CFR > Title 30 - Mineral Resources > CHAPTER I—MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR > SUBCHAPTER O—COAL MINE SAFETY AND HEALTH (parts 70 to 90) > PART 75—MANDATORY SAFETY STANDARDS—UNDERGROUND COAL MINES > SUBPART H—Grounding (§75.700 to §75.706) > 75.703-2—Approved grounding mediums.

75.703-2—Approved grounding mediums.

For purposes of grounding offtrack direct-current machines, the following grounding mediums are approved:
(a) The grounded polarity of the direct-current power system feeding such machines; or,
(b) The alternating current grounding medium where such machines are fed by an ungrounded direct-current power system originating in a portable rectifier receiving its power from a section power center. However, when such a medium is used, a separate grounding conductor must be employed.