The 2 most likely issues is either condensation forming in the motor windings when the motor isn't running, or a small short just starting to form in the flexible conduit feeding the motor. Since the blower / motor assembly is most likely sitting on springs, it is probably rocking around causing the connection point at the end of the flexible conduit (where there is SUPPOSED to be an anti short bushing) to rub into the insulation. When you meg it it won't show up because it is intermittent. Have your HVAC technician physically check the wiring and put his eyes on it. Look for a black spot. He may have to completely pull the wiring out of the flexible conduit to check it.

If it is condensation, many times it will meg good because it has dried up when you check it.

These two issues are very common and it is most likely not an issue with the drive.

Good luck and let us know what you find.

 

There was a bad batch of ribbon cables in those drives for awhile, while the drive is running, bump the right side of it where the ribbon cables are with the handle of a screwdriver and see if the drive goes into ground fault. If it does you need to replace the ribbon cables, I will see if I have the service bulletin somewheres.

 

Does the wire run in conduit? I had one where the wires ran in a channel. Couldn't find any issues until we were there at night, saw small arcing around the wires in the channel. Changed the wires and the problem went away.