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An over-center handle mechanism is provided to operate electrical equipment, such as a switch or breaker, housed in an electrical enclosure. The over-center handle mechanism includes an adaptor knob, a rotary actuator and a spring. The adaptor knob interfaces with the electrical equipment. The rotar

An over-center handle mechanism is provided to operate electrical equipment, such as a switch or breaker, housed in an electrical enclosure. The over-center handle mechanism includes an adaptor knob, a rotary actuator and a spring. The adaptor knob interfaces with the electrical equipment. The rotary actuator is connected to the adaptor knob, and includes a cam. A through-door handle is used to operate the rotary actuator, which in turn operates the electrical equipment via the adaptor knob. To optimize an angular torque feeling at the through-door handle, the over-center handle mechanism further includes the spring to provide an opposing force against movement of the cam of the rotary actuator, and thus, the through-door handle. A solid lubricant of PTFE may also be provided as an interface between the cam and the spring to reduce friction therebetween.

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1. An over-center handle mechanism to operate electrical equipment housed in an electrical enclosure, the over-center handle mechanism comprising: an adaptor knob to interface with the electrical equipment;a rotary actuator connected to the adaptor knob and including a cam having an outer cam surfac

1. An over-center handle mechanism to operate electrical equipment housed in an electrical enclosure, the over-center handle mechanism comprising: an adaptor knob to interface with the electrical equipment;a rotary actuator connected to the adaptor knob and including a cam having an outer cam surface, the rotary actuator being further connectable to a through-door handle for operating the electrical equipment via the rotary actuator from outside of the electrical enclosure; anda spring, positioned adjacent to the outer cam surface of the cam, to provide an opposing force against rotation of the cam of the rotary actuator. 2. The over-center handle mechanism of claim 1, wherein the spring includes a deflectable extending arm to apply a spring force on the outer cam surface of the cam of the rotary actuator. 3. The over-center handle mechanism of claim 2, wherein the spring includes two deflectable extending arms which are substantially parallel to each other, the cam being arranged between the two deflectable extending arms. 4. The over-center handle mechanism of claim 3, wherein each deflectable extending arm has a PTFE sleeve to interface with the outer cam surface of the cam. 5. The over-center handle mechanism of claim 3, wherein the cam has a substantially quadrilateral cross-section, which is arranged between the two deflectable extending arms of the spring. 6. The over-center handle mechanism of claim 2, further comprising: an adaptor knob shaft to connect the adaptor knob to the rotary actuator; anda housing mountable in the electrical enclosure, the housing having a first side and an opposing second side, the adaptor knob being arranged on the first side of the housing, the rotary actuator being arranged on the second side of the housing, the adaptor knob shaft extending through a through-hole in the housing to connect the adaptor knob to the rotary actuator. 7. The over-center handle mechanism of claim 6, wherein the spring has a closed end, and a free end with two deflectable extending arms, the closed end being supported on the second side of the housing. 8. The over-center handle mechanism of claim 7, wherein the closed end of the spring is bent at an angle relative to the free end, and the second side of the housing includes a spring slot to receive the closed end of the spring. 9. The over-center handle mechanism of claim 6, wherein the housing comprises a plate. 10. The over-center handle mechanism of claim 3, wherein the rotary actuator further includes: a first end having a first wall; anda second end opposite the first end, the second end having a second wall spaced apart from the first wall, the cam forming a bridge between the first wall and the second wall, the two deflectable extending arms arranged in a space between the first and second walls and arranged to apply a spring force against the outer cam surface from opposite sides of the cam. 11. The over-center handle mechanism of claim 1, wherein the spring adjusts an angular torque characteristic of the rotary actuator when operating the electrical equipment. 12. The over-center handle mechanism of claim 11, wherein the electrical equipment comprises an electrical switch, a circuit breaker or relay. 13. The over-center handle mechanism of claim 1, further comprising an adaptor knob shaft to connect the adaptor knob to the rotary actuator, wherein the rotary actuator further includes a socket to receive the adaptor knob shaft. 14. The over-center handle mechanism of claim 13, wherein the knob connector shaft includes a latch, and the cam includes a latch slot to receive the latch when the adaptor knob shaft is engaged in the socket of the rotary actuator. 15. The over-center handle mechanism of claim 14, wherein the adaptor knob shaft includes a pair of the latches, and the cam comprises two spaced apart U-shaped cam portions which form two latch slots therebetween to receive a respective latch from the pair of the latches. 16. The over-center handle mechanism of claim 13, wherein the cam has an asymmetrical cross-sectional shape to provide different angular torque profiles when operating the rotary actuator in a clockwise direction versus counter-clockwise direction. 17. The over-center handle mechanism of claim 13, wherein the dimension of the socket is configured to control an over-travel range in a clockwise or counter-clockwise direction for the rotary actuator. 18. The over-center handle mechanism of claim 1, wherein the rotary actuator further includes a shaft adaptor to provide for connection to the through-door handle. 19. The over-center handle mechanism of claim 1, further comprising the through-door handle.