When a HID strikes up it takes a huge surge of power mate. I dont know about American voltages, but in UK we have 240V. A contactor is essential here, many a grower has had the timer contacts fuse without one, and fires have been caused. I use a 400W HID, I burnt out 2 timers before i found out the cause . I use a contactor/relay now and havent had a problem since. If your light stays on after "off" time, or goes off and doesnt come on at the set time, your contacts have most likely fused in the timer. Personally i would never run without one, its one of the most important things you need for safety. As i said thats on our voltage, but even on 110v you still get a surge at strike up. Id post a link to the forum but its prob against the rules. Its essential mate, for us at least.