Abstract: At present, there exist different understandings of the functions of the earthed protection device. Through analysis and calculations, this paper suggests that the main function of such device is to provide protection against the human indirect touch of 6kV network and that the protection against the direct touch can notbe guaranteed. In the neutral point effective ground system, the permissible touch voltage is 50 V (on the ground), which serves as the main basis for the determination of the actuation value of the device. To ensure human safety, the safety current of the human body should not be greater than 30 mA in the surface and underground conditions of mines. To ensure the reliability of the power supply to the open-pit mines, it is not only necessary but also possible to achieve the longitudinal and transversal selectivity of the earthed protection device in the power networks of mines. This paper presents the selective protection scheme for reference by the design engineers.