Final answer:
The centrifugal switch opens at approximately 75% to 80% of the rated speed of the motor to transition from start to run winding.
Step-by-step explanation:
The centrifugal switch in an electric motor circuit opens at approximately 75% to 80% of the motor's rated speed. This switch is an essential component of a split-phase induction motor, used for starting the motor by shifting it from the start winding to the run winding. Once the motor reaches the rated speed, the centrifugal force pulls the weights in the switch outwards, eventually breaking the circuit and disconnecting the start winding. The exact percentage at which the switch opens can vary based on the motor design and application, but it generally occurs within this range to ensure smooth transition and avoid damage to the motor.