Which statement best describes a capacitor-start induction-run motor?

Which statement best describes a capacitor-start induction-run motor?

• A. It has a start winding and a run winding, with a capacitor in series with the start winding to create phase shift for starting torque, and a centrifugal switch to disconnect the start winding at about 75% of rated speed
• B. It has only a run winding and no starting winding
• C. The capacitor is permanently connected in series with the run winding
• D. It is not used for starting torque

Answer: (A)

A capacitor-start induction-run motor uses both a start winding and a run winding. To get enough starting torque, the current in the start winding must be shifted in phase relative to the run winding. Putting a capacitor in series with the start winding accomplishes this phase shift, creating a rotating magnetic field that starts the motor. A centrifugal switch then disconnects the start winding (and the capacitor) once the motor reaches roughly 75% of its rated speed, leaving only the run winding in circuit for normal operation. This arrangement provides high starting torque but clean, efficient running once up to speed. The other scenarios don’t provide the needed starting torque or rely on the capacitor in the wrong place for a capacitor-start design.

A capacitor-start induction-run motor uses both a start winding and a run winding. To get enough starting torque, the current in the start winding must be shifted in phase relative to the run winding. Putting a capacitor in series with the start winding accomplishes this phase shift, creating a rotating magnetic field that starts the motor. A centrifugal switch then disconnects the start winding (and the capacitor) once the motor reaches roughly 75% of its rated speed, leaving only the run winding in circuit for normal operation. This arrangement provides high starting torque but clean, efficient running once up to speed. The other scenarios don’t provide the needed starting torque or rely on the capacitor in the wrong place for a capacitor-start design.