“You don’t know what you’ve got ’til it’s gone.” That famous song lyric can be appropriately applied to the 2015 edition of NFPA 70E. What is gone? Zero is no longer one of the hazard/risk categories (HRCs).
Attorney: “Can you tell us how Mr. Smith died?”
Witness: “There was an electrical explosion. Something went wrong when he was working on the panel. A big fireball shot out that caught his clothing on fire. It was horrible.”
Everyone tenses up in anticipation as they hear the countdown, “three, two, one.” Then there’s an extremely loud BOOM and blinding light. Sparks fly everywhere, and smoke fills the test area. Laughter and perhaps even a high five frequently follow.
It goes up. It goes down. Sometimes, it is thought to be infinite (although it isn’t), and other times, it seems impossible to find. The available short-circuit current from the electric utility is one of the more important pieces of information for an arc flash hazard calculation study.
Two simple words, a total of six letters, help define which electrical equipment is required to have an arc flash label. Although these two words are used with good intentions, they can often leave a person second-guessing themselves.
Mistakes happen, and there are plenty of opportunities to make them when performing an arc flash calculation study. The good news is commercially available arc flash software can help simplify the study process and perhaps even reduce errors.
The first step in conducting an arc flash study is to obtain the data necessary to accurately represent the electrical system. Equations defined by IEEE 1584–IEEE Guide for Performing Arc Flash Hazard Calculations are at the heart of most studies and require a lot of data.