I went to check some lights in a Pediatric Clinic. Normally just have to replace a ballast. This one had a dual-lite emergency ballast in it, with 2 hot feeds. Lights would not work on emergency ballast. The regular ballast feeds through the emergency ballast(bunch of wires). There was no diagram for the wiring on the emergency ballast, so before I did anything I took voltage readings on the 2 hot feeds feeding the ballast. I had around 115 volts on one, and only 90 volts on the other one. I traced the conduit a little in the hallway above the ceiling and find that the wire that only has 90 volts is feeding other lights in the hallway with regular ballast, and the lights are working:D I wouldn't think they would work on that low voltage, but obviously there's a bunch of them working on it. I'm suppose to go back on a Saturday and try to trace the problem. I'm thinking that this may be the reason the emergency ballast is not working. Either the low voltage has burned the ballast up or it just won't "kick in" with that low voltage. Plus I'm sure the low voltage is not good for the rest of the lights. Any thoughts on what would make the voltage be low? Loose neutral somewhere maybe? It's looks like it's going to be a job trying to find it. This place is pretty big. I'll probably have to check some j boxes at random, starting close to the panel. Thanks for your input...