Why thermal relay can only be overload protection, and can not be short-circuit protection?
Thermal relay structure is different from the overload through the relay current increases, the relay inside the protective device heat, heat to a certain degree of relay action, to protect the motor.
As the bimetallic heat deformation takes a period of time, and the circuit is instantaneous current becomes very large, and bimetallic can not move in time, so the thermal relay can not achieve the role of short circuit protection.
Thermal relay is when the current is greater than the set current, the internal bimetallic heat distortion, so that the auxiliary contact action to protect
