Single TimerNormal household timers are not built to take the high inductive loads produced by HID ballasts. If used with a HID ballast the contacts inside the timer that open and close the timed circuit will overheat and weld together, breaking the timer and leaving your grow lights permanently on. The PowerPlant Heavy Duty Timer is different. It is designed to take high loads and has no problem dealing with the inductive loads produced by a 600w ballast