General purpose AC motors are electric motors driven by alternating current. AC motors require less maintenance than DC motors because they use a rotating magnetic field that does not require brushes. Some AC motors are dual wound, allowing them to operate at more than one voltage, providing more flexibility. The speed of a standard AC motor is determined by the power supply frequency and the number of electric magnetic poles in the motor. Single-phase AC motors are used with single-phase power typically found in homes. Three-phase AC motors work on three-phase electrical power, which is commonly found in large scale industrial applications. Three-phase IEC metric motors have metric dimensions and work on AC power.