I went on a service call yesterday. In a store downtown, a lady had a 250 watt metal halide light that would trip off then come back on. The breaker never trips, only the light. It would do this once, maybe twice a day, sometimes not at all. It is a fairly new fixture, isn't in a location where it would build up excessive heat and it is a 250w ballast.

The outlet that it is plugged into was originally a 220 outlet converted to a 110. Whoever had worked on it previously had used one of the hots and the ground as a neutral. Our fix was to use the other hot as a neutral and yes, we did go to every jbox we could trace and mark it neutral. Would using the ground as a neutral cause the light to trip? If not, what else?

Bad bulbs. HPS does the same thing

I agree a bad HPS bulb will cycle. I'm not sure about MH bulbs. I thought I saw it last week, but when I suggested a new bulb, the carpenters were all over me. They had already tracked it down to voltage drop when another piece of equipment started. Now, I don't think I've seen an MH bulb do that.

You probably had a high resistance ground ... this had the effect of lowering the voltage .... not enough volts, bulb would try to re-strike.

Should fixing the neutral fix this?