Electrical equipment approval requirements

Approved means the conductors and equipment must be acceptable under the definition of “approved” found in 1910.399, so use that definition to decide acceptability immediately. See the definition in 1910.303(a) and the approval definition at 1910.399.

• Practical tip: Acceptance Evidence — a listing or label for the identified purpose is commonly used to show suitability, but confirm the listing covers the exact use and environment you intend.1910.303(b)(1)(i).

Yes. A listing or labeling that identifies equipment for a specific purpose may be used as evidence of suitability for that purpose. See 1910.303(b)(1)(i).

• Practical action: Keep the listing/label documentation and follow any installation instructions included in the listing or label to demonstrate compliance.1910.303(b)(2).

Yes. Listed or labeled equipment must be installed and used in accordance with any instructions included in the listing or labeling. See 1910.303(b)(2).

• Practical tip: Keep copies of the listing/label instructions with the job file and train installers to follow them to avoid improper installations that could create recognized hazards.

Completed wiring installations must be free from short circuits and from grounds other than those required or permitted by the standard. See 1910.303(b)(3).

• Practical steps: Test for shorts and unintended grounds before energizing, and document insulation resistance or continuity checks as part of commissioning.

Equipment that interrupts current at fault levels must have an interrupting rating sufficient for the nominal circuit voltage and the available line-terminal current; equipment interrupting other currents must have a rating sufficient for the current to be interrupted. See 1910.303(b)(4).

• Practical actions: Verify manufacturer interrupting ratings against calculated available fault current at the equipment location and document the verification in the equipment selection records.

You must select and coordinate overcurrent devices, total circuit impedance, component short-circuit ratings, and other characteristics so protective devices will clear faults without causing extensive damage to electrical components. See 1910.303(b)(5).

• Practical steps: Perform coordination studies (time-current curves), confirm component short-circuit ratings exceed available fault currents, and document coordination decisions.

Unless identified for use in the operating environment, conductors and equipment must not be located in damp or wet locations, where exposed to gases, fumes, vapors, liquids, or other agents that deteriorate them, or where exposed to excessive temperatures. See 1910.303(b)(6).

• Practical tip: Use equipment rated for the environment (e.g., wet-location or chemical-resistant enclosures) and keep documentation that the equipment is identified for such use.1910.303(b)(1)(i).

Unused openings must be effectively closed to provide protection substantially equivalent to the equipment wall. See 1910.303(b)(7)(i).

• Practical action: Use listed blanking plates, plugs, or covers appropriate for the enclosure and environment to prevent access, moisture entry, and foreign-material contamination.

It means conductors must be arranged (racked) to provide ready and safe access for installation and maintenance in underground and subsurface enclosures entered by people. See 1910.303(b)(7)(ii).

• Practical tip: Route and support conductors on racks or trays with clear labeling and sufficient space so workers can safely inspect and service them.

Internal parts are noncompliant if they are damaged, contaminated by foreign materials (paint, plaster, cleaners, abrasives, corrosive residues), or have damaged parts that adversely affect safe operation or mechanical strength (broken, bent, cut, corroded, or overheated). See 1910.303(b)(7)(iii) and 1910.303(b)(7)(iv).

• Practical actions: Inspect equipment interiors before use, clean off contaminants with compatible methods, and repair or replace parts that are damaged or corroded.

Electric equipment must be firmly secured to the surface on which it is mounted; wooden plugs in masonry or similar materials are not considered secure fastening. See 1910.303(b)(8)(i).

• Practical tip: Use manufacturer-recommended anchors and hardware rated for the substrate and equipment weight; avoid makeshift fasteners that can loosen over time.

Equipment that relies on natural air circulation and convection for cooling must be installed so room airflow over exposed surfaces is not blocked by walls or adjacent equipment. See 1910.303(b)(8)(ii).

• Practical step: Maintain the clearance specified by the manufacturer for airflow and avoid tight enclosures or closely packed installations that reduce convection cooling.

No, conductors of dissimilar metals may not be intermixed in a terminal or splicing connector where physical contact occurs unless the device is specifically identified for that combination and conditions of use. See 1910.303(c)(1)(ii).

• Practical action: Use connectors or terminals listed for mixed-metal connections or use appropriately identified anti-oxidant compounds and devices rated for dissimilar metal use.1910.303(c)(1)(i).

Terminals that accept more than one conductor and terminals used to connect aluminum must be clearly identified for that purpose. See 1910.303(c)(2)(ii).

• Practical step: Verify terminals are marked on the device or in the documentation and use only identified terminals for splicing or multiple-conductor terminations.

Soldered splices must first be mechanically secure without solder, then soldered; all splices, joints, and free conductor ends must be covered with insulation equivalent to the conductors or with an insulating device identified for the purpose. See 1910.303(c)(3)(i).

• Practical action: Use listed wire connectors or heat-shrink insulation rated for the conductor type and environment, and ensure mechanical integrity before applying solder.

Parts that normally produce arcs, sparks, flames, or molten metal must be enclosed or separated and isolated from all combustible material. See 1910.303(d).

• Practical actions: Install proper enclosures, barriers, or maintain clearances between arcing parts and combustible materials to prevent fire or ignition hazards.

Electric equipment must bear the manufacturer's name, trademark, or other identifying marking and any necessary markings giving voltage, current, wattage, or other ratings. See 1910.303(e)(1)(i) and 1910.303(e)(1)(ii).

• Practical note: Markings must be durable enough to withstand the environment involved per 1910.303(e)(2). Keep records or photographs of labels for compliance documentation.

Disconnecting means for motors, appliances, services, feeders, and branch circuits must be legibly marked to indicate their purpose (unless purpose is evident) and must be capable of being locked in the open position. See 1910.303(f)(1), 1910.303(f)(2), and 1910.303(f)(4).

• Practical steps: Provide durable, readable labels on disconnects and use hasps/locks that allow authorized employees to lock disconnects during maintenance.

When circuit breakers or fuses are applied in compliance with manufacturer-marked series combination ratings, the equipment enclosure must be legibly marked in the field to indicate the application and must state: “Caution - Series Combination System Rated __ Amperes. Identified Replacement Component Required.” See 1910.303(f)(5)(i) and 1910.303(f)(5)(ii).

• Practical action: After applying a series combination rating, apply the required field marking where it is readily visible and keep documentation of the series rating used.

You must provide working space meeting the depth, width, and height requirements so maintenance and servicing while energized can be done safely: depth as indicated in Table S-1 measured from live parts or enclosure front, width equal to the equipment or at least 762 mm (30 in.), and clearance extending from floor to the required height so doors can open 90 degrees. See 1910.303(g)(1)(i).

• Practical steps: Consult Table S-1 (referenced in the rule) for specific depth values and ensure no storage occupies that working space per 1910.303(g)(1)(ii).

No, the working space required by the standard may not be used for storage; you must provide at least one suitably sized entrance to the working space, and indoor spaces around service equipment, switchboards, panelboards, and motor control centers must be illuminated. See 1910.303(g)(1)(ii), 1910.303(g)(1)(iii), and 1910.303(g)(1)(v).

• Practical tip: Keep the working space clear, provide the required clearances for door swing, and ensure permanent lighting or adequate adjacent lighting for safe operations.

Under 1910.303(g)(1)(vi), the minimum headroom is 1.91 m (6.25 ft) for installations built before August 13, 2007, and 1.98 m (6.5 ft) for installations built on or after August 13, 2007 (or not less than the height of the equipment when the equipment exceeds 1.98 m/6.5 ft).

• If equipment is taller than 1.98 m (6.5 ft), the headroom may not be less than the height of the equipment.

See 1910.303(g)(1)(vi).

Under 1910.303, the minimum clear working space in front of electric equipment 600 V or less depends on the voltage and the condition (A, B, or C); for example, for 0–150 V the required working space depth is 0.9 m (3.0 ft) for Condition C, and for 151–600 V it is 1.2 m (4.0 ft) for Condition C (see the full table for all values).

• Condition A: Exposed live parts on one side and no live or grounded parts on the other side, or exposed live parts on both sides effectively guarded by insulating material.
• Condition B: Exposed live parts on one side and grounded parts on the other side.
• Condition C: Exposed live parts on both sides with the operator between.

Refer to Table S‑1 in 1910.303 for the exact distances by voltage and condition.

Under 1910.303, insulated wire or insulated busbars operating at not over 300 volts are not considered live parts.

• This means working-clearance and guarding rules that specifically apply to exposed live parts may not apply to such insulated conductors, but other requirements (clearances, enclosures, guarding methods) still apply where relevant.

See 1910.303 for the governing provisions.

Under 1910.303(g)(1)(vii)(A)(1), the required dedicated space for indoor switchboards, panelboards, or motor control centers is the area equal to the width and depth of the equipment and extending from the floor to a height of 1.83 m (6.0 ft) above the equipment or to the structural ceiling, whichever is lower.

• That dedicated space must be kept clear for the electrical installation and is intended to protect the equipment and permit safe operation and maintenance.

See 1910.303(g)(1)(vii)(A)(1).

Under 1910.303(g)(1)(vii)(A)(2)–(4), foreign piping, ducts, or equipment generally may not be located in the dedicated space unless they are isolated or protected so they cannot damage the electrical equipment; sprinkler piping is permitted if it complies with the section.

• Foreign systems are allowed only if they are isolated by height, physical enclosures, or covers that prevent vehicular or accidental damage, or if protection is provided to avoid damage from condensation, leaks, or breaks.
• The dedicated space extends from the top of the electrical equipment to the structural ceiling.
• Sprinkler protection is permitted where the piping complies with the requirements in this section.
• Control equipment that must be adjacent to its operating machinery may be placed in the dedicated space.

See 1910.303(g)(1)(vii)(A)(2) and 1910.303(g)(1)(vii)(A)(3).

Under 1910.303(g)(1)(vii)(B), outdoor electric equipment must be installed in suitable enclosures and protected from accidental contact by unauthorized personnel, vehicular traffic, or accidental spillage or leakage from piping systems.

• Suitable enclosures and physical barriers (bollards, curbs, fences, or other guards) should prevent accidental damage or unauthorized access.

See 1910.303(g)(1)(vii)(B).

Under 1910.303(g)(2)(i), acceptable ways to guard live parts operating at 50 volts or more include: location in a room, vault, or similar enclosure accessible only to qualified persons; permanent partitions or screens sized to prevent accidental contact; placement on an elevated balcony or platform to prevent access by unqualified persons; or elevation of equipment 2.44 m (8.0 ft) or more above the floor.

• Each method is intended to prevent accidental contact or the insertion of conducting objects by unqualified persons.

See 1910.303(g)(2)(i) and its subsections A–D.

Under 1910.303(g)(2)(ii)–(iii), where electric equipment is likely to be exposed to physical damage you must provide enclosures or guards arranged and built strong enough to prevent such damage, and entrances to rooms or guarded locations containing exposed live parts must be marked with conspicuous warning signs forbidding unqualified persons to enter.

• Use robust guards, barriers, or enclosures where vehicular or mechanical damage is possible.
• Post clear warning signs at entrances to spaces with exposed live parts so only qualified persons enter.

See 1910.303(g)(2)(ii) and 1910.303(g)(2)(iii).

Under 1910.303(h)(2)(ii), outdoor electrical installations (other than certain equipment) must be enclosed by a wall, screen, or fence to deter access by unqualified persons; a fence must be at least 2.13 m (7.0 ft) high or a combination of at least 1.80 m (6.0 ft) of fence fabric plus a 305 mm (1 ft) or greater extension with three or more strands of barbed wire (or equivalent).

• The enclosure type must be designed for the hazards associated with the installation.

See 1910.303(h)(2)(ii).

Under 1910.303(h)(2)(iii), indoor high-voltage installations accessible to unqualified persons must be made with metal-enclosed equipment or be enclosed in a vault or an area to which access is controlled by lock; associated metal-enclosed equipment must be marked with appropriate caution signs; and ventilated dry‑type transformers (and similar equipment) must have openings designed to deflect foreign objects away from energized parts.

• These measures reduce the risk that unqualified persons or foreign objects will contact energized parts.

See 1910.303(h)(2)(iii) and subsections A–C.

Under 1910.303(h)(2)(v), outdoor enclosed equipment accessible to unqualified people must have ventilating openings designed to deflect inserted foreign objects, suitable guards where exposed to vehicular damage, designs that prevent easy removal of exposed nuts or bolts, locked doors or covers if the bottom of the enclosure is less than 2.44 m (8.0 ft) above grade, and doors/covers of pull boxes/splice or junction boxes secured (except heavy underground covers).

• These are practical protections to prevent access to live parts and to resist accidental or intentional tampering.

See 1910.303(h)(2)(v) and subsections A–E.

Under 1910.303(h)(4)(i), at least one entrance not less than 610 mm (24 in.) wide and 1.98 m (6.5 ft) high must be provided to access the working space about electric equipment over 600 volts.

• For switchboards and control panels exceeding 1.83 m (6.0 ft) in width, there must be an entrance at each end unless the layout permits continuous unobstructed exit travel or the working space is doubled.
• When an entrance is permitted at one end, its edge must be at least the minimum clear distance from the equipment as given in Table S‑2.

See 1910.303(h)(4)(i) and 1910.303(h)(4)(i)(A).

Under 1910.303(h)(5)(iii)(A)–(B) and (h)(5)(iv), entrances to buildings, rooms, or enclosures containing conductors or exposed live parts over 600 volts must be kept locked unless observed by a qualified person, must display permanent conspicuous warning signs stating “DANGER - HIGH VOLTAGE - KEEP OUT,” and the working spaces must be illuminated with lighting arranged so lamp changes or repairs do not endanger workers and so control points prevent contact with live parts when turning lights on.

• Keep entrances locked or under continuous observation by a qualified person.
• Post the specified danger sign conspicuously.
• Arrange lighting outlets and controls to protect workers from contacting live or moving parts while servicing the lighting.

See 1910.303(h)(5)(iii)(A), 1910.303(h)(5)(iii)(B), and 1910.303(h)(5)(iv).

Under 1910.303, back working space is not required behind dead-front switchboards or motor control centers where there are no renewable or adjustable parts on the back and all connections are accessible from other locations; however, if rear access is required to work on deenergized parts on the back of enclosed equipment, a minimum horizontal working space of 762 mm (30 in.) must be provided.

• This exception applies where no maintenance or component replacement is needed from the back.
• Provide the 762 mm (30 in.) horizontal clearance when rear access to deenergized parts is necessary for safe work.

See 1910.303 for these provisions.

They are not considered foreign if the piping or other facilities are provided for fire protection of the electrical installation. See 1910.303(h)(5)(vi).

• This is a limited exception: piping that is part of fire-protection systems (for example, sprinkler piping serving the electrical equipment) is treated as part of the electrical installation rather than a “foreign” system.
• For other piping or foreign systems, employers must still provide protection where necessary to avoid damage from condensation, leaks, or breaks as required in 1910.303(h)(5).

Employers must provide protection where necessary to avoid damage from condensation, leaks, and breaks in foreign systems. See 1910.303(h)(5).

• In practice this means assessing nearby piping, HVAC lines, or other systems that might leak or condensate and installing barriers, drip pans, rerouting, insulation, or other safeguards to prevent water or fluids from contacting electrical equipment.
• If the piping is part of the fire-protection system, it is not treated as a foreign system under 1910.303(h)(5)(vi).

The minimum clear working space for 601–2,500 volts (nominal to ground) under Condition A is 0.9 meters (3.0 feet). See Table S-2 in 1910.303.

• Condition A means exposed live parts on one side and no live or grounded parts on the other side, or exposed live parts on both sides effectively guarded by insulating material (see definitions in the table notes).

Condition A, B, and C describe the arrangement of live and grounded parts and determine the required depth of working space in front of electric equipment. See Table S-2 and its notes in 1910.303.

• Condition A: Exposed live parts on one side and no live or grounded parts on the other side of the working space, or exposed live parts on both sides that are effectively guarded by insulating material. Insulated wire or insulated busbars operating at not over 300 volts are not considered live parts.

• Condition B: Exposed live parts on one side and grounded parts on the other side.

• Condition C: Exposed live parts on both sides of the workspace (not guarded as in Condition A) with the operator standing between them.

• Use the appropriate condition to read the correct minimum clear distance from Table S-2 in 1910.303.

The minimum clear working space for 9,001 volts–25 kilovolts under Condition C is 2.8 meters (9.0 feet). See Table S-2 in 1910.303.

• Ensure you identify the correct Condition (A, B, or C) based on where live and grounded parts are located before applying the table value.

No—insulated wires or insulated busbars operating at not over 300 volts are not considered live parts for the purpose of determining working space Conditions. See the notes to Table S-2 in 1910.303.

• This means such insulated conductors do not change the Condition designation (A, B, or C) used to determine required clearances in the table, but always verify insulation integrity and suitability for the application.

Yes—concrete, brick, and tile walls are considered grounded surfaces. See the note in 1910.303.

• Treating those walls as grounded affects which Condition (A, B, or C) applies and therefore the required minimum clear working space from Table S-2.
• When planning clearances, assume those masonry walls are grounded unless a specific grounded-status assessment shows otherwise.

Working space is not required behind dead-front switchboards or control assemblies that have no renewable or adjustable parts on the back and where all connections are accessible from locations other than the back. However, when rear access is required to work on deenergized parts on the back of enclosed equipment, a minimum working space of 762 mm (30 in.) horizontally must be provided. See 1910.303.

• If fuses, switches, or other renewable/adjustable parts are located on the back, you must provide the working space.
• If you only need rear access for deenergized work, provide at least the 30‑inch horizontal clearance referenced above.

The minimum elevation for unguarded live parts above the working space at nominal voltages between phases of 601–7,500 volts is 19.0 feet (the table lists this elevation). See Table S-3 in 1910.303.

• The table gives elevations to keep unguarded live parts high enough to reduce accidental contact or arcing hazards; confirm the specific units and values in your copy of the standard and apply the value that matches your installation's voltage range.

Yes—there are allowed lower minimum elevations for installations built before certain dates: the minimum elevation may be 2.6 m (8.5 ft) for installations built before August 13, 2007, and it may be 2.4 m (8.0 ft) for installations built before April 16, 1981 if the nominal voltage between phases is in the range of 601–6,600 volts. See the notes to Table S-3 in 1910.303.

• These grandfathering provisions allow existing older installations to maintain previously accepted clearances, but newer installations must meet the current minimum elevations.

Yes—for installations built before April 16, 1981, the minimum depth of clear working space in front of electric equipment with a nominal voltage to ground above 25,000 volts may be the same as that for 25,000 volts under Conditions A, B, and C. See the notes to Table S-2 in 1910.303.

• This is another grandfathering allowance; for equipment installed after that date, use the depth values specified for the higher voltages.