C.F.R. » Title 30 » CHAPTER I—MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR › SUBCHAPTER K—METAL AND NONMETAL MINE SAFETY AND HEALTH › PART 56—SAFETY AND HEALTH STANDARDS—SURFACE METAL AND NONMETAL MINES › Subpart K—Electricity

30 C.F.R. § 56.12069

Lightning protection for telephone wires and ungrounded conductors

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Each ungrounded power conductor or telephone wire that leads underground and is directly exposed to lightning shall be equipped with suitable lightning arrestors of approved type within 100 feet of the point where the circuit enters the mine. Lightning arrestors shall be connected to a low resistance grounding medium on the surface and shall be separated from neutral grounds by a distance of not less than 25 feet.