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Published on: Mar 1, 2012 00:03:AM
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The term working distance appears 20 times in the 2012 Edition of NFPA 70E, the Standard for Electrical Safety in the Workplace. It appears 12 more times in the annexes. The working distance is an important component of the arc flash hazard analysis and is frequently listed on arc flash warning labels and in the arc flash report. IEEE 1584IEEE Guide for Performing Arc Flash Hazard Calculations 2002 defines the working distance as the dimension between the possible arc point and the head and body
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Published on: Jul 1, 2011 00:07:AM
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One of the first steps in performing an arc flash calculation study is to request short-circuit data from the electric utility company. This kind of request is pretty routine, and utilities have been providing this type of data for short-circuit studies for years. The problem is the data used for a short-circuit study may not be suitable for an arc flash study.
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Published on: May 1, 2011 00:05:AM
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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?
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Published on: Jan 1, 2011 00:01:AM
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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.
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Published on: Nov 1, 2010 00:11:AM
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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.
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Published on: Sep 1, 2010 00:09:AM
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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.
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Published on: Sep 1, 2010 00:09:AM
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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?
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Published on: Jul 1, 2010 00:07:AM
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Knowing how long an arc flash could last is the most important piece of information in predicting its severity. The 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.
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Published on: May 1, 2010 00:05:AM
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Begin at the End - What Answer Would You like to Have? Simplifying arc flash calculation studies Would you like to know a little secret about how to simplify an arc flash calculation study? Perform the study backward. Well, not actually backward, it just seems that way Performing the study: Arc rating incident energy. An arc flash calculation study (AFCS) is one method that can be used to determine the level of flame-resistant clothing and personal protective equipment (PPE) that is appropriate
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Published on: Oct 1, 2009 00:10:AM
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When a bomb goes off, the further you are from the explosion, the safer you will be. This same concept applies to arc flash hazards. Whether you are a properly protected and qualified person performing the work or just an observer, the distance between you and the arc flash can make all the difference in the world.
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Published on: Oct 1, 2009 00:10:AM
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The need for risk assessment is embodied in European Law through directive 89/391 and is transposed into UK Law through Management of Health and Safety at Work Regulations. Most people are familiar with the general principles of prevention as laid down in these documents and in other UK regulations. They say that Where an employer implements any preventative measures, he shall do so on the basis of the principles of prevention shown below. The authors shown in italics on how these principles can
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Published on: Sep 1, 2009 00:09:AM
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Working safely in accordance with the requirements of the Electricity at Work Regulations 1989 is about decision making. This includes the decision to work live in the first place through risk assessment. One of the factors that would need to be taken into account in deciding whether live proximity work could proceed is stated in the memorandum of guidance to the EAW Regulations the level of risk involved in working live and the effectiveness of the precautions available set against economic nee
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Published on: Sep 1, 2009 00:09:AM
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Read the label? Use as directed? It sounds like Im 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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Published on: Jul 1, 2009 00:07:AM
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Dynamite, gasoline, gunpowder and electricity: What do these have in common? Each one can explode. Something as simple as the slip of a screwdriver can cause the electric power system to act like a bomb. Technically known as an arc flash, this potentially devastating explosion can occur when accidental contact is made between energized conductors or between one conductor and a grounded surface, such as an equipment enclosure.
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Published on: May 1, 2009 00:05:AM
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It seems like the more you attempt to learn about arc flash and electrical safety, the more confusing it becomes. A mixture of -letters such as OSHA, NFPA 70E, NEC, IEEE 1584, ASTM F1506 seem to be the secret language used by the electrical safety industry. Who created this alphabet soup of standards, and how did we get here?
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Published on: Dec 1, 2007 00:12:AM
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This is the third article in a three part series about how to perform an arc flash hazard calculation study that was published in the December 2007 Edition of NFPA's NECDigest Magazine. The series breaks the study process down into indiviual steps.
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Published on: Oct 1, 2007 00:10:AM
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This is the second article in a three part series about how to perform an arc flash hazard calculation study that was published in the October 2007 Edition of NFPA's NECDigest Magazine. The series breaks the study process down into indiviual steps.
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Published on: Aug 1, 2007 00:08:AM
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This is the first article in a three part series about how to perform an arc flash hazard calculation study that was published in the August 2007 Edition of NFPA's NECDigest Magazine. The series breaks the study process down into indiviual steps.
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Published on: Jun 1, 2007 00:06:AM
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PPE happens to be last resort in the UK risk control hierarchy behind removing and avoiding the hazard altogether. There is evidence that some UK companies adopt a comfort/protection balance argument such that it is better to allow a lower level of arc protection PPE rather than to insist on better protection that will be difficult to enforce because workers will not wear for comfort reasons.
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Published on: Oct 1, 2006 00:10:AM
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NFPA 70E has given a whole new meaning to the phrase dress for success. No, this is not about which shirt or tie to wear for a job interview. In this case, success means that if the very rare but potentially deadly arc-flash occurs, your chance of surviving with either no injury or only minor injury is greatly increased. One slip of a screwdriver and an electric power system can act like a bomb releasing a tremendous amount of thermal energy, producing a blinding flash and pressure that sends mo
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Published on: Feb 1, 2005 00:02:AM
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The next time you are near the bulletin board at work, look for the poster that has the words Its the Law and OSHA on it. It has probably been hanging there for a very long time but most people never really notice it or seem to read it. Further down on the poster is the statement each employer shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to employees. This
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