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Regulations (Standards - 29 CFR)

Wiring methods, components, and equipment for general use. - 1910.305

OSHA Regulations (Standards - 29 CFR) - Table of Contents OSHA Regulations (Standards - 29 CFR) - Table of Contents
  • Standard Number: 1910.305
  • Standard Title: Wiring methods, components, and equipment for general use.
  • SubPart Number: S
  • SubPart Title: Electrical - Design Safety Standards for Electrical Systems


Wiring methods. The provisions of this section do not apply to the conductors that are an integral part of factory-assembled equipment.


General requirements -


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 continuity.


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.


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.



Uses permitted, 600 volts, nominal, or less. Temporary electrical power and lighting installations 600 volts, nominal, or less may be used only:


During and for remodeling, maintenance, repair, or demolition of buildings, structures, or equipment, and similar activities;


For experimental or development work, and


For a period not to exceed 90 days for Christmas decorative lighting, carnivals, and similar purposes.


Uses permitted, over 600 volts, nominal. Temporary wiring over 600 volts, nominal, may be used only during periods of tests, experiments, or emergencies.


General requirements for temporary wiring.


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.



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.


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.


No bare conductors nor earth returns may be used for the wiring of any temporary circuit.


Suitable disconnecting switches or plug connectors shall be installed to permit the disconnection of all ungrounded conductors of each temporary circuit.


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.


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.



Cable trays.


Uses permitted.


Only the following may be installed in cable tray systems:


Mineral-insulated metal-sheathed cable (Type MI);


Armored cable (Type AC);


Metal-clad cable (Type MC);


Power-limited tray cable (Type PLTC);


Nonmetallic-sheathed cable (Type NM or NMC);


Shielded nonmetallic-sheathed cable (Type SNM);


Multiconductor service-entrance cable (Type SE or USE);


Multiconductor underground feeder and branch-circuit cable (Type UF);


Power and control tray cable (Type TC);


Other factory-assembled, multiconductor control, signal, or power cables which are specifically approved for installation in cable trays; or



Any approved conduit or raceway with its contained conductors.


In industrial establishments only, where conditions of maintenance and 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 trays:


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 sunlight-resistant.


Type MV cables, where exposed to direct rays of the sun, shall be sunlight-resistant.


Cable trays in hazardous (classified) locations shall contain only the cable types permitted in such locations.


Uses not permitted. Cable tray systems may not be used in hoistways or where subjected to severe physical damage.


Open wiring on insulators -


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.



Conductor supports. Conductors shall be rigidly supported on noncombustible, nonabsorbent insulating materials and may not contact any other objects.


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.


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.


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.



Cabinets, boxes, and fittings -


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.


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.


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 volts, nominal:


Boxes shall provide a complete enclosure for the contained conductors or cables.


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.



Switches -


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 set.


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.


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.


Enclosures for damp or wet locations.


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.


Switches, circuit breakers, and switchboards installed in wet locations shall be enclosed in weatherproof enclosures.



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.


Flexible cords and cables -


Use of flexible cords and cables.


Flexible cords and cables shall be approved and suitable for conditions of use and location. Flexible cords and cables shall be used only for:




Wiring of fixtures;


Connection of portable lamps or appliances;


Elevator cables;


Wiring of cranes and hoists;


Connection of stationary equipment to facilitate their frequent interchange;


Prevention of the transmission of noise or vibration;


Appliances where the fastening means and mechanical connections are designed to permit removal for maintenance and repair; or



Data processing cables approved as a part of the data processing system.


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 receptacle outlet.


Unless specifically permitted in paragraph (g)(1)(i) of this section, flexible cords and cables may not be used:


As a substitute for the fixed wiring of a structure;


Where run through holes in walls, ceilings, or floors;


Where run through doorways, windows, or similar openings;


Where attached to building surfaces; or


Where concealed behind building walls, ceilings, or floors.


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.



Identification, splices, and terminations.


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.


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 spliced.


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.


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.



Fixture wires -


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.


Uses permitted. Fixture wires may be used:


For installation in lighting fixtures and in similar equipment where enclosed or protected and not subject to bending or twisting in use; or


For connecting lighting fixtures to the branch-circuit conductors supplying the fixtures.


Uses not permitted. Fixture wires may not be used as branch-circuit conductors except as permitted for Class 1 power limited circuits.


Equipment for general use -


Lighting fixtures, lampholders, lamps, and receptacles.


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.


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.



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.


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 parts.


Receptacles, cord connectors, and attachment plugs (caps).


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 rating.


A receptacle installed in a wet or damp location shall be suitable for the location.




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.


A means shall be provided to disconnect each appliance.



Each appliance shall be marked with its rating in volts and amperes or volts and watts.


Motors. This paragraph applies to motors, motor circuits, and controllers.


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.


Disconnecting means.


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.


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.



If a motor and the driven machinery are not in sight from the controller location, the installation shall comply with one of the following conditions:


The controller disconnecting means shall be capable of being locked in the open position.


A manually operable switch that will disconnect the motor from its source of supply shall be placed in sight from the motor location.


The disconnecting means shall plainly indicate whether it is in the open (off) or closed (on) position.


The disconnecting means shall be readily accessible. If more than one disconnect is provided for the same equipment, only one need be readily accessible.


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:


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 hoist;


If a group of motors is under the protection of one set of branch-circuit protective devices; or



If a group of motors is in a single room in sight from the location of the disconnecting means.


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.


Protection of live parts - all voltages.


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:


By installation in a room or enclosure that is accessible only to qualified persons;



By installation on a suitable balcony, gallery, or platform, so elevated and arranged as to exclude unqualified persons; or


By elevation 8 feet or more above the floor.


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.




The following paragraphs cover the installation of all transformers except the following:


Current transformers;


Dry-type transformers installed as a component part of other apparatus;


Transformers which are an integral part of an X-ray, high frequency, or electrostatic-coating apparatus;



Transformers used with Class 2 and Class 3 circuits, sign and outline lighting, electric discharge lighting, and power-limited fire-protective signaling circuits; and


Liquid-filled or dry-type transformers used for research, development, or testing, where effective safeguard arrangements are provided.


The operating voltage of exposed live parts of transformer installations shall be indicated by warning signs or visible markings on the equipment or structure.


Dry-type, high fire point liquid-insulated, and askarel-insulated transformers installed indoors and rated over 35kV shall be in a vault.


If they present a fire hazard to employees, oil-insulated transformers installed indoors shall be in a vault.


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.


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.



Any pipe or duct system foreign to the vault installation may not enter or pass through a transformer vault.


Materials may not be stored in transformer vaults.




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.


Capacitors rated over 600 volts, nominal, shall comply with the following additional requirements:


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.


For series capacitors (see 1910.302(b)(3)), the proper switching shall be assured by use of at least one of the following:


Mechanically sequenced isolating and bypass switches,


Interlocks, or



Switching procedure prominently displayed at the switching location.


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]

OSHA Regulations (Standards - 29 CFR) - Table of Contents OSHA Regulations (Standards - 29 CFR) - Table of Contents
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