Understanding Arc Flash
I often hear non-electrical-types quip the infamous adage “when it comes to electrical all I know is, don’t let the magic black smoke out..”, or some similar variant. If I had a nickel for every time I’ve heard that… But have you ever wondered …what exactly is that “black smoke”, where does it come from, and why is it so important that we don’t let it out?
Arc Flash is defined as the sudden release of energy (basically an electrical explosion) as the result of an electrical arc. To put that in a more qualitative context, during an arc flash event, temperatures can exceed 35,000 degrees Fahrenheit. By comparison, the Earth’s Sun burns at an astounding 9,900 degrees Fahrenheit. Keep in mind, the sun is approximately 92.9 million miles from the earth and it’s heat can still be deadly, in certain circumstances, even here on earth!
But extreme heat is just one of the hazards. The explosive force generated by a single phase-to-phase fault on a 480V system is comparable to 300 grams of TNT (equivalent to the blast from a mid-size car bomb), capable of inflicting severe physical damage to persons and equipment, vaporizing organic material, and turning chunks of molten metal and other materials into projectile hazards. Sound scary? It should, and it is! Now you know why that “magic black smoke” is best kept inside the box!
Arc Flash Studies are a critical element in workplace safety. So much so, that NFPA-70E, the Standard for Electrical Safety in the Workplace, affords a great deal of attention to the subject. Up until the issuance 2017 NEC, the detailed requirements for Arc Flash studies were mostly reserved to 70E, with little direction beyond simply providing a warning label. But in 2017, the NFPA steered the NEC a little closer towards alignment with 70E by adding more qualitative and quantitative requirements for service equipment rated 1200 Amps or more, which require some level of calculation of the available fault current and device clearing time. But this requirement still falls short of those prescribed in 70E.
So, when does 70E apply, and who enforces it? For a more detailed answer to that question, refer to our Arc Flash FAQs page, but in short, OSHA is the primary body which enforces compliance with 70E. Even though OSHA has not formally adopted 70E, it is referenced as an industry consensus standard, alongside other standards such as those developed by IEEE and ANSI, which together are used in providing evidence of non-compliance and identifying hazards.
Additionally, the requirements for Arc Flash Hazard Evaluation and Arc Flash Labeling as prescribed in 70E are defined as generally applicable to all cases except dwelling occupancies, so its not just limited to industrial applications.
Although designs issued for construction may meet applicable requirements as viewed under the lens of the current NEC, this does not necessarily ensure that once construction is completed and occupancy is achieved, the facility will satisfy OSHA requirements. In addition, facilities are also required to update the arc flash evaluations and labeling whenever the system is altered, and periodic reviews are required on intervals not less than every 5 years.
For more detailed information, and associated code references, visit our Arc Flash FAQs page.
Arc Flash is defined as the sudden release of energy (basically an electrical explosion) as the result of an electrical arc. To put that in a more qualitative context, during an arc flash event, temperatures can exceed 35,000 degrees Fahrenheit. By comparison, the Earth’s Sun burns at an astounding 9,900 degrees Fahrenheit. Keep in mind, the sun is approximately 92.9 million miles from the earth and it’s heat can still be deadly, in certain circumstances, even here on earth!
But extreme heat is just one of the hazards. The explosive force generated by a single phase-to-phase fault on a 480V system is comparable to 300 grams of TNT (equivalent to the blast from a mid-size car bomb), capable of inflicting severe physical damage to persons and equipment, vaporizing organic material, and turning chunks of molten metal and other materials into projectile hazards. Sound scary? It should, and it is! Now you know why that “magic black smoke” is best kept inside the box!
Arc Flash Studies are a critical element in workplace safety. So much so, that NFPA-70E, the Standard for Electrical Safety in the Workplace, affords a great deal of attention to the subject. Up until the issuance 2017 NEC, the detailed requirements for Arc Flash studies were mostly reserved to 70E, with little direction beyond simply providing a warning label. But in 2017, the NFPA steered the NEC a little closer towards alignment with 70E by adding more qualitative and quantitative requirements for service equipment rated 1200 Amps or more, which require some level of calculation of the available fault current and device clearing time. But this requirement still falls short of those prescribed in 70E.
So, when does 70E apply, and who enforces it? For a more detailed answer to that question, refer to our Arc Flash FAQs page, but in short, OSHA is the primary body which enforces compliance with 70E. Even though OSHA has not formally adopted 70E, it is referenced as an industry consensus standard, alongside other standards such as those developed by IEEE and ANSI, which together are used in providing evidence of non-compliance and identifying hazards.
Additionally, the requirements for Arc Flash Hazard Evaluation and Arc Flash Labeling as prescribed in 70E are defined as generally applicable to all cases except dwelling occupancies, so its not just limited to industrial applications.
Although designs issued for construction may meet applicable requirements as viewed under the lens of the current NEC, this does not necessarily ensure that once construction is completed and occupancy is achieved, the facility will satisfy OSHA requirements. In addition, facilities are also required to update the arc flash evaluations and labeling whenever the system is altered, and periodic reviews are required on intervals not less than every 5 years.
For more detailed information, and associated code references, visit our Arc Flash FAQs page.