On Fri, 11 Sep 2009 03:38:02 +0000 (UTC), Wayne Whitney
wrote:

On 2009-09-11, Tony Hwang wrote:
Wayne Whitney wrote:

A balanced surge on the hot returning on the neutral will have no
effect on the GFCI. Only if it leaks to ground will it trip a
GFCI.

You are talking theory, in real life out in the field, theory does
not stand always. After all I spent half a century working around
this kinda stuffs. After all nothing is PERFECT in this world.

Fine, nothing is PERFECT. The sensing coil in the particular GFCI
unit may be slightly out of balance, so that instead of just
responding to the differential current, it responds very slightly to
the total current. Or the appliance may have a small ground fault and
have excessive leakage current. Either way, if the GFCI trips on a
repated basis, something is defective and should be replaced.

Cheers, Wayne
Something is not RIGHT - but it may not have any ground fault - and
the GFCI may be to spec. Everything may be working according to it's
design - therefore NO FAULT. Just a design incompatability.