The thermal overload relay is an overload relay that uses the principle of current thermal effect and uses an electric heat sensitive bimetal as a sensitive component, also known as a thermal relay. The so-called electric heat-sensitive bimetal is obtained by heating and rolling two kinds of alloys with large difference in linear expansion coefficients. When heated, the bimetal is bent from the high expansion layer (active layer) to the low expansion layer (passive layer). When the current is too large (beyond the set value), the component acts due to "hot", so that its interlocking break contact cuts off the power of the controlled circuit and the protected device.
Thermal overload relays are used for motor overload protection and are available in a variety of versions. The thermal overload relay is easy to install and use, has full functions and low cost, and has been proven to be able to reliably protect the motor, so it has always played an important role.