Mxslick,
I'm pretty sure the fault was in the fixture itself because I was in the room at one point when I heard a *pop* come from the light and the CB tripped. I inspected all the branch wiring I could see and saw no evidence of arcing or damaged insulation. And though I couldn't find obvious damage in the fixture either, since I replaced it I haven't had any problems with the breaker tripping.
The total number of fixtures on this circuit is only five or six, it's a night-light circuit that's on 24 hours a day. Incidentially, both the problematic lights are on this circuit. However, none of the other lights have been affected.
To be honest I'm not even sure what I'd do to check for or resolve neutral harmonics. Would I check with a averaging current meter and then a true RMS meter and compare the measurements to determine if there's a difference?
And as far as temperature, all these ballasts are toasty. I know they're too hot to handle, but because they require 90C wire, I'd expect them to be at least 75C+. Even if the problem is thermal, I don't understand why it'd only be these two locations. There would have to be something in the enviroment that was making these two fixtures excessively hot and I haven't been able to find anything like that.
Thanks.
-John
