A circuit breaker (10, 12) includes a sensing circuit (48, 50, 52), a control circuit (46), an actuator (42), an operating mechanism, and an interlock mechanism (70, 94). The sensing circuit (48, 50, 52) is configured to generate the sense signal representative of a power signal flowing through a power circuit (54, 56, 58). The control circuit (46) has a frame (74, 76) and is configured to receive the sense signal and to provide a trip signal on a first terminal (68). The actuator (42) is external to the control circuit frame (74, 76) and has a second terminal (98) coupleable to the first terminal (68). The actuator (42) is configured to receive the trip signal on the second terminal (98). The operating mechanism is coupled to the actuator (42) and is configured to open and close the power circuit in response to actuation of a lever (36). The actuator (42) is configured to actuate the lever (36) in response to the trip signal. The interlock mechanism (70, 94) is coupled to at least one of the actuator (42) and the operating mechanism and is configured to actuate the lever (36) when the first terminal (68) is not coupled to the second terminal (98).