A centrifugal switch is an electric switch that operates using the centrifugal force created from a rotating shaft, most commonly that of an electric motor or gasoline engine. The switch is designed to activate or de-activate as a function of the rotational speed of the shaft.
Perhaps the most common use of centrifugal switches is within single-phase, split-phase induction motors. Here, the switch is used to disconnect the starting winding of the motor once the motor approaches its normal operating speed. In this case, the centrifugal switch consists of weights mounted to the shaft of the motor and held near the shaft by spring force. At rest, levers attached to the weights press a low-friction, non-conductive plate against a set of electrical contacts mounted to the motor housing, closing the contacts and connecting the starting winding to the power source. When the motor reaches a speed near its normal operating speed, centrifugal force overcomes the spring force and the weights swing out, raising the plate away from the electrical contacts. This allows the contacts to open and disconnects the starting winding from the power source; the motor then continues operating solely using its running winding. Motors using such a centrifugal switch make a distinct clicking noise when starting and stopping as the centrifugal switch opens and closes.