Can you Megger with a GFCI on the line you want to test?

[iMuse97]

Here's the situation: The client wants all installed wiring insulation integrity tested and recorded.

We Meggered all the feeders, Xfrmrs, etc., and then found that they wanted all branch circuit wiring tested as well. (When they said all, they meant ALL! no surprise really.)

Anyway, the foreman decides to disconnect the subpanels, and megger each phase. Problem: each branch circuit is on a GFCI breaker. Didn't work.

Do we have to lift each branch circuit conductor? It seems the only way at this point.

Another question: Did he destroy the QO120 GFCI breakers with the momentary test? The guys realized right away they shouldn't be doing this.

 

[nakulak]

what setting did they test with ? what piece of test equipment was used ?

 

[iMuse97]

tested @ 500V with an AVO Biddle MJ15 (battery powered).

 

[Pierre C Belarge]

You will need to remove the conductors from the GFCI circuit breakers to test the branch circuits.

 

[Pierre C Belarge]

Here's the situation: The client wants all installed wiring insulation integrity tested and recorded.

We Meggered all the feeders, Xfrmrs, etc., and then found that they wanted all branch circuit wiring tested as well. (When they said all, they meant ALL! no surprise really.)

Anyway, the foreman decides to disconnect the subpanels, and megger each phase. Problem: each branch circuit is on a GFCI breaker. Didn't work.

Do we have to lift each branch circuit conductor? It seems the only way at this point.

Another question: Did he destroy the QO120 GFCI breakers with the momentary test? The guys realized right away they shouldn't be doing this.

The electronics of the circuit breaker are not designed to be tested with a megger, the voltage most likely destroyed the circuitry.

 

[iMuse97]

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The electronics of the circuit breaker are not designed to be tested with a megger, the voltage most likely destroyed the circuitry.

That's what I have supposed. Fortunately only six of the breakers were treated to this test.

 

[iMuse97]

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The electronics of the circuit breaker are not designed to be tested with a megger, the voltage most likely destroyed the circuitry.

Thanks for the answers. Just wanting to confirm my suspicions.

 

[Pierre C Belarge]

The best way to check the GFCI breaker to see if it okay, is to take a 3 pound hammer and smash the breaker so you can see the inside of it.

You know what I mean.

 

[SG-1]

The best way to check the GFCI breaker to see if it okay, is to take a 3 pound hammer and smash the breaker so you can see the inside of it.

You know what I mean.

I'am a little guy so I use a 6lb. hammer for this test.

 

[winnie]

If you are lucky, the electronics of the GFCI placed enough load on the circuit that the voltage could never rise to the test voltage.

The 500V setting means 'try to put 500V onto the circuit and measure the current that you get'. If the resistance is too low then the meter will put out its maximum current and the voltage across the test resistance (the electronics) will be much less than 500V.

-Jon

 

[ELA]

GFCIs have MOVs inside that would clamp at approximately 150V.
Depending upon the maximum output current of the megger vs. the joule rating of the MOV you might estimate the likelyhood of failures.

 

[augie47]

For informational sake, let us know what the survival rate was on the GFCIs that were tested

 

[qcroanoke]

For informational sake, let us know what the survival rate was on the GFCIs that were tested

Augie and others,
Knowing that the GFIC's were subjected to that voltage would you feel safe leaving them in service if they appeared to be ok?

 

[augie47]

As for me, I tend to agree with Winnie in post #10.
If they still passsed the internal test, i would be satisfied.

 

[winnie]

I'd want to see the specs of the megohmmeter used, but a quick search suggests that many such meters limit their output to 2mA or less. This is less than is consumed by a GFCI in normal operation, so I would expect that the GFCI never saw more than normal supply voltage.

-Jon

 

[iMuse97]

Thanks for the info.
We will be powered up today or Monday, so I'll let you know
the failure rate of GFCI breakers under momentary Megger testing.

 

[iMuse97]

No, I did NOT forget--the power-up has finally been approved and is connected.

And though I will not recommend it to Forum members, the GFCI breakers
can sustain a momentary meggering without problems.

Of course the test readings are not accurate--there is some continuity
through the electronics of the GFCI. So there is no reason to do it, unless
you want to worry the middle management for two weeks while they are
waiting for power to see if anything was damaged.

 

[augie47]

Thanks for the feedback.

 

[glene77is]

I'am a little guy so I use a 6lb. hammer for this test.

SG,

I drill out the rivets,
then use a screw-driver to pry the shell apart.
I've done this on bunches of old OCPD
to see why they failed.
That would make another thread, but interesting.

I think this is called a "destructive test",
of course,
you could say it was already "destructed"
and this is an "educational test/activity".