Fault current protective switch - is opened when not all conductors are correctly connected to switch terminals

摘要

The middle or the neutral conductor is used as protective conductor, and its terminal lies pref. between the switch contact on the mains side, and following it a sum current transformer or electric lock. A switch is opened when voltage between the middle, neutral or protective conductor and one of the outer conductors is appreciably greater than the nominal voltage between an outer conductor and earth. The fault current switch opens when one or two outer conductors, and the middle or neutral conductor, are correctly connected to the fault current switch terminals, and the protective conductor branching off from the middle conductor does not pass through its own transformer. The transformers secondary winding directly trips the switch through a trip coil, or indirectly through the sum current transformer, when the protective conductor current exceeds a threshold, pref. still in a not dangerous range.