What would cause a pole 1200 rpm motor to spin at 1600 rpm given the supply voltage and frequency are correct?

A 1200 RPM motor is typically designed to operate at a specific synchronous speed determined by the supply frequency and the number of poles. If the motor is spinning at 1600 RPM while the supply voltage and frequency are correct, it may indicate that the motor is experiencing a phenomenon called "slip," which is reduced in this case, possibly due to a mechanical load being lighter than expected or a change in rotor design. Additionally, if the motor is a variable speed design or equipped with a drive that alters its speed characteristics, it could also be intentionally running at a higher RPM.