Mine grounding, factors that prohibit a universal grounding solution

A uniform grounding procedure interacts with MSHA, OSHA and the NEC over a wide range of articles. Those that encompass personal safety and GFCI requirements address ampacities of 7 mA. Those that address system fault currents and resistance grounding deal with excitation ampacities that are 5 to 7 orders of magnitude higher. The need for a sound grounding technique is quite clear. Sooner or later the system will be exposed to a major system fault that will stress the electrical distribution system to its design limits and place the operating staff in extreme danger. The authors discuss the following aspects of mine grounding systems: personnel safety; possible range of local earth impedance; on-site ground impedance measurements; isolation of ground fields; and the electrical power distribution options