In mining, effective grounding means that the path to ground from circuits, equipment, or conductor enclosures is permanent and continuous and has carrying capacity ample to conduct safely any currents liable to be imposed upon it. The path to ground associated with high-voltage alternating-current systems will have impedance low enough to limit potential above ground to a maximum of 100 V during the flow of ground fault current and to facilitate operation of the circuit protective devices. On low-voltage systems the sustained voltage above ground, appearing on the frames of power utilizing equipment during existence of a ground fault, will not be greater than 35 V; except when ground circuit check systems requiring higher voltage are used, a maximum of 100 V for a duration of 0.2 s is permissible. When bonded or mechanically connected track is available, such track is considered the grounding medium for direct current equipment only.