage present.

Carry out these three steps carefully and conscientiously, and you can be sure those unpleasant – and potentially dangerous – “belts” will be a thing of the past.

For more Made 2 Measure articles from Megger, click here.

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