GFCI And Pond Aerator Puzzle

JackJohnson

Homeowner has a 2 pole 50A GFCI connected to an outdoor hot tub via a subpanel near the tub. Works perfectly. Attempted to continue a line (240V) from the subpanel to another box with an outlet for a 240V pond aerator. When the metal can of the motor touches the pond water the gfci trips. I disconnected the hot tub from the hot tub subpanel and the symptoms remain even though the Aerator is the only item in the circuit. returned motor to Kasco. It checks ok. They did a hi-pot test, no leakage measurable. Borrowed a similar motor and the behavior is identical.

I only mention the hot tub because it seems to indicate that the GFCI is ok if it performs ok connected to it.

The line to the pond is approximately 65ft, and the aerator cable is 25ft, and yes, I tried a different aerator cable. In fact, I can submerge the cable (not the connection) and the breaker stays set until the can of the motor is dipped in the pond.

The engineer at Kasco has no answer for me. Anyone have any ideas?

Electric_Light

My guess is that the aerator or water-tight connection is faulty. I suspect the reason it trips immediately when motor is dipped is that the water is galvanically isolated and there is no path for leakage current to go, but grounded motor case provides a path, which causes the current to be diverted to ground, tripping the GFCI.

You have a potentially very dangerous situation. Put a piece of wire into the water and attach it to mA range of your DMM. With the aerator running but the motor not inside, touch the COM probe to something grounded.

The breaker should not trip and the meter should not indicate ANY current.

Do not commission the hot tub until this issue is completely resolved.

newenergy

Interesting, but could the pond not be grounded? Some kind of plastic liner?

MALCO.New.York

Say what?

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