Approval of electrical equipment

An installation or piece of electrical equipment is "approved" or "acceptable" if it is accepted, certified, listed, labeled, or otherwise determined to be safe by a nationally recognized testing laboratory (NRTL) recognized under 1910.7, or if it meets the limited alternative criteria in 1910.399.

• The standard explicitly lists three ways equipment/installation can be acceptable: NRTL acceptance/certification/listing/labeling; inspection/testing and compliance finding by a Federal, State, municipal, or local authority responsible for enforcing the National Electrical Code (NEC); or manufacturer test data for custom-made equipment showing it is safe for its intended use (which the employer must keep and make available).
• See the Approval of electrical equipment provision in 1910.399 for the exact text.

Yes—if the laboratory is a nationally recognized testing laboratory (NRTL) that OSHA has recognized under 1910.7, then its acceptance, certification, listing, or labeling makes the equipment acceptable under 1910.399.

• What matters is OSHA recognition under 1910.7, not where the lab is physically located.
• Always verify that the test laboratory appears on OSHA’s current list of recognized NRTLs (see 1910.7).

If equipment is custom-made for a particular customer, it is acceptable only when the manufacturer determines it is safe for its intended use based on test data, and the employer keeps those test data and makes them available for inspection by OSHA (the Assistant Secretary or authorized representatives) as required by 1910.399(3).

• Keep complete test reports and documentation the manufacturer used to show safety for the intended use.
• Make the documentation available to OSHA inspectors on request.
• The custom equipment must be designed and fabricated for a particular customer (not standard production equipment) to qualify for this route under 1910.399.

If no nationally recognized testing laboratory will accept or certify that kind of equipment, you can have the installation or equipment inspected or tested by another Federal agency or by a State, municipal, or local authority responsible for enforcing the National Electrical Code; if that authority finds the equipment in compliance with the NEC as applied in this subpart, it will be acceptable under 1910.399(2).

• Contact the authority that enforces the NEC in your jurisdiction (for example, the State electrical board or local inspector) and arrange an inspection or test.
• Obtain written documentation that the inspecting authority found the equipment/installation compliant with the NEC.
• Keep the compliance records available for OSHA inspection.

Evidence that equipment is "certified" includes a label, tag, or other record of certification showing the equipment was tested and found by a nationally recognized testing laboratory to meet standards or be safe for a specified manner of use, as described in the definitions in 1910.399.

• A visible label on the equipment from an OSHA-recognized NRTL is the most common form of proof.
• Other acceptable records include tags, certification letters, or test reports issued by the NRTL.
• Make sure the NRTL is one recognized under 1910.7.

When applied to an installation, "accepted" means that a nationally recognized testing laboratory has inspected it and found it to conform to specified plans or to procedures of applicable codes, as defined in 1910.399.

• This is an inspection-based acceptance by an NRTL rather than a simple label on a product.
• Keep documentation of the NRTL inspection or acceptance available for inspection by OSHA.

Under this subpart, "approved" means acceptable to the authority enforcing the subpart—the Assistant Secretary of Labor for Occupational Safety and Health—so approval follows the criteria in 1910.399.

• Practically, this means equipment must meet one of the acceptance paths in 1910.399: NRTL acceptance/certification/listing/labeling; inspection/testing by the appropriate NEC authority and a finding of NEC compliance; or manufacturer test data for custom equipment maintained by the employer.

Yes—if you rely on manufacturer test data to show that custom-made equipment is safe under 1910.399(3), the employer must keep those test data and make them available for inspection to the Assistant Secretary of Labor and authorized representatives (OSHA inspectors).

• Maintain clear, accessible test reports, protocols, and any calculations the manufacturer used.
• Provide electronic or paper copies during an inspection upon OSHA’s request.

Yes—1910.399(2) allows equipment or installations to be acceptable if a Federal agency or the State/municipal/local authority responsible for enforcing the National Electrical Code inspects or tests the equipment and finds it in compliance with the NEC as applied in this subpart.

• Ensure the inspecting authority is officially responsible for enforcing the NEC in that jurisdiction.
• Obtain written documentation of the inspection and NEC compliance finding and keep it available for OSHA inspection.

For wiring methods, "accessible" means capable of being removed or exposed without damaging the building structure or finish, or not permanently closed in by the building structure or finish; for equipment, "accessible" (admitting close approach) means not guarded by locked doors, elevation, or other effective means, as defined in 1910.399.

• For wiring: if you can expose or remove the wiring without tearing down structure or finish, it is accessible.
• For equipment: if a worker can approach closely without needing to defeat locks or climb to an elevated guarded area, it is accessible.
• These definitions help determine inspection, maintenance, and safety-protection requirements—see 1910.399 for the exact wording.

"Ampacity" is defined as the current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating, per the definitions in 1910.399.

• Ampacity determines conductor sizing, overcurrent protection, and safe operation.
• Using conductors with insufficient ampacity can cause overheating and fire hazards.
• Design and inspection should ensure conductor ampacity is appropriate for the installed conditions.

Under this subpart, "appliances" are utilization equipment (generally other than industrial) normally built in standardized sizes or types, installed or connected as a unit to perform one or more functions, according to the definition in 1910.399.

• Appliances include things like household-type units or standardized equipment that are installed as units (not custom-built industrial machines).
• Even so, their installation still must comply with applicable electrical rules; accepted/listed appliances with NRTL markings are generally acceptable under 1910.399.

An "attachment plug (plug cap)" is defined as a device that, by insertion in a receptacle, establishes a connection between the conductors of the attached flexible cord and the conductors connected permanently to the receptacle, per 1910.399.

• The definition is important for safe cord-and-plug connections, ensuring connectors used are appropriate and compatible with receptacles.
• Using improper or damaged attachment plugs can create shock or fire hazards; use NRTL-listed plugs and receptacles where required.

Yes—1910.399(2) allows acceptance when equipment of a kind that no NRTL accepts is inspected or tested by another Federal agency and found in compliance with the NEC as applied in this subpart.

• The Federal agency must inspect/test and find the equipment compliant with the NEC as applied in this subpart for it to be acceptable.
• Obtain written evidence of the Federal agency’s inspection and compliance finding and retain it for inspection by OSHA.

No—while NRTL listing/labeling is the primary route to acceptability under 1910.399(1), the standard allows two alternative routes: inspection/testing and NEC compliance verification by an appropriate Federal/State/local authority when no NRTL accepts the equipment, and manufacturer test data for custom-made equipment when kept and produced on request (see 1910.399(2) and (3)).

• Use NRTL-listed equipment when available, but if not available follow the alternative paths and keep the required documentation.

Yes—when the term "accepted" is applied to an installation, it means the installation has been inspected and found by a nationally recognized testing laboratory to conform to specified plans or to procedures of applicable codes, as defined in 1910.399.

• This is different from a simple product label; acceptance implies an NRTL inspected the installation against plans or procedures.
• Keep records of the NRTL acceptance inspection for OSHA review.

Wiring methods that are described as "accessible" are those that can be removed or exposed without damaging the building structure or finish, and such accessibility affects inspection and maintenance requirements; the installation must follow applicable code provisions and the definitions in 1910.399.

• Accessible wiring is typically intended to be inspected and serviced; concealed wiring (per the NEC and related provisions) may have different protection and inspection expectations.
• Follow the NEC and the installation requirements in the relevant subparts referenced by 1910.399 to ensure correct methods for accessible versus concealed wiring.

The authority enforcing this subpart is the Assistant Secretary of Labor for Occupational Safety and Health; therefore, "approved" means acceptable to the Assistant Secretary, as stated in the definition section of 1910.399.

• Practically, OSHA enforcement follows the acceptance paths described in 1910.399, including NRTL recognition under 1910.7.

Yes—1910.399 defines "certified" to include equipment of a kind whose production is periodically inspected by a nationally recognized testing laboratory and is accepted by the laboratory as safe for its intended use.

• Periodic production inspections by an NRTL may serve as the basis for certification; retain records of the NRTL’s production inspections and acceptance for OSHA review.

A Class I, Zone 2 location is an area where ignitable concentrations of flammable gases or vapors are not likely during normal operation and, if they do occur, will only exist for a short time. See the definition in 1910.399 for the full list of scenarios that qualify (for example, closed systems, positive mechanical ventilation that could fail, or locations adjacent to Zone 1).

• Reference: 1910.399.

A Class II, Division 1 location is an area where combustible dust is or may be suspended in the air under normal operating conditions in quantities sufficient to form explosive or ignitable mixtures, or where mechanical failure/abnormal operation could create such suspensions and ignition sources. The definition and examples (e.g., grain handling, starch plants, metal dust processing) are in 1910.399.

• Reference: 1910.399.

A Class II, Division 2 location is an area where combustible dust normally will not be suspended in the air in explosive quantities and accumulations normally won’t interfere with equipment operation, but dust may become suspended or accumulate during infrequent malfunctions or abnormal operations and could interfere with heat dissipation or be ignited by equipment failure. See the definition and note in 1910.399.

• Reference: 1910.399.

Combustible dusts that are electrically nonconductive include dusts from grain and grain products, pulverized sugar and cocoa, dried egg and milk powders, pulverized spices, starch, potato and wood flour, oil meal, dried hay, and other organic materials; dusts containing magnesium or aluminum are highlighted as particularly hazardous. The examples and cautions appear in 1910.399.

• Reference: 1910.399.

A Class III, Division 1 location is where easily ignitable fibers or flyings are handled, manufactured, or used; Class III, Division 2 is where such easily ignitable fibers are stored or handled other than during manufacturing. The standard lists common workplaces and materials for each division in 1910.399.

• Reference: 1910.399.

An 'explosion-proof apparatus' is equipment enclosed in a case designed to withstand an internal explosion of a specified gas or vapor and prevent ignition of the surrounding atmosphere by sparks, flashes, or explosion products, and it must operate at an external temperature that will not ignite the surrounding flammable atmosphere. That definition is given in 1910.399.

• Reference: 1910.399.

A 'competent person' is someone capable of identifying existing and predictable hazards in the surroundings or working conditions that are unsanitary, hazardous, or dangerous to employees and who is authorized to take prompt corrective action to eliminate them. See the definition in 1910.399.

• Reference: 1910.399.

'Exposed' (as applied to live parts) means parts capable of being inadvertently touched or approached nearer than a safe distance because they are not suitably guarded, isolated, or insulated; for wiring methods it means on or attached to the surface or behind panels designed to allow access. These definitions are in 1910.399. For the special meaning used in 1910.308(e), 'exposed' describes circuits positioned such that a failure of supports or insulation could permit contact with another circuit.

• References: 1910.399 and 1910.308(e).

'Enclosed' means surrounded by a case, housing, fence, or walls that will prevent accidental contact with energized parts. An 'enclosure' is the case or housing (or fence or walls) around apparatus to prevent contact with energized parts or to protect equipment from physical damage. See these definitions in 1910.399.

• Reference: 1910.399.

'Grounded' simply means connected to the earth or to a conducting body that serves in place of the earth. 'Grounded, effectively' means intentionally connected to earth through a ground connection or connections of sufficiently low impedance and sufficient current-carrying capacity to prevent voltages that could create undue hazards to equipment or people. Both definitions appear in 1910.399.

• Reference: 1910.399.

A 'bare' conductor has no covering or electrical insulation; a 'covered' conductor is encased within material not recognized as electrical insulation by the subpart; and an 'insulated' conductor is encased within material recognized as electrical insulation by the subpart. These conductor definitions are provided in 1910.399.

• Reference: 1910.399.

'Deenergized' means free from any electrical connection to a source of potential difference and from electrical charge; not having a potential different from earth. 'Dead front' means equipment without live parts exposed to a person on the operating side. See the definitions in 1910.399.

• Reference: 1910.399.

A 'feeder' is all circuit conductors between the service equipment, the source of a separate derived system, or other power supply source and the final branch-circuit overcurrent device. The term is defined in 1910.399.

• Reference: 1910.399.

A location adjacent to a Class I, Zone 1 area is considered Class I, Zone 2 if ignitable concentrations of flammable gases or vapors could be communicated from the Zone 1 area, unless such communication is prevented by adequate positive-pressure ventilation supplied from clean air and effective safeguards against ventilation failure. This adjacency rule is described in 1910.399.

• Reference: 1910.399.

Equipment is "identified" when it has been approved as suitable for the specific purpose, function, use, environment, or application called out in the rule. See Definition of "identified" in 1910.399.

• Employers commonly determine suitability by relying on investigations or certifications from a nationally recognized testing laboratory, an inspection agency, or another organization recognized as "acceptable" under 1910.7.
• An "identified" determination should be specific to the intended environment and use (for example, a device listed for dry locations may not be identified for use in wet locations). See 1910.399 definition of "identified" for the concept and 1910.7 for recognized testing organizations.

A piece of equipment is "listed" if it appears on a published list by a nationally recognized laboratory that inspects production and states the equipment meets recognized standards or tests; it is "labeled" if the equipment has an attached label, symbol, or mark from such a laboratory indicating compliance. See Definitions of "listed" and "labeled" in 1910.399.

• "Listed" emphasizes inclusion on the laboratory's published list and meeting the applicable standard.
• "Labeled" emphasizes a physical marking on the product showing the lab's identification and that production is periodically inspected.
• Both concepts rely on the role of nationally recognized testing laboratories discussed in 1910.7.

A label from a nationally recognized testing laboratory strongly supports that equipment is "identified" for its specified purpose, but you must still verify the label covers the exact application, environment, and function you need. See 1910.399 definition of "labeled" and "identified" and consult the criteria for recognized organizations in 1910.7.

• Check the label/listing scope (for example: rated voltages, indoor/outdoor, wet/damp location, heating, or specific equipment types).
• A label that indicates periodic factory inspection and compliance with a relevant standard is persuasive evidence of suitability, but you must ensure the listed use matches your workplace conditions.

"Guarded" means that the hazard is covered, shielded, fenced, enclosed, or otherwise protected with suitable covers, barriers, rails, screens, mats, or platforms to prevent people or objects from contacting the danger point. See Definition of "guarded" in 1910.399.

• Guarding reduces the likelihood of accidental contact with live parts or moving electrical equipment.
• The method of guarding should be suitable to remove the likelihood of approach to the point of danger; labeling alone is not "guarding." Refer to the equipment-specific requirements in 1910.306 for how enclosures and guarding interact with wiring and equipment installations.

A ground-fault circuit interrupter (GFCI) is a device intended to protect people by deenergizing a circuit within a set time when current to ground exceeds a predetermined value that is less than the supply circuit's overcurrent device trip level. See Definition of GFCI in 1910.399.

• GFCIs are used where leakage currents to ground create a risk of electric shock (for example, in wet or damp locations, near water, or for portable tools).
• Installation specifics and where GFCIs are required or recommended are covered elsewhere in the electrical rules such as 1910.306 and related wiring provisions.

A dry location is not normally subject to dampness or wetness; a damp location is partially protected but subject to moderate moisture (e.g., some basements or under canopies); a wet location is one that is saturated with water or exposed to weather. See Definitions of "dry location," "damp location," and "wet location" in 1910.399.

• Select equipment rated for the location: equipment listed or labeled for wet locations is required where saturation or direct exposure occurs.
• When in doubt, choose equipment with the higher degree of protection (e.g., wet-location rated) or consult the installation requirements in 1910.306.

A "qualified person" is someone who has received training and demonstrated skills and knowledge in the construction and operation of electrical equipment and installations and the hazards involved. See Definition of "qualified person" in 1910.399.

• Whether a worker is "qualified" depends on the specific equipment and circumstances; someone may be qualified for one task but not for another.
• Training requirements that apply to qualified persons are described in 1910.332(b)(3), which employers should consult to ensure the necessary training and demonstration of ability.

"Sealable equipment" is equipment enclosed in a case or cabinet with means to seal or lock it so live parts cannot be accessed without opening the enclosure; it may or may not operate while sealed. See Definition of "sealable equipment" in 1910.399.

• Sealing is used to prevent unauthorized access to live parts and to indicate tampering.
• Whether sealing or locking is required depends on the specific equipment rules and installation requirements; review equipment-specific provisions in 1910.306 and related sections for when enclosures must be lockable or sealed.

"Readily accessible" means capable of being reached quickly for operation, renewal, or inspections without having to climb over or remove obstacles or resort to portable ladders, chairs, etc.; equipment should be reachable so those needing ready access can get to it quickly. See Definition of "readily accessible" in 1910.399.

• When installing disconnects, circuit breakers, or other controls, ensure clear access per this definition and consult applicable installation rules in 1910.306 for specifics.

A "raceway" is an enclosed channel of metal or nonmetallic materials designed to hold wires, cables, or busbars, and raceways include rigid metal conduit, electrical metallic tubing, flexible conduit, surface raceways, wireways, busways, and others. See Definition of "raceway" and examples in 1910.399 and the list of examples in that section.

• Use the appropriate raceway type for the environment, mechanical protection, and code requirements; consult 1910.306 for installation and protection requirements.

"Live parts" are energized conductive components. See Definition of "live parts" in 1910.399.

• Working near live parts requires clear procedures to prevent accidental contact, such as guarding, insulated tools, safe work practices, and potentially lockout/tagout under relevant standards.
• Employers should follow electrical safety requirements in 1910.332 and other applicable parts of 1910 when employees may be exposed to live parts.

For the purposes of 1910.306(g), "heating equipment" includes any equipment used for heating purposes where heat is generated by induction or dielectric methods. See Definition of "heating equipment" in 1910.399 and the specific provision at 1910.306(g).

• If your equipment generates heat by induction or dielectric heating, treat it as "heating equipment" for the installation and protection rules in 1910.306(g).

OSHA gives examples that investigations by a nationally recognized testing laboratory through listing and labeling, or by an inspection agency or other organization recognized under "acceptable" in 1910.7 are ways to determine equipment suitability. See the note to the definition of "identified" in 1910.399.

• Typical evidence includes: a listing on the laboratory's published list, an attached label or mark indicating compliance, and periodic factory inspections by the laboratory.
• Confirm the scope of the listing/label to ensure it covers the intended environment and application.

No — "isolated (as applied to location)" simply means the location is not readily accessible to persons unless special means for access are used; it does not by itself make the area safe or remove the need for training, controls, or PPE. See Definition of "isolated (as applied to location)" in 1910.399.

• Even if a location is isolated, employees who must enter it still need appropriate hazard assessments, training, and controls under relevant standards such as 1910.332 for electrical safety training.
• "Isolated" describes accessibility, not the presence or absence of hazards.

Yes — electrical equipment that must be "approved" needs to be evaluated and listed by a recognized testing laboratory and used in accordance with that listing and the standards that govern installations. Employers should rely on equipment that is marked and listed by a Nationally Recognized Testing Laboratory (NRTL) when the occupational standard or the employer’s program requires approval.

• "Approved" means the equipment has been evaluated, tested, and listed by a recognized organization; see the recognition of testing laboratories at 1910.7.
• Use equipment in the manner and environment for which it was listed; modifications, improper installation, or use outside the listed conditions can void the approval.
• Installation and safe use must also meet the electrical installation requirements in 1910.306, so approval alone does not replace proper installation and workplace safeguards.

Cited authorities: 1910.7 and 1910.306.

A switchboard is a large single panel, frame, or assembly of panels that houses switches, overcurrent devices, buses, and usually instruments, and it is generally accessible from the rear as well as the front and not intended to be installed in cabinets. That definition drives installation and working-space expectations under the electrical installation rules.

• The definition of "switchboard" is in 1910.399 and makes clear switchboards are typically accessed from both front and rear.
• Because switchboards are normally accessible, installation and safety requirements in 1910.306 apply — for example, provide the required clear working space, maintain access for operation and maintenance, and observe enclosure and guarding requirements.
• For specifics about required clearances and working space around electrical equipment, consult the applicable paragraphs of 1910.306, including the provisions addressing working spaces and access at 1910.306(g).

Cited authorities: 1910.399 and 1910.306 (including 1910.306(g)).

Yes — Type USE single, parallel, or cable conductor assemblies recognized for underground use may have a bare copper concentric conductor applied, and those constructions do not require an outer overall covering.

• The definition and allowance are set out in 1910.399, which explicitly states these constructions do not require an outer overall covering.
• Even when a construction is permitted without an outer covering, installation and grounding/insulation practices must still meet the electrical installation requirements in 1910.306 so the assembly is safe for use in its intended underground application.
• Follow manufacturer instructions and applicable portions of 1910.306 to ensure mechanical protection, connection methods, and grounding are correct for the site conditions.

Cited authorities: 1910.399 and 1910.306.