GFCI question


Hello Group.
I have a problem with a GFCI tripping every time I turn on my shop fan. This line has a 40" shop fan (on a wall switch) and three outlets. I can use the outlets fine, but when I turn on the fan, it runs for about ten seconds and then it trips the GFCI. It was wired by a licensed electrician and worked fine for ten years. What is the best way to figure out what's bad, the fan motor, the GFCI, or maybe the breaker? Any advice?
Thanks.
unklerichie
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Since the breaker is not tripping it can probably be removed from the equation. Plug the fan into another GFI in another part of the house or replace the GFI that you are now using and see what happens in either case.
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The fan is wired to a switch through the wall. I can't plug it in somewhere else. I'm betting you're correct about the GFI. I'll replace it tomorrow. Many thanks, John.
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Replace it with a standard outlet and the problem will go away.
s
The fan is wired to a switch through the wall. I can't plug it in somewhere else. I'm betting you're correct about the GFI. I'll replace it tomorrow.
Many thanks, John.
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The problem is something leaking power. Changing a socket won't make power leak go away.
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The GFI is probably working just fine and doing its job. These detect when there is a short to ground. Electric motors have all sorts of exposed wires inside and dust can get in there and cause a little short to ground.
Try blowing out the fan motor with compressed air or having the motor serviced.

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Blowing out a motor with compressed air is a quick way to be buying it's replacement.
Soft paint brush and a vacuum , and yes you sometimes have to open the thing up.
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OH PLEEEEEASE....... I've been blowing motors out for 40+ years and have NEVER damaged one yet. You'll do more damage poking a vacuum nozzle or paint brush in there.
s
Blowing out a motor with compressed air is a quick way to be buying it's replacement.
Soft paint brush and a vacuum , and yes you sometimes have to open the thing up.
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A 40" fan has to have a pretty good sized motor and takes several seconds for it to come up to speed. Everything being reactive, while it is starting, it is creating reverse EMF (electro-motive-force) which, during that time, is making the current in the two feed wires go out of phase with each other. THAT can pop a GFCI; they just don't work well with large inductive loads like electric motors.
Please let us know if changing out the GFI helps anything because IMO it won't, but I'd be pleased to be wrong.
Also, if the insides of the fan are dirty, dusty, full of fuzz and coated with whatever from the air, that can cause small currents to flow from the hot to the earth ground which might also trip a GFCI.
It sounds like the fan gets turning pretty good before the GFI pops, so you could, JUST IN THIS ONE CASE, try starting the fan, when the GFI pops, quickly reset it and see if the fan will continue to start up. If it still pops, you could try VERY CAREFULLY (ELECTRICITY CAN *KILL* YOU) TRY shorting around the GFCI with a lead until the fan gets running. Then remove the bypass; If the fan continues to run, there is there is no problem with the fan. \\ But if the GFCI pops, then there is definitely a probelen with the fan or the wiring to it.
I'd use a little Radio Shack clip lead to do the shorting across the GFCI (from input/source side to load side, NOT load to load!). Kill the breaker, put the clip leads on, have somoeone turn on the breaker, carefully remove the clip lead by the insulated handles, and see if the fan keeps going. If so, it's 99% going to be EMF issues which most any GFCI will pop on. Note: If the GFCI should pop while the clip leads are attached, it means one of them is not getting a good connection; kill power, clean the area you want to attach it to, and try again.
DONE WRONG, THIS CAN BE VERY DANGEROUS! NEVER TOUCH ANYTHING ELECTRICAL OR ANY METAL NEAR THE ELECTRICAL PART WHILE THE BREAKER IS ON! If you aren't experienced around electricity see if you can find an experienced buddy to do these things for you; it might be the best advice.
BTW, GFCI's are down in cost these days and there ARE some that are made for higher loads than the standard 15 amps, although they cost more.
HTH
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TWayne wrote:
...

on the two feed wires will not be "out of phase". A large capacitor to ground would be such a reservoir, but that is a ground fault, and the GFCI should trip for that.
...

differences in the motor during acceleration that could cause a ground fault during acceleration. OP didn't mention whether this motor had a centrifugal switch controlling the start winding.
Most likely you have a ground fault in the motor. It may be solid or it may be intermittent. Have you tried measuring the resistance from hot to ground for the motor?
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Since Neutral and Ground are tied together back in the breaker box, that's not going to prove anything without disconnecting the wires and even then without a voltage to break down the gap it likely wouldn't show anything but the resistance part of the fan motor. I wouldn't even bother with that; it'll measure near zero, only a few ohms to a hundred or so depending on the fan motor coils.
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TWayne wrote:
...

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The way you tell what the problem is. Notice when the GFCI trips. If the GFCI trips consistenly with one appliance other, then the problem is with the appliance. For example, if one appliance consistently runs for a couple seconds and then trips the GFCI, you can be fairly sure that one appliance has a power leak.
A standard socket might keep the appliance running, but won't be as safe. It's unlikely anyone will be shocked by a 40 inch shop fan, especially if the fan is properly grounded. So, a non GFCI socket may be a work around for you.
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