In 2018, major changes were made to the calculations and procedures for determining arc-flash incident energy levels from the original 2002 edition of the IEEE Std. 1584, IEEE Guide for Performing Arc-Flash Hazard Calculations. Now, three years since its release, facility owners and arc-flash service providers still debate how, when, and where to apply the new calculation methods. While the changes improve calculation accuracy and can enhance safety, they do require a significant amount of equipment information to be gathered and used in the calculation process. The questions being asked include:
- What are the changes?
- Why have these changes been made?
- How do you apply the new calculations?
- How do you determine the needed information on the equipment?
- And in the end, will it make a difference?
This article is presented in two parts:
Part I includes a brief history and evolution of electrical safety over the past 50 years. It was during this period that OSHA was formed and NFPA began developing the 70E standard. I refer to this as the Jurassic Period for electrical safety. We will review key changes to IEEE 1584 from the initial edition in 2002 to the second edition in 2018 and examine the calculation process and variables included in the calculations.
Part II (NETA World Summer 2022) will compare the calculation results between the 2002 and 2018 methods. We’ll wrap up the second part of this article by discussing the relevant impact of these changes and how they affect the calculated incident energy levels that we depend on to select adequate PPE. Practical concepts will be offered for applying equipment variables and streamlining the process of adopting the new calculation methodology.
ARC-FLASH HAZARDS, SAFETY, AND ANALYSIS HISTORY
Electrical arc-flash hazards have been a danger to workers since the early attempts to produce and harness electricity. So why has it only received attention over the past 25 years? Only during the past few decades has the science caught up with our desire and need to protect our workers from these hazards. Research, development, testing, and safety clothing/materials have finally advanced and matured to provide us a more accurate understanding of this dangerous phenomenon and the ability to protect against serious injury from arc-flash incident energy. Before understanding that electrical injuries resulted from two primary hazards — shock and arc flash — electrical injuries were lumped into a single category: shock and electrocution. Arc flash, and the injuries from arc flash, existed and were observed, but the hazard and injury had not yet been given a separate classification; they were simply electrical-related injuries.
To combat American worker exposure to hazards and injuries, the Occupational Safety and Health Administration (OSHA) was created by the Occupational Safety and Health Act (OSH Act) of 1970, which was signed into law by President Richard M. Nixon. This document has evolved over the years, but one of the original sections that remains intact and is often considered a catch-all section is commonly referred to as the General Duty Clause. This clause states:
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 likely to cause death or serious physical harm to his employees.
The OSH Act establishes the “what” the employer must do to keep their workers safe. Once this “what” was established, OSHA began looking for ways to define “how” to keep workers safe. OSHA did not have the authority or jurisdiction to establish the “how” to keep workers safe, so they turned to the National Fire Protection Association’s National Electrical Code (NFPA 70). While some of the original language related to electrical hazards was taken from the NEC, OSHA quickly realized that this document was not well suited for defining how to keep workers safe. Not wanting to include the “how” in federal law due to the bureaucratic red tape required to change federal law, OSHA again turned to the National Fire Protection Association to develop a guide that would provide employers the “how” to create a safe working environment that could easily be kept up-to-date.
At OSHA’s request, NFPA formed the 70E committee in 1976. The first edition of NFPA 70E, Electrical Safety Requirements for Employee Workplaces was published in 1979; it only contained Part 1: Installation Safety Requirements. The second edition, published in 1981, included Part 2: Safety-Related Work Practices. In 1983, the third edition added Part 3: Safety Related Maintenance Requirements. Minor updates were included in several subsequent editions. The 1995 edition (now the Standard for Electrical Safety Requirements for Employee Workplaces) included major updates and major revisions of Part 1 and Part 2. This edition introduced the concept of “limits of approach” and — for the first time — “arc flash hazards.” The 2021 edition is currently the latest published edition.
That brings us to IEEE Std. 1584, IEEE Guide for Performing Arc-Flash Hazard Calculations, initially released in 2002. Those involved in arc-flash studies are likely familiar with the recommendations and calculations this guide established based on the available information from science and research efforts at that time. During the period this guide was being developed, most knowledge of the subject was based on research and equations developed by Ralph Lee and test data that had been analyzed from about 300 arc-flash laboratory tests. By the time the 2018 edition of IEEE 1584 was developed, much more extensive research and testing had been completed involving some 1,800 arc-flash tests. As a result, much more detailed and accurate empirically derived equations were developed and included in this second edition.
Today, the National Electrical Code (NFPA 70), NFPA 70E, OSHA, and IEEE 1584 are used to identify, quantify, and protect workers from electrical hazards. Additionally, various vendors have been involved in developing clothing materials to help protect workers from arc-flash incident energy. The combination of these evaluations, calculations, procedures, and protective clothing, along with training and educating employers and employees, has dramatically reduced the number of electrical injuries resulting from arc-flash incident energy exposure.
WHAT IS IEEE 1584?
The latest edition of IEEE 1584 contains updated empirical equations and calculation methods based on the latest research and test data and improves the accuracy of arcing current, incident energy, and arc-flash boundary values. It states:
This guide provides mathematical models for designers and facility operators to apply in determining the arc-flash hazard distance and the incident energy to which a worker could be exposed during their work on or near electrical equipment.
Those involved in performing arc-flash calculations should be familiar with these changes, the impact they have on PPE requirements, and the impact the changes have on clients that have existing arc-flash studies, labels, and established safety procedures.
IEEE 1584 is a guide, and its use is not mandated by law. The scope and content of IEEE 1584 is very different from NFPA 70E. NFPA 70E outlines aspects of electrical safe work practices while IEEE 1584 focuses solely on the science of arc-flash calculations. Additionally, NFPA 70E is a consensus standard where public input is considered and voted on when changes are made. IEEE 1584 is developed by a committee having expertise or “interests” in the subject. The content of the guide is based on research and science.
I usually get a lot of attention when I mention that IEEE 1584 is a guide and not mandated by law. More eyebrows are raised when I state that NFPA 70E, while it is a standard and not a guide, is also not mandated by law. While both of these documents are often used as a foundation for electrical safety policies and calculations, there is no law mandating their use.
The enforceable law falls under OSHA’s purview. When an accident occurs or OSHA gets involved in your business, they don’t cite NFPA 70E or IEEE 1584, they cite OSHA law. With that said, if your electrical safety policy and procedures are deeply rooted in the guidance and procedures included in NFPA 70E and IEEE 1584, you have a much stronger argument than if you have created your own policies that are not closely aligned with the documents.
MAJOR CHANGES IN THE 2018 EDITION OF IEEE 1584
To provide comprehensive coverage of this topic, this section compares the first (2002) and second (2018) editions of IEEE 1584 and discusses the significant differences.
What has changed in IEEE 1584? Just about everything! It would be easier to talk about what hasn’t changed. Why all the changes? Has the physics of an arc flash changed? No, but with additional experiments, testing, and observations, our understanding of arc events and arc-event modeling has significantly improved. Let’s get started reviewing what has stayed the same and which changes in the guide are the most relevant.
2002 and 2018 editions of IEEE 1584 exclude calculations for DC systems. Currently, there is not enough scientific data available to develop an accurate mathematical model for DC systems. This is the result of several factors. First, the almighty dollar! Research and testing must be funded. While there has been some research, sufficient testing and research to establish accurate models for all types of DC systems has not been conducted. DC systems, depending on their source, act differently under arc-fault conditions. Transit, wind farm, solar farm, battery, and UPS systems have unique responses to arc-fault conditions. Each of these systems must be tested and studied individually to establish accurate models.
Both editions also exclude single-phase systems, although guidance and recommendations are provided related to handling arc-flash analysis of single-phase systems. Using these recommendations will likely result in a conservative result (i.e., calculated values will likely be higher than actually encountered incident energy levels).
Low/Lower-Voltage vs. Medium/Higher-Voltage Systems and Equipment
What is low voltage? What is medium voltage? Differences in the definition of these terms across various standards and organizations has existed since the beginning of the electrification era. Voltage classifications and definitions have been revised in the latest edition of IEEE 1584. In the 2002 edition, low voltage was considered 1,000 V and below; medium voltage was above 1,000 V (up to 15 kV for the purposes of the guide). However, the latest edition of IEEE 1584 refers to one voltage class that we will call “lower voltage” that covers systems and equipment operating at 600 V and below. Equipment operating above 600 V (up to 15 kV for the purposes of this guide) is referred to as higher-voltage equipment and systems. The methods for calculating arcing current, incident energy (IE), and arc-flash boundary (AFB) vary based on these voltage classifications.
One of the few things that has undergone little change is the valid bolted-fault current levels for calculating arcing current, IE, and AFB. For lower-voltage equipment (208 V to 600 V), the valid range of bolted-fault current is 500 A to 106 kA. For higher-voltage equipment (601 V to 15 kV), the valid range is 200 A to 65 kA. Under the original edition of the guide, the valid ranges were 208 V to 15 kV and 700 A to 106 kA. The equations and calculation methods contained in IEEE 1584 are not valid if the system voltages or bolted-fault current levels being analyzed are outside of these limits.
When calculating incident energy, the size of enclosure (where an arc could occur) comes into play. Some enclosure sizes (very large) do not tend to direct or influence the arc flash. However, smaller enclosures may amplify or direct the incident energy towards the worker, thus amplifying the incident energy to which the worker is exposed. To account for this, a correction factor has been added that adjusts the impact of the incident energy on the worker based on enclosure size. The “enclosure-type correction factor” (2002) term has been changed to “enclosure-size correction factor” (2018).
System Grounding Variable
The system grounding variable (2002) has been eliminated in the 2018 edition.
The new calculation methods include an electrode configuration factor. This new factor has turned the arc-flash study industry upside down and introduces new challenges to perform an accurate analysis. In 2002, bus or electrode orientation was not a factor. However, research has shown that the orientation of the electrodes where the arc is initiated can have a significant impact on the IE to which a worker is exposed. Varying coefficients are used in the calculations based on the electrode orientation.
IEEE 1584 has defined three electrode orientations for metal-enclosed equipment and two electrode orientations for open-air equipment.
- For metal-enclosed equipment, these bus orientations are VCB (vertical conductors/electrodes inside a metal box/enclosure); VCBB (vertical conductors/electrodes terminated in an insulating barrier inside a metal box/enclosure); and HCB (horizontal conductors/electrodes inside a metal box/enclosure.
- For open-air equipment, the two bus orientations are VOA (vertical conductors/electrodes in open air); and HOA (horizontal conductors/electrodes in open air).
Since the electrode configuration factor can significantly affect the IE results, the study engineer must be familiar with the construction of the equipment and determine the possible bus configurations that could be involved in the arc event. The effect of electrode orientation can be seen in the example calculations included at the end of this article.
During recent testing, the equations used to calculate IE were found to be not valid when the arc source is approached. This is due to hot plasma gasses located near the arc source. The new IEEE 1584 guide indicates that the equations are only valid 12 inches and beyond from the arc source. Distances less than this would likely be involved in the arc plasma, and calculations within this proximity are not modeled accurately by the provided equations.
In the previous version of the IEEE guide, systems that I refer to as “low-energy systems” (my term) were described as follows:
Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply.
This equipment was exempted from arc-flash analysis because it was believed that the limited energy supplied in these systems would not generate IE greater than 1.2 cal/cm2. However, recent analysis has shown that IE greater than 1.2 cal/cm2 can be experienced within these systems.
The revised statement concerning this equipment is:
Sustainable arcs are possible but less likely in three-phase systems operating at 240 V nominal or less with an available short-circuit current less than 2,000 A.
Available fault current from a 125 kVA transformer at 240 V or 208 V is typically higher than the new 2,000 A lower limit. This significant change will result in more equipment required to be analyzed for risks and hazards. Additionally, identification of which equipment is required to be included in a study won’t fully be known until a short-circuit study has been completed.
Now that we’ve covered some of the differences related to physical factors between the original 2002 edition and the updated 2018 edition of the guide, let’s dive into the changes to the calculation process. The calculation process has changed from relatively simple first-order logarithmic equations to very complex sixth-order logarithmic equations involving a multitude of variable coefficients based on the physical factors we previously covered. To avoid death by mathematical boredom, I have avoided a detailed examination and comparison of the equations and will focus on a high-level review of the new calculation process. For those interested in the details of the mathematics, you can purchase the IEEE 1584 guide and enjoy hours of deciphering the complex relationships between circuit voltages, fault current, arcing current, electrode orientation and gaps, and enclosure dimensions. I say that with tongue-in-cheek because if you are involved in calculating arc-flash incident energy levels for the protection of personnel, you should gain a thorough understanding of these equations and the various relationships and factors included in these equations.
For the purposes of this paper and describing the calculation process, lower-voltage equipment will refer to equipment operating at 600 V or less. Equipment operating above 600 V and up to 15 kV is referred to as higher-voltage equipment. We will primarily focus on the calculation process for lower-voltage equipment for several reasons:
- It’s where the majority of work occurs.
- It is more prevalent in our industry.
- The calculation process is much simpler than the calculations for higher-voltage equipment.
This process is presented in the typical order in which you would calculate the various values that ultimately result in the incident energy level at a given working distance.
Lower-Voltage Calculation Process
- Intermediate average arcing current. The first value we calculate is the intermediate average arcing current. This value is calculated and based on the system voltage category. For the low-voltage calculation, this value is normalized at 600 V. This calculation utilizes the bolted-fault current, electrode gap, and bus orientation. Several different coefficients are utilized in the calculation based on the bus orientation and normalized voltage. Tables for these coefficients are included in the guide. The normalized, intermediate average arcing-current value will be adjusted for the specific system open-circuit voltage in the next step.
- Arcing current. The arcing current at the open-circuit voltage is then calculated using the intermediate average arcing current, system open-circuit voltage, and bolted-fault current. The guide refers to this as the “final” arcing current. However, we will see that there is another calculation after this one (using a reduced arcing current), so referring to this as “final” can be a bit confusing.
- Arc duration. The arc duration is dependent on the arcing current and the upstream protective device clearing time. To determine this time, the upstream device protective characteristics must be examined to determine the time duration required to clear the fault based on the arcing current value. Remember, this may be the first upstream device or a device further upstream. Also realize that the duration is based on the arcing current and not the bolted-fault current. The arcing current can be much less than the bolted-fault current, so the upstream protective device may not activate in the instantaneous region, resulting in a much longer duration and increased exposure to arcing energy.
- Enclosure-size correction factor. We must now determine whether the enclosure where the arc could occur will affect the intensity or level of exposure to the arc-flash incident energy. The enclosure-size correction factor is a new variable that replaces the previously used variable based on enclosed or open air arcs. In the 2018 guide, the factor for open air is 1.0. For arcs that occur in enclosures, the enclosure-size correction factor is based on how the enclosure size affects the intensity of the IE on a worker at the enclosure opening.
This calculation has several steps and many variations, making it difficult to describe without causing serious confusion and discussing various equations. To simplify this explanation, I will describe the steps, but omit the details of the variations that one might encounter.
- First, you need to know the actual enclosure dimensions.
- From these measurements, you calculate the equivalent enclosure dimensions.
- These equivalent enclosure dimensions are then used to calculate an equivalent enclosure size.
- The equivalent enclosure size is then used to calculate the enclosure-size correction factor.There are also special considerations and calculations for what is defined as shallow enclosures. Shallow enclosure considerations apply only to low-voltage calculations and only when both enclosure dimensions (width and height) are less than 20 inches and the enclosure is less than 8 inches deep. This type of enclosure may be encountered for smaller low-voltage disconnects and subpanels.
- Incident energy. We now have the various values that allow us to calculate incident energy. IE is calculated at the applicable voltage class. For this low-voltage example, our voltage classification is for ≤ 600 V. This calculation includes variables such as intermediate average arcing current (at 600 V), arcing current (at actual open-circuit voltage), event duration (determined by the arcing current and upstream protective device), bolted-fault current, working distance, enclosure-size correction factor, electrode spacing (gap), and numerous (13) coefficients based on electrode orientation and normalized voltage.
- Arc-flash boundary. After calculating IE in the previous step, we can now calculate the arc-flash boundary (AFB). The AFB is calculated based on variables including intermediate average arcing current (at 600 V), arcing current (at actual open-circuit voltage), event duration, bolted-fault current, enclosure-size correction factor, electrode spacing (gap), and numerous coefficients (13) based on electrode orientation and normalized voltage. The arc-flash boundary is the distance from the arc source where the incident energy is 1.2 cal/cm2.
- Arcing current variation correction factor. In the 2002 edition of the guide, consideration was given to the possibility that the actual arcing current could be less than calculated because of variations in the power system. To account for these variations where the actual arcing current could be less than calculated, IE is also calculated using a reduced (85%) arcing current value. While small variations in arcing current can result in small variations in IE and AFB, the primary concern for arcing current being less than calculated is the duration of the event due to the response of the upstream overcurrent protective device. If the arcing current falls below the sensing level of the instantaneous element of an overcurrent protective device, a significant increase in event duration, IE, and AFB can result. An IEEE paper suggests varying the available fault current by 50% and examining the effects on the arc duration and associated IE. However, this method came under scrutiny due to the lack of supporting documentation and test data to establish this as an accurate general practice for determining minimum possible fault current levels. Recent test data indicates that the variation in current for lower-voltage systems was much greater than for higher-voltage systems. For typical lower-voltage systems, current variations from the calculations of 12%–16% were observed. This compares closely to the 15% (85% factor) used in the 2002 methodology. At higher voltages, the variation was found to be significantly smaller.
Therefore, the possibility of current variation resulting in a longer event duration and higher IE for lower-voltage equipment is much greater than for higher-voltage equipment. In the 2018 edition of the guide, an arcing current variation correction factor/reduced arcing current is calculated. The effects of the reduced arcing current are examined, and the worst-case values are then used for IE and AFB.
Higher-Voltage Calculation Process
The calculation process for higher-voltage systems is a bit more complex compared to low-voltage systems. Therefore, we will not cover the details of the higher-voltage calculation process (601 V–15 kV) in this paper. The key difference in the higher-voltage calculation process is the use of an iterative process with normalized values that are then interpolated to the specific system voltage.
The new calculation process contains additional iterations and factors as well as more complicated equations using numerous coefficient variables. This complexity makes the process of accurately modeling and determining incident energy and arc-flash boundaries more challenging than using the previous 2002 guide and methods. Several good software applications are available that reliably perform these complex calculations. However, as I remember from my programming classes in college, garbage in equals garbage out!
Several variables that are determined by the study engineer and the data collector affect the accuracy of the model. Experience, knowledge, and understanding the variables and system equipment are extremely important for an accurate model and calculations. Only qualified engineers who are familiar with the equipment being modeled and have the experience to understand the calculations and analysis should be engaged in performing these studies.
Part 1 covered a brief history of electrical safety as it has changed over the past few decades to improve worker safety, from OSHA establishing the “what” to NFPA 70E establishing the “how” and IEEE 1584 defining the “method” for calculating and quantifying arc-flash hazard. The first edition of IEEE 1584 in 2002 was based on the limited data and knowledge of arc-flash physics at the time, but the effort has contributed to reducing life-threatening and serious injury caused from arc flash. Since then, much research has been conducted, and arc-rated fabrics have improved.
Now, with the 2018 edition of IEEE 1584, we see further refined and improved accuracy of arc-flash calculations. However, this refined and improved accuracy comes with a challenge of gathering additional information about equipment. Is gathering this additional information practical? Does it add value? Those are both great questions. We will explore more details about the updates to IEEE 1584 and discuss some practical considerations in Part II of this article in the Summer 2022 edition of NETA World.
 IEEE. IEEE 1584-2002, IEEE Guide for Performing Arc-Flash Hazard Calculations, New York, NY.
 IEEE. IEEE 1584-2018, IEEE Guide for Performing Arc-Flash Hazard Calculations, New York, NY.
 Occupational Safety & Health Administration [OSHA]. Regulation 29 U.S.C. § 654, 5(a)1, 1970. Retrieved from www.osha.gov/laws-regs/oshact/section5-duties.
 Jooma, Z. (n.d.). History of the NFPA 70E. Retrieved from www.eandcspoton.co.za/resources/docs/Hazardous/History_of_the_NFPA.pdf.
 Balasubramanian, I and Graham, A.M. “Impact of Available Fault Current Variations on Arc-Flash Calculations,” 2009 Record of Conference Papers — Industry Applications Society 56th Annual Petroleum and Chemical Industry Conference, Anaheim, CA, 2009, pp. 1-8.
Steve Park, PE, brings 40+ years of experience in the power system industry to his position as Vertiv’s Director of Technical Training. Steve oversees technical training for Vertiv’s North America field services including AC power products, DC power products, thermal management systems, monitoring, and independent testing services for High Voltage Maintenance (HVM) and Electrical Reliability Services (ERS). Much of his career and expertise is from various roles while employed by HVM and ERS involving power system studies, engineering and test reports, cable testing, forensic investigations, test procedures/practices, and quality assurance. Steve gained a deep understanding of the power system industry during his career in the U.S. Air Force, where he served 14 years on active-duty service as a high-voltage lineman, electrical power distribution engineer, and instructor of electrical engineering at the Air Force Institute of Technology (AFIT). Steve earned BSEE and MSEE degrees in electrical engineering from Purdue University and an MBA from Indiana Wesleyan University. Steve has been a registered Professional Engineer since 1992.