ST09 Series Thermal Protector Working Principle：

ST09 thermostat is a double-pole, double-throw, resettable or manual reset ultra-current (up to 250VAC 63A) temperature controller. The plastic structural parts isolate the bimetal disc that senses the temperature and the beryllium copper metal part that passes the current, preventing the thermal effect generated by the current from heating the bimetal disc, causing it to open in advance and improving the accuracy of the protection temperature.