The appraisal of the response of distribution networks to the excitation of lightning electro magnetic pulse (LEMP) requires the availability of accurate models of LEMP-illuminated lines. These models should be able to take into account the presence of shielding wires or neutral conductors and of their relevant groundings. Aim of this paper is the estimation of the influence of the line grounding, with particular reference to the grounding electrode model, on the calculated values of lightning-induced voltages in overhead power distribution lines.