The validity of the Rusck coupling model and its equivalence to the model by Agrawal, Price and Gurbaxani have already been demonstrated for the case of a perfectly conducting ground and a vertical stroke channel. However, in spite of its popularity, the restriction of an infinite soil conductivity imposes a strong limitation on the use of the model for the analysis of realistic situations. In this paper, a procedure is proposed to extend the Rusck's model to the case of a finite ground conductivity so as to enable the calculation of lightning-induced transients on overhead lines taking into account the soil electrical parameters. The validity of the model is demonstrated through comparisons of simulation results with measured lightning-induced voltages and currents obtained from scale model and rocket-triggered lightning experiments.