(a)
Grounding method. Lighting arrester grounding and all
grounding of circuits, equipment, or wire runways, which are intended to be a
permanent and effective protective measure shall be made in accordance with the
methods specified in §§
39.61-
39.70 (relating to methods of
protective grounding).
(b)
Circuits required to be grounded. Circuits installed in rooms
to which other than properly qualified electrical workmen have access, or in
rooms where nonelectrical processes are liable to distract the attention of the
electrical operator from the purely electrical operations, shall be permanently
grounded in accordance with §§
39.61-
39.70 except that the following
circuits are not required to be grounded:
(1)
Circuits on two-wire, direct-current systems.
(2) Circuits entirely unexposed to leakage or
induction from higher voltage circuits, either through overhead construction or
through transformers or other devices. It is recommended, however, that all
three-wire, not delta three-phase, circuits, even if unexposed, have their
neutrals grounded; and that multiphase circuits, even if unexposed where partly
used for lighting, be so arranged and grounded that the lighting circuits have
the lowest practical voltage ground.
(3) Circuits over 150 volts to ground.
Reference should be made to §
39.199 (relating to guarding or
isolating live parts).
(4) Electric
furnace and welding circuits. Reference should be made to §
39.263 (relating to guarding live
parts).
(c)
Grounding noncurrent-carrying metal parts. Under the hazardous
conditions given in this subsection, fixed electrical utilization equipment
shall, if practicable, have the exposed noncurrent-carrying metal parts, such
as frames of motors, cranes, cars, and switchboards, cases of transformers and
oil switches, and casings of wiring and conductors permanently grounded.
Reference should be made to §§
39.61-
39.70 and
39.281-
39.285. The following conditions
shall be considered hazardous:
(1) Operations
at voltages over 150 to ground, wherever equipment is located.
(2) Locations where explosives, inflammable
gas or inflammable flyings normally exist in dangerous quantities.
(3) Cases where exposed grounded surfaces,
such as metal frames of other machines, plumbing fixtures, and conducting
floors or walls, exist within the reach of persons when touching the metal
parts under consideration. Grounded surfaces within 5 feet horizontally of the
parts considered and within 8 feet vertically of the floor shall be considered
within reach.
(d)
Exceptions. Except as set out in subsection (c)(2) and (3) no
ground connection need be made to expose metal frames of switchboards, motors,
or lighting fixtures connected to direct current trolley or third rail circuit,
if such frames are effectively insulated from ground, and if the metal frames
in question are so located with reference to insulating floors or platforms
that persons may not readily touch the metal frames in question without
standing on such floors or platforms.
(e) Parts of machines, such as name plates,
screws in wood, and similar small parts which are not liable to become alive,
except under very unusual circumstances, are not considered as coming under the
rule and may be left ungrounded.
