The current transformer in ET-N* type detects the main circuit current,deals with overcurrent protection, and protects the load equipment. Sincethe applicable frequency of the built-in current transformer is 50/60Hz, ifthe power frequency decreases (inverter operating frequency is low), theiron core of the current transformer is saturated and only small signal canbe detected against the main circuit current, and the operatingcharacteristics of the ET-N* type will change. For the reasons describedabove, it is not possible to drive the motor with the inverter power supplysince it can not protect the motor.