In article ,
wrote:

The clipper is a double insulated device and so only has two wires in
the cord. Where does the current go? It doesn't matter which way the
cord is plugged. It is not a polarized plug so I have tried both ways.
Still, almost always when the clipper is turned off the GFCI trips.
Could this be from back EMF from the motor winding? A power surge when
the magnetic field collapses? I have looked some online for the answer
and haven't found it yet.

Here's the explanation I read, quite some time ago. It still makes
sense to me.

A GFCI tries to accurately measure the imbalance in the current flow
between the hot and neutral wires, and trip the breaker if a
significant imbalance appears. The imbalance would (goes the
thinking) exist if and only if there's a current leak from hot, to
ground (bypassing the neutral return).

GFCI balance sensors are not perfect. They usually consist of
something like a toroidal transformer, with the hot and neutral wires
forming one winding, and a sense winding forming the other. Any
imbalance between the hot and neutral wire current flows would induce
a current in the sense winding, while (in principle) perfectly
balanced and opposed hot/neutral currents would result in no net
magnetic flux and thus no current induced in the sense winding.

The balance of these toroidal transformers is necessarily imperfect.
The hot and neutral wire paths aren't identical, sometimes one is
wound a bit more tightly than the other, and they aren't the identical
distance away from the sense winding. Hence, there's some difference
in inductive coupling within the transformer, and some difference in
capacitive coupling between the two "balanced" wires, and the sense
winding.

This imbalance tends to be worse at high frequencies where e.g. the
difference in capacitive coupling makes a difference.

When a motor-operated device is switched off, and creates a switching
arc due to inductive "kickback", the arc creates a burst of
high-frequency energy (easily covering the AM band and sometimes going
up to VHF). Even if the hot and neutral currents are perfectly
balanced (and they may not be - there might be some capacitive
coupling between the device and the operator's hand) the less-than-
perfect balance in the current sensor can allow a small blip of
current to be induced in the sense winding... and this can trip the
GFCI.

If the device contains a snubber, this may not happen. A GFCI with a
snubber/EMI filter at its output (and I suspect that some of these do
exist) would be less vulnerable to this sort of false trip.