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OT-Will GFIs trip on motor winding capacitance?

Had a funny one happen yesterday. The kitchen garbage disposal was running, but sounded like it was full of scrap iron because one of the rivets holding a flail onto the spinning macerating disk had loosened and letting that flail chatter against the housing, making a horrid scraping.sound.

I picked up a same brand/same size replacement disposal at HD and got it swapped out in a record breaking (for me) 36 minutes, winning my bet with SWMBO who scoffed when I told her she's be able to use the kitchen sink in 45 minutes or so. (She's usually the winner, my repair project time estimates are generally low by at least 200%.)

When I turned on the water and flipped the wall switch, the disposal motor didn't start. After saying, "WTF?" I tried the electric can opener which I knew was on the same circuit as the disposal. When it didn't run either I went down to the panel and found the GFI breaker for that circuit was tripped. I reset it and when I came back to the kitchen the can opener worked fine. I flipped the switch for the disposal and the GFI breaker popped again.

I checked my wiring at the disposal and to my embarrassment I found that the stranded neutral motor lead wire hadn't "caught" in the wire nut, and was just hidden inside it, but not connected to the supply neutral. Things were sort of tight and cramped inside the wiring compartment of the disposal, but that's really no excuse for my sloppy job, is it?

Anyway connecting that motor wire to the neutral side of the supply put things right.

I'm assuming that the motor's winding to ground capacitance caused current to flow through the supply side of the GFI which wasn't returning on the neutral side, and that unbalance tripped the GFI.

If it wasn't such a PIA to crawl under the sink again, I'd disconnect that neutral lead and test my theory.

Comments?

Jeff

Reply to
Jeff Wisnia
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Reply to
Bob Swinney

Yup, that's what an electrical engineering type told me(I consult with him on my designs at the plant). both hot and neutral go through the same toroid. As long as the current on both is equal (but opposite sign, I guess), there is no induced current. If the neutral wasn't made, the inrush would trip it. You can also get GFI breakers for equipment protection instead of personnel protection. I think it's 30 mA imbalance instead of 10 mA. I use them on electric tracing circuits.

Hmmm, that raises a question: can you get a GFI for 220 single phase? It seems like it should work, but I've never seen one.

Pete Keillor

Reply to
Peter T. Keillor III

When I use wire nuts I always strip the wires a little long, hold the wires together and even up the insulation and grab bare ends in the jaws of my electrician's pliers and twist them together (clockwise, seen from the end). Then I cut the twisted wires to stripping length at a 45 degree or so angle and put the wire nut on the twisted together wires. If necessary, I "upgrade" one size on the wire nut to get a good grip and a fully shielded junction.

My feeling is that life is too short to have a hot lead jump out of a wire nut in a box that is grounded and/or that may have a bare neutral or ground floating around in it.

I had a licensed electrician tell me I should not do that but he was unable to come up with a reference in the electrical code to explain why he felt that way.

Reply to
Jack Erbes

With 100% certainty yes you can get a 220 single phase GFI. I have one on my hot tub and so do millions of other people. A 50A GFI 220 breaker costs about $50. OUCH!

Grant Erwin

Reply to
Grant Erwin

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