[Title 29 CFR 1910.304]
[Code of Federal Regulations (annual edition) - July 1, 2002 Edition]
[Title 29 - LABOR]
[Subtitle B - Regulations Relating to Labor (Continued)]
[Chapter Xvii - OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT]
[Part 1910 - OCCUPATIONAL SAFETY AND HEALTH STANDARDS]
[Subpart S - Electrical]
[Sec. 1910.304 - Wiring design and protection.]
[From the U.S. Government Printing Office]
29LABOR52002-07-012002-07-01falseWiring design and protection.1910.304Sec. 1910.304LABORRegulations Relating to Labor (Continued)OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENTOCCUPATIONAL SAFETY AND HEALTH STANDARDSElectrical
Sec. 1910.304 Wiring design and protection.
(a) Use and identification of grounded and grounding conductors. (1)
Identification of conductors. A conductor used as a grounded conductor
shall be identifiable and distinguishable from all other conductors. A
conductor used as an equipment grounding conductor shall be identifiable
and distinguishable from all other conductors.
(2) Polarity of connections. No grounded conductor may be attached
to any terminal or lead so as to reverse designated polarity.
(3) Use of grounding terminals and devices. A grounding terminal or
grounding-type device on a receptacle, cord connector, or attachment
plug may not be used for purposes other than grounding.
(b) Branch circuits--(1) [Reserved]
(2) Outlet devices. Outlet devices shall have an ampere rating not
less than the load to be served.
(c) Outside conductors, 600 volts, nominal, or less. Paragraphs
(c)(1), (c)(2), (c)(3), and (c)(4) of this section apply to branch
circuit, feeder, and service conductors rated 600 volts, nominal, or
less and run outdoors as open conductors. Paragraph (c)(5) applies to
lamps installed under such conductors.
(1) Conductors on poles. Conductors supported on poles shall provide
a horizontal climbing space not less than the following:
(i) Power conductors below communication conductors--30 inches.
(ii) Power conductors alone or above communication conductors: 300
volts or less--24 inches; more than 300 volts--30 inches.
(iii) Communication conductors below power conductors with power
conductors 300 volts or less--24 inches; more than 300 volts--30 inches.
(2) Clearance from ground. Open conductors shall conform to the
following minimum clearances:
(i) 10 feet--above finished grade, sidewalks, or from any platform
or projection from which they might be reached.
(ii) 12 feet--over areas subject to vehicular traffic other than
truck traffic.
(iii) 15 feet--over areas other than those specified in paragraph
(c)(2)(iv) of this section that are subject to truck traffic.
(iv) 18 feet--over public streets, alleys, roads, and driveways.
(3) Clearance from building openings. Conductors shall have a
clearance of at least 3 feet from windows, doors, porches, fire escapes,
or similar locations. Conductors run above the top level of a window are
considered to be out of
[[Page 841]]
reach from that window and, therefore, do not have to be 3 feet away.
(4) Clearance over roofs. Conductors shall have a clearance of not
less than 8 feet from the highest point of roofs over which they pass,
except that:
(i) Where the voltage between conductors is 300 volts or less and
the roof has a slope of not less than 4 inches in 12, the clearance from
roofs shall be at least 3 feet, or
(ii) Where the voltage between conductors is 300 volts or less and
the conductors do not pass over more than 4 feet of the overhang portion
of the roof and they are terminated at a through-the-roof raceway or
approved support, the clearance from roofs shall be at least 18 inches.
(5) Location of outdoor lamps. Lamps for outdoor lighting shall be
located below all live conductors, transformers, or other electric
equipment, unless such equipment is controlled by a disconnecting means
that can be locked in the open position or unless adequate clearances or
other safeguards are provided for relamping operations.
(d) Services--(1) Disconnecting means--(i) General. Means shall be
provided to disconnect all conductors in a building or other structure
from the service-entrance conductors. The disconnecting means shall
plainly indicate whether it is in the open or closed position and shall
be installed at a readily accessible location nearest the point of
entrance of the service-entrance conductors.
(ii) Simultaneous opening of poles. Each service disconnecting means
shall simultaneously disconnect all ungrounded conductors.
(2) Services over 600 volts, nominal. The following additional
requirements apply to services over 600 volts, nominal.
(i) Guarding. Service-entrance conductors installed as open wires
shall be guarded to make them accessible only to qualified persons.
(ii) Warning signs. Signs warning of high voltage shall be posted
where other than qualified employees might come in contact with live
parts.
(e) Overcurrent protection. (1) 600 volts, nominal, or less. The
following requirements apply to overcurrent protection of circuits rated
600 volts, nominal, or less.
(i) Protection of conductors and equipment. Conductors and equipment
shall be protected from overcurrent in accordance with their ability to
safely conduct current.
(ii) Grounded conductors. Except for motor running overload
protection, overcurrent devices may not interrupt the continuity of the
grounded conductor unless all conductors of the circuit are opened
simultaneously.
(iii) Disconnection of fuses and thermal cutouts. Except for service
fuses, all cartridge fuses which are accessible to other than qualified
persons and all fuses and thermal cutouts on circuits over 150 volts to
ground shall be provided with disconnecting means. This disconnecting
means shall be installed so that the fuse or thermal cutout can be
disconnected from its supply without disrupting service to equipment and
circuits unrelated to those protected by the overcurrent device.
(iv) Location in or on premises. Overcurrent devices shall be
readily accessible to each employee or authorized building management
personnel. These overcurrent devices may not be located where they will
be exposed to physical damage nor in the vicinity of easily ignitible
material.
(v) Arcing or suddenly moving parts. Fuses and circuit breakers
shall be so located or shielded that employees will not be burned or
otherwise injured by their operation.
(vi) Circuit breakers. (A) Circuit breakers shall clearly indicate
whether they are in the open (off) or closed (on) position.
(B) Where circuit breaker handles on switchboards are operated
vertically rather than horizontally or rotationally, the up position of
the handle shall be the closed (on) position. (See Sec. 1910.302(b)(3).)
(C) If used as switches in 120-volt, fluorescent lighting circuits,
circuit breakers shall be approved for the purpose and marked ``SWD.''
(See Sec. 1910.302(b)(3).)
(2) Over 600 volts, nominal. Feeders and branch circuits over 600
volts, nominal, shall have short-circuit protection.
[[Page 842]]
(f) Grounding. Paragraphs (f)(1) through (f)(7) of this section
contain grounding requirements for systems, circuits, and equipment.
(1) Systems to be grounded. The following systems which supply
premises wiring shall be grounded:
(i) All 3-wire DC systems shall have their neutral conductor
grounded.
(ii) Two-wire DC systems operating at over 50 volts through 300
volts between conductors shall be grounded unless:
(A) They supply only industrial equipment in limited areas and are
equipped with a ground detector; or
(B) They are rectifier-derived from an AC system complying with
paragraphs (f)(1)(iii), (f)(1)(iv), and (f)(1)(v) of this section; or
(C) They are fire-protective signaling circuits having a maximum
current of 0.030 amperes.
(iii) AC circuits of less than 50 volts shall be grounded if they
are installed as overhead conductors outside of buildings or if they are
supplied by transformers and the transformer primary supply system is
ungrounded or exceeds 150 volts to ground.
(iv) AC systems of 50 volts to 1000 volts shall be grounded under
any of the following conditions, unless exempted by paragraph (f)(1)(v)
of this section:
(A) If the system can be so grounded that the maximum voltage to
ground on the ungrounded conductors does not exceed 150 volts;
(B) If the system is nominally rated 480Y/277 volt, 3-phase, 4-wire
in which the neutral is used as a circuit conductor;
(C) If the system is nominally rated 240/120 volt, 3-phase, 4-wire
in which the midpoint of one phase is used as a circuit conductor; or
(D) If a service conductor is uninsulated.
(v) AC systems of 50 volts to 1000 volts are not required to be
grounded under any of the following conditions:
(A) If the system is used exclusively to supply industrial electric
furnaces for melting, refining, tempering, and the like.
(B) If the system is separately derived and is used exclusively for
rectifiers supplying only adjustable speed industrial drives.
(C) If the system is separately derived and is supplied by a
transformer that has a primary voltage rating less than 1000 volts,
provided all of the following conditions are met:
(1) The system is used exclusively for control circuits,
(2) The conditions of maintenance and supervision assure that only
qualified persons will service the installation,
(3) Continuity of control power is required, and
(4) Ground detectors are installed on the control system.
(D) If the system is an isolated power system that supplies circuits
in health care facilities.
(2) Conductors to be grounded. For AC premises wiring systems the
identified conductor shall be grounded.
(3) Grounding connections. (i) For a grounded system, a grounding
electrode conductor shall be used to connect both the equipment
grounding conductor and the grounded circuit conductor to the grounding
electrode. Both the equipment grounding conductor and the grounding
electrode conductor shall be connected to the grounded circuit conductor
on the supply side of the service disconnecting means, or on the supply
side of the system disconnecting means or overcurrent devices if the
system is separately derived.
(ii) For an ungrounded service-supplied system, the equipment
grounding conductor shall be connected to the grounding electrode
conductor at the service equipment. For an ungrounded separately derived
system, the equipment grounding conductor shall be connected to the
grounding electrode conductor at, or ahead of, the system disconnecting
means or overcurrent devices.
(iii) On extensions of existing branch circuits which do not have an
equipment grounding conductor, grounding-type receptacles may be
grounded to a grounded cold water pipe near the equipment.
(4) Grounding path. The path to ground from circuits, equipment, and
enclosures shall be permanent and continuous.
[[Page 843]]
(5) Supports, enclosures, and equipment to be grounded--(i) Supports
and enclosures for conductors. Metal cable trays, metal raceways, and
metal enclosures for conductors shall be grounded, except that:
(A) Metal enclosures such as sleeves that are used to protect cable
assemblies from physical damage need not be grounded; or
(B) Metal enclosures for conductors added to existing installations
of open wire, knob-and-tube wiring, and nonmetallic-sheathed cable need
not be grounded if all of the following conditions are met: (1) Runs are
less than 25 feet; (2) enclosures are free from probable contact with
ground, grounded metal, metal laths, or other conductive materials; and
(3) enclosures are guarded against employee contact.
(ii) Service equipment enclosures. Metal enclosures for service
equipment shall be grounded.
(iii) Frames of ranges and clothes dryers. Frames of electric
ranges, wall-mounted ovens, counter-mounted cooking units, clothes
dryers, and metal outlet or junction boxes which are part of the circuit
for these appliances shall be grounded.
(iv) Fixed equipment. Exposed non-current-carrying metal parts of
fixed equipment which may become energized shall be grounded under any
of the following conditions:
(A) If within 8 feet vertically or 5 feet horizontally of ground or
grounded metal objects and subject to employee contact.
(B) If located in a wet or damp location and not isolated.
(C) If in electrical contact with metal.
(D) If in a hazardous (classified) location.
(E) If supplied by a metal-clad, metal-sheathed, or grounded metal
raceway wiring method.
(F) If equipment operates with any terminal at over 150 volts to
ground; however, the following need not be grounded:
(1) Enclosures for switches or circuit breakers used for other than
service equipment and accessible to qualified persons only;
(2) Metal frames of electrically heated appliances which are
permanently and effectively insulated from ground; and
(3) The cases of distribution apparatus such as transformers and
capacitors mounted on wooden poles at a height exceeding 8 feet above
ground or grade level.
(v) Equipment connected by cord and plug. Under any of the
conditions described in paragraphs (f)(5)(v)(A) through (f)(5)(v)(C) of
this section, exposed non-current-carrying metal parts of cord- and
plug-connected equipment which may become energized shall be grounded.
(A) If in hazardous (classified) locations (see Sec. 1910.307).
(B) If operated at over 150 volts to ground, except for guarded
motors and metal frames of electrically heated appliances if the
appliance frames are permanently and effectively insulated from ground.
(C) If the equipment is of the following types:
(1) Refrigerators, freezers, and air conditioners;
(2) Clothes-washing, clothes-drying and dishwashing machines, sump
pumps, and electrical aquarium equipment;
(3) Hand-held motor-operated tools;
(4) Motor-operated appliances of the following types: hedge
clippers, lawn mowers, snow blowers, and wet scrubbers;
(5) Cord- and plug-connected appliances used in damp or wet
locations or by employees standing on the ground or on metal floors or
working inside of metal tanks or boilers;
(6) Portable and mobile X-ray and associated equipment;
(7) Tools likely to be used in wet and conductive locations; and
(8) Portable hand lamps.
Tools likely to be used in wet and conductive locations need not be
grounded if supplied through an isolating transformer with an ungrounded
secondary of not over 50 volts. Listed or labeled portable tools and
appliances protected by an approved system of double insulation, or its
equivalent, need not be grounded. If such a system is employed, the
equipment shall be distinctively marked to indicate that the tool or
appliance utilizes an approved system of double insulation.
[[Page 844]]
(vi) Nonelectrical equipment. The metal parts of the following
nonelectrical equipment shall be grounded: frames and tracks of
electrically operated cranes; frames of nonelectrically driven elevator
cars to which electric conductors are attached; hand operated metal
shifting ropes or cables of electric elevators, and metal partitions,
grill work, and similar metal enclosures around equipment of over 750
volts between conductors.
(6) Methods of grounding fixed equipment. (i) Non-current-carrying
metal parts of fixed equipment, if required to be grounded by this
subpart, shall be grounded by an equipment grounding conductor which is
contained within the same raceway, cable, or cord, or runs with or
encloses the circuit conductors. For DC circuits only, the equipment
grounding conductor may be run separately from the circuit conductors.
(ii) Electric equipment is considered to be effectively grounded if
it is secured to, and in electrical contact with, a metal rack or
structure that is provided for its support and the metal rack or
structure is grounded by the method specified for the non-current-
carrying metal parts of fixed equipment in paragraph (f)(6)(i) of this
section. For installations made before April 16, 1981, only, electric
equipment is also considered to be effectively grounded if it is secured
to, and in metallic contact with, the grounded structural metal frame of
a building. Metal car frames supported by metal hoisting cables attached
to or running over metal sheaves or drums of grounded elevator machines
are also considered to be effectively grounded.
(7) Grounding of systems and circuits of 1000 volts and over (high
voltage)--(i) General. If high voltage systems are grounded, they shall
comply with all applicable provisions of paragraphs (f)(1) through
(f)(6) of this section as supplemented and modified by this paragraph
(f)(7).
(ii) Grounding of systems supplying portable or mobile equipment.
(See Sec. 1910.302(b)(3).) Systems supplying portable or mobile high
voltage equipment, other than substations installed on a temporary
basis, shall comply with the following:
(A) Portable and mobile high voltage equipment shall be supplied
from a system having its neutral grounded through an impedance. If a
delta-connected high voltage system is used to supply the equipment, a
system neutral shall be derived.
(B) Exposed non-current-carrying metal parts of portable and mobile
equipment shall be connected by an equipment grounding conductor to the
point at which the system neutral impedance is grounded.
(C) Ground-fault detection and relaying shall be provided to
automatically de-energize any high voltage system component which has
developed a ground fault. The continuity of the equipment grounding
conductor shall be continuously monitored so as to de-energize
automatically the high voltage feeder to the portable equipment upon
loss of continuity of the equipment grounding conductor.
(D) The grounding electrode to which the portable or mobile
equipment system neutral impedance is connected shall be isolated from
and separated in the ground by at least 20 feet from any other system or
equipment grounding electrode, and there shall be no direct connection
between the grounding electrodes, such as buried pipe, fence, etc.
(iii) Grounding of equipment. All non-current-carrying metal parts
of portable equipment and fixed equipment including their associated
fences, housings, enclosures, and supporting structures shall be
grounded. However, equipment which is guarded by location and isolated
from ground need not be grounded. Additionally, pole-mounted
distribution apparatus at a height exceeding 8 feet above ground or
grade level need not be grounded.
[46 FR 4056, Jan. 16, 1981; 46 FR 40185, Aug. 7, 1981, as amended at 55
FR 32015, Aug. 6, 1990]