What does the start relay disconnect when the motor reaches about 2/3 of its full speed?

The correct response indicates that both the start capacitor and the start relay are disconnected when the motor reaches about 2/3 of its full speed. This is a fundamental aspect of single-phase motor operation, particularly in systems using a capacitor start motor.

When the motor begins its cycle, the start capacitor provides the necessary extra phase shift to allow the motor to start. As the motor starts up and reaches a certain speed, specifically around 2/3 of its full speed, the start relay detects this increase in speed. The primary function of the relay is to disconnect the start capacitor from the circuit at this point. This is to ensure that the capacitor does not remain in the circuit longer than needed, which could lead to overheating or damage.

In conjunction with this, the relay itself is designed to open the circuit, effectively disengaging the components that are no longer required for maintaining operation once the motor is running at its normal speed. This process is important for the efficiency and longevity of the motor. If the start capacitor and relay were not disengaged, it could lead to operational issues or failure of the motor.

Thus, the correct answer reflects an understanding of how single-phase motors utilize a start relay and capacitor to transition from starting to running conditions efficiently.