A synchronous motor is an induction motor that operates directly from AC power or from a variable frequency drive (VFD), and rotates at an exact multiple of the line frequency (or set speed). Common synchronous induction motor speeds at 60 Hz are 1800 RPM (4-pole) and 3600 RPM (2-pole). A unique feature of the AC synchronous motor is that there is no rotor "slip." The rotating magnetic field in the stator and the magnetic field in the rotor are "locked" in step as long as the load on the output shaft is within nameplate ratings.