Section 77.701-1 - Approved methods of grounding of equipment receiving power from ungrounded alternating current power systemsFor purposes of grounding metallic frames, casings and other enclosures of equipment receiving power from ungrounded alternating current power systems, the following methods of grounding will be approved:
(a) A solid connection between the metallic frame; casing, or other metal enclosure and the grounded metallic sheath, armor, or conduit enclosing the power conductor feeding the electric equipment enclosed;(b) A solid connection to metal waterlines having low resistance to earth;(c) A solid connection to a grounding conductor extending to a low-resistance ground field; and,(d) Any other method of grounding, approved by an authorized representative of the Secretary, which insures that there is no difference in potential between such metal enclosures and the earth.