Arc Flash Dictionary

Accessible (as applied to equipment)
Admitting close approach; not guarded by locked doors, elevation, or other effective means

Accessible (as applied to wiring methods)
Capable of being removed or exposed without damaging the building structure or finish or not permanently closed in by the structure or finish of the building

Accessible, Readily (Readily Accessible)

Capable of being reached quickly for operation, renewal, or inspections without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, and so forth

Acceptable to the authority having jurisdiction

Arc Flash Hazard
A dangerous condition associated with the release of energy caused by an electric arc

Arc Flash Hazard Analysis
A study investigating a worker’s potential exposure to arc flash energy, conducted for the purpose of injury prevention and the determination of safe work practices, arc flash boundary, and the appropriate levels of personal protective equipment (PPE)

Arc Flash Suit (Flash Suit)
A complete arc-rated clothing and equipment system that covers the entire body, except for the hands and feet

Arc Rating
The value attributed to materials that describes their performance to exposure to an electrical arc discharge. The arc rating is expressed in cal/cm2 and is derived from the determined value of the arc thermal performance value (ATPV) or energy of break-open threshold (EBT) (should a material system exhibit a break-open response below the ATPV value). Arc rating is reported as either ATPV or EBT, whichever is the lower value

Attachment Plug (Plug Cap) (Plug)
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

Authority Having Jurisdiction (AHJ)
An organization, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure

Performing a function without the necessity of human intervention

Balaclava (Sock Hood)
An arc-rated hood that protects the neck and head except for facial area of the eyes and nose

Bare-Hand Work
A technique of performing work on energized electrical conductors or circuit parts, after the employee has been raised to the potential of the conductor or circuit part

A physical obstruction such as tapes, cones, or A-frame-type wood or metal structures intended to provide a warning about and to limit access to a hazardous area

A physical obstruction that is intended to prevent contact with equipment or energized electrical conductors and circuit parts or to prevent unauthorized access to a work area

Bonded (Bonding)
Connected to establish electrical continuity and conductivity

Bonding Conductor or Jumper
A reliable conductor to ensure the required electrical conductivity between metal parts required to be electrically connected

Boundary, Arc Flash (Flash Protection Boundary)
When an arc flash hazard exists, an approach limit at a distance from a prospective arc source within which a person could receive a second degree burn if an electrical arc flash were to occur

Boundary, Limited Approach
An approach limit at a distance from an exposed energized electrical conductor or circuit part within which a shock hazard exists

Boundary, Prohibited Approach
An approach limit at a distance from an exposed energized electrical conductor or circuit part within which work is considered the same as making contact with the electrical conductor or circuit part

Boundary, Restricted Approach
An approach limit at a distance from an exposed energized electrical conductor or circuit part within which there is an increased risk of shock, due to electrical arc-over combined with inadvertent movement, for personnel working in close proximity to the energized electrical conductor or circuit part

Branch Circuit
The circuit conductors between the final over-current device protecting the circuit and the outlet(s)

A structure that stands alone or that is cut off from adjoining structures by fire walls with all openings therein protected by approved fire doors

An enclosure that is designed for either surface mounting or flush mounting and is provided with a frame, mat, or trim in which a swinging door or doors are or can be hung

Circuit Breaker
A device designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined over-current without damage to itself when properly applied within its rating

Suitable for carrying electric current

Conductor, Bare
A conductor having no covering or electrical insulation whatsoever

Conductor, Covered
A conductor encased within material of composition or thickness that is not recognized by NFPA 70E as electrical insulation

Conductor, Insulated
A conductor encased within material of composition and thickness that is recognized by NFPA 70E as electrical insulation

A device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected

Current-Limiting Over-current Protective Device
A device that, when interrupting currents in its current-limiting range, reduces the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor having comparable impedance

An assembly of a fuse support with either a fuseholder, fuse carrier, or disconnecting blade. The fuseholder or fuse carrier may include a conducting element (fuse link), or may act as the disconnecting blade by the inclusion of a non-fusible member

Free from any electrical connection to a source of potential difference and from electrical charge; not having a potential different from that of the earth

A unit of an electrical system that carries or controls electric energy as its principal function

Disconnecting Means
A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply

Disconnecting (or Isolating) Switch (Disconnector, Isolator)
A mechanical switching device used for isolating a circuit or equipment from a source of power

Dwelling Unit
A single unit, providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking, and sanitation

Electrical Hazard
A dangerous condition such that contact or equipment failure can result in electric shock, arc flash burn, thermal burn, or blast

Electrical Safety
Recognizing hazards associated with the use of electrical energy and taking precautions so that hazards do not cause injury or death

Electrically Safe Work Condition
A state in which an electrical conductor or circuit part has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary

Surrounded by a case, housing, fence, or wall(s) that prevents persons from accidentally contacting energized parts

The case or housing of apparatus, or the fence or walls surrounding an installation to prevent personnel from accidentally contacting energized parts or to protect the equipment from physical damage

Electrically connected to, or is, a source of voltage

A general term, including material, fittings, devices, appliances, luminaires, apparatus, machinery, and the like, used as a part of, or in connection with, an electrical installation

Exposed (as applied to energized electrical conductors or circuit parts)

Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to electrical conductors or circuit parts that are not suitably guarded, isolated, or insulated

An accessory such as a locknut, bushing, or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function

An over-current protective device with a circuit-opening fusible part that is heated and severed by the passage of over-current through it

The earth

Ground Fault
An unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally non-current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth

Grounded (Grounding)
Connected (connecting) to ground or to a conductive body that extends the ground connection

Grounded, Solidly
Connected to ground without inserting any resistor or impedance device

Grounded Conductor
A system or circuit conductor that is intentionally grounded

Ground-Fault Circuit Interrupter (GFCI)
A device intended for the protection of personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a Class A device

Grounding Conductor, Equipment (EGC)
The conductive path installed to connect normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both

Grounding Electrode

A conducting object through which a direct connection to earth is established

Grounding Electrode Conductor
A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system

Covered, shielded, fenced, enclosed, or otherwise protected by means of suitable covers, casings, barriers, rails, screens, mats, or platforms to remove the likelihood of approach or contact by persons or objects to a point of danger

Incident Energy
The amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event. One of the units used to measure incident energy is calories per centimeter squared (cal/cm2)

Incident Energy Analysis
A component of an arc flash hazard analysis used to predict the incident energy of an arc flash for a specified set of conditions

Separated from other conducting surfaces by a dielectric (including air space) offering a high resistance to the passage of current

Interrupter Switch
A switch capable of making, carrying, and interrupting specified currents

Interrupting Rating
The highest current at rated voltage that a device is identified to interrupt under standard test conditions

Isolated (as applied to location)
Not readily accessible to persons unless special means for access are used

Equipment or materials to which has been attached a label, symbol, or other identifying mark of an organization that is acceptable to the authority having jurisdiction and converned with product evaluation, that maintains periodic inspection of production of labeled equipment or materials, and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner

Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation of services, and whose listing states that either the equipment, material, or service meets appropriate designated standards or has been tested and found suitable for a specified purpose

A complete lighting unit consisting of a lamp or lamps, together with the parts designed to distribute the light, to position and protect the lamps and ballast (where applicable), and to connect the lamps to the power supply. It may also include parts to protect the light source or the ballast or to distribute the light. A lampholder is not a luminaire

Motor Control Center
An assembly of one or more enclosed sections having a common power bus and principally containing motor control units

A point on the wiring system at which current is taken to supply utilization equipment

Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault

Operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is not an overload

A single panel or group of panel units designed for assembly in the form of a single panel, including buses and automatic over-current devices, and equipped with or without switches for the control of light, heat, or power circuits; designed to be placed in a cabinet or cutout box placed in or against a wall, partition, or other support; and accessible only from the front

Premises Wiring (System)

Interior and exterior wiring, including power, lighting, control, and signal circuit wiring together with all their associated hardware, fittings, and wiring devices, both permanently and temporarily installed. This includes: (a) wiring from the service point or power source to the outlets; or (b) wiring from and including the power source to the outlets where there is no service point. Such wiring does not include wiring internal to appliances, luminaires, motors, controllers, motor control centers, and similar equipment

Qualified Person
One who has demonstrated the skills and knowledge to the construction and operation of the electrical equipment and installations and has received safety training to recognize and avoid the hazards involved

An enclosed channel of metal or nonmetallic materials designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this standard. Raceways include, but are not limited to, rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, liquid-tight flexible conduit, flexible metallic tubing, flexible metal conduit, electrical metallic tubing, electrical nonmetallic tubing, under-floor raceways, cellular concrete floor raceways, cellular metal floor raceways, surface raceways, wireways, and busways

A receptacle is a contact device installed at the outlet for the connection of an attachment plug. A single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is two or more contact devices on the same yoke

Service Drop
The overhead conductors between the utility electric supply system and the service point

Service Lateral
The underground conductors between the utility electric supply system and the service point

Service Point
The point of connection between the facilities of the serving utility and the premises wiring

Shock Hazard
A dangerous condition associated with the possible release of energy caused by contact or approach to energized electrical conductors or circuit parts

Short-Circuit Current Rating

The prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria

Single-Line Diagram
A diagram that shows, by means of single lines and graphic symbols, the course of an electric circuit or system of circuits and the component devices or parts used in the circuit or system

Special Permission
The written consent of the authority having jurisdiction

Step Potential
A ground potential gradient difference that can cause current flow from foot to foot through the body

That which is built or constructed

Switch, Isolating
A switch intended for isolating an electric circuit from the source of power. It has no interrupting rating, and it is intended to be operated only after the circuit has been opened by some other means

A large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, over-current and other protective devices, buses, and usually instruments. Switchboards are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets

Switchgear, Arc-Resistant
Equipment designed to withstand the effects of an internal arcing fault and that directs the internally released energy away from the employee

Switchgear, Metal-Clad
A switchgear assembly completely enclosed on all sides and top with sheet metal, having draw-out switching and interrupting devices, and all live parts enclosed within grounded metal compartments

Switchgear, Metal-Enclosed
A switchgear assembly completely enclosed on all sides and top with sheet metal except for ventilating openings and inspection windows), containing primary power circuit switching, interrupting devices, or both, with buses and connections. This assembly may include control and auxiliary devices. Access to the interior of the enclosure is provided by doors, removable covers, or both. Metal-enclosed switchgear is available in non-arc-resistant or arc-resistant constructions

Switching Device
A device designed to close, open, or both, one or more electric circuits

Touch Potential
A ground potential gradient difference that can cause current flow from hand to hand, hand to foot, or another path, other than foot to foot, through the body

Not connected to ground or to a conductive body that extends the ground connection

Unqualified Person
A person who is not a qualified person

Utilization Equipment
Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes

Provided with a means to permit circulation of air sufficient to remove an excess of heat, fumes, or vapors

Voltage (of a Circuit)
The greatest root-mean-square (rms) (effective) difference of potential between any two conductors of the circuit concerned

Voltage, Nominal
A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277 volts, 600 volts). The actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment

Working On (energized electrical conductors or circuit parts)
Intentionally coming in contact with energized electrical conductors or circuit parts with the hands, feet, or other body parts, with tools, probes, or with test equipment, regardless of the personal protective equipment a person is wearing. There are two categories of “working on”: Diagnostic (testing) is taking readings or measurements of electrical equipment with approved test equipment that does not require making any physical change to the equipment; repair is any physical alteration of electrical equipment (such as making or tightening connections, removing or replacing components, etc.)