Megger Question

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Little Bill

Little Bill

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Tennessee NEC:2017
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Semi-Retired Electrician
I have a probable short in some underground wiring that is tripping the breaker. I decided to check with my megger and am confused with the results.
When checked with the different voltages applied I get a reading of 0.00 Mg-ohms.
Is that saying it's open/infinity or the resistance is less than a Mg-ohm?

I would think I would get a kilo reading if it's less than a Mg-ohm. I checked with just ohms/resistance, no voltage and it read in the kilo range. All these were hot to neutral & hot to ground tests.

I'm 99% sure the problem is with this run of wiring as I can disconnect it and the breaker holds. I'm just not understanding the megger reading.
 
Little Bill said:
I have a probable short in some underground wiring that is tripping the breaker. I decided to check with my megger and am confused with the results.
When checked with the different voltages applied I get a reading of 0.00 Mg-ohms.
Is that saying it's open/infinity or the resistance is less than a Mg-ohm?

I would think I would get a kilo reading if it's less than a Mg-ohm. I checked with just ohms/resistance, no voltage and it read in the kilo range. All these were hot to neutral & hot to ground tests.

I'm 99% sure the problem is with this run of wiring as I can disconnect it and the breaker holds. I'm just not understanding the megger reading.
Click to expand...

That's a dead short. The resistance is below the meggers range.

I'll often see 30 kohms on a multi meter. But 0 on a megger
 
Little Bill said:
Thanks, I don't use the meter enough to get used to it.
That's why I was getting a low kilo reading with just ohms test.
Click to expand...

Try your megger with the leads not connected to anything and you will see the infinity reading.
Then short the leads together and you will see the reading for a dead short.
 
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