This paper describes an improved model of rotating loads in complex load areas. The first section of the paper concentrates on the theoretical aspects of load modeling in harmonic penetration studies with a particular reference to the rotating part of the load. The second section illustrates the results achieved from the experimental surveys conducted both in the laboratory and at a major industrial customer, in order to validate the model proposed in the field. The third section describes the calibration stage of the proposed model based on results from a statistical survey conducted at manufacturers on parameter variation vs. frequency with a large sample of both LV and MV induction motors. Finally, some guidelines are also provided for a correct use of the proposed model in system studies concerning harmonic penetration within electric distribution networks.