ARC FLASH HAZARDS OVERVIEW BASICS AND TUTORIALS

Arc-fl ash hazard is defi ned as a dangerous condition associated with the release of energy caused by an electric arc. The arc current creates a brilliant flash of light, a loud noise, intense heat, and a rapidly moving pressure wave.

The products of arc-fault are ionized gases, metal vapors, molten metal droplets, and shrapnel that shower the immediate vicinity of the arcing fault. The electrical arc burns make up a substantial portion of injuries from electrical malfunctions.

The extremely high temperatures of the electrical arc can cause fatal and major burns at distances of 5–10 ft from the arcing equipment. Therefore, the focus of industry on electrical safety and recognition of arc-fl ash burns as having great signifi cance highlighted the need for protecting employees from all arc-fl ash hazards.

The NEC-2008, Article 110-16 Flash protection, states in part that switchboards, panelboards, industrial control panels, and motor control centers that are in other than dwelling occupancies and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn qualified persons of potential electric arc-flash hazards.

It is implied that flash protection is required when examining, adjusting, servicing, or maintaining energized
equipment. The equipment shall be fi eld marked (labeled) to warn qualified persons of potential electric arc-flash hazards.

Let us now take a look at how the requirements for field labeling of equipment can be accomplished. In order to generate an arc fl ash hazard label, an arc-flash hazard analysis study has to be conducted to determine the arc energy available at a given equipment.

Therefore an arc-flash hazard analysis is performed in conjunction with the short-circuit study and protective device coordination study. Results of the short-circuit study are used to calculate the three-phase fault current from which the arcing fault current is determined. Results of protective device coordination study are used to determine the time required for the electrical protective devices to clear the arcing fault current conditions.

Results of both short circuit and protective device coordination studies are used to perform an arc-flash hazard analysis. Results of arc-flash hazard analysis are used to identify the fl ash protection boundary and the incident energy at assigned working distances for the electrical equipment. The flash protection boundary and the incident energy calculated in the arc-flash hazard analysis evaluation are based on taking credit for the protective relays and devices in removing the arc.

Therefore it is important that these protective devices be kept in good working condition to maintain the validity of the arcfl ash hazard analysis results.

In view of the requirements for arc-flash hazard analysis, it has become even more important now to maintain and test breakers and protective devices on a regular basis to ensure their reliability.

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