Of all the ground faults that can occur in medium-voltage networks from the standpoint of human and equipment safety, the most problematic is a ground fault in a medium-voltage/low-voltage substation. The grounding system of a lowvoltage network is directly connected to the grounding electrode of the substation. Therefore, each increase in the potential of the grounding electrode of the substation is transmitted directly via the neutral conductor into the customer’s installation. For these reasons, in this article a detailed investigation is presented of the problem of determining the neutral conductor voltage in a low-voltage network during a ground fault at the medium-voltage level in a supply substation that is an element of a medium-voltage network with an isolated neutral point (star point). A computer model is presented for the analysis of the neutral conductor voltage in actual distribution networks. Two characteristic distribution networks located on karstic terrain are analyzed. The results obtained are compared to the results of measurements.