What is a megger test?

Answer 1

• If you are referring to a megohm meter, it is a test of the insulation properties of such things as electric wiring, motor windings and high power antenna mounts.

  We use a "megger" or "meg out" electrical wiring and equipment to see if it is shorted to ground in any way.

  The megger uses much higher voltages to check resistance than a normal Volt-ohm meter.

  Ideally, you want infinity resistance but I've installed 460 volt motors with 750 meg ohms resistance to ground and had no problem.

• On the whole megger testing is non destructive. What happens is a DC voltage is applied to the device or winding under test. It is an insulation test to see is the insulation has been injured in any way to cause a short circuit when normal power is applied to it.

  On my megger there are 3 ranges 300V, 750V, and 1000 volts. Applying the proper voltage is essential to not damaging the device you are testing.

  Working voltages up to 240 volts should use the 300 range.

  Working voltages up to 600 volts use the 750 volt range and working voltages above 600 use the 1000 volt range.

  As you can see if you used the 1000 volt range on a device that had a working voltage of say 24 volts you could damage the insulation just by testing it. So meggering a device is non destructive if you use the tester as its instructions tell you to.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.