Abstract: A molded case circuit breaker wherein a movable contact arm (8) is operated between open and closed positions with a stationary contact (4b) by an operating mechanism which controls an overcenter toggle drive spring (12) and which is automatically openable upon sensing overload conditions by releasing a latched lever (10) for carrying the line of action of the drive spring (12) across the pivot (8a) of the movable contact arm (8). The current sensing trip means (16) for unlatching the latched lever (10) is formed of a shape memory effect alloy to provide a significant amount of travel of the latching end thereof in response to a narrow band of current thereby to insure release of the latch lever (10) without need for calibrating the breaker.

Abstract: A pair of heaters (16,18) are mounted within a breaker housing (2) in spaced relation to a temperature responsive actuator element (30) for indirectly heating that element in response to current flow in the heaters. Each heater is provided with a wiring terminal member (6,8) for selectively individually connecting one or the other heater in circuit with a branch circuit to be protected. One heater (16) is selected to generate greater amounts of heat than the other heater (18) when subjected to the same current levels.

Abstract: A heater strip (12) is disposed in spaced relation to a temperature responsive actuator element (20) for indirectly heating that element in response to current flow in the heater (12). An adjustable heat sink (22) is disposed in spaced proximity to the actuator element (20) for removing heat from the actuator element by radiation therefrom through air to the heat sink in a first position and adjustable to be in thermally conductive engagement with the actuator in a second position for increasing the efficiency of heat transfer from the actuator to the heat sink. Increased current flow in the protected branch circuit is required to cause the actuator (20) to attain its predetermined actuation temperature as the heat sink is adjusted to increase the efficiency of heat transfer between the actuator (20) and the heat sink.

Abstract: A residential or commercial circuit breaker of the narrow case type, typically having a width of 3/4 inch or 1 inch, is provided with a single-piece nonlaminated slot motor 102 mounted within the case 2 and around current carrying conductors 8 and 12 for concentrating magnetic repulsive force and boosting contact separation force. A dramatic increase in short circuit interruption capacity is achieved, at minimal cost.