A circuit breaker comprising: - a housing; - a circuit breaker mechanism having a tripped state and an untripped state; - a switch handle having an off position and an on position and configured to toggle the circuit breaker mechanism between the tripped state and the untripped state; and, - an actuator module adapted to move the switch handle from the off position to the on position, wherein the actuator module is a self-contained modular assembly adapted to be attached to and removed from the housing as a unit, having a channel formed therein, characterized in that the housing has a channel formed therein, the channel being defined by at least two side walls, each having a detent formed therein, the detents facing each other with the channel therebetween; and in that the actuator module comprises: • at least two legs, each having an outwardly extending protrusion formed thereon, the protrusions facing away from each other and being sized, shaped and located to engage the detents formed in the side walls of the channel of the housing when the actuator module is mounted within the channel; and • a locking clip moveable from an unlocked position, in which flexing of the legs toward each other is permitted, and a locked position, in which flexing of the legs toward each other is limited or prevented, such that when the actuator module is mounted within the channel so that the protrusions engage the detents and the locking clip is in the locked position, removal of the actuator module is inhibited, the locking clip comprising a generally flat member generally defining a plane, wherein the locking clip is slideable within the plane from the unlocked position to the locked position and wherein the locking clip is further moveable from the locked position to the unlocked position so as to facilitate removal of the actuator module from the channel of the housing. - a housing; - a circuit breaker mechanism having a tripped state and an untripped state; - a switch handle having an off position and an on position and configured to toggle the circuit breaker mechanism between the tripped state and the untripped state; and, - an actuator module adapted to move the switch handle from the off position to the on position, wherein the actuator module is a self-contained modular assembly adapted to be attached to and removed from the housing as a unit, having a channel formed therein, • at least two legs, each having an outwardly extending protrusion formed thereon, the protrusions facing away from each other and being sized, shaped and located to engage the detents formed in the side walls of the channel of the housing when the actuator module is mounted within the channel; and • a locking clip moveable from an unlocked position, in which flexing of the legs toward each other is permitted, and a locked position, in which flexing of the legs toward each other is limited or prevented, such that when the actuator module is mounted within the channel so that the protrusions engage the detents and the locking clip is in the locked position, removal of the actuator module is inhibited, the locking clip comprising a generally flat member generally defining a plane, wherein the locking clip is slideable within the plane from the unlocked position to the locked position and wherein the locking clip is further moveable from the locked position to the unlocked position so as to facilitate removal of the actuator module from the channel of the housing.