On Dec 28, 9:14*pm, (Doug Miller) wrote:
In article , Terry wrote:





On Dec 24, 2:34=A0pm, "HeyBub" wrote:
BobK207 wrote:

I have had trouble with motor loads tripping GFI's.

The fact that it trips when the fan is turned "off" leads me to
believe what you're seeing is not a true ground fault (current leakage
to ground) but "merely" a difference between the instantaneous
currents on the hot & neutral wires.

I'm an ME but I did study some motor & circuit stuff in
school.......here's my best attempt at an explanation, =A0when the fan
is turned off, =A0the magnetic field of the windings of the motor
collapses & induces a current back thru the neutral (since the hot
lead is switched & therefore open).

The field collapses 60 times a second when running...

120 times per second

Whether it collapses 60, 120, or a thousand times a second when running is not
relevant, because when the fan is running, both wires are connected to the
GFCI. With power to the fan routed through a single-pole switch so that only
the hot conductor is opened by the switch, only *one* wire is connected to the
GFCI, thus making it possible for the collapsing field to cause imbalanced hot
and neutral currents at the GFCI.



With only "one" wire connected to the GFI there is no difference of
potential either. It kind of makes induced currents impossible too,
but run with it.

Want to bet on the double pole switch?