Thermal protectors / Bimetallic switches

The thermal protectors or bimetallic switches are used for automatic temperature monitoring and are embedded in the winding heads of the motors.

In contrast to the PTC thermistors, bimetallic switches do not need a monitoring relay. They limit the heating of equipment or parts and reset themselves again automatically after cooling.

The bimetallic disc in the switches snaps abruptly from its convex to the concave state when temperature increases to a maximum permitted value. The contact is moved away vertically from the contact plate. The contact is now open (type S01 / S06). With NO- contact (normally open – type S08), the previously opened contact closes and activates a current circuit. Thus, e.g. signalers are switched on. Only after significant cooling does the bimetal disc automatically return to its original position.