—The electrical arc occurring in the sliding contact between the supply contact line and the current collector (pantograph) of an electrical locomotive is a fast transient phenomenon able to progressively degrade the line-to-pantograph contact quality and consequently the continuity of operation. A reliable tool for the arc event detection installed on each locomotive could allow a predictive maintenance of both contact line and locomotive pantograph, with a consequent improvement of the continuity of operation of the railway system. This paper represents the first step in the development of such a monitoring system. In detail, it provides a first electrical characterization of the sliding contact and, through an electrical model, it investigates the conductive effects on the overhead contact line.