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 thermally responsive shape memory effect (SME) element (4) is positioned adjacent a fixed heater (40) for moving away from the heater to a switch actuating "memory" position as current induced temperature increases, thereby establishing changes in heat transfer coefficient between the heater (40) and thermally responsive element (4) for each increment of movement. An intermediate switch actuating lever (22) is carried on a movable range adjustment lever (16) to vary pretravel of an SME driven plunger (12). The SME element is resettable against a fixed stop (2c) for achieving accurate repetitive resetting of the device.

Abstract: A shape memory effect (SME) spring (20) is thermally responsive to currents sensed in itself or in a heater element (66) to pivot an actuator (16) against a bias spring (22) to operate a switch (32) in response to sensed currents above a given level. The actuator (16), bias spring (22) and SME spring (20) are carried by a pivotally mounted support beam (12) which is driven by an ambient temperature compensation mechanism (40,52) to change the amount of switch actuating travel of the actuator (16) in response to ambient temperature changes. The ambient temperature compensation mechanism comprises a pivotal lever (42,54) translationally coupled (42a,54a, 12b) to the support beam (12). In a first embodiment the lever (42,54) is driven by a temperature sensitive bimetal (46), and in a second embodiment it is driven by a temperature sensitive SME spring (58) biased to a reference position by an adjustable (62) spring (60).