Safety relay circuit for large power contactors

摘要

An apparatus and method for monitoring main contacts and auxiliary contacts of a power contactor is disclosed. The apparatus includes four circuits, the first of which has an on state in which a coil of the contactor is energized, and an off state. The first circuit switches from the off state to the on state when a power source is electrically connected to the first circuit if an additional signal is also present, and then remains in the on state until the power source is disconnected. The second circuit prevents the additional signal from being received by the first circuit when the auxiliary contact is in a position indicating that one of the main contacts is welded. The third circuit causes the first circuit to be disconnected from the power source when the fourth circuit provides a signal indicating that one of the auxiliary contacts is welded.