30 C.F.R. § 75.521 Lightning arresters; ungrounded and exposed power conductors and telephone wires.
Title 30 - Mineral Resources
Each ungrounded, exposed power conductor and each ungrounded, exposed telephone wire that leads underground shall be equipped with suitable lightning arresters of approved type within 100 feet of the point where the circuit enters the mine. Lightning arresters shall be connected to a low resistance grounding medium on the surface which shall be separated from neutral grounds by a distance of not less than 25 feet. [38 FR 4975, Feb. 23, 1973]
Title 30: Mineral Resources
PART 75—MANDATORY SAFETY STANDARDS—UNDERGROUND COAL MINES
Subpart F—Electrical Equipment—General
§ 75.521 Lightning arresters; ungrounded and exposed power conductors and telephone wires.
