Molded case circuit breaker with a movable lower electrical contact

Abstract

A molded case circuit breaker includes a movable lower electrical contact assembly having a formed stationary conductor member, a movable lower contact arm, a lower contact secured to the upper end of the movable lower contact arm for physically and electrically contacting separate upper electrical contacts, and a lower contact arm torsion spring. An integral longitudinal end of the stationary conductor member extends from the base of the circuit breaker to form an external terminal of the circuit breaker. The opposite longitudinal end of the stationary conductor member receives a rotatable pin fixedly secured to the movable lower contact arm for rotation therewith. The lower contact arm torsion spring has an elongated torsion spring arm disposed in contact with an elongated inclined cam surface located on the underside of the movable lower contact arm to bias the lower contact secured thereto into engagement with the upper electrical contact. A groove is provided along the elongated cam surface of the lower contact arm within which a torsion spring arm of the torsion spring may be releasably received. Upon the occurrence of a high level short circuit or fault current condition, as the movable lower contact arm separates from the upper electrical contact the torsion spring arm moves along the elongated inclined cam surface of the arm which is so contoured that the force of the torsion spring opposing the movement of the movable lower contact arm is minimized, thereby enabling the rapid separation of the upper and lower electrical contacts.