When the household appliances does not work normally, the electric current increases and the ambient temperature rises, exceeds the temperature setting value of the thermal protector, automatically disconnects the electric circuit, so that the electric appliance is protected. When the device is cooled to a safe temperature, the contact can be closed automatically. The PTC Heater also provides over-current protection: when the circuit is short-circuited, or when the motor is stuck, because the current increases rapidly, on the bimetal plate, it produces a thermal effect, which causes the heat-sensing plate to use the principle of torque to cut off the current contact quickly.