Normal 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. This means that no separate contactor is required, saving you money. It is a 24 hour, 15 minute segmental timer, with 96 switching operations within a 24 hour period (every 15 mins). The heavy duty contacts mean it can take high inductive loads. It is suitable for timing 600w HID ballasts, is very reliable and has a high quality timer unit. Along with a robust case design with socket and timer dust/moisture covers. This unit is ideal for timing 400w and 600w ballasts. Do not use more than one 600w ballast per timer.