A Question for a GFI guru

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 macerating disk had loosened and let 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. And, for sure none of the supply or neutral leads were contacting gounded metal. 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
--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can smile when things are going wrong, you've thought of someone
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So, you asking a question or just showing off :-)
I say you got it right...almost.
The current that would flow through the winding to ground capacitance would never return through the neutral, it becomes leakage current to ground. But with no neutral, it still represents an imbalance and thus the trip.
Nice job on the quick changeout. It seems whenever I do a job that involves plumbing, even the minimal amount of plumbing involved in changing a disposal, some pipe or fitting somewhere, usually in a completely different area of the house, starts to leak, just in spite.
Just pick'n nits....
Paul Franklin
wrote: <snip>

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Paul Franklin wrote:

Nah, I've got time on my hands and SWMBO is off at the Boston Ballet for the afternoon, which wild horses couldn't drag me to..And my inquiring mind wants to learn what's really happening.

Since the neutral is (or should be) at ground potential, I'm betting that when things are properly connected some sort of autotransformer action in the motor windings adds an equal and opposite "capacitive current" into the neutral return to keep the GFI happy whenever there was power applied to the motor.
Jeff
--
Jeff Wisnia (W1BSV + Brass Rat '57 EE)

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What he said.
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You climbed to the top of the Guru Mountain to ask me *THAT*!!!!
You are only entitled to one answer, and you have angered the spirits by wasting your one answer on that. Just for that, the evil demons and I will see to it that your snow blower will throw a rod, and the gas valve on your furnace will faill in February. Your dining room lights will flicker, and your garage door will stick in the "up" position. Your toilets will start to swirl to the left to flush, and the hot and cold pipes will be reversed on your bath tub.
Ah, sigh. Since you have troubled the Genie to ask, it is fair to say.
The windings in the motor often have small energy leaks to ground. There is also a capacitor which can leak. It's usually minor, and the GFI doesn't notice.
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Christopher A. Young
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