My motor is rated at 1725 RPM at 60hz. Standard US electrical is 60hz. That would be the normal operating frequency. 3 phase inverter motors controlled by a VFD can be run over or under the base frequency to control the speed. Because my motor is a low cost import inverter motor the general consensuses is that it could be run up to 120hz which would double the speed of the motor. I currently have it set to 105hz max which gives me 6000 rpm at the spindle with the pulley ratio.