Features of electromagnetic field of a cable as a source in the CSAMT method used for the exploration and monitoring tasks solution are analyzed. For the CSAMT modification with a powerful source and long-range action of thousands kilometers the waveguide zone of the cable is allocated. Differences of the electromagnetic field structure in the waveguide zone are analyzed in comparison with the usually allocated near-field, intermediate and far-field zones. Technique of CSAMT data correction in the intermediate zone and practical example of its using are described.