[Title 29 CFR 1910.305]
[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. 1910.305 - Wiring methods, components, and equipment for general use.]
[From the U.S. Government Printing Office]
29LABOR52002-07-012002-07-01falseWiring methods, components, and equipment for general use.1910.305Sec. 1910.305LABORRegulations Relating to Labor (Continued)OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENTOCCUPATIONAL SAFETY AND HEALTH STANDARDSElectrical
Sec. 1910.305 Wiring methods, components, and equipment for general use.
(a) Wiring methods. The provisions of this section do not apply to
the conductors that are an integral part of factory-assembled equipment.
(1) General requirements--(i) Electrical continuity of metal
raceways and enclosures. Metal raceways, cable armor, and
other metal enclosures for conductors shall be metallically joined
together into a continuous electric conductor and shall be so connected
to all boxes, fittings, and cabinets as to provide effective electrical
(ii) Wiring in ducts. No wiring systems of any type shall be
installed in ducts used to transport dust, loose stock or flammable
vapors. No wiring system of any type may be installed in any duct used
for vapor removal or for ventilation of commercial-type cooking
equipment, or in any shaft containing only such ducts.
(2) Temporary wiring. Temporary electrical power and lighting wiring
methods may be of a class less than would be required for a permanent
installation. Except as specifically modified in this paragraph, all
other requirements of this subpart for permanent wiring shall apply to
temporary wiring installations.
(i) Uses permitted, 600 volts, nominal, or less. Temporary
electrical power and lighting installations 600 volts, nominal, or less
may be used only:
(A) During and for remodeling, maintenance, repair, or demolition of
buildings, structures, or equipment, and similar activities;
(B) For experimental or development work, and
(C) For a period not to exceed 90 days for Christmas decorative
lighting, carnivals, and similar purposes.
(ii) Uses permitted, over 600 volts, nominal. Temporary wiring over
600 volts, nominal, may be used only during periods of tests,
experiments, or emergencies.
(iii) General requirements for temporary wiring. (A) Feeders shall
originate in an approved distribution center. The conductors shall be
run as multiconductor cord or cable assemblies, or, where not subject to
physical damage, they may be run as open conductors on insulators not
more than 10 feet apart.
(B) Branch circuits shall originate in an approved power outlet or
panelboard. Conductors shall be multiconductor cord or cable assemblies
or open conductors. If run as open conductors they shall be fastened at
ceiling height every 10 feet. No branch-circuit conductor may be laid on
the floor. Each branch circuit that supplies receptacles or fixed
equipment shall contain a separate equipment grounding conductor if run
as open conductors.
(C) Receptacles shall be of the grounding type. Unless installed in
a complete metallic raceway, each branch circuit shall contain a
separate equipment grounding conductor and all receptacles shall be
electrically connected to the grounding conductor.
(D) No bare conductors nor earth returns may be used for the wiring
of any temporary circuit.
(E) Suitable disconnecting switches or plug connectors shall be
installed to permit the disconnection of all ungrounded conductors of
each temporary circuit.
(F) Lamps for general illumination shall be protected from
accidental contact or breakage. Protection shall be provided by
elevation of at least 7 feet from normal working surface or by a
suitable fixture or lampholder with a guard.
(G) Flexible cords and cables shall be protected from accidental
damage. Sharp corners and projections shall be avoided. Where passing
through doorways or other pinch points, flexible cords and cables shall
be provided with protection to avoid damage.
(3) Cable trays--(i) Uses permitted. (a) Only the following may be
installed in cable tray systems:
(1) Mineral-insulated metal-sheathed cable (Type MI);
(2) Armored cable (Type AC);
(3) Metal-clad cable (Type MC);
(4) Power-limited tray cable (Type PLTC);
(5) Nonmetallic-sheathed cable (Type NM or NMC);
(6) Shielded nonmetallic-sheathed cable (Type SNM);
(7) Multiconductor service-entrance cable (Type SE or USE);
(8) Multiconductor underground feeder and branch-circuit cable (Type
(9) Power and control tray cable (Type TC);
(10) Other factory-assembled, multiconductor control, signal, or
power cables which are specifically approved for installation in cable
(11) Any approved conduit or raceway with its contained conductors.
(b) In industrial establishments only, where conditions of
supervision assure that only qualified persons will service the
installed cable tray system, the following cables may also be installed
in ladder, ventilated trough, or 4 inch ventilated channel-type cable
(1) Single conductor cables which are 250 MCM or larger and are
Types RHH, RHW, MV, USE, or THW, and other 250 MCM or larger single
conductor cables if specifically approved for installation in cable
trays. Where exposed to direct rays of the sun, cables shall be
(2) Type MV cables, where exposed to direct rays of the sun, shall
(c) Cable trays in hazardous (classified) locations shall contain
only the cable types permitted in such locations.
(ii) Uses not permitted. Cable tray systems may not be used in
hoistways or where subjected to severe physical damage.
(4) Open wiring on insulators--(i) Uses permitted. Open wiring on
insulators is only permitted on systems of 600 volts, nominal, or less
for industrial or agricultural establishments and for services.
(ii) Conductor supports. Conductors shall be rigidly supported on
noncombustible, nonabsorbent insulating materials and may not contact
any other objects.
(iii) Flexible nonmetallic tubing. In dry locations where not
exposed to severe physical damage, conductors may be separately enclosed
in flexible nonmetallic tubing. The tubing shall be in continuous
lengths not exceeding 15 feet and secured to the surface by straps at
intervals not exceeding 4 feet 6 inches.
(iv) Through walls, floors, wood cross members, etc. Open conductors
shall be separated from contact with walls, floors, wood cross members,
or partitions through which they pass by tubes or bushings of
noncombustible, nonabsorbent insulating material. If the bushing is
shorter than the hole, a waterproof sleeve of nonconductive material
shall be inserted in the hole and an insulating bushing slipped into the
sleeve at each end in such a manner as to keep the conductors absolutely
out of contact with the sleeve. Each conductor shall be carried through
a separate tube or sleeve.
(v) Protection from physical damage. Conductors within 7 feet from
the floor are considered exposed to physical damage. Where open
conductors cross ceiling joints and wall studs and are exposed to
physical damage, they shall be protected.
(b) Cabinets, boxes, and fittings--(1) Conductors entering boxes,
cabinets, or fittings. Conductors entering boxes, cabinets, or fittings
shall also be protected from abrasion, and openings through which
conductors enter shall be effectively closed. Unused openings in
cabinets, boxes, and fittings shall be effectively closed.
(2) Covers and canopies. All pull boxes, junction boxes, and
fittings shall be provided with covers approved for the purpose. If
metal covers are used they shall be grounded. In completed installations
each outlet box shall have a cover, faceplate, or fixture canopy. Covers
of outlet boxes having holes through which flexible cord pendants pass
shall be provided with bushings designed for the purpose or shall have
smooth, well-rounded surfaces on which the cords may bear.
(3) Pull and junction boxes for systems over 600 volts, nominal. In
addition to other requirements in this section for pull and junction
boxes, the following shall apply to these boxes for systems over 600
(i) Boxes shall provide a complete enclosure for the contained
conductors or cables.
(ii) Boxes shall be closed by suitable covers securely fastened in
place. Underground box covers that weigh over 100 pounds meet this
requirement. Covers for boxes shall be permanently marked ``HIGH
VOLTAGE.'' The marking shall be on the outside of the box cover and
shall be readily visible and legible.
(c) Switches--(1) Knife switches. Single-throw knife switches shall
be so connected that the blades are dead when the switch is in the open
position. Single-throw knife switches shall be so placed that gravity
will not tend to close them. Single-throw knife switches approved for
use in the inverted position shall be provided with a locking device
that will ensure that
the blades remain in the open position when so set. Double-throw knife
switches may be mounted so that the throw will be either vertical or
horizontal. However, if the throw is vertical a locking device shall be
provided to ensure that the blades remain in the open position when so
(2) Faceplates for flush-mounted snap switches. Flush snap switches
that are mounted in ungrounded metal boxes and located within reach of
conducting floors or other conducting surfaces shall be provided with
faceplates of nonconducting, noncombustible material.
(d) Switchboards and panelboards. Switchboards that have any exposed
live parts shall be located in permanently dry locations and accessible
only to qualified persons. Panelboards shall be mounted in cabinets,
cutout boxes, or enclosures approved for the purpose and shall be dead
front. However, panelboards other than the dead front externally-
operable type are permitted where accessible only to qualified persons.
Exposed blades of knife switches shall be dead when open.
(e) Enclosures for damp or wet locations. (1) Cabinets, cutout
boxes, fittings, boxes, and panelboard enclosures in damp or wet
locations shall be installed so as to prevent moisture or water from
entering and accumulating within the enclosures. In wet locations the
enclosures shall be weatherproof.
(2) Switches, circuit breakers, and switchboards installed in wet
locations shall be enclosed in weatherproof enclosures.
(f) Conductors for general wiring. All conductors used for general
wiring shall be insulated unless otherwise permitted in this Subpart.
The conductor insulation shall be of a type that is approved for the
voltage, operating temperature, and location of use. Insulated
conductors shall be distinguishable by appropriate color or other
suitable means as being grounded conductors, ungrounded conductors, or
equipment grounding conductors.
(g) Flexible cords and cables--(1) Use of flexible cords and cables.
(i) Flexible cords and cables shall be approved and suitable for
conditions of use and location. Flexible cords and cables shall be used
(B) Wiring of fixtures;
(C) Connection of portable lamps or appliances;
(D) Elevator cables;
(E) Wiring of cranes and hoists;
(F) Connection of stationary equipment to facilitate their frequent
(G) Prevention of the transmission of noise or vibration;
(H) Appliances where the fastening means and mechanical connections
are designed to permit removal for maintenance and repair; or
(I) Data processing cables approved as a part of the data processing
(ii) If used as permitted in paragraphs (g)(1)(i)(c), (g)(1)(i)(f),
or (g)(1)(i)(h) of this section, the flexible cord shall be equipped
with an attachment plug and shall be energized from an approved
(iii) Unless specifically permitted in paragraph (g)(1)(i) of this
section, flexible cords and cables may not be used:
(A) As a substitute for the fixed wiring of a structure;
(B) Where run through holes in walls, ceilings, or floors;
(C) Where run through doorways, windows, or similar openings;
(D) Where attached to building surfaces; or
(E) Where concealed behind building walls, ceilings, or floors.
(iv) Flexible cords used in show windows and showcases shall be Type
S, SO, SJ, SJO, ST, STO, SJT, SJTO, or AFS except for the wiring of
chain-supported lighting fixtures and supply cords for portable lamps
and other merchandise being displayed or exhibited.
(2) Identification, splices, and terminations. (i) A conductor of a
flexible cord or cable that is used as a grounded conductor or an
equipment grounding conductor shall be distinguishable from other
conductors. Types SJ, SJO, SJT, SJTO, S, SO, ST, and STO shall be
durably marked on the surface with the type designation, size, and
number of conductors.
(ii) Flexible cords shall be used only in continuous lengths without
splice or tap. Hard service flexible cords No. 12 or larger may be
repaired if spliced so that the splice retains the insulation,
outer sheath properties, and usage characteristics of the cord being
(iii) Flexible cords shall be connected to devices and fittings so
that strain relief is provided which will prevent pull from being
directly transmitted to joints or terminal screws.
(h) Portable cables over 600 volts, nominal. Multiconductor portable
cable for use in supplying power to portable or mobile equipment at over
600 volts, nominal, shall consist of No. 8 or larger conductors
employing flexible stranding. Cables operated at over 2,000 volts shall
be shielded for the purpose of confining the voltage stresses to the
insulation. Grounding conductors shall be provided. Connectors for these
cables shall be of a locking type with provisions to prevent their
opening or closing while energized. Strain relief shall be provided at
connections and terminations. Portable cables may not be operated with
splices unless the splices are of the permanent molded, vulcanized, or
other approved type. Termination enclosures shall be suitably marked
with a high voltage hazard warning, and terminations shall be accessible
only to authorized and qualified personnel.
(i) Fixture wires--(1) General. Fixture wires shall be approved for
the voltage, temperature, and location of use. A fixture wire which is
used as a grounded conductor shall be identified.
(2) Uses permitted. Fixture wires may be used:
(i) For installation in lighting fixtures and in similar equipment
where enclosed or protected and not subject to bending or twisting in
(ii) For connecting lighting fixtures to the branch-circuit
conductors supplying the fixtures.
(3) Uses not permitted. Fixture wires may not be used as branch-
circuit conductors except as permitted for Class 1 power limited
(j) Equipment for general use--(1) Lighting fixtures, lampholders,
lamps, and receptacles. (i) Fixtures, lampholders, lamps, rosettes, and
receptacles may have no live parts normally exposed to employee contact.
However, rosettes and cleat-type lampholders and receptacles located at
least 8 feet above the floor may have exposed parts.
(ii) Handlamps of the portable type supplied through flexible cords
shall be equipped with a handle of molded composition or other material
approved for the purpose, and a substantial guard shall be attached to
the lampholder or the handle.
(iii) Lampholders of the screw-shell type shall be installed for use
as lampholders only. Lampholders installed in wet or damp locations
shall be of the weatherproof type.
(iv) Fixtures installed in wet or damp locations shall be approved
for the purpose and shall be so constructed or installed that water
cannot enter or accumulate in wireways, lampholders, or other electrical
(2) Receptacles, cord connectors, and attachment plugs (caps). (i)
Receptacles, cord connectors, and attachment plugs shall be constructed
so that no receptacle or cord connector will accept an attachment plug
with a different voltage or current rating than that for which the
device is intended. However, a 20-ampere T-slot receptacle or cord
connector may accept a 15-ampere attachment plug of the same voltage
(ii) A receptacle installed in a wet or damp location shall be
suitable for the location.
(3) Appliances. (i) Appliances, other than those in which the
current-carrying parts at high temperatures are necessarily exposed, may
have no live parts normally exposed to employee contact.
(ii) A means shall be provided to disconnect each appliance.
(iii) Each appliance shall be marked with its rating in volts and
amperes or volts and watts.
(4) Motors. This paragraph applies to motors, motor circuits, and
(i) In sight from. If specified that one piece of equipment shall be
``in sight from'' another piece of equipment, one shall be visible and
not more than 50 feet from the other.
(ii) Disconnecting means. (A) A disconnecting means shall be located
in sight from the controller location. However, a single disconnecting
means may be located adjacent to a group of
coordinated controllers mounted adjacent to each other on a multi-motor
continuous process machine. The controller disconnecting means for motor
branch circuits over 600 volts, nominal, may be out of sight of the
controller, if the controller is marked with a warning label giving the
location and identification of the disconnecting means which is to be
locked in the open position.
(B) The disconnecting means shall disconnect the motor and the
controller from all ungrounded supply conductors and shall be so
designed that no pole can be operated independently.
(C) If a motor and the driven machinery are not in sight from the
controller location, the installation shall comply with one of the
(1) The controller disconnecting means shall be capable of being
locked in the open position.
(2) A manually operable switch that will disconnect the motor from
its source of supply shall be placed in sight from the motor location.
(D) The disconnecting means shall plainly indicate whether it is in
the open (off) or closed (on) position.
(E) The disconnecting means shall be readily accessible. If more
than one disconnect is provided for the same equipment, only one need be
(F) An individual disconnecting means shall be provided for each
motor, but a single disconnecting means may be used for a group of
motors under any one of the following conditions:
(1) If a number of motors drive special parts of a single machine or
piece of apparatus, such as a metal or woodworking machine, crane, or
(2) If a group of motors is under the protection of one set of
branch-circuit protective devices; or
(3) If a group of motors is in a single room in sight from the
location of the disconnecting means.
(iii) Motor overload, short-circuit, and ground-fault protection.
Motors, motor-control apparatus, and motor branch-circuit conductors
shall be protected against overheating due to motor overloads or failure
to start, and against short-circuits or ground faults. These provisions
shall not require overload protection that will stop a motor where a
shutdown is likely to introduce additional or increased hazards, as in
the case of fire pumps, or where continued operation of a motor is
necessary for a safe shutdown of equipment or process and motor overload
sensing devices are connected to a supervised alarm.
(iv) Protection of live parts--all voltages. (A) Stationary motors
having commutators, collectors, and brush rigging located inside of
motor end brackets and not conductively connected to supply circuits
operating at more than 150 volts to ground need not have such parts
guarded. Exposed live parts of motors and controllers operating at 50
volts or more between terminals shall be guarded against accidental
contact by any of the following:
(1) By installation in a room or enclosure that is accessible only
to qualified persons;
(2) By installation on a suitable balcony, gallery, or platform, so
elevated and arranged as to exclude unqualified persons; or
(3) By elevation 8 feet or more above the floor.
(B) Where live parts of motors or controllers operating at over 150
volts to ground are guarded against accidental contact only by location,
and where adjustment or other attendance may be necessary during the
operation of the apparatus, suitable insulating mats or platforms shall
be provided so that the attendant cannot readily touch live parts unless
standing on the mats or platforms.
(5) Transformers. (i) The following paragraphs cover the
installation of all transformers except the following:
(A) Current transformers;
(B) Dry-type transformers installed as a component part of other
(C) Transformers which are an integral part of an X-ray, high
frequency, or electrostatic-coating apparatus;
(D) Transformers used with Class 2 and Class 3 circuits, sign and
outline lighting, electric discharge lighting, and power-limited fire-
protective signalling circuits; and
(E) Liquid-filled or dry-type transformers used for research,
development, or testing, where effective safeguard arrangements are
(ii) The operating voltage of exposed live parts of transformer
installations shall be indicated by warning signs or visible markings on
the equipment or structure.
(iii) Dry-type, high fire point liquid-insulated, and askarel-
insulated transformers installed indoors and rated over 35kV shall be in
(iv) If they present a fire hazard to employees, oil-insulated
transformers installed indoors shall be in a vault.
(v) Combustible material, combustible buildings and parts of
buildings, fire escapes, and door and window openings shall be
safeguarded from fires which may originate in oil-insulated transformers
attached to or adjacent to a building or combustible material.
(vi) Transformer vaults shall be constructed so as to contain fire
and combustible liquids within the vault and to prevent unauthorized
access. Locks and latches shall be so arranged that a vault door can be
readily opened from the inside.
(vii) Any pipe or duct system foreign to the vault installation may
not enter or pass through a transformer vault.
(viii) Materials may not be stored in transformer vaults.
(6) Capacitors. (i) All capacitors, except surge capacitors or
capacitors included as a component part of other apparatus, shall be
provided with an automatic means of draining the stored charge after the
capacitor is disconnected from its source of supply.
(ii) Capacitors rated over 600 volts, nominal, shall comply with the
following additional requirements:
(A) Isolating or disconnecting switches (with no interrupting
rating) shall be interlocked with the load interrupting device or shall
be provided with prominently displayed caution signs to prevent
switching load current.
(B) For series capacitors (see Sec. 1910.302(b)(3)), the proper
switching shall be assured by use of at least one of the following:
(1) Mechanically sequenced isolating and bypass switches,
(2) Interlocks, or
(3) Switching procedure prominently displayed at the switching
(7) Storage batteries. Provisions shall be made for sufficient
diffusion and ventilation of gases from storage batteries to prevent the
accumulation of explosive mixtures.
[46 FR 4056, Jan. 16, 1981; 46 FR 40185, Aug. 7, 1981]