Thanks, guys, I really appreciate your responses.
These are interior 400W MH multi-tap lights approx. 18' off the floor. I have them in the 208 volt leg, and the voltage is high, approx. 218 volts. There are six of these units on a 20-amp cicuit protected with a std. Square D QO SP breaker. It just occurred to me that this breaker is probably rated 120 volt, and I should be using the 120 volt tap on the ballast.
The breaker seems to be tripping instantly, and usually resets fine. It is also an intermittent problem. This area has gas heaters, so I'd describe it as very dry.
Dave
