I have a GFCI outlet that is in a garage which is feeding other outlets in the garage and also feeds two garage door openers.
When both doors are operated simultaneously the GFCI will trip off. If only one door at a time is operated then it is fine.
What would cause the GFCI to trip? I do not believe it is due to load or could it be? I thought a GFCI only tripped when it sensed a difference in the neutral current compared to the line current. The openers are Genie screw drive type openers that operate double wide doors. If that makes any difference.
I'm not sure whether your GFCIs incorporate normal overload protection as well. Over here most don't, but a few models have it.
Are both motors actually starting simultaneously? The inductive load could cause some types to trip in this case.
One thing I would check for straight away is a neutral-to-ground short on the circuit. If such a short exists, it could be the the parallel path isn't carrying enough current to trip on one motor, but is on two. I've had that sort of problem several times.
GFI's are prone to nuisance tripping from electrical noise. Perhaps when both operators are being used they are causing enough garbage on the line to cause a trip.
You could try installing GFI's in such a manner that the garage door receptacles are not being protected by the GFI's. I don't know how many new receptacles this would take, but you can get them for as little as $6 or $7 apiece. You'll have to work ot the cost versus aggravation factor yourself.
Few things are harder to put up with than the annoyance of a good example.
I have found that GFI just keep tripping when on motors above 1/4 to 3/4 hp start up. No longer wire up motor loads to GFIs Have been putting them in circuit after motor load. Have had garbage disposals, refrigerators, freezers, dishwasers,gas furnances as well as garage door openers trip them. Just not worth the time and continual trouble calls to do it any other way.
I'm seeing more and more problems of this nature here as well, because whole-house GFIs with a sensitivity of 30mA are becoming increasingly common, even where no GFI is actually required. I'll try to put "problem" loads on a non-GFI busbar if possible, or swap to a 100mA type, other factors permitting. If that doesn't work, we can get time-delayed GFIs, which normally fix it. Mucho pesos, though....
[This message has been edited by pauluk (edited 09-19-2001).]