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The paper presents an original analytical procedure for the determination of the ground fault current distribution in the cases when a feeding line is composed of three single-core cables. The procedure takes into account the existence of all three cable sheaths as the return path for the ground-fault current. The reduction factor for these types of cables as given by the cable manufacturer takes into consideration only the existence of the metal sheath of a faulted single-core cable. As a consequence of that, the estimations of the safety conditions (step and touch voltages) on the grounding systems of the supplied stations are too severe. For the high-voltage cables, a certain, sufficiently low reduction factor achieved by an increase of the sheath cross-section can be demanded from the manufacturer. In both cases, too conservative values for the reduction factor lead to unnecessary expenditures. The quantitative analysis performed in this paper shows that the reduction factor for three single-core cables belonging to the same line is significantly lower in comparison to the situation when each of these cables is treated separately.