Subpart S - Electrical

Subpart S provides the electrical standards that address the practical safeguarding of employees in the workplace. According to the standard on introduction, this subpart has two distinct sections:

  • Section One - Design safety standards for electrical systems
    • Design safety standards for electric utilization systems (Includes all electric equipment and installations used to provide electric power and light for employee workplaces)
    • Specific purpose equipment and installations
    • Hazardous (classified) locations
    • Special systems (over 600 volts)
  • Section Two - Safety-related work practices

To learn if subpart S applies to you, go to Does "Subpart S - Electrical" Apply to You?

Special Requirements

Tab/Accordion Items

Scope: This standard provides general electrical requirements for electrical installations and utilization equipment installed or used within or on buildings, structures, and other premises.

Qualified person - One who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.

Special Requirements: Labels, instructions, identified, listed, markings, inspection, approved, qualified person, warning signs, caution signs

1910.303(b)(2) - Installation and use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

1910.303(b)(6) - Deteriorating agents. Unless identified for use in the operating environment, no conductors or equipment shall be located in damp or wet locations; where exposed to gases, fumes, vapors, liquids, or other agents that have a deteriorating effect on the conductors or equipment; or where exposed to excessive temperatures.

1910.303(c)(1)(i) - Devices such as pressure terminal or pressure splicing connectors and soldering lugs shall be identified for the material of the conductor and shall be properly installed and used.

1910.303(c)(1)(ii) - Conductors of dissimilar metals may not be intermixed in a terminal or splicing connector where physical contact occurs between dissimilar conductors (such as copper and aluminum, copper and copper-clad aluminum, or aluminum and copper-clad aluminum) unless the device is identified for the purpose and conditions of use.

1910.303(c)(2)(ii) - Terminals for more than one conductor and terminals used to connect aluminum shall be so identified.

1910.303(c)(3)(ii) - Wire connectors or splicing means installed on conductors for direct burial shall be listed for such use.

1910.303(e)(1) - Identification of manufacturer and ratings. Electric equipment may not be used unless the following markings have been placed on the equipment:

  • 1910.303(e)(1)(i) - The manufacturer's name, trademark, or other descriptive marking by which the organization responsible for the product may be identified; and
  • 1910.303(e)(1)(ii) - Other markings giving voltage, current, wattage, or other ratings as necessary.

1910.303(e)(2) - Durability. The marking shall be of sufficient durability to withstand the environment involved.

1910.303(f)(1) - Motors and appliances. Each disconnecting means required by this subpart for motors and appliances shall be legibly marked to indicate its purpose, unless located and arranged so the purpose is evident.

1910.303(f)(2) - Services, feeders, and branch circuits. Each service, feeder, and branch circuit, at its disconnecting means or overcurrent device, shall be legibly marked to indicate its purpose, unless located and arranged so the purpose is evident.

1910.303(f)(3) - Durability of markings. The markings required by paragraphs (f)(1) and (f)(2) of this section shall be of sufficient durability to withstand the environment involved.

1910.303(f)(5) - Marking for series combination ratings. [Reference paragraph (f)(5)(i) - (ii)].

1910.303(g)(1)(ii) - Working space required by this standard may not be used for storage. When normally enclosed live parts are exposed for inspection or servicing, the working space, if in a passageway or general open space, shall be suitably guarded.

1910.303(g)(2)(i) - Except as elsewhere required or permitted by this standard, live parts of electric equipment operating at 50 volts or more shall be guarded against accidental contact by use of approved cabinets or other forms of approved enclosures or by any of the following means:

  • 1910.303(g)(2)(i)(A) - By location in a room, vault, or similar enclosure that is accessible only to qualified persons;
  • 1910.303(g)(2)(i)(B) - By suitable permanent, substantial partitions or screens so arranged so that only qualified persons will have access to the space within reach of the live parts. Any openings in such partitions or screens shall be so sized and located that persons are not likely to come into accidental contact with the live parts or to bring conducting objects into contact with them.

1910.303(g)(2)(iii) - Entrances to rooms and other guarded locations containing exposed live parts shall be marked with conspicuous warning signs forbidding unqualified persons to enter.

1910.303(h)(2)(i) - Electrical installations in a vault, room, or closet or in an area surrounded by a wall, screen, or fence, access to which is controlled by lock and key or other approved means, are considered to be accessible to qualified persons only. The type of enclosure used in a given case shall be designed and constructed according to the hazards associated with the installation.

1910.303(h)(2)(iii) - The following requirements apply to indoor installations that are accessible to other than qualified persons: [Reference paragraph (h)(2)(iii)(A) - (C)].

  • 1910.303(h)(2)(iii)(B) - Metal-enclosed switchgear, unit substations, transformers, pull boxes, connection boxes, and other similar associated equipment shall be marked with appropriate caution signs;

1910.303(h)(2)(iv) - Outdoor electrical installations having exposed live parts shall be accessible to qualified persons only.

1910.303(h)(5)(ii) - If switches, cutouts, or other equipment operating at 600 volts, nominal, or less, are installed in a room or enclosure where there are exposed live parts or exposed wiring operating at over 600 volts, nominal, the high-voltage equipment shall be effectively separated from the space occupied by the low-voltage equipment by a suitable partition, fence, or screen. However, switches or other equipment operating at 600 volts, nominal, or less, and serving only equipment within the high-voltage vault, room, or enclosure may be installed in the high-voltage enclosure, room, or vault if accessible to qualified persons only.

1910.303(h)(5)(iii) - The following requirements apply to the entrances to all buildings, rooms, or enclosures containing exposed live parts or exposed conductors operating at over 600 volts, nominal:

  • 1910.303(h)(5)(iii)(A) - The entrances shall be kept locked unless they are under the observation of a qualified person at all times; and
  • 1910.303(h)(5)(iii)(B) - Permanent and conspicuous warning signs shall be provided, reading substantially as follows: “DANGER - HIGH VOLTAGE - KEEP OUT.” 

Scope: This standard provides electrical requirements for electrical installations and utilization equipment installed or used within or on buildings, structures, and other premises.

Competent person - One who is capable of identifying existing and predictable hazards in the surroundings or working conditions that are unsanitary, hazardous, or dangerous to employees and who has authorization to take prompt corrective measures to eliminate them.

Qualified person - One who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.

Special Requirements: Identifiable (posted), markings/marked, listing, assured equipment grounding conductor program (written), inspections, tests, competent person, procedures, records, qualified person, warning signs, authorized personnel, references other standards

1910.304(a)(1)(i) - A conductor used as a grounded conductor shall be identifiable and distinguishable from all other conductors.

1910.304(a)(1)(ii) - A conductor used as an equipment grounding conductor shall be identifiable and distinguishable from all other conductors.

1910.304(b)(1) - Identification of multiwire branch circuits. Where more than one nominal voltage system exists in a building containing multiwire branch circuits, each ungrounded conductor of a multiwire branch circuit, where accessible, shall be identified by phase and system. The means of identification shall be permanently posted at each branch-circuit panelboard.

1910.304(b)(2)(iv)(C)(3) - A nongrounding-type receptacle may be replaced with a grounding-type receptacle where supplied through a ground-fault circuit-interrupter; the replacement receptacle shall be marked "GFCI Protected" and "No Equipment Ground;" an equipment grounding conductor may not be connected to such grounding-type receptacles.

1910.304(b)(3)(ii)(C) - Where the ground-fault circuit-interrupter protection required by paragraph (b)(3)(ii)(B) of this section is not available for receptacles other than 125-volt, single-phase, 15-, 20-, and 30-ampere, the employer shall establish and implement an assured equipment grounding conductor program covering cord sets, receptacles that are not a part of the building or structure, and equipment connected by cord and plug that are available for use or used by employees on those receptacles. This program shall comply with the following requirements:

  • 1910.304(b)(3)(ii)(C)(1) - A written description of the program, including the specific procedures adopted by the employer, shall be available at the jobsite for inspection and copying by the Assistant Secretary of Labor and any affected employee;
  • 1910.304(b)(3)(ii)(C)(2) - The employer shall designate one or more competent persons to implement the program;
  • 1910.304(b)(3)(ii)(C)(3) - Each cord set, attachment cap, plug, and receptacle of cord sets, and any equipment connected by cord and plug, except cord sets and receptacles which are fixed and not exposed to damage, shall be visually inspected before each day's use for external defects, such as deformed or missing pins or insulation damage, and for indications of possible internal damage. Equipment found damaged or defective shall not be used until repaired;
  • 1910.304(b)(3)(ii)(C)(4) - The following tests shall be performed on all cord sets and receptacles which are not a part of the permanent wiring of the building or structure, and cord- and plug-connected equipment required to be grounded: [Reference paragraph (b)(3)(ii)(C)(4)(i) - (iii)].
  • 1910.304(b)(3)(ii)(C)(6) - Tests performed as required in paragraph (b)(3)(ii)(C) of this section shall be recorded. This test record shall identify each receptacle, cord set, and cord- and plug-connected equipment that passed the test and shall indicate the last date it was tested or the interval for which it was tested. This record shall be kept by means of logs, color coding, or other effective means and shall be maintained until replaced by a more current record. The record shall be made available on the jobsite for inspection by the Assistant Secretary and any affected employee.

1910.304(e)(2)(i) - Services over 600 volts, nominal. Service-entrance conductors installed as open wires shall be guarded to make them accessible only to qualified persons.

1910.304(e)(2)(ii) - Services over 600 volts, nominal. Signs warning of high voltage shall be posted where unqualified employees might come in contact with live parts.

1910.304(f)(1)(iii) - A disconnecting means shall be provided on the supply side of all fuses in circuits over 150 volts to ground and cartridge fuses in circuits of any voltage where accessible to other than qualified persons so that each individual circuit containing fuses can be independently disconnected from the source of power. However, a current-limiting device without a disconnecting means is permitted on the supply side of the service disconnecting means. In addition, a single disconnecting means is permitted on the supply side of more than one set of fuses as permitted by the exception in 1910.305(j)(4)(vi) - wiring methods, components, and equipment for general use, for group operation of motors, and a single disconnecting means is permitted for fixed electric space-heating equipment.

1910.304(f)(1)(iv) - 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 or in the vicinity of easily ignitable material.

1910.304(f)(1)(viii) - Circuit breakers used as switches in 120-volt and 277-volt, fluorescent lighting circuits shall be listed and marked "SWD."

1910.304(g)(1)(v)(C) - Systems to be grounded. 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:

  • 1910.304(g)(1)(v)(C)(2) - The conditions of maintenance and supervision ensure that only qualified persons will service the installation.

1910.304(g)(1)(v)(E) - If the system is a high-impedance grounded neutral system in which a grounding impedance, usually a resistor, limits the ground-fault current to a low value for 3-phase ac systems of 480 volts to 1000 volts provided all of the following conditions are met:

  • 1910.304(g)(1)(v)(E)(1) - The conditions of maintenance and supervision ensure that only qualified persons will service the installation.

1910.304(g)(6)(vii)(B) - Listed or labeled portable tools and appliances if protected by an approved system of double insulation, or its equivalent, and distinctively marked.

Scope: This standard provides electrical requirements for electrical installations and utilization equipment installed or used within or on buildings, structures, and other premises.

Qualified person - One who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.

Special Requirements: Markings/marked, signs, qualified person, approved, authorized, identified, nameplate, warning label, switching procedure (displayed)

1910.305(b)(3)(iii) - 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.

1910.305(c)(3)(ii) - Single-throw knife switches, molded-case switches, switches with butt contacts, and circuit breakers used as switches shall be connected so that the terminals supplying the load are deenergized when the switch is in the open position. However, blades and terminals supplying the load of a switch may be energized when the switch is in the open position where the switch is connected to circuits or equipment inherently capable of providing a backfeed source of power. For such installations, a permanent sign shall be installed on the switch enclosure or immediately adjacent to open switches that read, "WARNING -- LOAD SIDE TERMINALS MAY BE ENERGIZED BY BACKFEED."

1910.305(d)(1) - Switchboards with exposed live parts. Switchboards that have any exposed live parts shall be located in permanently dry locations and shall be accessible only to qualified persons.

1910.305(d)(2) - Panelboard enclosures. Panelboards shall be mounted in cabinets, cutout boxes, or enclosures designed 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.

1910.305(g)(1)(i) - Flexible cords and cables shall be approved for conditions of use and location.
 
1910.305(g)(1)(iii) - If used as permitted in paragraphs (g)(1)(ii)(C), (g)(1)(ii)(G), or (g)(1)(ii)(I) of this section, the flexible cord shall be equipped with an attachment plug and shall be energized from an approved receptacle outlet.
 
1910.305(h)(7) - Splices. Portable cables may not be operated with splices unless the splices are of the permanent molded, vulcanized, or other approved type.
 

1910.305(h)(8) - Terminations. Termination enclosures shall be suitably marked with a high voltage hazard warning, and terminations shall be accessible only to authorized and qualified employees.

1910.305(i)(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.

1910.305(j)(1)(iv) - Fixtures installed in wet or damp locations shall be identified for the purpose and shall be so constructed or installed that water cannot enter or accumulate in wireways, lampholders, or other electrical parts.

1910.305(j)(3)(iii) - Each electric appliance shall be provided with a nameplate giving the identifying name and the rating in volts and amperes, or in volts and watts. If the appliance is to be used on a specific frequency or frequencies, it shall be so marked. Where motor overload protection external to the appliance is required, the appliance shall be so marked.

1910.305(j)(3)(iv) - Marking shall be located so as to be visible or easily accessible after installation.

1910.305(j)(4)(ii) - An individual disconnecting means shall be provided for each controller. A disconnecting means shall be located within sight of 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 that is to be locked in the open position.

1910.305(j)(6)(ii)(D)(3) - Switching procedure prominently displayed at the switching location.

Scope: This standard provides electrical requirements for electrical installations and utilization equipment installed or used within or on buildings, structures, and other premises, primarily for specific purpose equipment (i.e., outside lights, circuses, cranes, hoists, elevators, welders) and installations.

Qualified person - One who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.

Special Requirements: Qualified person, signs, labels, listed, identified, references other standards

1910.306(a)(2)(iii) - Doors or covers giving access to uninsulated parts of indoor signs or outline lighting exceeding 600 volts and accessible to other than qualified persons shall either be provided with interlock switches to disconnect the primary circuit or shall be so fastened that the use of other than ordinary tools will be necessary to open them.

1910.306(c)(5) - Elevators, dumbwaiters, escalators, moving walks, wheelchair lifts, and stairway chair lifts. Location. The disconnecting means shall be located where it is readily accessible to qualified persons.

1910.306(c)(6)(ii) - Elevators, dumbwaiters, escalators, moving walks, wheelchair lifts, and stairway chair lifts. The disconnecting means shall be provided with a sign to identify the location of the supply-side overcurrent protective device.

1910.306(c)(8) - Elevators, dumbwaiters, escalators, moving walks, wheelchair lifts, and stairway chair lifts. Warning sign for multiple disconnecting means. A warning sign shall be mounted on or next to the disconnecting means where multiple disconnecting means are used and parts of the controllers remain energized from a source other than the one disconnected. The sign shall be clearly legible and shall read “WARNING - PARTS OF THE CONTROLLER ARE NOT DEENERGIZED BY THIS SWITCH.”

1910.306(g)(1)(iv) - Induction and dielectric heating equipment. Warning labels or signs that read “DANGER - HIGH VOLTAGE - KEEP OUT” shall be attached to the equipment and shall be plainly visible where persons might contact energized parts when doors are opened or closed or when panels are removed from compartments containing over 250 volts ac or dc.

1910.306(h)(4)(iii) - Power supply circuits and receptacles for portable electric equipment. Receptacles on circuits supplied by an isolating transformer with an ungrounded secondary:

1910.306(k)(2)(iii) - Carnivals, circuses, fairs, and similar events. Flexible cords and cables shall be listed for extra-hard usage. When used outdoors, flexible cords and cables shall also be listed for wet locations and shall be sunlight resistant.

1910.306(k)(2)(v) - Carnivals, circuses, fairs, and similar events. Open conductors are prohibited except as part of a listed assembly or festoon lighting installed in accordance with 1910.304(c) - wiring design and protection.

1910.306(k)(2)(vi) - Carnivals, circuses, fairs, and similar events. Flexible cords and cables shall be continuous without splice or tap between boxes or fittings. Cord connectors may not be laid on the ground unless listed for wet locations. Connectors and cable connections may not be placed in audience traffic paths or within areas accessible to the public unless guarded.

1910.306(k)(2)(vii) - Carnivals, circuses, fairs, and similar events. Wiring for an amusement ride, attraction, tent, or similar structure may not be supported by another ride or structure unless specifically identified for the purpose.

1910.306(k)(4)(iii) - Carnivals, circuses, fairs, and similar events. Portable distribution and termination boxes. Receptacles shall have overcurrent protection installed within the box. The overcurrent protection may not exceed the ampere rating of the receptacle, except as permitted in 1910.305(j)(4) - wiring methods, components, and equipment for general use, for motor loads.

1910.306(k)(4)(iv)(A) - Carnivals, circuses, fairs, and similar events. Where ac single-pole portable cable connectors are used, they shall be listed and of the locking type. Where paralleled sets of current-carrying single-pole separable connectors are provided as input devices, they shall be prominently labeled with a warning indicating the presence of internal parallel connections. The use of single-pole separable connectors shall comply with at least one of the following conditions: [Reference paragraph (k)(4)(iv)(A)(1) - (3)].

1910.306(k)(4)(iv)(B) - Carnivals, circuses, fairs, and similar events. Single-pole separable connectors used in portable professional motion picture and television equipment may be interchangeable for ac or dc use or for different current ratings on the same premises only if they are listed for ac/dc use and marked to identify the system to which they are connected.

Scope: This standard provides the requirements for electric equipment and wiring in locations that are classified depending on the properties of the flammable vapors, liquids or gases, or combustible dusts or fibers that may be present therein and the likelihood that a flammable or combustible concentration or quantity is present. 

Special Requirements: Authorized, documented, approved, employer demonstrates, protection techniques, zone classification system, division classification system, protection techniques, registered professional engineer, classified areas, listed, marked

1910.307(a)(4) - Division and zone classification. In Class I locations, an installation must be classified as using the division classification system meeting paragraphs (c), (d), (e), and (f) of this section or using the zone classification system meeting paragraph (g) of this section. In Class II and Class III locations, an installation must be classified using the division classification system meeting paragraphs (c), (d), (e), and (f)  of this section.
 
1910.307(b) - Documentation. All areas designated as hazardous (classified) locations under the Class and Zone system and areas designated under the Class and Division system established after August 13, 2007 shall be properly documented. This documentation shall be available to those authorized to design, install, inspect, maintain, or operate electric equipment at the location.
 
1910.307(c) - Electrical installations. Equipment, wiring methods, and installations of equipment in hazardous (classified) locations shall be intrinsically safe, approved for the hazardous (classified) location, or safe for the hazardous (classified) location. Requirements for each of these options are as follows: [Reference paragraph (c)(1) - (3)].
 
1910.307(e) - Equipment in Division 2 locations. Equipment that has been approved for a Division 1 location may be installed in a Division 2 location of the same class and group. General-purpose equipment or equipment in general-purpose enclosures may be installed in Division 2 locations if the employer can demonstrate that the equipment does not constitute a source of ignition under normal operating conditions.
 
1910.307(f) - Protection techniques. The following are acceptable protection techniques for electric and electronic equipment in hazardous (classified) locations. [Reference paragraph (f)(1) - (10)].
 
1910.307(g)(1) - Scope. Employers may use the zone classification system as an alternative to the division classification system for electric and electronic equipment and wiring for all voltage in Class I, Zone 0, Zone 1, and Zone 2 hazardous (classified) locations where fire or explosion hazards may exist due to flammable gases, vapors, or liquids.
 
1910.307(g)(3) - Protection techniques. One or more of the following protection techniques shall be used for electric and electronic equipment in hazardous (classified) locations classified under the zone classification system. [Reference paragraph (g)(3)(i) - (viii)].
 

1910.307(g)(4)(i) - Classification of areas and selection of equipment and wiring methods shall be under the supervision of a qualified registered professional engineer.

1910.307(g)(5)(i) - Equipment that is listed for a Zone 0 location may be installed in a Zone 1 or Zone 2 location of the same gas or vapor. Equipment that is listed for a Zone 1 location may be installed in a Zone 2 location of the same gas or vapor.

1910.307(g)(5)(ii) - Equipment shall be marked in accordance with paragraph (g)(5)(ii)(A) and (g)(5)(ii)(B) of this section, except as provided in (g)(5)(ii)(C).

1910.307(g)(5)(ii)(A) - Equipment approved for Class I, Division 1 or Class 1, Division 2 shall, in addition to being marked in accordance with (c)(2)(ii), be marked with the following: [Reference paragraph (g)(5)(ii)(A)(1) - (3)].

1910.307(g)(5)(ii)(C) - Equipment that the employer demonstrates will provide protection from the hazards arising from the flammability of the gas or vapor and the zone of location involved and will be recognized as providing such protection by employees need not be marked.

Scope: This standard provides the general requirements for all circuits and equipment operated at over 600 volts.

Special Requirements: Signs, authorized qualified person, supervision, classification, listed, markings, references other standards

1910.308(a)(5)(iv) - Where fused cutouts are not suitable to interrupt the circuit manually while carrying full load, an approved means shall be installed to interrupt the entire load. Unless the fused cutouts are interlocked with the switch to prevent opening of the cutouts under load, a conspicuous sign shall be placed at such cutouts reading: "WARNING – DO NOT OPERATE UNDER LOAD."

1910.308(a)(5)(vi)(B) - Where more than one switch is installed with interconnected load terminals to provide for alternate connection to different supply conductors, each switch shall be provided with a conspicuous sign reading: "WARNING – SWITCH MAY BE ENERGIZED BY BACKFEED."

1910.308(a)(6)(i) - A metallic enclosure shall be provided on the mobile machine for enclosing the terminals of the power cable. The enclosure shall include provisions for a solid connection for the grounding terminal to effectively ground the machine frame. The method of cable termination used shall prevent any strain or pull on the cable from stressing the electrical connections. The enclosure shall have provision for locking so only authorized qualified persons may open it and shall be marked with a sign warning of the presence of energized parts.

1910.308(a)(6)(ii) - All energized switching and control parts shall be enclosed in effectively grounded metal cabinets or enclosures. Circuit breakers and protective equipment shall have the operating means projecting through the metal cabinet or enclosure so these units can be reset without locked doors being opened. Enclosures and metal cabinets shall be locked so that only authorized qualified persons have access and shall be marked with a sign warning of the presence of energized parts. Collector ring assemblies on revolving-type machines (shovels, draglines, etc.) shall be guarded.

1910.308(b)(2) - Emergency illumination. Emergency illumination shall include all required means of egress lighting, illuminated exit signs, and all other lights necessary to provide illumination. Where emergency lighting is necessary, the system shall be so arranged that the failure of any individual lighting element, such as the burning out of a light bulb, cannot leave any space in total darkness. 

1910.308(b)(3)(i) - A sign shall be placed at the service entrance equipment indicating the type and location of on-site emergency power sources. However, a sign is not required for individual unit equipment.
 
1910.308(b)(3)(ii) - Where the grounded circuit conductor connected to the emergency source is connected to a grounding electrode conductor at a location remote from the emergency source, there shall be a sign at the grounding location that shall identify all emergency and normal sources connected at that location.
 
1910.308(c)(1) - Classification. Class 1, Class 2, and Class 3 remote control, signaling, or power-limited circuits are characterized by their usage and electrical power limitation that differentiates them from light and power circuits. These circuits are classified in accordance with their respective voltage and power limitations as summarized in paragraphs (c)(1)(i) through (c)(1)(iii) of this section. 
 
1910.308(c)(2) - Marking. A Class 2 or Class 3 power supply unit shall be durably marked where plainly visible to indicate the class of supply and its electrical rating.
 
1910.308(d)(1) - Classifications. Fire alarm circuits shall be classified either as nonpower limited or power limited. 
 
1910.308(d)(4) - Identification. Fire alarm circuits shall be identified at terminal and junction locations in a manner that will prevent unintentional interference with the signaling circuit during testing and servicing. Power-limited fire alarm circuits shall be durably marked as such where plainly visible at terminations. 
 
1910.308(e) - Communications systems. This paragraph applies to central-station-connected and non-central-station-connected telephone circuits, radio and television receiving and transmitting equipment, including community antenna television and radio distribution systems, telegraph, district messenger, and outside wiring for fire and burglar alarm, and similar central station systems. These installations need not comply with the provisions of 1910.303 - general, through 1910.308(d) - special systems, except for 1910.304(c)(1) - wiring design and protection, and 1910.307 - hazardous locations
 
1910.308(e)(1)(i) - A listed primary protector shall be provided on each circuit run partly or entirely in aerial wire or aerial cable not confined within a block.
 
1910.308(e)(1)(ii) - A listed primary protector shall be also provided on each aerial or underground circuit when the location of the circuit within the block containing the building served allows the circuit to be exposed to accidental contact with electric light or power conductors operating at over 300 volts to ground.
 
1910.308(e)(1)(iii) - In addition, where there exists a lightning exposure, each interbuilding circuit on premises shall be protected by a listed primary protector at each end of the interbuilding circuit.
 
1910.308(g)(1) - Scope. Paragraph (g) of this section covers integrated electrical systems, other than unit equipment, in which orderly shutdown is necessary to ensure safe operation. An integrated electrical system as used in this section shall be a unitized segment of an industrial wiring system where all of the following conditions are met:
  • 1910.308(g)(1)(ii) - The conditions of maintenance and supervision ensure that only qualified persons will service the system.
1910.308(g)(2) - Location of overcurrent devices in or on premises. Overcurrent devices that are critical to integrated electrical systems need not be readily accessible to employees as required by 1910.304(f)(1)(iv) - wiring design and protection, if they are located with mounting heights to ensure security from operation by nonqualified persons.

Scope: This standard provides the training requirements for employees who face a risk of electric shock that is not reduced to a safe level by the electrical installation requirements of 1910.303 through 1910.308.

Note: Employees in occupations listed in Table S-4 face such a risk and are required to be trained. Other employees who also may reasonably be expected to face a comparable risk of injury due to electric shock or other electrical hazards must also be trained.

Special Requirements: Training, qualified person, unqualified person, safety related work practices, references other standards

1910.332(b)(1) - Practices addressed in this standard. Employees shall be trained in and familiar with the safety-related work practices required by 1910.331 through 1910.335 that pertain to their respective job assignments.

1910.332(b)(2) - Additional requirements for unqualified persons. Employees who are covered by paragraph (a) of this section but who are not qualified persons shall also be trained in and familiar with any electrically related safety practices not specifically addressed by 1910.331 through 1910.335 but which are necessary for their safety.

1910.332(b)(3) - Additional requirements for qualified persons. Qualified persons (i.e., those permitted to work on or near exposed energized parts) shall, at a minimum, be trained in and familiar with the following: [Reference paragraph (b)(3)(i) - (iii)].
 
1910.332(c) - Type of training. The training required by this section shall be of the classroom or on-the-job type. The degree of training provided shall be determined by the risk to the employee.

Scope: This standard provides the requirements pertaining to safe work practices.  

Special Requirements: Safety-related work practices, employer demonstrates, locked/tagged, tagging, procedures (written), qualified person, inspections, tests, visual determination, precautionary techniques, approved, protective measures, housekeeping duties, references other standards

1910.333(a) - General. Safety-related work practices shall be employed to prevent electric shock or other injuries resulting from either direct or indirect electrical contacts, when work is performed near or on equipment or circuits which are or may be energized. The specific safety-related work practices shall be consistent with the nature and extent of the associated electrical hazards.

1910.333(a)(1) - Deenergized parts. Live parts to which an employee may be exposed shall be deenergized before the employee works on or near them, unless the employer can demonstrate that deenergizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations. Live parts that operate at less than 50 volts to ground need not be deenergized if there will be no increased exposure to electrical burns or to explosion due to electric arcs.

1910.333(a)(2) - Energized parts. If the exposed live parts are not deenergized (i.e., for reasons of increased or additional hazards or infeasibility), other safety-related work practices shall be used to protect employees who may be exposed to the electrical hazards involved. Such work practices shall protect employees against contact with energized circuit parts directly with any part of their body or indirectly through some other conductive object. The work practices that are used shall be suitable for the conditions under which the work is to be performed and for the voltage level of the exposed electric conductors or circuit parts. Specific work practice requirements are detailed in paragraph (c) of this section.

1910.333(b)(1) - Application. This paragraph applies to work on exposed deenergized parts or near enough to them to expose the employee to any electrical hazard they present. Conductors and parts of electric equipment that have been deenergized but have not been locked out or tagged in accordance with paragraph (b) of this section shall be treated as energized parts, and paragraph (c) of this section applies to work on or near them.

1910.333(b)(2) - Lockout and tagging. While any employee is exposed to contact with parts of fixed electric equipment or circuits which have been deenergized, the circuits energizing the parts shall be locked out or tagged or both in accordance with the requirements of this paragraph. The requirements shall be followed in the order in which they are presented (i.e., paragraph (b)(2)(i) first, then paragraph (b)(2)(ii), etc.).

1910.333(c)(2) - Work on energized equipment. Only qualified persons may work on electric circuit parts or equipment that have not been deenergized under the procedures of paragraph (b) of this section. Such persons shall be capable of working safely on energized circuits and shall be familiar with the proper use of special precautionary techniques, personal protective equipment, insulating and shielding materials, and insulated tools.

1910.333(c)(3) - Overhead lines. If work is to be performed near overhead lines, the lines shall be deenergized and grounded, or other protective measures shall be provided before work is started. If the lines are to be deenergized, arrangements shall be made with the person or organization that operates or controls the electric circuits involved to deenergize and ground them. If protective measures, such as guarding, isolating, or insulating are provided, these precautions shall prevent employees from contacting such lines directly with any part of their body or indirectly through conductive materials, tools, or equipment. 

Note: The work practices used by qualified persons installing insulating devices on overhead power transmission or distribution lines are covered by 1910.269 - electric power generation, transmission, and distribution, of this part, not by 1910.332 through 1910.335 of this part. Under paragraph (c)(2) of this section, unqualified persons are prohibited from performing this type of work.

1910.333(c)(3)(i)(A) - When an unqualified person is working in an elevated position near overhead lines, the location shall be such that the person and the longest conductive object he or she may contact cannot come closer to any unguarded, energized overhead line than the following distances: [Reference paragraph (c)(3)(i)(A) - (B)].

1910.333(c)(3)(ii) - Qualified persons. When a qualified person is working in the vicinity of overhead lines, whether in an elevated position or on the ground, the person may not approach or take any conductive object without an approved insulating handle closer to exposed energized parts than shown in Table S-5 unless:  [Reference paragraph (c)(3)(ii)(A) - (C)].

1910.333(c)(3)(iii)(A)(3) - If the equipment is an aerial lift insulated for the voltage involved, and if the work is performed by a qualified person, the clearance (between the uninsulated portion of the aerial lift and the power line) may be reduced to the distance given in Table S-5.

1910.333(c)(6) - Conductive materials and equipment. Conductive materials and equipment that are in contact with any part of an employee's body shall be handled in a manner that will prevent them from contacting exposed energized conductors or circuit parts. If an employee must handle long dimensional conductive objects (such as ducts and pipes) in areas with exposed live parts, the employer shall institute work practices (such as the use of insulation, guarding, and material handling techniques) which will minimize the hazard.

1910.333(c)(9) - Housekeeping duties. Where live parts present an electrical contact hazard, employees may not perform housekeeping duties at such close distances to the parts that there is a possibility of contact, unless adequate safeguards (such as insulating equipment or barriers) are provided. Electrically conductive cleaning materials (including conductive solids such as steel wool, metalized cloth, and silicon carbide, as well as conductive liquid solutions) may not be used in proximity to energized parts unless procedures are followed which will prevent electrical contact.

Scope: This standard provides requirements for use of equipment.

Special Requirements: Inspections, tests, qualified person, equipment rating, checks, approved, references other standards

1910.334(a)(2)(i) - Portable cord- and plug-connected equipment and flexible cord sets (extension cords) shall be visually inspected before use on any shift for external defects (such as loose parts, deformed and missing pins, or damage to outer jacket or insulation) and for evidence of possible internal damage (such as pinched or crushed outer jacket). Cord- and plug-connected equipment and flexible cord sets (extension cords) which remain connected once they are put in place and are not exposed to damage need not be visually inspected until they are relocated.

1910.334(a)(2)(ii) - If there is a defect or evidence of damage that might expose an employee to injury, the defective or damaged item shall be removed from service, and no employee may use it until repairs and tests necessary to render the equipment safe have been made.

1910.334(a)(2)(iii) - When an attachment plug is to be connected to a receptacle (including any on a cord set), the relationship of the plug and receptacle contacts shall first be checked to ensure that they are of proper mating configurations.

1910.334(a)(4) - Conductive work locations. Portable electric equipment and flexible cords used in highly conductive work locations (such as those inundated with water or other conductive liquids), or in job locations where employees are likely to contact water or conductive liquids, shall be approved for those locations.

1910.334(b)(3) - Overcurrent protection modification. Overcurrent protection of circuits and conductors may not be modified, even on a temporary basis, beyond that allowed by 1910.304(e) - wiring design and protection, the installation safety requirements for overcurrent protection.

1910.334(c)(1) - Use. Only qualified persons may perform testing work on electric circuits or equipment. 
 
1910.334(c)(2) - Visual inspection. Test instruments and equipment and all associated test leads, cables, power cords, probes, and connectors shall be visually inspected for external defects and damage before the equipment is used. If there is a defect or evidence of damage that might expose an employee to injury, the defective or damaged item shall be removed from service, and no employee may use it until repairs and tests necessary to render the equipment safe have been made.
 
1910.334(c)(3) - Rating of equipment. Test instruments and equipment and their accessories shall be rated for the circuits and equipment to which they will be connected and shall be designed for the environment in which they will be used. 
 
1910.334(d) - Occasional use of flammable or ignitible materials. Where flammable materials are present only occasionally, electric equipment capable of igniting them shall not be used, unless measures are taken to prevent hazardous conditions from developing. Such materials include, but are not limited to: flammable gases, vapors, or liquids; combustible dust; and ignitible fibers or flyings. Note: Electrical installation requirements for locations where flammable materials are present on a regular basis are contained in 1910.307 - hazardous locations.

Scope: This standard provides requirements pertaining to safeguards used for personnel protection.  

Special Requirements: Inspected, tests, unqualified person, warning signs, tags, attendants, alerting techniques, references other standards

1910.335(a)(1)(i) - Employees working in areas where there are potential electrical hazards shall be provided with, and shall use, electrical protective equipment that is appropriate for the specific parts of the body to be protected and for the work to be performed. Note: Personal protective equipment requirements are contained in subpart I  - personal protective equipment of this part (1910).

1910.335(a)(1)(ii) - Protective equipment shall be maintained in a safe, reliable condition and shall be periodically inspected or tested, as required by 1910.137 -electrical protective devices.

1910.335(a)(2)(ii) - Protective shields, protective barriers, or insulating materials shall be used to protect each employee from shock, burns, or other electrically related injuries while that employee is working near exposed energized parts which might be accidentally contacted or where dangerous electric heating or arcing might occur. When normally enclosed live parts are exposed for maintenance or repair, they shall be guarded to protect unqualified persons from contact with the live parts.
 
1910.335(b) - Alerting techniques. The following alerting techniques shall be used to warn and protect employees from hazards which could cause injury due to electric shock, burns, or failure of electric equipment parts:
  • 1910.335(b)(1) - Safety signs and tags. Safety signs, safety symbols, or accident prevention tags shall be used where necessary to warn employees about electrical hazards which may endanger them, as required by 1910.145 - specifications for accident prevention signs and tags.
  • 1910.335(b)(2) - Barricades. Barricades shall be used in conjunction with safety signs where it is necessary to prevent or limit employee access to work areas exposing employees to uninsulated energized conductors or circuit parts. Conductive barricades may not be used where they might cause an electrical contact hazard.
  • 1910.335(b)(3) - Attendants. If signs and barricades do not provide sufficient warning and protection from electrical hazards, an attendant shall be stationed to warn and protect employees.
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