These heavy-duty Mechanical Time Switches are designed for commercial, industrial and residential applications and have the highest motor load ratings in the industry. They provide up to 12 ON/OFF operations each day with a minimum ON/OFF time of 1 hour. This model is designed to turn OFF a gas fired swimming pool heater approximately 20 minutes before the filter pump shuts down. This eliminates the problem of pounding and knocking due to overheated water, reduces scale and lime deposits and extends the service life of the heater.