An actuator assembly (22) for an electrical power switch apparatus, the actuator assembly (22) having a housing (24) and a plunger (30) positioned within the housing (24) where the plunger (30) is movable between a set position and an actuated position. The plunger (30) includes a compression spring (38) to provide a pre-load thereto that biases the plunger (30) away from the set position and toward the actuated position. A magnet (42) contained in the housing (24) and positioned proximate to the plunger (30) establishes a magnetic force which overcomes the pre-load of the compression spring (38) and maintains the plunger (30) in a set position. A coil assembly (46), that when energized, produces an electromagnetic force which bucks the magnetic force established by the magnet (42) allowing the plunger (30) to be propelled by the compression spring (38) to the actuated position. A screw (54) extends through an opening (56) in the plunger (30) for engagement with the compression spring (38) so that rotation of the screw (54) results in the adjustment or calibration of the pre-load of the compression spring (38).