You look at the arc flash warning label and scratch your head. Danger! No PPE Category Found. No personal protective equipment (PPE) category? Now what? This type of language is often on arc flash warning labels when the calculated incident energy exceeds 40 calories per centimeter squared (cal/cm2). What is so special about the number 40? The fear of the Arc Blast is not always well founded.
NEC 240.87 has addressed a potentially hazardous situation beginning with the 2011 edition. When selective coordination is critical, e.g., minimizing the extent of an outage, a common design practice is to use a main circuit breaker without an instantaneous tripping function and feeder breakers with one. Without an instantaneous, the main can time delay up to 30 cycles or 0.5 seconds greatly increasing the arc flash hazard.
One sentence in the IEEE 1584 Standard, IEEE Guide for Performing Arc-Flash Hazard Calculations, frequently has people scratching their heads: Equipment below 240V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply. What does this sentence mean? What is so significant about 240 volts and 125 kilovolt-amperes? Download: 125 kVA / 240 Volt Exception About Jim Phillips: Electrical Power and Arc Flash Training Programs –
A lot can happen in two seconds. What may seem like the blink of an eye can feel like an eternity, especially during an arc flash. When calculating the incident energy as part of an arc flash study, sometimes the IEEE 1584 equations can produce unusually large values. Although many variables are included in these calculations, the two most significant are the magnitude of arcing short-circuit current and the duration of the arc flash. Question 1: How long? The duration
This article by Jim Phillips provides an overview of how to perform an arc flash study. It was originally presented at the 2010 NETA Conference. InterNational Electrical Testing Association. BUY NOW Arc Flash Calculation Study Many separate codes, standards and…
Determining the arc flash duration is the most important piece of information in predicting its severity. The arc flash duration is usually dependent on how fast an upstream protective device will trip. The longer it takes, the greater the incident energy and resulting hazard. Download: Arc Flash Duration
The NESC’s Arc Flash Requirements first appeared in the 2007 Edition. Determining how much incident energy could be available at a piece of equipment or location on a line is something you do not want to discover from a field test (accidental or intentional this means the only alternative is to predict it from calculations) Beginning with the 2007 NESC, The Arc Flash Requirements are:
Begin at the End – What Answer Would You like to Have? Simplifying the arc flash study – Would you like to know a little secret about how to simplify an arc flash studies? Perform the study backward. Well, not actually backward, it just seems that way Performing the study: Arc rating > incident energy. An arc flash study is one method that can be used to determine the level of arc-rated clothing and personal protective equipment that is appropriate for protection
Reduce Arc Flash Accidents Using Totally Integrated Automation: Several years ago Henry was the maintenance manager at a large manufacturing facility. He was married, had a very upbeat personality, a good position at the company, and was pleasant to be around. One day, Henry was trying to track…
Read the label? Use as directed? It sounds like I’m reading a prescription bottle. However, the warning label produced from an arc flash calculation study contains more than just the words Warning! Arc Flash and Shock Hazard It actually holds a lot of very specific information that can be used when preparing for work where electrical hazards may exist.
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