In this paper, a general model for voltage and currents induced by the primary and secondary field couplings in a multiconductor cable system buried in lossy earth, and illuminated by an external electromagnetic field is presented. Generalized form of equivalent transmission line equations (ETLEs) obtained from this model are presented, which could analyze many of the associated problems, involving the field couplings in underground transmission systems. These equations are then used to derive general solutions for the currents and potentials induced by the external fields along the underground conductors.