Larry,
Well, I don't know yet. There are four leads on the load side of the switch: red, red w/white stripe, purple, and purple w/white stripe. I think each hanging fixture has it's own relay, and that there are two relays for the four banks of lay-ins.
This configuration would be consistent with the observations, and as you said, it's then a simple matter of finding the bad relay.
Escept it's not in the ceiling box above the non-working fixture, and I can't find a panel of relays. And the maintenance man and I really "tossed" the place! I mean we searched it very thoroughly.
The roof over the main chapel area (where the non-op fixture is) is a flat roof with no attic space. The banks of lay-ins are in a dropped ceiling. I suppose I ought to look there for the relays, as a last resort.
I'm banking on the distance mesurement via TDR to give me a gross indication of possible location, and then a wire tracer to led me to it. The low-v cable is in EMT, though, so I'll have to squirt signal onto the pipe and just follow the strongest signal. Or put tone on the control wiring and look for signal at outlet boxes. X-ray vision would be nice...the building is reinforced concrete.
I'm the third electrical contractor to troubleshoot this problem. First guy told the maintenance man that the problem was the splices at the ceiling box, but he never came back to check (fear of heights, eh?)
The second one said that it was the fixture ballasts, and that he was gonna come back and lower the fixture to ground level to work on it (my guess is that it weighs 70-80 pounds). He never came back.
So, finding and fixing the problem is now a challenge.
Thanks for the help. I will report back when I've revisited the site.
Cliff
