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GFI Question

Why would a GFI trip only when a motor shuts off? Full story is hot tub with water pump and air injector which is a motor which pumps outside air thru the jets to create lots of turbulence in the water.

When the main 240V GFI breaker is turned on the water pump turns on, the air pump turns on, and the heater turns on, if the temp is low. Tub runs for 23 seconds and trips the breaker. The 23 seconds corrsponds to the point where the air injector pump turns off. I verified the air pump by manually turning it off via the control panel before the 23 seconds was up. It tripped the breaker immediately when i did that. Breaker tripped when the motor turns off! Disconnecting the air pump motor removes the problem and the tub is happy.

It appears to be a capacitor start motor based on the lump on top.

The environment is warm, dry, and clean. The tub is 7 years old. The air injector is rarely used except for the start-up sequence.

The breaker was replaced last year, due to a bad connection causing overheating of the wires at the breaker.

Replacing either the motor or expensive breaker or both is one way to find out but is the expensive way.

Why would a motor trip a GFI when it shous off?

Thanks, Rich

Reply to
Popper
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Check the grounding of the spa. There should be a green or bare ground wire connected to the control/junction box in the spa and in the electrical service. This wire should be unbroken from start to finish. no splices.

Reply to
SQLit

When the motor is shut off there is the inductive "kick" which may couple into ground rather than arcing across the just opened contact.

You can test this theory by placing a "snubber" across the contact which opens. (A small cap in series with a small resistor would be your "snubber.")

BUT: you may have some marginal leakage already. Other posters have mentioned "the usual suspect" including partial insulation failure combined with wet wires or damp motor windings or just water (and dirt) where it shouldn't be.

Reply to
John Gilmer

Your theory of an inductive kick has been considered, but the main pump motor does not cause the breaker to trip when the motor shuts off. Nor does the heater element, although there is little inductance. Both of those facts tend to indicate that it is not the breaker itself. If I had marginal leakage already, it would seem that the kick would be in a diection so as to oppose the leakage, not add to it. All three power devices are run by relays on a PCB in a metal box inside the tub enclosure. It is clean, warm and dry. I do not know if the relays are contact type or solid state, but I guess the latter. They are like 1 inch encapsulated cubes on the PCB.

I just disconnected the air pump since it is foolish to inject cold air this time of year.

-- Rich, still puzzled.

Reply to
Popper

If I understand it, you've already proved that it's something to do with the airpump circuit, right? If so, try substituting a non-reactive load in place of the air pump - perhaps a bunch of light bulbs of wattage equivalent to the air pump - temporarily, to see what happens. If it trips, you know it is not an inductive kick from the motor. If it does not trip, then you know it is something to do with the air pump motor - inductive kick, leakage, intermittent short, whatever.

Reply to
ehsjr

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