The most frequently asked question that I receive regarding the 2018 edition of IEEE 1584 is:
“How do I determine the electrode configuration?”
The 2002 edition was based on arc flash tests with the electrodes oriented in a vertical configuration. When performing an arc flash study based on the 2002 edition, there were only two options available – an arc flash in an enclosure and an arc flash in open air – both based on a vertical electrode configuration.
Since the original 2002 edition was published, additional research has shown that incident energy can be influenced by the electrode configuration. As a result, many new tests were conducted using additional new electrode configurations including vertical electrodes that terminate into an insulating barrier as well as horizontal electrodes in an enclosure/box and in air. This is in addition to the original vertical configurations in an enclosure and in air. The additional configurations and the resulting Continue reading →
I have been receiving many questions lately about the status of the next edition of the standard: IEEE 1584 – IEEE Guide for Arc-Flash Hazard Calculations. As Vice-Chair of the IEEE 1584 working group, I would like to provide an update about the progress and current status.
The formal voting process (known as a Sponsor Ballot) for the next edition of IEEE 1584 was actually completed during August of 2017. However, that was only the beginning of a very long process. As part of the first round of balloting, many comments were submitted by the voters which needed to be formally addressed. There are over 160 people in the ballot pool that represent a wide cross section of the industry.
The IEEE 1584 Working Group voted to establish a Ballot Resolution Committee (BRC) which includes the Chair, Secretary and me along with a few others that represent various sectors of the industry. Continue reading →
National Electrical Code 110.9 Interrupting Ratings states that:
Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that is available at the line terminals of the equipment.
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To comply with this requirement, a short circuit studies is typically performed to determine the available fault current for comparison to the protective devices interrupting rating. The results of a short circuit study are also a critical component for other studies such as an arc flash study. Requesting the available short-circuit data from the electric utility company should be one of the first tasks in performing the study. This information is very important because it defines the magnitude of current that could flow from the utility and is used as a starting point for arc flash calculations.
In addition to requesting this data for normal operating conditions, for an arc flash study the request should also include minimum short-circuit current conditions, if available. The minimum condition could be for a utility transformer or transmission line out of service or similar scenario. The minimum value can then be used to determine if the lower current could result in a protective device operating more slowly, which may increase the total incident energy during an arc flash.
Having been in charge of the Short Circuit Studies group for a very large electric utility company in a past life, the accuracy of the Continue reading →
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, gray areas can lead to confusion, second-guessing and wondering how everyone else does it. Continue reading →
Does the standard contain new information to consider for arc flash analysis?
No because we’re still on the 2002 edition. The new edition won’t get released until probably next year at the earliest.
As to answering your question, sort of yes and no. Three areas I know will change somewhat: 1. The “lower cutoff” (the old 125 kVA comment/rule) will likely change, probably downward in terms of what is “covered” under this exception but also it sounds like the “1 transformer” part may change to something a little more flexible such as a simple bolted fault cutoff. 2. They have a lot more data to work with. It is my understanding that the 2002 equations are within about 10-15% of the new equations. I’ve seen 3 possible new equations. The first is that EPRI and others have expanded into other areas for “device specific” equations so even though that’s the section that sees little attention, it might change. Second there’s the Wilkins simplified as well as the Wilkins time-domain models. In the past IEEE 1584 kind of covered everything out there and I wouldn’t be surprised if this one does something similar so both get honorable mentions. Both models fit the data a little better. The time domain model is the best but computationally complex to use. Finally I’ve heard that they are getting away from the “jump” that occurs at 1 kV due to the implementation differences between the medium voltage and low voltage models in terms of having a single empirical calculation or at least one that passes through the same point at 1 kV. 3. There has been a lot of discussion and rumbling about a lot more conditons/situations such as having more than just the existing 3 box cases and including electrode orientation which accounts for very problematic situations such as some switchgear. I’d expect that this is where the data gathering is going to have to increase substantially. Everything else just revises the model a bit. READ MORE
Our interest in determining accurate onset to second degree burn energy and its significance in computing the arc flash boundary is focused on the prevention of injury to the skin of a human who might be exposed to an arc-flash. During the last two decades different formulas have been proposed to calculate incident energy at an assumed working distance, and the arc flash boundary in order to determine arc rated personal protective equipment for Qualified Electrical Workers. Among others, the IEEE Standard P1584 Guide for Performing Arc-Flash Hazard Calculations [1584 IEEE Guide for Performing Arc-Flash Hazard Calculations. IEEE Industry Applications Society. September 2002] and formulas provided in Annex D of NFPA 70E [NFPA 70E Standard for Electrical Safety in the Workplace. 2012.] and CSA Z462 [ CSA Z462 Workplace electrical safety Standards. 2012.] Workplace Electrical Safety Standard are the most often utilized in the industry to perform arc flash hazard analysis. The formulas are based on incident energy testing performed and calculations conducted for selected range of prospective fault currents, system voltages, physical configurations etc.
Use of Incident Energy as a Measure of Burn Severity in Arc Flash Boundary Calculations The IEEE P1584 Standard was developed by having incident energy testing performed based on methodology described in the ASTM F1959-99 standard. The incident energy to which the worker’s face and chest could be exposed at working distance during an electrical arc event was selected as a measure for determining hazard risk category and calculating the arc flash boundary. The incident energy of 1.2 cal/cm2 ( 5.0 J/cm2 ) for bare skinwas selected in solving the equation for the arc flash boundary in IEEE P1584 [1584 IEEE Guide for Performing Arc-Flash Hazard Calculations. IEEE Industry Applications Society. September 2002. page 41]. Also, NFPA 70E [NFPA 70E Standard for Electrical Safety in the Workplace. 2012. page 10] states that “a second degree burn is possible by an exposure of unprotected skin to an electric arc flash above the incident energy level of 1.2 cal/cm2 ( 5.0 J/cm2 )” and assumes 1.2 cal/cm2 as a threshold incident energy level for a second degree burn for systems 50 Volts and greater [NFPA 70E Standard for Electrical Safety in the Workplace. 2012. page 26].The IEEE 1584 Guidestates that “the incident energy that will cause a just curable burn or a second degree burn is 1.2 cal/cm2 (5.0 J/cm2 )” [1584 IEEE Guide for Performing Arc-Flash Hazard Calculations. IEEE Industry Applications Society. September 2002. page 96]. To better understand these units, IEEE P1584 refers to an example of a butane lighter. Quote: “if a butane lighter is held 1 cm away from a person’s finger for one second and the finger is in the blue flame, a square centimeter area of the finger will be exposed to about 5.0 J/cm2 or 1.2 cal/cm2 “. However IEEE P1584 equations (5.8) and (5.9) for determining the arc flash boundary can also be solved with other incident energy levels as well such as the rating of proposed personal protective equipment (PPE). The important point to note here is that threshold incident energy level for a second degree burn or onset to second degree burn energy on a bare skin is considered constant value equal to 1.2 cal/cm2 (5.0 J/cm2) in IEEE P1584 Standard.
Flash Fire Burn Experimentations and Observations
Much of the research which led to equations to predict skin burns was started during or immediately after World War II. In order to protect people from fires, atomic bomb blasts and other thermal threats it was first necessary to understand the effects of thermal trauma on the skin. To name the few, are the works done by Alice M. Stoll, J.B.Perkins, H.E.Pease, H.D.Kingsley and Wordie H. Parr. Tests were performed on a large number of anaesthetized pigs and rats exposed directly to fire. Some tests were also performed on human volunteers on the fronts of the thorax and forearms. A variety of studies on thermal effects have been performed and thermal thresholds were identified for different degree burns. We will focus on second degree burn as this is the kind of burn used to determine the arc flash boundary in engineering arc flash analysis studies.
Alice Stoll pursued the basic concept that burn injury is ultimately related to skin tissue temperature elevation for a sufficient time. Stoll and associates performed experimental research to determine the time it takes for second degree burn damage to occur for a given heat flux exposure. Stoll showed that regardless of the mode of application of heat, the temperature rise and therefore the tolerance time is related to heat absorbed by the skin[Stoll, A.M., Chianta M.A, Heat Transfer Through Fabrics. Naval Air Development Center. Sept. 1970]. Results of this study are represented in Figure 1 line (A) along with other studies discussed below. READ MORE
It is a municipal system, very rural, and has long single phase runs with low fault current. For example: 2400 delta single phase lateral ends up with about 92A fault current at the end of the run. The run is 7.5 miles with AAAC Ames and a 40K fuse on the txf secondary. The only fusing is on the secondary side of a stepdown transformer (13.2kv primary). Trying to use ArcPro and the fault current is too low (<200A lower limit). IEEE 1584 is for 3 phase faults but did try it and got an absurd value.
Any ideas on how to figure the incident energy? READ MORE
It has been a while since a question of the week was asked about the Arc Flash Boundary. This is the distance from a prospective arc flash where the incident energy is 1.2 cal/cm^2 which is the generally accepted value for the onset of a second degree burn. IEEE 1584 has a method for calculating this distance.
Since electrical safety practices continue to evolve, this week’s question is about the Arc Flash Boundary. Although the AFB is required to be on the warning label and is a calculated value, many are opting to keep unprotected/unqualified workers further away from a possible arc flash during live work (which should be kept to a minimum). This week’s question:
For your (client’s) electrical safety practices, do you use: Select up to 2 answers
Calculated AFB Something larger (please explain) Keep unprotected people out of the electrical room It depends
An arc flash study can be a bit complicated if you are new to this field. Knowing where to begin, what to include, how far to go, how to use the software etc. can seem like an insurmountable undertaking. WORSE – you are going to contract the study and don’t know what to ask for. The good news, there are many well qualified consultants that can help guide you through the process. The bad news – there are plenty of people ready to take advantage of the situation once they realize this might be your first study. Continue reading →
The surface area of the earth is approximately 197 million square miles, and IEEE 1584—IEEE Guide for Performing Arc-Flash Hazard Calculations has been covering more of it every day since it was first published almost 11 years ago. Although the IEEE 1584 standard has its roots in the United States, it has gained widespread international use as the most common method for performing arc flash calculation studies. Continue reading →
IEEE 1584 – Where It All Began – 2002 A lot has happened since 2002 when IEEE 1584 – IEEE Guide for Arc-Flash Hazard Calculations was first published. The development of this land mark document included conducting over 300 arc flash tests which were used to create the empirically derived equations. Applicable for three phase calculations and voltages ranging from 208 volts to 15,000 volts, four main calculation Continue reading →
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 1584—IEEE 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 of the worker positioned in place to perform the assigned task.” Continue reading →
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. Continue reading →
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. Continue reading →
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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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.
Arc Flash Calculation Study Many separate codes, standards and related documents are available regarding electrical safety and arc flash. However, a standardized recommended practice or guide that integrates all of the components into an Arc Flash Calculation Study does not presently exist. Continue reading →
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 from the thermal energy of an arc flash. Continue reading →
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