Program Policy Manual - VOLUME V - Mine Safety and Health ...

MSHA PROGRAM POLICY MANUAL VOLUME V
Subpart H Grounding
77.700-1 Approved Methods of Grounding
Approved methods of grounding the metallic enclosures of electric
equipment receiving power from ungrounded alternating-current
power systems are contained in Section 77.701-1.
Approved methods of grounding the metallic enclosures of electric
equipment powered from direct-current power systems are contained
in Section 77.701-2.
Subpart H does not specify approved methods of grounding the
metallic enclosures of stationary equipment receiving power from
low- and medium-voltage, solidly grounded alternating-current
systems. Nevertheless, Section 77.701 requires that such
enclosures be grounded by methods approved by an authorized
representative of the Secretary. An inspector shall not approve
any method of grounding that does not include a solid connection
to a grounding conductor which extends to the grounded point of
the power source. The grounded power conductor of a solidly
grounded alternating-current power system may serve as the
equipment grounding conductor only between the grounded point of
the power source and the grounded enclosure of the service
disconnecting means for a building or other stationary facility.
The grounded point of the power source and the metallic enclosure
of each service disconnecting means shall be connected to an
acceptable grounding medium such as metal waterlines having lowresistance
to earth, a low-resistance ground field, etc.
Subpart H does not specify approved methods of grounding the
metallic enclosures of portable or mobile equipment receiving
power from high-voltage systems since the requirements for
grounding such enclosures are specifically contained in Section
77.802.
This Section specifies approved methods of grounding metallic
sheaths, armors and conduits enclosing power conductors. The
approved methods of grounding listed in this Section are similar
in that they each require a solid connection to an acceptable
grounding medium. In resistance-grounded systems, the only
acceptable grounding medium is the grounded neutral of the system.
In other systems, an acceptable ground medium includes:
1. Metal waterlines having low-resistance to earth;
2. A low-resistance ground field; or
3. Any other grounding medium which ensures that there is no
difference in potential between the metallic enclosures
February 2003 (Release V-33) 185