Abstract: A circuit interrupter comprising an automatic trip unit connected to an interrupting unit for tripping the interrupting unit to open separable contacts in response to an overcurrent, the automatic trip unit being a replaceable unit selected from a plurality of differing types of trip units including an electronic trip unit and a thermally responsive electromagnetic trip unit.

Abstract: A multi-pole circuit interrupter having a first pole unit provided with an operating mechanism and a second pole unit provided with no operating mechanism. Each of the pole units comprises a movable contact, a stationary contact, and a contact arm assembly for supporting the movable contact of the respective pole unit including a first contact arm and a second contact arm pivotally supported by a common pin. The first contact arm in the first pole unit have an elongated guide hole extending in a direction of movement of the movable contact and is directly connected to the operating mechanism. The second contact arm has an elongated hole extending substantially in a longitudinal direction thereof. A spring-biased sliding pin extends through the elongated hole and the guide hole.