ECN Forum Forums General Topics of the Trade General Discussion Area Megger

There are many cases in residential, and commercial wiring where a megger should be used but is not.
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"110.7 Insulation Integrity

Completed wiring installations shall be free from short circuits and from grounds other than as required or permitted in Article 250."
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There is a difference between an installer, and a craftsman, the installers today, seem to have a just get it done additude, where the crafstman, will take the time to test the installation, As i see it, their has been a continous dumbing down of the trade, since the mid 60's, It's up to everyone in the trade, to raise the bar.

[This message has been edited by LK (edited 08-26-2005).]

I do not see that 110.7 requires the use of a Megameter.

I see that it requires that circuits are free from short circuits and from grounds.

That can easily be determined without a mega.

Maybe this is just a local thing for Pete and I but I have been doing this a while in many different types of electrical construction and very few electricians or ECs own a Mega.

The company I work for now has quite a few, some that interface with a lap top to give very detailed reports.

This is used when the job specifications require it, or if we have to verify damaged wiring.

LK, I can figure out if I have a short or a ground fault with a continuity tester. Why do I need a Megger to comply with that code section?

Furthermore, let's say I skin some insulation off a wire as it's pulled into PVC. Is a Megger going to be able to tell me that I compromised the insulation? My guess is no.

Peter

Peter,

What if it is RMC? not PVC, the megger will find faults, where an ohmmeter will not, it's breakdown your looking for not continuity when testing for insulation.

One handy piece of equipment to have, is a megger, with AFCI's and GFCI.s in branch circuits, the megger sure helps find circuit problems that cause these devices to trip.



[This message has been edited by LK (edited 08-26-2005).]

Fair enough. But even RMC or EMT is not a guarantee that it will work. If the nick is on the inside of a bundle or wires, and there's no wire lube to "short" the nick to the pipe, I can't see how it would work either.

All I'm saying is that a Megger has limitations, and very few electricians used them in my area.

Yes you are right, not all insulation failures will show, but use of a megger will avoid serious faults, from becomming a hazzard.

I feel, that using a good insulation breakdown tester, can prevent serious injury and property damage, we tend to speed jobs up, and loose site of some of the basic things that should be done.

Peter,
I would disagree with that.
A Megger test shows you the Resistance of the Insulation between conductors and between conductors and ground.
The use of a higher voltage is to adequately stress the insulation.
Now, usually there is a capacitive effect between wires either in a cable or in a conduit to some degree anyway, causing (albeit small) leakage currents and that is with all of the insulation intact in it's original state.
If however, you skin one of the wires, the capacitive effect is going to be a lot higher (ie: less insulation, more current flow) in that particular spot.
A megohm meter would pick that up regardless of the type of conduit.

Mike,

That is the reason we use a megger, not an ohm meter, we are looking for potential insulation failures.
We found a wire fault, in underground pool feed circuit, that was in PVC, the megger indicated leakage, sure eniough, when we pulled out the old wires one was nicked.

OK, I'm listening and learning. Keep it coming. Maybe one day I'll use one these things.

Peter

Peter,

I was going to send you some more megger information. but then i thought, you might be out shopping for one tonight.