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Arc Rating
The maximum incident energy resistance demonstrated by a material (or a layered system of materials) prior to breakopen or at the onset of a second-degree skin burn. Arc rating is normally expressed in cal/cm2.


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.


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.

Electrical 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.

Electrically Safe Work Condition
A state in which the conductor or circuit part to be worked on or near 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.

Electrically connected to or having a source of voltage.

Exposed (as applied to live parts)
Capable of being inadvertently touched or approached nearer than a safe distance by a person. It is applied to parts that are not suitably guarded, isolated, or insulated.


Flame-Resistant (FR)
The property of a material whereby combustion is prevented, terminated, or inhibited following application of a flaming or non-flaming source of ignition, with or without subsequent removal of the ignition source. Flame resistance can be an inherent property of the material, or it can be imparted by a specific treatment applied to the material.

Flash Hazard
A dangerous condition associated with the release of energy caused by an electric 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 and the appropriate levels of PPE.

Flash Protection Boundary
An approach limit at a distance from exposed live parts within which a person could receive a second degree burn if an electrical arc flash were to occur.


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).


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 concerned 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.

Limited Approach Boundary
An approach limit at a distance from an exposed live part within which a shock hazard exists.


Prohibited Approach Boundary
An approach limit at a distance from an exposed live part within which work is considered the same as making contact with the live part.


Qualified Person
One who has skills and knowledge related to the construction and operation of the electrical equipment and installations and has received safety training on the hazards involved.


Restricted Approach Boundary
An approach limit at a distance from an exposed live 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 live part.


Unqualified Person
A person who is not a qualified person.

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