There are three types of AC motors that are used to drive fans: 3-phase motors, permanent split capacitor (PSC) motors, and shaded pole motors. The type of motor required for a given application will be dictated by the input voltage available in the application and the amount of power required to drive the fan. PSC and shaded pole motors will be used for single phase AC input. Shaded pole motors are suited for low power fans. When a more powerful single phase fan is used, a PSC motor will be required. Shaded pole motors are more cost effective but are limited by their lower power. PSC motors require an external capacitor for proper operation. A 3-phase AC motor is needed when the application has 3-phase AC input.