The transition over resonance of a vibratory system, excited by rotating unbalances, is important in terms of the maximum vibrational amplitude produced and the power demand on the drive for the cross-over. For drive by AC 3 phase squirrel cage induction motors, the phenomenon is studied with the help of nondimensional paramaters. It is observed that, for low damping, the transitional power demand can be many times more than that at the steady state. A procdure is outlined for the selection of a suitable drive motor to meet this demand. The steady state power requirements of the vibrator is also clarified. An expression is also given for estimating the maximum amplitude of vibration during the cross-over. © 1986.