What is in this article?:
- The Secret to Understanding Arc Flash Calculations
- Chapter 1, Safety-Related Work Practices (Art. 100 Definitions)
- Informative Annex C, Limits of Approach
- Informative Annex D, Incident Energy and Arc Flash Boundary Calculation Methods
- Informative Annex H, Guidance on Selection of Protective Clothing and Other Personal Protective Equipment
Applying notes from Annexes C, D, and H of 2012 NFPA 70E
Chapter 1, Safety-Related Work Practices (Art. 100 Definitions)
The definitions in Chapter 1 include the terms used in the calculations, which help you understand the concept.
Boundary, arc flash. 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 occurred.
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.
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.
Incident energy. The amount of energy impressed on a surface, at 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.
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 to recognize and avoid the hazards involved.
Unqualified person. A person who is not a qualified person.
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.