External DC overcurrent electronic trip unit for circuit breaker

A DC circuit breaker comprising:

• at least one contact configured to be coupled between a source of DC power and a DC load;
• a thermomagnetic trip circuit operable in accordance with a first time-current curve that defines:
• a first time-current region (1TCR) where the contact, starting in a closed state, remains in the closed state in response to the contact being exposed to a combination of current and time in the 1TCR, and
• a second time-current region (2TCR) where the contact, starting in the closed state, switches to an open state in response to the contact being exposed to a combination of current and time in the 2TCR;
• and
• an electronic trip circuit operable in accordance with a second time-current curve that defines:
• a third time-current region (3TCR) where the contact, starting in the closed state, remains in the closed state in response to the contact being exposed to a combination of current and time in the 3TCR, and
• a fourth time-current region (4TCR) where the contact, starting in the closed state, switches to the open state in response to the contact being exposed to a combination of current and time in the 4TCR,
• wherein:
• each combination of current and time comprises a total time that DC current flows in the contact and a level of the DC current flowing in the contact at said total time,
• at least a part of the 1TCR and a part of the 4TCR overlap and have first time-current pairs or points in common, and
• at least a part of the 2TCR and a part of the 3TCR overlap and have second time-current pairs or points in common.