Operating principle [t-head2-nnp]

The CMD (Contactor Monitoring Device) monitors the main contacts of a contactor for welding. It compares the contactor control voltage with the state of the main contactors and indicates this reliably with a mirror contact (IEC EN 60947-4-1 Ann. F). If the contactor coil is de-energized and the contactor does not drop out, the CMD trips the backup circuit-breaker, motor-protective circuit-breaker or switch-disconnector via an undervoltage release.

The CMD also monitors the functioning of the internal relay using an additional auxiliary make contact of the monitored contactor. For this the auxiliary make and break contact is positively driven. The break contact is designed as a mirror contact.