Definitions for electrical subpart

Under 1926.449, "approved" means the equipment or installation is acceptable to the Assistant Secretary of Labor — in other words, it meets the acceptance criteria set out in this section. See the full definition in 1926.449 for details on how an installation or piece of equipment becomes acceptable.

An installation or equipment is acceptable if a qualified testing laboratory has accepted, certified, listed, labeled, or otherwise determined it to be safe for installation and use. This is one of the specific paths to approval described in 1926.449.

If no qualified testing laboratory accepts or certifies that kind of equipment, the equipment may be acceptable if inspected or tested and found to be in compliance by another Federal agency or the State/municipal/local authority responsible for enforcing the National Electrical Code. This acceptance path is described in 1926.449(b).

Custom-made equipment can be acceptable if the manufacturer determines it is safe for its intended use based on test data, and the employer keeps that test data and makes it available for inspection by OSHA. This path to acceptance is set out in 1926.449(c).

When applied to wiring methods, "accessible" means the wiring can be removed or exposed without damaging the building structure or finish, and it's not permanently closed in by the building's structure or finish. See the wiring-specific definition in 1926.449.

When applied to equipment, "accessible" means you can get close enough to the equipment (it is not guarded by locked doors, elevation, or other effective means) so you can work on it safely. The equipment definition of "accessible" appears in 1926.449.

"Ampacity" is the continuous current (in amperes) a conductor can carry under the conditions of use without exceeding its temperature rating. Knowing ampacity matters because selecting conductors with insufficient ampacity can cause overheating and fire hazards. The term is defined in 1926.449.

OSHA defines "appliances" as utilization equipment (generally non-industrial) usually built in standard sizes or types and installed or connected as a unit to perform one or more functions. See the appliance definition in 1926.449.

To show custom-made equipment is accepted under 1926.449(c), an employer should:

• Keep the manufacturer's test data demonstrating the equipment is safe for its intended use, and
• Make that test data available for inspection to OSHA (the Assistant Secretary) and authorized representatives.

Keeping clear, dated test reports on file is the practical compliance action.

The definition explains that the authority enforcing Subpart K is the Assistant Secretary of Labor for Occupational Safety and Health, and therefore "approved" means acceptable to that authority under the criteria in 1926.449.

Under 1926.449, "bonding" means permanently joining metal parts to create a conductive path that assures electrical continuity and can safely carry any current likely to occur. Bonding is used to prevent shock and ensure safety where metal parts could become energized.

A "bonding jumper" is a reliable conductor used specifically to ensure the required electrical conductivity between metal parts that must be electrically connected. It differs from other conductors because its primary purpose is to maintain electrical continuity between metal parts for safety, as defined in 1926.449.

A "branch circuit" is the circuit conductors between the final overcurrent device protecting the circuit and the outlet(s). This matters because the branch circuit's ampacity and protection must match to prevent overloading; see the definition in 1926.449.

A "cabinet" is an enclosure designed for surface or flush mounting and provided with a frame, mat, or trim in which a swinging door or doors are or may be hung. This enclosure definition is in 1926.449.

"Certified" equipment must have been tested and found by a qualified testing laboratory to meet applicable test standards or be safe for a specified use, and the kind must be periodically inspected by that laboratory; certified equipment must bear a label, tag, or other record of certification. See the certification rules in 1926.449.

For 600 volts nominal or less, a "circuit breaker" is a device designed to open and close a circuit by nonautomatic means and to open automatically on a predetermined overcurrent without injuring itself when used within rating; for over 600 volts, it is a switching device capable of making, carrying, and breaking currents under normal conditions and specified abnormal conditions. Both definitions are in 1926.449.

Class I locations are areas where flammable gases or vapors may be present in the air in quantities sufficient to form explosive or ignitible mixtures. A Class I, Division 1 location is where ignitible concentrations may exist under normal conditions or frequently during operations; a Class I, Division 2 location is where such gases are normally confined within closed systems or prevented by ventilation and would become hazardous only in case of accidental rupture or abnormal operation. See the Class I definitions in 1926.449.

When classifying hazardous locations, you should consider the amount of flammable material that could escape in an accident, quality of ventilation, total area involved, and the industry’s record of explosions or fires; these factors are discussed in 1926.449.

Class II locations are hazardous because of combustible dust. A Class II, Division 1 location is where combustible dust may be suspended in air in explosive quantities under normal conditions or due to equipment failure; a Class II, Division 2 location is where dust is not normally suspended and accumulations are normally insufficient to cause hazards, or dust may be suspended only because of infrequent equipment malfunction. See the definitions in 1926.449.

Class III locations are hazardous because of easily ignitible fibers or flyings that are not likely to be suspended in the air in quantities sufficient to ignite; the Class III categories and divisions are defined in 1926.449.

Under 1926.449, the definitions of "approved" and "qualified person" as used in Subpart K replace those in 1926.32 when applying Subpart K rules. In practical terms, that means you must use the specific Subpart K definitions (in 1926.449) for those terms when working with electrical requirements in this subpart.

A Class III, Division 1 location is a place where easily ignitible fibers or materials producing combustible flyings are handled, manufactured, or used.

• Examples of materials specifically listed include rayon, cotton (including linters and waste), sisal, jute, hemp, tow, sawdust, woodchips, excelsior, and similar easily ignitible fibers and flyings as defined in 1926.449.

A Class III, Division 2 location is one where easily ignitible fibers are stored or handled except during the manufacturing process.

• The key difference is that Division 1 covers handling, manufacturing, or use (active processing), while Division 2 covers storage or handling when not in a manufacturing process, as defined in 1926.449.

A collector ring is an assembly of slip rings used to transfer electrical energy from a stationary to a rotating member.

• It's commonly used on rotating machinery where power or signals must pass between fixed wiring and moving parts; see the definition in 1926.449.

"Concealed" means rendered inaccessible by the structure or finish of the building and includes wires in concealed raceways even if they can later be withdrawn.

• Wires in concealed raceways are treated as concealed wiring even if removal could make them accessible; see the definition in 1926.449.

A bare conductor has no covering or insulation; a covered conductor is encased in material not recognized as electrical insulation; an insulated conductor is encased in material that is recognized as electrical insulation.

• These are distinct definitions for safe handling and wiring methods in 1926.449.

A controller is a device or group of devices that governs, in a predetermined manner, the electric power delivered to the apparatus it serves.

• Use the definition in 1926.449 to determine whether equipment must be treated as a controller for installation and safety requirements.

"Dead front" means equipment that has no live parts exposed to a person on the operating side.

• Dead-front assemblies protect operators from accidental contact with energized parts and are defined in 1926.449.

An "enclosure" is the case or housing of apparatus or fence/walls that prevent personnel from accidentally contacting energized parts or protect equipment from damage; "enclosed" means surrounded by such a case, housing, fence, or walls.

• These definitions help determine when guarding or barriers are required and are found in 1926.449.

An explosion-proof apparatus is one enclosed in a case that can withstand an internal explosion of a specified gas or vapor and prevent ignition of the surrounding atmosphere; it also must operate at external temperatures that won't ignite the surrounding flammable atmosphere.

• The definition and dual protection requirements are in 1926.449.

For live parts, "exposed" means capable of being inadvertently touched or approached closer than a safe distance because parts 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.

• See both uses of "exposed" in the definitions at 1926.449.

You must consider that condition when a circuit is positioned so that failure of supports or insulation could allow it to contact another circuit, creating a hazard.

• This note is specifically referenced for communications systems in 1926.449 and tied to 1926.408(d).

A feeder comprises all circuit conductors between the service equipment (or generator switchboard of an isolated plant) and the final branch-circuit overcurrent device.

• Use this definition to identify the conductors that supply multiple branch circuits as found in 1926.449.

A fitting is an accessory such as a locknut, bushing, or other part intended primarily to perform a mechanical rather than an electrical function.

• Recognizing fittings helps separate mechanical components from electrical devices under 1926.449.

A fuse (over 600 volts, nominal) is an overcurrent protective device with a fusible element that heats and severs under overcurrent conditions and includes all parts forming a unit capable of performing the prescribed functions.

• The parenthetical "over 600 volts, nominal" indicates this specific definition applies to higher-voltage fuses as provided in 1926.449.

A "ground" is a conducting connection to earth or a conducting body that serves in place of the earth; "grounded" means connected to earth or its substitute; an "equipment grounding conductor" connects noncurrent-carrying metal parts of equipment to the system grounded conductor and/or grounding electrode conductor at the service or separately derived system.

• These definitions are important for proper grounding and bonding and are in 1926.449.

"Grounded, effectively" (over 600 volts, nominal) means permanently connected to earth through a ground connection of sufficiently low impedance and ampacity so that ground-fault current cannot build up to voltages dangerous to personnel.

• This higher-voltage grounding requirement is defined in 1926.449.

A ground-fault circuit interrupter is a device that protects personnel by deenergizing a circuit or portion of it within a set time when current to ground exceeds a predetermined value less than that required to trip the supply circuit's overcurrent device.

• The GFCI definition and purpose are provided in 1926.449.

"Guarded" means covered, shielded, fenced, enclosed, or otherwise protected by suitable means (covers, barriers, rails, screens, mats, etc.) to remove the likelihood of approach to a dangerous point or contact by persons or objects.

• Use this definition to determine when and how to protect employees from electrical hazards as stated in 1926.449.

An isolated power system includes an isolating transformer (or equivalent), a line isolation monitor, and ungrounded circuit conductors; it is used where continuity of power and limited ground-fault current are required.

• The definition appears in 1926.449 and can guide selection of systems for sensitive or critical electrical installations.

A "qualified person" is one familiar with the construction and operation of the equipment and the hazards involved.

• For regulatory context, see the definition in 1926.449 and related qualifications guidance in 1926.32.

"Listed" equipment is included in a qualified testing laboratory's published list stating it meets appropriate standards or is suitable for a specified use; "labeled" means a label, symbol, or mark from such a laboratory indicates compliance or performance.

• Using listed/labeled equipment helps ensure acceptability for specific purposes and is defined in 1926.449.

A raceway is a channel designed expressly for holding wires, cables, or busbars and may be metal or insulating material; it includes rigid metal conduit, electrical metallic tubing, flexible metal conduit, wireways, busways, underfloor raceways, and similar systems.

• Knowing what qualifies as a raceway is important for wiring method compliance under 1926.449.

"Overcurrent" is any current exceeding equipment rating or conductor ampacity and can result from overload, short circuit, or ground fault; an "overload" is operation of equipment or a conductor in excess of its normal full-load rating that, if it persists, would cause damage or dangerous overheating (and is not a fault like a short circuit).

• These distinctions are defined in 1926.449 and affect selection of protection devices.

A receptacle is the contact device at an outlet where a single attachment plug connects; a single receptacle is one contact device on a yoke and a multiple receptacle contains two or more receptacles in one device. Under 1926.449 the standard defines a "receptacle" as a contact device installed at the outlet for the connection of a single attachment plug, specifies that a single receptacle is a single contact device with no other contact device on the same yoke, and that a multiple receptacle is a single device containing two or more receptacles.

Practical points:

• Look at the device: if it houses two or more plug openings in one unit, it is a multiple receptacle; one opening on the yoke is a single receptacle.
• Use the correct rated device for the intended load and environment (indoor/outdoor, wet/dry) and follow manufacturer ratings.

Reference: see the definition of "Receptacle" in 1926.449.

Service is the conductors and equipment that deliver energy from the electricity supply to the building's wiring system; service conductors are the supply conductors that extend from the street main or transformers to the premises' service equipment; a service drop is the overhead conductors from the last pole or aerial support to the point they splice to the building's service-entrance conductors. These definitions come directly from 1926.449.

Practical points:

• "Service equipment" (see below) is typically located near where the service conductors enter the building so the main disconnect and overcurrent protection are readily accessible.
• A "service drop" is the utility's overhead connection to the structure; it is distinct from the building's "service-entrance conductors" where the two are joined outside the building.

Reference: definitions of "Service", "Service conductors", and "Service drop" are in 1926.449.

A separately derived system is a premises wiring system powered by a generator, transformer, or converter winding that has no direct electrical connection (including a solidly connected grounded conductor) to supply conductors from another system. 1926.449 defines it this way.

Why it matters:

• Being "separately derived" affects grounding and bonding arrangements (for example, neutral-to-ground bonding typically occurs at the separately derived source per electrical practice); it means the system must be treated as electrically isolated from the supply system.
• On a construction site, recognizing a separately derived system helps determine correct grounding, transfer switch configuration, and safe procedures for connecting or paralleling equipment.

Reference: definition of "Separately derived system" in 1926.449.

Service equipment is the equipment (usually a circuit breaker or switch and fuses and their accessories) located near the point where supply conductors enter a building or structure, intended to be the main control and means of cutoff of the electrical supply. This definition is in 1926.449.

Practical points:

• Because service equipment is intended to be the main control and cutoff, it is typically installed close to where the utility service enters the premises so it can be accessed quickly in an emergency.
• Maintain required access and working space around service equipment so employees can operate, inspect, or de-energize the equipment safely.

Reference: see "Service equipment" in 1926.449.

A switchboard is a large single panel, frame, or assembly of panels with switches, buses, instruments, and overcurrent and other protective devices mounted on the face or back; switchboards are generally accessible from the rear as well as the front and are not intended to be installed in cabinets. This definition appears in 1926.449.

How that differs from a panelboard (practical):

• Switchboards are larger assemblies intended for higher-capacity distribution and usually allow rear access; they are not designed to be enclosed in cabinets.
• Panelboards are generally smaller distribution boxes designed to be installed in cabinets or enclosures (see the cross-reference to "Panelboard" in 1926.449).

Reference: definition of "Switchboard" in 1926.449.

"Voltage, nominal" is a convenient assigned value used to designate a circuit's voltage class (for example, 120/240, 480Y/277); the actual operating voltage can vary within a range that still allows satisfactory operation. "Voltage to ground" is, for grounded circuits, the voltage between a given conductor and the grounded point or conductor; for ungrounded circuits, it is the greatest voltage between the given conductor and any other conductor. These definitions are in 1926.449.

Why this matters for equipment selection:

• Equipment and insulation ratings are specified by nominal voltage classes; selecting gear rated for the nominal voltage ensures safe operation despite normal voltage variation.
• Knowing the correct voltage-to-ground is essential for grounding, overcurrent protection coordination, and selecting insulating and clearances appropriate for the system.

Reference: definitions of "Voltage, nominal" and "Voltage to ground" in 1926.449.