The lights are obviously causing or contributing to your
problem. This seems obvious from the fact that restoring
the proper grounding of the lights led to the GFCI tripping
plus the fact that the previous owner removing the ground
plugs for a reason.
I believe that even with newer ballast systems, some
fluorescent light systems can confuse GFCI circuitry due
to the small capacitive losses created between the bulbs
themselves and the metal reflectors which are in close
proximity to the bulbs. This is a nuisance ground fault -
a genuine loss of current to ground but not a safety issue.
The problem is that background nuisance ground faults
are cummulative and they can create nuisance GFCI
tripping. If they don't trip the GFCI, then they increase
its sensitivity by preloading it with some small level
of ground fault.
Before you invest in new ballasts or new fixtures, I'd
suggest doing some research to be certain that it is not
just the starting cycle of the lights which contributes to
the ground faults. Hopefully you'll get some good advise
on this newsgroup on the issue of capacitive losses
during fluorescent light operation. If not, there is probably
a lot of information which can be located with "Google".
Is there any consensus on whether fluorescent lights might normally
cause nuiscance gfci trips? And if so, is there anything that can be
done? These are the long, 48'' dual-bulb overhead lights, on a 20A GFCI
Some background on the problem:
The lights (3 sets of them) are hanging in a detatched garage, and
plugged into a string of outlets on the ceiling, which are connected
through a single wall switch.
The _entire_ garage circuit is fed from a dedicated 20A GFCI
receptacle-but-not-a-receptacle (looks just like a receptacle, but
missing the outlets, and has just the GFCI part) in the basement of the
house, about 15' away. The wire runs underground using UF cable to the
garage, with ground wire, then to the problematic lighting run and a
few unswitched wall outlets.
I think I have narrowed down the tripping to the lighting outlets. The
ground path could be in the outlets themselves, the plugs/cords for the
lights, or somewhere internal to the fluorescent lights (the
ballast/filter, I am guessing).
Previous owner had chopped off all of the ground prongs on the lights,
so no tripping, but the lights didn't turn on reliably. I put the
prongs back on, so now I get reliable lights, but frequent gfci