I do some hydroponic growing for a hobby. I use some small submersible pumps and air pumps. Because the nutrient solution is essentially a salt solution, I use GFCI for personal protection against shock.
A timer is used to turn the pumps on and off. I have been getting occasional trips upon turning the pumps off. This makes me think that the problem comes from inductive kicks when the switch is opened. I have put about 0.2 microfarads between the hot and neutral lines. That seems to solve the problem for now.
I am not sure just how the problem arises. My guess is that the inductive kick must be breaking down insulation so that I get some ground current during the inductive spike. That cannot be good for the long term integrity of the insulation.
To get a better handle on the problem, I was thinking of removing the ground connection to the pumps to see if I still get trips upon opening of the switch. Without a ground connection, it would be impossible to get ground fault current unless there is an external ground connection, such as me being grounded and sticking my hand into the reservoir. The GFCI would still protect me in such a situation.
So my question is: What other mechanism can be at work to cause trips other than breakdown to ground?
bill