Thermal Overload Relays

Thermal overload relays are electronic components, which are often used in overcurrent, phase failure protection and 3-phase power imbalance protection for AC motors or other electrical equipment, circuit. As a type of overload protection component, thermal relay has wide applications in production due to its small size, simple structure and low price.

Thermal overload relay is composed of heating element, bimetal, contact and a set of transmission and adjustment mechanism. Relay coil is represented by a long box symbol in circuit. When the motor is overloaded, the current passing through the heating element exceeds the setting current, and the bimetallic sheet is heated up and bends away from the gusset, causing the normally closed contact to break. This will de-energize the contactor coil connected to the normally closed contact. The main contact of contactor is disconnected, and then the main circuit of motor is cut off, thus realizing overload protection function.