Bimetallic switch

A bimetallic switch is a control engineering component which causes a certain action once a defined temperature is reached, e.g. switching off a process in order to avoid overheating. It is based on the fact that under changing thermal conditions every metal expands or contracts according to a fixed thermal expansion coefficient. Hence the bimetal, a component made of two connected strips of different metals (e.g. steel and zinc), bends when the temperature changes. Once the bending strain reaches the limit defined by the designer of the switch, the bimetallic switch is activated.

The bimetallic switch is defined by its nominal operating temperature. They are available as normally open or normally closed devices. In case of exceeding the nominal operating temperature, the (load) electrical circuit is opened or closed depending on the version. The change enables, for example, the starting of a fan, or the activation of an alarm. They limit the temperature of equipment or parts, and automatically reset after cooling. Heat transfer is possible from all sides by convection, radiation or conduction in gaseous or solid media.