30 CFR § 75.700-1
Approved methods of grounding.
Metallic sheaths, armors and conduits in resistance grounded systems where
the enclosed conductors are a part of the system will be approved if a solid
connection is made to the neutral conductor; in all other systems, the
following methods of grounding will be approved:
(a) A solid connection to a borehole casing having low resistance to
(b) A solid connection to metal waterlines having low resistance to
(c) A solid connection to a grounding conductor, other than the
neutral conductor of a resistance grounded system, extending to a low
resistance ground field located on the surface;
(d) Any other method of grounding, approved by an authorized
representative of the Secretary, which ensures that there is no difference in
potential between such metallic enclosures and the earth.