The efficiency of electrical complexes depends directly on the level of power supply system reliability, which comprises extensive and branched distribution networks. A complex of single-phase ground fault (SPGF) relay protection and automation devices (RPA) is used to reduce the economic losses from the failure of the electrical receivers’ distribution networks. This paper presents a study of the protection sensitivity factor, taking into account the influence of the network capacity and the resistance during a fault. The results of this study determined the minimum permissible values of the sensitivity factor that ensures the stable operation of the protection device. This was achieved by taking into account the influence of the transient resistance at the point of short circuit. The practical significance of the study is as follows: the obtained characteristics will allow for the development of new functional logic circuits for SPGF protection. The practical implementation of the obtained results will allow for the following: to increase the sensitivity and selectivity of current non-directional protections in conditions of incomplete short circuits; to ensure the reliable functioning of technological equipment and responsible consumers; to reduce the level of electrical injuries of service personnel; and to reduce economic losses associated with the repair of damaged electrical receivers.