Megger and GFCI

[gar]

110521-0949 EDT

Bill:

Using the Leviton as a reference the input L-G and N-G meggered values will be full scale of the megger. But, L-N will be some low value.

If one is going to megger the circuit on the input side of a GFCI, then do this L-G and N-G with the GFCI connected. Then disconnect the line and neutral wires at the input to the GFCI and megger those input wires L-N.

This will provide information on the supply wires to the GFCI and the GFCI for L-G and N-G, and only L-N for the wires.

.

 

[wptski]

110521-0949 EDT

Bill:

Using the Leviton as a reference the input L-G and N-G meggered values will be full scale of the megger. But, L-N will be some low value.

If one is going to megger the circuit on the input side of a GFCI, then do this L-G and N-G with the GFCI connected. Then disconnect the line and neutral wires at the input to the GFCI and megger those input wires L-N.

This will provide information on the supply wires to the GFCI and the GFCI for L-G and N-G, and only L-N for the wires.

.

gar:

Yes, that's what I've saying.

 

[ELA]

110520-2031 EDT

Bill:

The GFCI I referenced is a receptacle. The measurements I made on it are in free space, nothing connected.

When tripped there is absolutely nothing conductive connected to the output points. The only material in contact is the molded plastic enclosure. Thus, you will get only a very large resistance measurement across the output terminals when tripped.


.

Gar,
Your statement above about the output terminals is incorrect -as stated.
At least with respect to the Leviton brand you mentioned (e.g. #7599).

I have also examined these devices and retraced the schematic a while back. As you know the 1851 data sheet you referenced is not current.

In the Leviton #7599 the status LED is connected to the output terminals. Try connecting 120V to the output terminals, when in the tripped state and you will see the LED lit.

 

[wptski]

110521-0949 EDT

Bill:

Using the Leviton as a reference the input L-G and N-G meggered values will be full scale of the megger. But, L-N will be some low value.

If one is going to megger the circuit on the input side of a GFCI, then do this L-G and N-G with the GFCI connected. Then disconnect the line and neutral wires at the input to the GFCI and megger those input wires L-N.

This will provide information on the supply wires to the GFCI and the GFCI for L-G and N-G, and only L-N for the wires.

.

gar:

My bad! That should have been 3.3K ohms not 3.3M. At 50V using a Fluke 1507 it read zero ohms but in its ohms function it read 3.3K ohms. At 50V using a AEMC 1060 it read 3K ohm and using its ohms function, it read 3.3K ohms.

 

[brian john]

Brian, isn't the 1meg rule mainly for motors? I have a neta chart that I go by for cables.

Also, If these pumps are so critical to her, I'm thinking about offering to trend these pumps for her.

The megger I have is no good for that. I was considering picking up a 1507 or an ideal 61-797. Any thoughts on those two?

I see one meg spec?d in Division 16 documents and on drawings all the time, for cable, busway and switchboards.

 

[gar]

110521-2039 EDT

WARNING! Do not megger either the input or output wires going to or coming from a GFCI with more than maybe 50 V DC. A maximum for this voltage may need evaluation. Really you should disconnect all the wires to the GFCI before meggering the wires.


ELA:

You are correct. I failed to see the little spring contacts on the PC board that connect the LED series string to the output terminals.

Yes the LED indicator is a series combination of the LED, a diode, and resistor across the output terminals. I do not know the reverse breakdown of the diode, but it could be as low as 200 V. It would be better if it was 400 V. Diode current limitation is no problem based on its size. The resistor is 36,000 ohms.

This means the output wires should be disconnected from the GFCI if one is to megger the output wires. It is necessary to be careful how much inverse voltage is applied to the diode and how much forward current to the resistor. 100 V DC maximum reverse should be OK for the diode, but maybe too high for the resistor on DC with the diode forward biased.

With a Fluke 27 in either polarity, diode or ohms position, I read infinite across the Leviton output terminals. With a Simpson 270 with + on the hot terminal the reading on the 10,000 X range is 80,000 ohms. Infinite with the opposite polarity.

I thought you were going to disappear. It is good you did not because you caught my mistake.


Bill:

Could your reading have been in the 30,000 range?

.

 

[ELA]

ELA:
I thought you were going to disappear. It is good you did not because you caught my mistake.

.

I did become "invisible" for a short while

 

[wptski]

110521-2039 EDT

WARNING! Do not megger either the input or output wires going to or coming from a GFCI with more than maybe 50 V DC. A maximum for this voltage may need evaluation. Really you should disconnect all the wires to the GFCI before meggering the wires.


ELA:

You are correct. I failed to see the little spring contacts on the PC board that connect the LED series string to the output terminals.

Yes the LED indicator is a series combination of the LED, a diode, and resistor across the output terminals. I do not know the reverse breakdown of the diode, but it could be as low as 200 V. It would be better if it was 400 V. Diode current limitation is no problem based on its size. The resistor is 36,000 ohms.

This means the output wires should be disconnected from the GFCI if one is to megger the output wires. It is necessary to be careful how much inverse voltage is applied to the diode and how much forward current to the resistor. 100 V DC maximum reverse should be OK for the diode, but maybe too high for the resistor on DC with the diode forward biased.

With a Fluke 27 in either polarity, diode or ohms position, I read infinite across the Leviton output terminals. With a Simpson 270 with + on the hot terminal the reading on the 10,000 X range is 80,000 ohms. Infinite with the opposite polarity.

I thought you were going to disappear. It is good you did not because you caught my mistake.


Bill:

Could your reading have been in the 30,000 range?

.

gar:

I checked one I had played with and was RESET. I checked OL in one direction and something high the other way but I forget exactly what.

No, I just thought that it read 3.3M but when I tried the Fluke 1507 and AEMC 1060 and got 3.3K, I tried the Fluke 189 again. Not sure what happened the first time, maybe a brain fart?