At what approximate percentage of synchronous speed does a centrifugal switch operate in a split-phase motor?

In a split-phase motor, the centrifugal switch is designed to disconnect the start winding of the motor once it reaches an approximate percentage of synchronous speed. This is crucial for the motor’s proper operation, as the start winding is only needed to help bring the motor up to speed.

Operating around 75% of synchronous speed is ideal for the centrifugal switch to activate and ensure that the start winding is disengaged before the motor reaches a full operational speed. This timing is particularly critical to prevent overheating and potential damage to the windings, as the start winding is not built for continuous operation.

Substantially lower speeds, such as 50%, would not provide enough inertia for the motor to overcome starting challenges, hence the switch would still be engaged. Approaching 90% or 100% synchronous speed would delay disengagement unnecessarily, risking damage to the start winding due to prolonged engagement. Therefore, the optimal operation at around 75% efficiently balances the need for initial starting support while ensuring the safety and longevity of the motor components.