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?
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.
Replace it with a standard outlet and the problem will go away.
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.
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
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.
Blowing out a motor with compressed air is a quick way to be buying
Soft paint brush and a vacuum , and yes you sometimes have to open the
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
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.
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?
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.
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
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