“Don’t touch that dial” is an old phrase from the 1960s television era that an announcer would say just before “Batman” or another program cut to a commercial. They would pronounce it so authoritatively that you wouldn’t dare change the channel.
“Properly” and “Maintained”—these two words always come up when discussing arc flash hazards. Why? Because protective devices such as circuit breakers and relays that have not been properly maintained may not operate as quickly as they should.
There are many frequently asked questions about performing an arc-flash study (risk assessment) and understanding electrical safety requirements. A careful read of standards such as NPFA 70E or IEEE 1584 can answer some questions. Yet, other questions can be more complex.
I’ve heard it all before. “What were they thinking when they wrote this standard? If I were them, this is how I would have done it.” When it comes to arc flash and electrical safety standards, complaints, armchair quarterbacking and second-guessing follow as soon as the latest edition comes out.
“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.