On 9/4/2011 9:09 AM, Dave wrote:
On Sun, 04 Sep 2011 13:57:52 +0100,
wrote:
Why should a 1hp motor trip a GCFI, its an earth fault current trip not a
current overload device.

That's something I can't answer because my electrical knowledge is
pretty limited. However, the small 8" desk fan I use in my bathroom
which is plugged into a GFI outlet, occasionally trips the GFI when I
turn the fan on. What could be the explanation for that?

GFCIs are tripped by a current imbalance: if the currrent on the hot and
the neutral differ by more than 20mA, it trips.

Inductive loads such as those presented by electric motors put the
return current slightly out of phase with the supply current. If the
amplitude of the phase difference exceeds 20mA, the GFCI trips.