The term ELECTRICAL CONTRACTOR, as used in this article, shall mean any person engaged in the business of installing or altering, by contract, electrical equipment for the utilization of electricity supplied for light, heat or power, not including radio apparatus or equipment for wireless reception of sounds and signals, conductors and other equipment installed for or by public utilities, including common carriers which are under the jurisdiction of the Illinois Commerce Commission, for use in their operation as public utilities; but the term ELECTRICAL CONTRACTOR does not include employees employed by such contractor to do or supervise such work.