The correct answer is: C. 80 to 90
A centrifugal switch is a device that is used to disconnect the auxiliary winding of a motor when the motor reaches a certain speed. This is done to prevent the auxiliary winding from overheating. The auxiliary winding is used to start the motor, but it is not needed once the motor is up to speed.
The centrifugal switch is typically located on the motor shaft, and it consists of a weight that is attached to a lever. When the motor starts, the weight is pulled down by centrifugal force, and the lever moves to disconnect the auxiliary winding.
The centrifugal switch is typically set to disconnect the auxiliary winding at about 80 to 90% of synchronous speed. This means that the auxiliary winding will be disconnected when the motor is running at about 80 to 90% of its maximum speed.
The other options are incorrect because they do not represent the typical range at which a centrifugal switch disconnects the auxiliary winding.