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I have my entire aquarium running off one GFCI. My lights are plugged into the top outlet and all of my pumps/etc are plugged into the other. If everything is running and I cut the switch (on the power strip) off, it occasionally trips the GFCI. If I do the same thing with the lights off, this never happens. This is especially annoying since the lights are metal halides and take forever to come back up.

  • The breaker hasn't tripped since I hooked everything up (a year ago)
  • The lights pull about 6 amps
  • The pumps/etc pull about 2 amps

If I put a second GFCI to split the load up, would that fix my problem (I realize that I can't feed the second GFCI from the first)?

I'm up for alternative suggestions short of running another circuit.

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You might try a snubber between the power strip and the GFCI, to eliminate any electromagnetic interference produced by suddenly switching off the pumps.

Alternatively, trying a power strip that doesn't have surge protection could solve the problem. Surge suppressors typically route surges to the grounding conductor, which could cause upstream GFCIs to trip (assuming the surge is large enough).

  • I'd never heard of a snubber; both sound like good suggestions. I'll be sure to let you know if either work. – Gary Nov 16 '14 at 15:27
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A characteristic called inductance makes some electrical devices behave like a flywheel; when current is flowing, it will want to keep flowing. Just as it takes torque to stop a flywheel, it takes voltage to stop current.

Some kinds of motors have significant inductance; if current is flowing from hot, through the motor, to neutral when the switch is opened on the power strip current will continue to flow from hot to neutral for at least a tiny fraction of a second. If there were no surge suppressor, the current would most likely arc through the switch. A surge protector with a voltage clamp between the hot and the grounding conductors, however, may offer a better current path. Current will go out the neutral wire of the motor, then the neutral wire of the power strip, the neutral return of the GFCI, and the neutral wire back to the panel. It will then travel through the grounding conductor wire back to the surge suppressor (bypassing the GFCI's sensing), through the clamping device, and back to the motor's hot wire.

A GFCI will trip if it sees current flow through the hot wire but not the neutral wire, or vice versa. In this scenario, the GFCI will see current in the neutral wire which didn't return through the hot wire, and thus recognize that as a situation where it should trip.

Some surge suppressors have one voltage clamp between the hot and grounding conductors, and between the neutral and grounding conductors, but none directly between the hot and neutral conductors. Getting a unit with a clamp between the hot and neutral wires may reduce false tripping, since the clamp between hot and neutral would offer a better path than the aforementioned one through the grounding lead, and that better path would not go through the neutral lead of the GFCI.

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