meghing issue

[apprenticemike]

we have a generator at our jobsite that we puleed a few parallel 500 mcms to.. we meggered the wire after pulling it in.. after re meggering the wire after being landed we found it was not passing.. there are no visible knicks in the wire and we had a good journeyman land these. we also tested the wire with another meghometer with the same result so we know it is not our instrument. does anyone have any idea why it may not be passing now? does anyone have any experience with this?

 

[don_resqcapt19]

What are the conductors connected to? What is the voltage of the generator? Does it use a 3 pole or 4 pole transfer switch?

 

[wawireguy]

Might be reading through whatever you landed it on. Since you megged it before you landed it I'd probably think it was the disconnect or whatever you connected it to that it was reading off of.

 

[eric9822]

we have a generator at our jobsite that we puleed a few parallel 500 mcms to.. we meggered the wire after pulling it in.. after re meggering the wire after being landed we found it was not passing.. there are no visible knicks in the wire and we had a good journeyman land these. we also tested the wire with another meghometer with the same result so we know it is not our instrument. does anyone have any idea why it may not be passing now? does anyone have any experience with this?

If the generator has a grounded neutral you need to disconnect that before meggering. Also if there are PT's installed they may need to be disconnected as well.

 

[K8MHZ]

Also check for moisture at the end of the conductors.

How bad do the conductors fail? Can you see the fault with a DVOM?

I try to meg one strata at a time.

I think by isolating the conductors from their terminals you can eliminate the conductors as being an issue.

I would also be hesitant to connect a megger to the output terminals of a generator unless I knew what the parameters should be for pass or fail. The are likely not the same as the conductors.

You also stand the chance of damaging the generator by pushing 500 - 1000 volts DC into it. Who knows what sort of electronic equipment may be part of the circuit?