Single-phase motors are the most common fan motors, as they are in most smaller fans and operate off alternating current (AC) power. Each cycle dips and peaks as electricity runs through it, making it a motor which runs off a low amount of electricity, costing little money and putting little strain on the motor's mechanical operations. This allows these motors to last for a long period of time without breaking down. These motors can also be converted to different phases, but it is usually less expensive to just buy a larger motor than convert a single-phase motor.
Split-phase motors are used for larger industrial fans, or fans in larger pieces of equipment which have a medium amount of electricity running through them. These motors have start and run windings, both of which are energized when the motor is started, allowing a large amount of durability over a longer period of time. However, due to the fact these motors are often used with heavy-duty pieces of equipment which are put under increased strain, many of these split-phase motors have automatic shut-offs so they do not burn out and have to be replaced.
Capacitor-start motors are used almost solely for fans which are part of larger pieces of industrial equipment. This motor has a capacitor in a series with a starting winding. It provides more than double the torque with less current then the split-phase motor, allowing it to start and run effectively with heavy loads and increased strain. There is also a safety shut-off on many of these capacitor-start fan motors so they don't burn out and become a costly replacement part. These motors are supposed to shut down once they have reached 75 percent of their load capacity, though this can be disabled.