External DC Overcurrent Electronic Trip Unit for Circuit Breaker

Disclosed is a DC circuit breaker including at least one contact configured to be coupled between a source of DC power and a DC load and a method of controlling the closed and open state of the contact. The DC circuit breaker includes a thermomagnetic trip circuit and an electronic trip circuit. The electronic trip circuit is responsive to a sensed level of DC current flowing in the contact in a closed state for accumulating an indication of the total time the DC current is sensed. The accumulated indication of the total time the DC current is sensed is compared to a predetermined value or level and, in response to the accumulated indication exceeding the predetermined value or level, the contact is caused to switch from a closed state to an open state.