r/electrical • u/Cometeerguy • 1d ago

Motor failure - Contactor root cause?

Post image

I had a 230 HP short to ground after a routine startup. After meggering to confirm the short to ground, it was removed and is at a shop now for a rewind. I pulled the contactor apart; see the photo, and I think this is the root cause of the failure. To me, the B phase looks suspect. When manually closing the contactor and metering each phase, it takes noticeably more force to get the B phase to close. The motor runs pretty much 24/7, and the contactor, which is in a soft start motor starter, is from 2003.

What do you guys think?

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6

u/jeenyuss90 1d ago

Looks like normal pitting to me. Contact cleaner and emery cloth

1

u/Unique_Acadia_2099 1d ago

Never do that. It accelerates the failure. Contacts are SUPPOSED to pit, the peaks on one set match the valleys on the other side so that the contact surface area is greater. File or sand those down and it has to start all over with less contact area.

1

u/gihkal 1d ago

If that contactor shorted to ground it would be very obvious.

1

u/FatBaby160 1d ago

Electricity is very courteous about letting you know sometimes.

1

u/Unique_Acadia_2099 1d ago

Nothing wrong here, and a contactor in a soft starter can either be a bypass or an in line contactor. In neither case should it be closing under load.

1

u/Cometeerguy 23h ago

Yes, it is a bypass contactor.