150909-2351 EDT
JHZR2:
When you try to switch off the current flow to an inductor you do not have a high rate of change of current, but rather on an instantaneous basis the current is the same before and after you open the switch. Rather you have a very high rate of change of voltage, and it reverses from what was applied before the switch was opened.
A shunt resistor is a waste of power to reduce the change of voltage, but it doesn't change the fact that the voltage changes instantaneously. The shunt resistor only limits the peak voltage.
A shunt capacitor, or filter is better.
I believe a rapid rate of change of voltage is capacitively coupled inside the GFCI to the SCR gate to trigger the SCR. Nothing to do with the current sensing function of the GFCI.
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