800 Amp Bucket Tripping

[Drake5265]

It hasn't rained in like 2 or 3 days now I didn't think that those reading would be that low maybe I need to find where we attach to the ground ring at lol

 

[Drake5265]

I have located the problem with a branch circuit in the panel fed by the 800 amp circuit breaker it is caused by the branch circuit powering a rooftop air handler it rained this morning the breaker tripped I megged it out and my result was the B phase wire had a reading of .096 MOhms

 

[Electric-Light]

I have located the problem with a branch circuit in the panel fed by the 800 amp circuit breaker it is caused by the branch circuit powering a rooftop air handler it rained this morning the breaker tripped I megged it out and my result was the B phase wire had a reading of .096 MOhms

What test voltage?

.096Mohm is 96kOhm, which even at 277v, it would only let through 2.9mA (3/1000th of an A). Allow fluctuation for environmental variations and drop it to 1kOhm and you're still only pulling 300mA (which is just about the right current of a properly working 3 lamp fixture), it's not even remotely close to activating overload or shot circuit.

 

[ptonsparky]

What test voltage?

.096Mohm is 96kOhm, which even at 277v, it would only let through 2.9mA (3/1000th of an A). Allow fluctuation for environmental variations and drop it to 1kOhm and you're still only pulling 300mA (which is just about the right current of a properly working 3 lamp fixture), it's not even remotely close to activating overload or shot circuit.

Mmmm. I sure have failed a lot of underground and motors with better readings. Guess I have been wrong for several years now. Strange that things 'worked' after correcting such a small problem.

My semieducated guess from here is he is on the right track.

 

[hurk27]

What test voltage?

.096Mohm is 96kOhm, which even at 277v, it would only let through 2.9mA (3/1000th of an A). Allow fluctuation for environmental variations and drop it to 1kOhm and you're still only pulling 300mA (which is just about the right current of a properly working 3 lamp fixture), it's not even remotely close to activating overload or shot circuit.

What your missing is carbon flashover, you don't apply the resistance like you would a load.

96kohm is a very good indicator of bad insulation that with the right conditions will flash over into a bolted fault.