What is the function of the switch that opens when a split phase motor has almost reached full speed?

The function of the switch that opens when a split phase motor has almost reached full speed is to disengage the starting mechanism of the motor to allow it to operate efficiently. This switch is commonly referred to as the start switch. In a split phase motor, the start switch is activated when power is first applied, enabling the auxiliary winding to provide the necessary phase shift for starting the motor.

Once the motor accelerates to a certain speed, the start switch opens, disconnecting the starting winding from the circuit. This is essential because if the starting winding were to remain engaged during normal operation, it could become subject to excessive overheating and could lead to motor failure. Consequently, the precise operation of this switch ensures safe and efficient functioning of the motor by transitioning from the start phase to the run phase seamlessly.

While the other options mention types of switches, they do not accurately describe the specific function of disengaging the starting mechanism once the split phase motor reaches operational speed.