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.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.