The working principle of a thermal relay is that the current flowing through the heating element generates heat, causing the bimetallic strip with different expansion coefficients to deform. When the deformation reaches a certain distance, it pushes the connecting rod to act, disconnecting the control circuit, thereby de-energizing the contactor and breaking the main circuit, achieving overload protection for the motor.
As an overload protection component for motors, the thermal relay has been widely used in production due to its small size, simple structure, and low cost.