Heres a couple of things to check;
Make sure the input voltage is matched to tap on the ballast.Ballasts frequently have multiple hookups (different wires or tabs to hook to)for different voltages,
if the voltage coming in is 240 volt and its hooked to the 208 volt tap, or vice versa the input is 208 volt and tapped to the 240 Volt tap either situation will shorten lamp and/or ballast life.
Check that the photocontrol (A.K.A. photocell or PEC)is hooked correctly, if the line and load wires are reversed, the PEC will stay closed (ON),all night,but will turn itself OFF and ON during daylight with the frequency of its time delay (PECs usually have a time delay of a couple of minutes to up to 10 or 15 minutes to stop car headlights and similar things from shutting them OFF).This will severly reduce life of lamps and ballasts.
Make sure that there are no 120 Volt loads tapped off the switched line to the lights.With the other line live all the time,the 400 Watt lights will be in series with the 120 Volt load, and this can burn out lamps due to the starting electrodes in the lamps still trying to fire even though the input voltage is less than 1/2.(Odds are probably slim of that one but it is a possibility, I know several years ago I beat my head against a wall quite a bit before I figured out that was occuring at one of my customers businesses).
Make sure the breaker is OFF to BOTH incoming lines before working on these fixtures,if only the PEC is OFF,there is still 120 Volts to the fixture.
When just changing lamps,there is 120 Volts on the screw shell of the lampholder even with the PEC OFF,so if someone touched the base of the lamp when screwing it in, they could be shocked and/or seriously hurt.
Chuck
