Overload Relays
SIEMENS overload relays up to 100A have been designed for inverse-time delayed protection of loads with normal starting against excessive temperature rises due to overload or phase failure. An overload or a phase failure result in an increase of the motor current beyond the set rated motor current. In electronic overloads, this current rise is detected by the current transformers integrated into the devices and evaluated by corresponding electronic circuits which then output a pulse to the auxiliary contacts. Via heating elements in thermal overloads, this current rise heats up the bimetal strips inside the device which then bend and as a result trigger the auxiliary contacts by means of a tripping mechanism. The auxiliary contacts then switch off the load by means of a contactor.
