The working principle of universal transfer switch is mainly to drive the contact system through the operating mechanism to realize the on-off control of the circuit. Specifically, when the operator rotates the handle, the rotating shaft and gears of the operating mechanism will drive the movable contact to move and contact or separate from the static contact, thus realizing the switching of the circuit. In this process, the contact pressure spring ensures the contact pressure between the movable contact and the static contact to ensure the stable connection of the circuit.