Arc Flash Evaluation calculates the incident energy and arc flash boundary for each location in a power system. Arc Flash saves time by automatically determining trip times from the protective device settings and arcing fault current values. Incident energy and arc flash boundaries are calculated following the NFPA 70E, IEEE 1584 and NESC standards. Clothing requirements are specified from a user-defined clothing library. Clearing times can be automatically reduced based on current-limiting capabilities.
Electric shock hazards, including electrocution, have been studied since the introduction of electricity. More recently, however, the dangers of arc flash have come to the forefront of electrical safety programs and procedures. This is because arc flash hazards pose an everyday risk in plants across the world, possessing the potential to destroy equipment and seriously injure, or kill, employees.
In order to accurately determine the arc flash hazard at each electrical assembly in an industrial or commercial facility — and thus determine how best to protect people and equipment — it is first necessary to conduct a short-circuit study, coordination study, and then an arc flash hazard analysis of the entire power distribution system. Let’s take a closer look at what’s involved in this process.
Arc Flash Hazard Analysis
Collection of data is the first task at hand. The data collected includes the arrangement of components on a one-line drawing with nameplate specifications of every device. Also required are details of the lengths and cross-sectional area of all cables. The electric utility should be contacted for information, including the minimum and maximum fault currents that can be expected at the electrical service entrance to the facility.
Once the data has been collected, a short-circuit analysis followed by a coordination study should be performed. The resultant data can then be fed into the equations described by either NFPA 70E-2004 or IEEE Standard 1584-2002 (see Arc Flash Regulations and Standards). These equations produce the necessary flash protection boundary distances and incident energy levels expected at various points on the system. Such boundary distances and incident energy levels are then used to determine the minimum personal protective equipment (PPE) required to maintain personnel safety.
The initial data collected and calculated results can then be used to perform a sensitivity study to obtain breaker/fuse characteristics, which lower the PPE requirement. To achieve this goal, existing circuit protective devices may need to be replaced, generally by more modern counterparts. It is expected that the outcome of this sensitivity study, when implemented, will result in many Category 4 PPE requirements being decreased to Category 1 or 2.
The National Fire Protection Association (NFPA), Institute of Electrical and Electronics Engineers (IEEE), and Occupational Safety and Health Administration (OSHA) work together to develop regulations and standards that best protect personnel and equipment against electrical hazards, including arc flash. Four separate industry standards focus on the prevention of arc flash incidents:
NFPA 70-2005, National Electrical Code (NEC)
NFPA 70E-2004, Standard for Electrical Safety in the Workplace
IEEE Standard 1584-2002, Guide for Performing Arc Flash Hazard Calculations
OSHA 29 Code of Federal Regulations (CFR) Part 1910 Subpart S
Recently, NFPA standard 70E has had an increased profile, thanks to changes in the NEC and OSHA. Both organizations are now referring to it in their documents. Companies not complying with these standards will most likely be cited and fined for any arc flash-related incident.