Thermal overload relays are economic electromechanical protection devices for the main circuit
Working Principle ofThermal Overload Relay
A thermal relay works depending upon the above-mentioned property of metals. The basic working principle of thermal relay is that, when a bimetallic strip is heated up by a heating coil carrying over the current of the system, it bends and makes normally open contacts.
Construction of Thermal Relay
The construction of a thermal relay is quite simple. As shown in the figure above the bimetallic strip has two metals – metal A and metal B.