The function of the CMD is to monitor the
main contacts of a contactor against welding. For this the
control voltage of the contactor is compared with the state
of the main contacts which is reliably monitored using a
mirror contact (IEC EN 60947-4-1 Appendix F). If the coil is
de-energized and the contactor does not drop out the CMD
trips the upstream circuit-breaker/motor-protective
circuit-breaker/disconnect switch via an under voltage
release.
