Supply Voltage upto 550 V.* Dual Voltage motors.* Wider operating voltages e.g. + 10%, or + 6% to -15%* Supply frequency 60 Hz. - 25 Hz.* Wider frequency tolerance + 5%* Lower synchronous speeds, like 500 & 375 rpm.* 2 or 3 speed pole changing motors.* Motors with higher class of insulation ( class F or H )* Motors with thermal protection.