Cause for GFCI tripping

I have been having some trouble with GFCI tripping by a submersible pump. At first, it was happening when the pump was turned off. Today it was happening very often.

The pump is used for hydroponics. Because this involves pumping salty water around with lots of splashing and tubing failures, I am very wary about using such equipment without GFCI.

Today was a very warm day. When I first used the pump, it seemed to be working well. Then I got my first trip. After that, it would only run a few seconds before the tripping. I measured the resistance with a digital meter between a power lead and the grounding pin with a hand held digital meter. It was in the vicinity of 7M?.

What I think is happening, is that there is a leakage between the winding or other part of the motor to the case. It may be nonlinear such as moisture getting in there. Running the pump probably causes the insulation resistance to heat up and drop in value. It also would be no surprise if going from meter test voltage increases leakage current nonlinearly.

In the end, I ran the pump without GFCI protection, but was careful to avoid getting shocked. The pump did have a grounded case. Everything went well.

Bill

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<salmonegg
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I forgot to add that when the pump is turned off, there may be a high voltage transient that pumps just a bit extra current through leakage resistance. That may account for what I got earlier trips when the pump was turned off.

Bill

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<salmonegg

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