Help me Make my GCFI Stop Tripping

Chips O'Toole

H-M Supporter - Gold Member
H-M Supporter Gold Member
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Jun 15, 2017
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My Gorton 375 grinder arrived. Unfortunately, I can't use it. The outlets in my workshop are on a GFCI circuit, and every time I turn the motor on, it trips the GFCI instantly. I have connected the motor power leads directly to the hot and neutral lines, and the GFCI still trips, so it has to be a motor issue. The motor starts and runs fine on a normal circuit. The resistance between the hot and neutral motor leads, when disconnected from the switch, is 2 ohms.

I figured I would change the motor's capacitors and see if it helped, because that's all I can do short of taking it to a shop. I got the motor out of the grinder, and now I'm stumped. It has some kind of fancy vibration-isolation hubs on it, and I can't figure out how to get them off. Also, I don't see the capacitors. I assume that if I get the end of the motor casing off, I will eventually find a capacitor in there somewhere.

I thought I knew a few things about AC motors, and one of the things I thought I knew was that they used start capacitors. Now I'm reading that this is not always the case. Not sure what to think about the motor I'm working on now.

I would like to find out a) why the motor is tripping the GFCI, b) how to open it up, and c) whether it has capacitors in it. It's a 1725-RPM 1/4-HP 110V motor. Tips appreciated.

02 04 20 Gorton 375 grinder on pallet small.jpg

02 04 20 Gorton 375 grinder motor small.jpg
 
I seem to semi-regularly replace GFI outlets for false trips. I know that's the case because I replace them and the tripping stops. Sometimes I find them full of fried black ants, no kidding. As a test, try plugging it into a different GFI outlet.

On the other hand, it could be trying to save your life. The resistance you saw between the black and white wires is about right, so that alone isn't the issue. What's important is the resistance from the white and black wires to the ground wire; it had better be near infinite resistance. I doubt it's the caps, if they exist. Also inspect the wiring closely, you never know what you get when you buy someone's "surprise package", and electricity is something to respect.
 
Ive had to replace gfi outlets on the outside of my house which had outlet covers on them. Rarely used and one day I couldnt plug anything in them without tripping. Replaced outlet with a new gfi and haven’t had a problem since. Any problem on the nuetral side will cause it also they are sensitive.
 
Good idea. It takes veeery little leakage to trip those things. Even slightly conductive dust touching the right points will do it.
 
While working on a remodel last year, I ran into a new style breaker that was code for new electric installs. It basically would trip if there was any spark whatsoever detected. It was impossible to run almost any power tool. I don’t remember all of the specifics, other than it was a pita and we just ran extension cords from the garage!
 
I suggest that you take your motor to a electric motor place and ask them to test the motor with a megger(AKA as megohmmeter) . The insulation on your motor may not be up to snuff or there may be some contaminates causing a high resistance short. The GFI could be at fault, too. Try the motor on a different GFI. Also, you may have a split phase motor which does not use capacitors.
 
While working on a remodel last year, I ran into a new style breaker that was code for new electric installs. It basically would trip if there was any spark whatsoever detected. It was impossible to run almost any power tool. I don’t remember all of the specifics, other than it was a pita and we just ran extension cords from the garage!
Arc fault interrupters, a good idea which in practice isn't so hot. A friend of mine had them in his breaker box in a new home. Any lightning strike within a mile or so would shut off circuits at random. He ended up yanking the ones that powered the sump pumps in his basement when they went out during a torrential downpour during a thunderstorm and got him 6 inches of water in the basement.

GFCI breakers can be a pain and where GFCI is required, kitchen and bathroom, it is better to use GFCI outlets.
 
I'd be inclined to think your problem is a faulty GFCI. Here on the farm, we have several GFCI outlets outdoors, and fairly often they need to be replaced. Like kb58 mentioned, it's not uncommon for ants to get up in them and short them out. An electrician once told me that apparently, they produce some sort of imperceptible hum that attracts insects. Also, there is an issue with humidity where you and I live. Around here, these outlets are notorious for short life span, and that's definitely been my experience.

If you have a 'good' GFCI' outlet, you might try replacing it with the one that shorts out. If it works, you know it's the outlet. If it doesn't, then you know you need to go to Plan B.

Regards,
Terry
 
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