Switches of the F series with a minimum size are very suitable for the installation in confined conditions. The switching principle consists of a central contact which opens or closes the circuit of the application when there is a temperature input by means of a pressure spring, and a thermo-bimetal snap-disc.

Due to the low mass, a very fast response of the switch is possible. The heat is thereby preferably absorbed by the round contact surface of the switch, and transmitted to the bimetallic element.

In addition to the direct protection of smaller electrical drives and devices with a rated power of up to approx. 750W, F series switches are often used as thermal sensors. In twin or triple configurations, they provide a triggering element in the control circuit for contactors, thus also able to thermally protect larger three-phase Motors.