How to Perform an Arc Flash Study – Part 5 Incident Energy and Arc Flash Boundary Calculations

The final part of this series examines incident energy and arc flash boundary calculations for the 480V panelboard example used in this series. IEEE 1584—IEEE Guide for Performing Arc Flash Hazard Calculations defines incident energy as, “The amount of thermal energy impressed on a surface, a certain distance from the source, generated during an electric arc event.” It can be used to determine the arc rating of protective clothing and equipment as part of an arc flash risk assessment.

Two important variables are the arcing fault current and the arc duration. The arcing fault current was addressed in part 2. The arc duration defines the total exposure by evaluating the time current characteristic of the protective device that is expected to operate and clear the arc flash. Part 4 concluded that the device for this example will operate in 1 electrical cycle, or 0.167 seconds.

Working distance

IEEE 1584 defines the working distance as the distance between the potential arc source and the face and chest of the worker. Incident energy varies exponentially with the inverse of the distance, the greater the distance, the less incident energy and vice versa. IEEE 1584 lists “typical” working distances of 18 inches for low-voltage equipment such as panels and motor control centers, 24 inches for low-voltage switchgear and 36 inches for medium-voltage equipment. However, the specific task must also be considered when defining this distance. For the 480V panelboard example, 18 inches is used.

Electrode configuration

Another important variable is the electrode configuration. The first edition of IEEE 1584 was based on two electrode configurations: referred to as box configuration (enclosure) and an open configuration (in air). In each case the electrodes were oriented vertically, which is today’s equivalent of vertical conductors/electrodes inside a metal box/enclosure (VCB) and vertical conductors/electrodes in open air (VOA). Based on subsequent research, it was determined that the incident energy can be greatly affected by other electrode orientations and influence the trajectory of the arc. For an enclosure, this led to the introduction of vertical conductors/electrodes terminated in an insulating barrier inside a metal box/enclosure (VCBB) and horizontal conductors/electrodes inside a metal box/enclosure (HCB). HOA is for open air. 

Table 1 provides a comparison of the incident energy and arc flash boundary based on the VCB, VCBB and HCB configurations. The incident energy increases with VCBB, and increases more with HCB. For panelboards such as this example, VCB is typically used, as well as VCBB if the feeder terminates into a circuit breaker, possibly behaving like VCBB. The temptation to default to the worst case HCB should be avoided unless it is a realistic configuration. It would likely not be used unless a conductor or bus was directed toward the worker.

Jim Phillips

Enclosure size

When an arc flash occurs, the enclosure has a focusing effect on the incident energy. The IEEE 1584 equations for the incident energy and arc flash boundary calculations are based on a normalized 20-inch-by-20-inch enclosure opening. If the enclosure opening is larger, the energy will less focused, resulting in less energy per unit area. Table 2 compares the calculated incident energy using the VCB configuration and 18-inch working distance with different enclosure sizes ranging from 20-inches-by-20-inches to 36-inches-by-36 inches.

Jim Phillips

Arc flash boundary

IEEE 1584 defines the arc flash boundary as “A distance from a prospective arc source at which the incident energy is calculated to 1.2 cal/cm2.” This is the value of incident energy where arc rated clothing and associated protective equipment is required. Tables 1, 2 and 3 also include the arc flash boundary to illustrate the effect of the electrode configuration, enclosure size and arc duration on the boundary.


The calculation results in part 5 indicates the incident energy is low, and in some cases less than 1.2 cal/cm2. This is due to the very fast 1-cycle clearing time. The duration is often considered the most critical variable, and if the duration increases, the incident energy increases proportionally. Table 3 illustrates the effect that longer arc durations may have.

Arc flash studies can be complex, requiring important decisions regarding the variables used. Each must be carefully considered because they can all significantly impact the results.

This article was originally published in the May 2022 Edition of Electrical Contractor Magazine.

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How to Perform an Arc Flash Study – Part 4 Arc Duration and Time Current Curves

The duration of an arc flash is typically defined by how long it takes an upstream overcurrent device to operate and clear the fault. This requires using the device’s time current characteristic (TCC), which is based on the specific device type, rating, settings (if available) and manufacturer. Recalling my circuit breaker manufacturer days, even the year the device was produced is important as TCCs can change over time.

The TCC for the device used in this example is illustrated in the figure. The horizontal axis is plotted in amps multiplied by a factor of 10. This means that the 10A on the graph is rescaled to represent 10A times 10, or 100A, and the 100 represents 100A times 10, or 1,000A, etc.

The vertical axis represents time in seconds. Each axis employs a logarithmic scale that is nonlinear and used when analyzing a large range of quantities, such as time and current in this case. Instead of increasing in equal increments, each interval, or decade as it is known, increases by a factor of 10.

TCC basics

The TCC of a circuit breaker will have at least two distinct parts. The upper left band is commonly referred to as the time-delay or overload region. This may be either a thermal element or an electronic or digital element. The sloping curve is commonly referred to as an “inverse-time” characteristic because current and time are inverse from each other. The more current flowing through the device, the less time it takes to operate. The band, or thickness, is based on the operating and clearing time, as well as manufacturer’s tolerance.

The horizontal portion of the TCC to the lower right represents the time it takes to trip instantaneously, which means no intentional time delay. The thickness of the instantaneous band represents the time it takes the device to open and clear the fault, which in this case is one electrical cycle or 0.0167 seconds. Some devices may take several cycles to trip instantaneously.

The vertical band in the middle is the transition point between overload and instantaneous operation, commonly called the instantaneous trip setting. If the current falls to the left of the band, the device operates in the time delay region. If it falls to the right, then it trips instantaneously. If the current lands in the middle of the band, it is uncertain which element will operate; although there is specific current value for the transition from overload to instantaneous, there is also a plus/minus tolerance, so the actual point is somewhere within the band. If the arcing current falls within the band, worst case assumes it could trip in the overload region, resulting in a significant time delay.

Arc duration and TCCs

To determine how long it should take a device to operate for a specific current, the current is located on the horizontal axis and a line is drawn upward until it intersects the top of the curve. Looking to the left indicates the corresponding time.

The graph shown represents the TCC of the 225A circuit breaker used in our example. It is located upstream from the panel under study and is the device that should trip and clear the arc flash.

The second part of this series, “Calculating an Arcing Fault Current” provided the calculated arcing fault current of 23,010A, or 23.01 kA. Specific conditions were used, such as a 1-inch bus gap and VCCB electrode orientation. This current is labeled on the instantaneous part of the TCC toward the lower right of the graph. Drawing a line at this value to the top of the TCC and then drawing a line to the left to determine the duration indicates the device should trip in 0.0167 seconds, or one electrical cycle. This value is used as the arc duration and part of the incident energy calculation in a subsequent part of this series.

When performing an arc flash study, a problem could occur if the arcing current is too low and passed within or to the left of the vertical band. This would indicate the device operates in the time-delay region that would greatly increase the arc duration and resulting incident energy. When the results of an arc flash study indicate a large incident energy at a given location, it often means the arcing current was too low for the designated overcurrent device to trip instantaneously

This article was originally published in the March 2022 Edition of Electrical Contractor Magazine.

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How to Perform an Arc Flash Study – Part 3
Arc Duration

Time is everything when an arc flash occurs.  The longer the duration, the greater the incident energy exposure – which is directly proportional to the duration.

The 2018 Edition of IEEE 1584 defines the arc duration, also referred to as clearing time as:

The total time between the beginning of a specified overcurrent and the final interruption of the circuit at rated voltage.

The term clearing time is also referenced because the arc duration is normally based on how long it takes an upstream overcurrent protective device to interrupt and clear the arcing fault current.  A simple enough concept except how do you determine which device would likely interrupt and how do you determine the actual duration? 

Determining Which Device
When the arcing current from an arc flash jumps across an air gap, it results in a conducting plasma which could engulf other conductors and escalate as well as propagate to other locations.  If the plasma propagates to the line side of the main device such as the main in panel PP-1 shown in Figure 1, then even if the main does trip, the arc flash may not be cleared. It may continue until a device further upstream such as the feeder in the Main Distribution Panel (MDP) trips. A similar situation may occur if the arc flash originates on the line side of the main device.

One Line Example - Brainfiller

FIGURE 1. One Line Diagram – Which Device Defines the Arc Duration.

Because of the uncertainty about whether the main device would interrupt and clear an arc flash, a common approach is to consider the clearing time of a device outside the area that could be impacted by the arc flash.  This would be a device in a separate enclosure such as the feeder located in MDP.

For equipment such as metal clad switchgear where devices are located in individual compartments, engineering judgment must be used when considering whether the main would be unaffected by an arc flash on a feeder.

Determining the Duration
Determining the protective device clearing time depends on the device’s tripping characteristic as well as the magnitude or arcing current.   As a minimum, overcurrent protective devices will have two distinct tripping characteristics.  The overload region which provides a time delay for lower magnitude currents and the instantaneous region which will trip for higher magnitude currents.  In the electrical power world, the term “instantaneous” means no intentional time delay.  There is an unintentional delay of up to several electrical cycles which is the time it takes the device to physically open and clear the arc flash.

The device type such as whether it is a molded case or electronic trip circuit breaker, current limiting fuses and whether it has adjustable settings all help define the tripping characteristic.  In addition, the condition of maintenance of the device is important.  If a device is old and poorly maintained will it perform as expected?  Maybe not which could lead to a longer arc duration.   

Too long – Two Seconds
If the arcing short circuit current is a lower magnitude such as what happens with higher impedances of long conductors or smaller transformers, analysis of the device may indicate it may trip in the overload region for the arc flash – which can take several seconds or more.  In this case, even though the lower current results in a less intense arc flash, the duration could lead to a larger total incident energy.  

For cases where there are long clearing times, IEEE 1584 contains language that many people refer to as the “2 second rule”. Although not actually a rule, this language permits capping the arc duration used in the calculation at 2 seconds.  The actual language states:

If the total protective device clearing time is longer than two seconds (2 s); consider how long a person is likely to remain in the location of the arc flash. It is likely that a person exposed to an arc flash will move away quickly if it is physically possible, and 2 s usually is a reasonable assumption for the arc duration to determine the incident energy.

The language contains caveats such as the decision to use two seconds requires engineering judgment based on the task, location and the person’s ability to move away.  The concept is based on human reaction and response.  If there is a threat such as an arc flash, the person reacts and responds automatically.  Also, even though the term “arc duration” is used in this language, two seconds does not mean the arc extinguishes in two seconds, it is referring to a person’s exposure.

Part 4 will address the use of time-current characteristics to determine the arc duration.

This article was originally published in the January 2022 Edition of Electrical Contractor Magazine.

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How to Perform an Arc Flash Study – Part 2
Arcing Fault Current

Arcing Fault Current – Effect of Gap, Voltage and Electrode Configuration
An arc flash occurs when short circuit current jumps across an air gap between energized conductors. The event is normally the result of initial (and inadvertent) contact between energized conductors which creates the short circuit.  During the event, the conductors or a conducting object may either melt back or be blown back producing an air gap. When current flows across the gap, it ionizes the air resulting in a conducting plasma and thermal cloud. IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations refers to this as the Arcing Fault Current which is defined as:


How to Perform an Arc Flash Study – Part 1
Based on the Latest Edition of IEEE 1584

Performing an arc flash study can be complex enough but the latest edition of IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations has taken it to a whole new level.  In this first in a series of articles, I will take you through the steps of performing an arc flash study.

 The Evolution of Arc Flash Studies
Quite a bit has changed since arc flash studies went mainstream in the early 2000’s.  Standards like NFPA 70E – Standard for Electrical Safety in the Workplace and the latest edition of IEEE 1584 continue to evolve and improve.  Standards like these, coupled with advancements in arc rated clothing and personal protective equipment (PPE) as well as changes to electrical design practices have all helped create a much safer workplace.

The main components of an arc flash study are Continue reading

Warning! No Arc Flash Hazard Exists!

I’m sure that title raised a few eyebrows but before you send me an email telling me how I got this wrong, hang in there for the rest of the thought.   I receive questions about this phrase on a pretty regular basis.

It’s no secret that 1.2 cal/cm2 is the generally accepted value of incident energy exposure where the onset of a second-degree burn may occur.  This is also the value that triggers the need for arc rated clothing and protective equipment.  

However, having a prospective incident energy below 1.2 cal/cm2 can cause confusion as some will place the phrase “NO ARC FLASH HAZARD EXISTS” on the arc flash label as a result.  When I ask why this phrase is on the label, I receive the response that it’s because the incident energy is less than 1.2 cal/cm2.  – BEEP – Wrong Answer!

If the prospective incident energy is less than 1.2 cal/cm2, remember that is at the working distance and it only means that it is below the threshold where the onset of a second-degree burn may occur.  It does NOT mean there is no injury possible. What about first-degree burns?  What about the hands or other parts of the body being closer than the working distance?  What about…  You get the idea.  There IS still a hazard it is just not commonly considered a major hazard that requires arc rated PPE at the working distance.   

I am asked about using this phrase so often that a while ago I decided to ask a more general survey question about arc flash hazards at 208 Volts at the website  I was surprised to see almost 20% of the respondents to the survey indicate they did not believe an arc flash hazard exists at 208 Volts.

The survey and discussion are found here:

The working distance is very important because it is the distance from the arc flash source that is used to calculate the incident energy where a worker’s head and torso would likely be located. This makes understanding the working distance a very important part of an electrical safety training program.   Just because the incident energy is listed as less than 1.2 cal/cm2 at 18 inches for example, doesn’t mean it will be that low for hands and other parts of the body that are closer. It increases as the working distance decreases.

I can hear this scene being played out in a legal setting.  

Attorney: “I am sorry to hear that you received a burn injury on your hand but why where you not wearing arc flash protection?”  

Response: “Because the label stated – No Arc Flash Hazard Exists”  

Really? Fade to black, game over.

2021 NFPA 70E – Major Changes

Jim Phillips, P.E.

2021 NFPA 70EEvery three years I have the privilege of writing the NFPA 70E Major Changes article for National Electrical Contractor Association’s magazine: Electrical Contractor.   The 2021 edition of this standard will be available September 4, 2020 so it’s time to take a sneak peek and see what is in store this time around.   This article is based on my article that was published in the May 2020 issue of Electrical Contractor.

Disclaimer:  Although I am Vice-Chair of IEEE 1584, International Chair of IEC TC78 Live Working, Technical Committee Member of NFPA 70E and involved with many other codes and standards committees, the views expressed here are mine and may or may not represent the views of any of the above committees.

This article focuses on the more significant changes and is based on what was known at the time it was written. It does not include every change and some language was paraphrased. The reader should always refer to the final approved version once it is published. Continue reading

2021 NFPA 70E – Review of Major Changes

2021 NFPA 70E

2021 NFPA 70E – Major Changes

By Jim Phillips

The 2021 Edition of NFPA 70E is right around the corner and with it – many changes.

Every three years I have the privilege of writing about the upcoming changes for the National Electrical Contractor Association’s Electrical Contractor Magazine.

A summary of the major changes for the 2021 edition was published in the May 2020 Edition of Electrical Contractor Magazine.


I will also be conducting a FREE live streaming class at 10:00 AM Pacific/1:00 PM Eastern Time on June 18th to discuss the major changes.

2021 NFPA 70E Changes Article

Live Streaming 2021 NFPA 70E Update – June 18, 2020


Other Upcoming Live Streaming Classes:

Arc Flash Studies – IEEE 1584

Electrical Power System Engineering Course

Captain Murphy, Dirty Harry and Electrical Safety

Murphy's Law - Sled

Rocket Sled that Inspired “Murphy’s Law”

OK, not the most professional sounding title for an article about electrical safety.  But play along, you will be able to connect the dots rather quickly.

 Captain Murphy
Around seventy years ago, Captain Murphy was an aerospace engineer who worked on safety-critical systems.  He became involved with high-speed rocket sled experiments used to determine what G-forces a human could experience while being hurled down the rails at an alarming speed – 632 miles per hour back then. Note: speeds today can exceed well over 6000 miles per hour!

The “passenger” would be restrained by a harness that contained a series of measurement sensors – however, during the sled’s run, the sensors were not functioning!  A subsequent investigation found Continue reading

Plasma – Modify the Arc Rating or Modify the Incident Energy Calculations?

Plasma – Modify the Arc Rating or Modify the Incident Energy Calculations?

I am frequently asked questions about the application of the 2018 edition of IEEE 1584 – especially electrode configurations and more specifically, about HCB (Horizontal Conductors/Electrodes inside a Metal Box/Enclosure).

I recently had the privilege of co presenting a paper at the IEEE Electrical Safety Workshop that focused on PPE, arc ratings and the arc flash hazard. I made a last-minute addition to the presentation that was not included in the published paper.  It provides a direct correlation between using the 2018 IEEE 1584 HCB configuration and conclusions from a 2010 technical paper about de-rating PPE for outward convective flows Continue reading

Case Study – Arc Flash While Switching – Normal Operation?

A common question that I often hear in my NFPA 70E and IEEE 1584 Arc Flash Studies training courses is:

“Can simply operating a device such as a fusible switch or circuit breaker cause an arc flash?”


I respond to the question with a very specific answer which is:

 “It depends.”



Arc Flash Aftermath

Learning the Hard Way

A good friend of mine here in Arizona has a client that found the answer the hard way. An electrical contractor was performing electrical work at their facility.  The work involved creating an electrically safe work condition at the 277Y/480 Volt main service switchboard following NFPA 70E 120.5 Process of Establishing and Verifying an Electrically Safe Work Condition.

The main service switchboard contained four separate mains as permitted by NEC 230.71 – commonly referred to as the Six Disconnect Rule. One of the mains was a 1200 Amp bolted pressure switch with 1200 Amp fuses that fed a downstream distribution switchboard in another room. As required by NEC 240.95, ground fault protection was also provided on the main since the disconnect exceed 1000 amps and was a solidly grounded 277Y/480V system.

The work began by interrupting the load by opening each of the smaller fusible disconnects at the downstream switchboard.  Once the load was interrupted, the 1200 Amp main was opened along with the three other mains. However, the line side of the mains in the switchboard remained energized – and still hazardous.

To completely de-energize the switchboard, Continue reading

IEEE 3000 Series Standards – Update

My 1974 IEEE Gray Book from College – Now part of the 3000 Series of IEEE Standards

I have been a fan of the IEEE “Color Books” going all the way back to my Senior Year in college – yep, I had a class based on the 1974 Edition of the IEEE Grey Book!  Unlike so many other standards, the 13 IEEE Color Book series included many practical examples, pictures, diagrams and were always a great resource.

But (you saw that word coming) there was a lot of overlap between the different books creating the risk of subjects being out of synch over time.  For example, the topic of short circuit calculations/analysis could be found in the Gray Book (IEEE Std. 241), Buff Book (IEEE Std. 242), Red Book (IEEE Std. 141), Brown Book (IEEE Std. 399), and Violet Book (IEEE Std. 551) In addition to the overlap, the sheer size of each book would mean the revision process would sometimes take forever (or at least seem that way).

Beginning over a decade ago, IEEE began transitioning Continue reading

DC Arc Flash Calculations

290 MW PV Installation in SW Arizona

When the 2018 Edition of IEEE 1584 was published last year, one subject was conspicuously absent –  DC arc flash.  DC power systems are everywhere and include sources such as rectifiers, photo-voltaic installation, transit systems and more.  The number and scale of DC systems continue to grow.

The original IEEE 1584 project for developing the next generation arc flash model had quite an ambitious scope and budget.  However, during the critical fundraising period in the early years, the great recession occurred and the DC effort had to be saved for another day.

To address arc flash protection for DC systems, many Continue reading

Evolution of Arcing Short Circuit Current Calculations

Arc Flash Duration Defined by Clearing Time of Upstream Protective Device 

One of the main variables that is part of an arc flash study is the arcing short circuit current.  However, going back through the evolution of arc flash calculations, consideration was not always given to this value.  Due to the impedance of the arc, the arcing current will always be less than the bolted short circuit current and the lower value could lead to a greater incident energy. Why?  Because the lower current could result in the upstream protective device taking longer to operate leading to a longer arc flash duration.

Let’s take a look at a few milestones regarding arcing current calculations up through the use of the Arcing Current Variation Factor found in the 2018 Edition of IEEE 1584. Continue reading

History of IEEE – 135 Years and going strong!

I was at the IEEE PCIC Conference in Vancouver, British Columbia last week where I had the privilege of being part of the first presentation with three great colleagues (actually thee great friends) The topic was the new IEEE 1584 standard.

During the presentation while I was looking out into the 1000 plus faces, it occurred to me, “I wonder how many people know how IEEE began?”  So, in case that very important question has been keeping you up at night, here is the short history from IEEE’s website. Continue reading

History of Arcing Short Circuit Calculations – 1980’s to Now

One of the main variables used for incident energy and arc flash boundary calculations is the arcing short circuit current. How the arcing current is calculated has gone through an evolution beginning back in the 1980’s up through today.

The arcing current will always be less than the “bolted” short circuit determined by performing a “traditional” short circuit study that is used to evaluate the interrupting rating of protective devices.  During an arc flash, the short circuit current flows across an air gap which introduces an arcing impedance.  The result is that the arcing short circuit current Continue reading

Interview with Jim Phillips – How the New IEEE 1584 Standard Affects Arc Flash Risk Assessments in Europe

By: Rebecca Frain – Managing Director, Electrical Safety UK, Rotherham, England – A Brainfiller, Inc. Strategic Partner.

Recently I had the opportunity to interview Jim Phillips regarding the new IEEE 1584 standard and what to expect with some of the new changes. In addition to being Associate Director for Electrical Safety UK and founder of, Jim is also Vice-Chair of IEEE 1584 and International Chair of IEC TC 78 – Live Working.

As an introduction, IEEE 1584 – IEEE Guide for Performing Arc Flash Hazard Calculations was first published in 2002 and is the standard that defines the equations and methods used in many of the arc flash software packages used for arc flash risk assessments. The second edition was published towards the end of 2018 and is a real game changer.  Jim will be the Keynote Speaker at the upcoming International Arc Flash Conference on Tuesday September 24, 2019 in Manchester. Continue reading

Just Published – IEC 61482-1-1

It is once again a privilege to announce the recent publication of IEC 61482-1-1:2019 Live working – Protective clothing against the thermal hazards of an electric arc – Part 1-1: Test methods – Method 1: Determination of the arc rating (ELIM, ATPV and/or EBT) of clothing materials and of protective clothing using an open arc.  This standard is one of the dozens of standards that fall under IEC Technical Committee 78 that I have the privilege to Chair.

IEC 61482-1-1:2019 specifies test method procedures to determine the arc rating of flame resistant clothing materials and garments or assemblies of garments intended for use in clothing for workers if there is an electric arc hazard. An open arc under controlled laboratory conditions is used to determine the values of ELIM, ATPV or EBT of materials, garments or assemblies of garments. Continue reading

UK’s Electrical Review – 2018 Edition of IEEE 1584 – Major Changes

One of my latest articles regarding the new 2018 IEEE 1584 Standard was recently published in the United Kingdom’s premier publication Electrical Review.  In this article I take you through the major changes to new IEEE 1584 Standard – IEEE Guide for Performing Arc Flash Hazard Calculation Studies and what it means for arc flash studies and risk assessments.

View Article: 2018 IEEE 1584 – UK Electrical Review Magazine

This article is published in advance of the upcoming International Arc Flash Conference where I will be discussing the changes and providing calculation examples illustrating the new standard.

The conference will be held on Tuesday, September 24, 2019 in Manchester, England.  For more information: International Arc Flash Conference

What is CENELEC?

I just returned from a CENELEC TC78 Live Working Standards meeting in Brussels, Belgium a few days ago and it occurred to me that many people may not know what CENELEC is – or does.

CENELEC is the European Committee for Electrotechnical Standardization and is responsible for standardization in the electrotechnical engineering field. CENELEC prepares voluntary standards, which help facilitate trade between countries, create new markets, cut compliance costs and support the development of a Single European Market.

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2018 IEEE 1584 – Enclosure Size Adjustment Factor

Ever since the 2018 Edition of IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations was published a few months ago,  people continue to sift through the many  changes that have occurred.  One of the more significant changes is the introduction of a correction factor to adjust the calculated incident energy and arc flash boundary to account for the effect of the enclosure size.

When an arc flash occurs, the size of the enclosure can influence the arc flash hazard.  The smaller the enclosure, the more concentrated the energy is – focusing it more towards the worker resulting in greater incident energy exposure.  The opposite is also true.  Larger enclosures have Continue reading

Electrode Configuration and 2018 IEEE 1584

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

Arc Flash, Second Degree Burns (My Wife and a Chili Cookoff)

Yes, you read the title correctly – Second degree burns, my wife and a chili cookoff! And it all took place at home. But, before I get into that story, let me back up a bit.

Standards such as NFPA 70E, IEEE 1584 and several others address the arc flash hazard in terms of incident energy with the severity quantified in terms of calories per square centimeter (cal/cm2).  The generally accepted value for “the onset of a second degree burn” is 1.2 cal/cm2 as shown in the following examples.

The NFPA 70E definition of the Arc Flash Boundary contains an Informational Note that references the “the onset of a second degree burn on unprotected skin is likely to occur at an exposure of 1.2 cal/cm2

“The onset of a second-degree skin burn injury based on the Stoll curve.” is also found in Informational Note 3 of the definition of Arc Rating. Continue reading

2018 IEEE 1584 – 125 kVA Transformer Exception DELETED!

125 kVA – Going, going, gone!
After much speculation about the fate of the 125 kVA transformer “exception”, the 2018 Edition of IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations has finally been published and made it official.  The 125 kVA transformer exception has been deleted!

In its place is the new language:

“Sustainable arcs are possible but are less likely in three-phase systems operating at 240 V nominal or less with an available short circuit current below 2000A” Continue reading

IEEE 1584 – Changes to the Next Edition

It has been sixteen long years since IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations was first published in 2002.  This standard was highly celebrated back then because for the first time there was an internationally recognized standard that provided a method to calculate the arcing short circuit current, incident energy and arc flash boundary.  The results of these calculations are often listed on arc flash/equipment labels and have become an integral part of arc flash studies and risk assessments globally.

However, it did not take long before the focus began to shift towards what comes next. Continue reading

Don’t Automatically Reset a Circuit Breaker that Trips!

Circuit Breaker SettingsThe circuit breaker just tripped.  Production is down, alarms are sounding in the background.  Panic time.  For many, this scenario would mean quickly re-set the circuit breaker and “see what happens.”  Not the best idea – the question needs to be asked – why did the circuit breaker trip?  This situation can become an even larger problem if the circuit breaker has setting adjustments.  Before I go any further, let’s back up a few steps. Continue reading

IEC Standard 60900 was just published.

IEC 60900The fourth edition of IEC Standard 60900 Live working – Hand tools for use up to 1,000 V AC and 1,500 V DC was just published.  This standard is applicable to insulated, insulating and hybrid hand tools used for working live or close to live parts at nominal voltages up to 1000 V AC and 1 500 V DC.

This fourth edition cancels and replaces the third edition, published in 2012. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: Continue reading

Effective Training Presentations – A Few Tips From Jim’s 35+ Years Of Experience.

Bull by the HornsFor many, it is nightmare scenario.  Your department manager just came by and asked you to prepare and present a short training program for a client.   It doesn’t matter if it is about Electrical Safety, Arc Flash, the latest National Electrical Code or any one of an infinite number of topics, your reaction could range anywhere from feeling faint to watching your life pass before your eyes or any number of other responses.  Today, training has become more important than ever and there is an increasing likelihood that someday you may be called upon to put on the show – if you haven’t already.

I conducted my first training program “under duress” back in the very early 1980’s.  It was exactly the scenario above – the department Continue reading

Zero-Sequence Impedance and Incident Energy

A question that I am often asked either on-line or in one of my arc flash training classes is in regards to incident energy calculations and line-ground short circuit current:

“Since it is possible for the line-to-ground short circuit current to be greater than the three- phase current, could the line-to-ground condition be the worst case for incident energy calculations using IEEE 1584 equations?”

The short answer: No.

The longer answer: Let’s look at the equations for each short circuit calculation using symmetrical components.

The equation for calculating the three-phase fault current is: Continue reading

IEC 61482-2 Second Edition Just Released!

IEC 61482-2As the International Chair of IEC TC78 Live Working Committee, I am excited to announce the recent publication of the second edition of IEC Standard 61482-2 Live working – Protective clothing against the thermal hazards of an electric arc – Part 2: Requirements.

This revised standard is applicable to protective clothing used in work where there is the risk of exposure to an electric arc hazard.  The document specifies requirements and test methods applicable to materials and garments for protective clothing for electrical workers against the thermal hazards of an electric arc. Continue reading

PCIC Conference – ANSI vs. IEC Short Calculations and Arc Flash Studies

The 65th Annual IEEE-PCIC Conference will be held this year in Cincinnati, Ohio on September 24-26.

This year I will have both my “IEEE hat” and “IEC hat” on and join a couple of colleagues in presenting a technical paper comparing the use of ANSI vs. IEC short circuit calculations as part of an arc flash study.  The official title is: “Comprehensive Overview and Comparison of ANSI vs. IEC Short Circuit Calculations: Using IEC Short Circuit Results in IEEE 1584 Arc Flash Calculations” Continue reading

IEEE 1584 Status Update

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

40 cal/cm^2 Deleted – But Some Confusion Remains.

140 cal/cm^2 Arc Flash Suit

When the topic of incident energy above 40 calories per square centimeter (cal/cm^2) comes up, the discussion can be quite interesting.  People will sometimes refer to the high values in terms of a bomb or some other sensationalized description.  Although a higher calculated incident energy can be more hazardous, all is not as it appears to be. Is the large value due to a very strong source or is it simply due to a protective device possibly taking a long time to clear?    Each will behave differently.

When performing an arc flash study, if the calculated incident energy exceeds cal/cm^2 at any locations. people often just shake their head and ask, “Now what do we do?”
 We need to place the equipment into an electrically safe work condition but that in itself poses some risk.

When the 40 cal/cm^2 value is exceeded, it is often treated like an absolute go/no-go threshold and can trigger many different responses and comments that are not always correct. Above 40 cal/cm^2, arc flash labels may have the statement “No PPE Available.” This value also frequently triggers using the signal word “DANGER” on the label.  There may be comments made such as, “Above that value, the blast pressure will kill you.” My favorite sensationalized comment that I have heard is, “Above that level, PPE just Continue reading

IEEE and IEC Standards Update

By Jim Phillips

March has been a busy month for me with Standards Committee work.  I just returned home from three weeks of travel that included IEEE Standards meetings in Ft. Worth, Texas and various IEC meetings held at British Standards Institute (BSI) in London, U.K.

On the IEEE front, the IEEE 1584 Standard where I am Vice-Chair, has made significant progress over the past year and has completed the formal consensus ballot process, resolution of numerous comments from the balloters and has proceeded though another round of balloting. This new edition will provide more detailed equations for the calculation of incident energy from an arc flash as well as more detailed arcing current and arc flash boundary equations.  Although I can’t provide a date when it will finally be published, the draft has been clearing Continue reading

Short Circuit Calculations with Transformer and Source Impedance

Short Circuit Calculations – Transformer and Source Impedance

An infinite bus short circuit calculation can be used to determine the maximum short circuit current on the secondary side of a transformer using only transformer nameplate data.  This is a good (and simple) method for determining the worst case MAXIMUM short circuit current through the transformer since it ignores the source/utility impedance.  Ignoring the source impedance means it is assumed to be zero and voltage divided by zero is infinite, hence the often-used term “infinite bus” or “infinite source”.

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Global Use of IEEE 1584

IEEE 1584 – It’s a Small World
The world’s electrical systems do not discriminate when it comes to electrical safety.  Electric shock, electrocution and arc flash hazards can occur anywhere on the planet that has electricity.  An interesting side note is that according to an International Energy Agency Report, around 1.2 Billion people do not have electricity.  Hard to imagine as I type this on my laptop, with good lighting and the heat pump working away.

Earth at night

IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations has been gaining global traction every day since it was first published in 2002. Although the IEEE 1584 standard has its roots in the United States, it has gained widespread international use as the most common method for Continue reading

Arc Flash Labels – Information No Longer Required (maybe)

New Label ExceptionNew Exception 130.5(H) Exception No. 2 – Arc Flash Label Information May Not Be Required.
It is amazing how the requirements for arc flash labels have evolved with each new edition of NFPA 70E. Known as Arc Flash Warning Labels by the National Electrical Code and Equipment Labels according to NFPA 70E 130.5(H), most people simply refer to them as arc flash labels.

What first began as a simple requirement to warn people of the arc flash hazard, has morphed into a list of required information found in NFPA 70E 130.5(H).  As an example the evolution of label requirements was the information to aid in selecting Personal Protective Equipment and Arc Rated Clothing.  In the past, the requirements began with Hazard Risk Category Tables, then it became using the Hazard Risk Category Tables OR the calculated incident energy.  Today the Hazard Risk Category Table is now the PPE Category Table and there is an array of options listed in 130.5(H). Another evolution was with the term originally known as Flash Protection Boundary.  It was later changed to Arc Flash Protection Boundary and finally to Arc Flash Boundary.  It is interesting to look at labels today and see what term is being used.  You still see some of the earlier terms but regardless of terminology, the Arc Flash Boundary remains as the distance (approach limit) from an arc source where the incident energy is 1.2 calories/centimeter2  (cal/cm2).  This is boundary is for the case when an arc flash hazard exists.

Fast forward to the 2018 Edition of NFPA 70E and yet another change to the labeling requirements has been added.  130.5(H) Exception No. 2 now permits eliminating the detailed information from the arc flash label!

No Information on the Label??!!           What?  Huh?  Are you kidding me?

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The Elephant in the Room – Condition of Maintenance and Properly Maintained

panel not properly maintainedThe 2018 Edition of NFPA 70 provides a new definition for the term “Condition of Maintenance” :

BUY NOW: 2018 NFPA 70E Changes Part 1

The state of the electrical equipment considering the manufacturers’ instructions, manufacturers’ recommendations, and applicable industry codes, standards and recommended practices.

Another term that is cited in NFPA 70E is “Properly Maintained” —these two words often will have people scratching their heads. And often, developing a legal disclaimer. The term is often a hot topic (pun intended) when discussing the arc flash hazard. Why? Because protective devices such as circuit breakers and relays that have not been properly maintained may not operate as quickly as they should. This means that during an arc flash, a longer duration will result in a greater total incident energy, creating an even greater arc flash hazard.

Calculating the prospective incident energy from an arc flash depends on many variables including the available short-circuit current and the time it takes an upstream protective device to clear the fault. IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations provides equations that can be used for Continue reading

Don’t Be a Dummy – Poster

While I was conducting a 2 day electrical safety training program for a large electric utility, we took a substation tour for a demonstration.  Upon entering the control house, there it was.  A pole top rescue dummy just begging to be photographed and have a caption added.

Of course the first thing that came to mind (after I stopped laughing) was the seriousness of working around the hazards associated with electricity. One wrong move and anyone can be like the dummy.

Download your copy of the poster here.  Don’t be a dummy! Continue reading

IEEE Opens Its European Technology Center in Vienna, Austria

IEEE continues to expand its global presence with the opening of the European Technology Center in Vienna. The ribbon-cutting ceremony and official opening were just recently held on September 22. The center will provide support and services to the European technical community, focusing specifically on the needs of academia, government, and industry. In addition, the center will contribute to IEEE’s programs globally. The new office is located in the Austrian Standards Institute building.

“Establishing the European Technology Center marks an important step in furthering IEEE’s global, strategic activities within Europe and beyond,” says Karen Bartleson, 2017 IEEE president and CEO. “We see a strong foundation Continue reading

Electrical Safety Training – More then just “Checking the Box”

Jim Phillips, P.E.

One word.  Deadly!  If someone performs energized electrical work without being properly trained, the results can be catastrophic – and deadly!  I have seen this play out regularly during accident investigations and legal cases.  The victim was either not properly trained, or perhaps ignored a few steps from the electrical safety training program.

Many companies are very pro-active and make sure their employees are not only trained, but that they receive refresher training at least every three years based on NFPA 70E requirements.  Many even use shorter intervals for refresher training or updates.  Either way, refresher training is important for staying up to date with current standards and it can be a reminder to those that pick up bad habits along the way.

Electrical Safety Training – More than “Checking the Box”

However, a looming problem is that for some companies, training is either way down the list for various reasons or was not very thorough.  I have seen many companies that simply want to “check the box” i.e. state they had training without much regard to what the content was and check it off their to do list.  after all, what could possibly go wrong?

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IEC TC 78 Live Working Standards

By Jim Phillips, P.E.
International Chairman IEC TC 78

Jim at the IEC Central Office in Geneva

As the International Chairman of IEC TC 78, a frequent question that I receive is “What is IEC TC 78?”

IEC is the acronym for the International Electrotechnical Commission based in Geneva, Switzerland.  TC 78 standards for Technical Committee 78 which is the Live Working Committee.  This committee is responsible for over 40 different International Live Working standards and documents and is represented by 42 countries via National Committees which includes 136 individuals known as Experts. Before I go any further, let’s back up a few steps first. Continue reading

The 2017 NEC and Arc Flash

By Jim Phillips

The 2017 National Electrical Code (NEC) contains several changes regarding arc flash:

Download FREE Arc Flash Calculations

  • 110.16(B) Arc-Flash Hazard Warning of Service Equipment
  • 240.87 Arc Energy Reduction (Circuit Breakers)
  • 240.67 Arc Energy 
Reduction (Fuses)

The severity of an arc flash is largely dependent on two key variables which include the available short-circuit current and the duration of the arc flash. The short-circuit current is determined by performing a short circuit study involving extensive calculations. The duration is normally defined by determining how long it takes an upstream overcurrent device, such as a circuit Continue reading

Arc Flash Labels and ANSI Z535

If you ask five different people what an arc flash label should look like, you will likely receive five different answers.  Although there are no hard and fast rules regarding the label format, there are some minimal requirements found in NFPA 70E, Standard for Electrical Safety in the Workplace, and NFPA 70, National Electrical Code (NEC).

American National Standards Institute’s Z535 Series, known as “Series of Standards for Safety Signs and Tags.” is referenced as additional guidance by NFPA 70E for the labels.  However, it is interesting that according to a survey conducted at, a large percentage Continue reading

Utility Short Circuit Data – Different Formats

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.

Download FREE Arc Flash Calculations

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

2018 NFPA 70E Update – What’s New? What’s Changed?

Published: June 2017

By Jim Phillips 
Based on Jim’s article originally published in the
May 2017 Issue of Electrical Contractor Magazine.

It is hard to imagine that three years have passed since I wrote the 2015 NFPA 70E update article for Electrical Contractor Magazine My latest article about the changes for the 2018 Edition was just published in last month’s May issue and is also printed here.

Once again there are many significant changes such as a major reorganization of Article 120, the introduction of many new definitions, an even greater emphasis on the Risk Assessment, moving the hierarchy of risk control methods to mandatory language and the deletion of the informational note containing the 40 cal/cm2 reference. So get a jump on bringing your electrical safety and arc flash training programs in line with the soon to be released 2018 Edition of NFPA 70E.

Around 2,500 years ago, the Greek philosopher Heraclitus is credited with the saying, “The only thing that is constant is change.” Who knew this ancient proverb would apply to NFPA 70E, Standard for Electrical Safety in the Workplace? The 2018 edition is right around the corner, and once again, change is a constant theme. From both minor and major revisions to new additions and major reorganizations, this 11th edition contains many changes.

This article does not contain every change, and some language is paraphrased due to space limitations. Since the final document has not yet been formally approved, additional changes are possible before publication. Therefore, refer to the final approved version once it is published.

Continue reading

Arc Flash Study Top 10 FAQs Part #2

How Does Everyone Else Do This?

By Jim Phillips

3-Part Series



  1. Does your company or client permit energized work where the incident energy is greater than 40 calories per centimeter squared (cal/cm2)?

Continue reading

Arc Flash Study Top 10 FAQs Part #1

How Does Everyone Else Do This?

By Jim Phillips

3-Part Series


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

Electrical Safety Training: It Will Save Your Life!

By Jim Phillips

Performing electrical work without being properly trained can be deadly. I have seen this hold true during numerous investigations.

Many companies proactively provide employee training and refresher courses at least every 3-years. Some companies use shorter intervals for refresher training. However, for others, training is not thorough or a low priority. Some simply just want to check training off their to-do lists without much regard to safety for self or employees. In the end, does it matter? Continue reading

Short Circuit Data – Per Unit, Amps and Symmetrical Components

Making Sense of the Numbers
Utility Company Short-circuit Data For Arc Flash Studies

Electrical Contractor Magazine – November 2012
Jim Phillips, P.E.

One of the first steps in performing an arc flash hazard calculation study is to request the short-circuit data from the electric utility company. This information is critical 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, it should also be requested based on 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.

Too many numbers—now what?
Unfortunately, a single standardized format for short-circuit data does not exist. Instead, depending on the individual utility, data may be provided in one of several different formats such as the following:

• Short-circuit amperes (A)
• Short-circuit megavolt-amperes (MVA)
• Per-unit and symmetrical components

Of course, with multiple formats, confusion could (and often does) result. I will compare the different formats using a three-phase short-circuit current of 6,000A at the 23-kilovolt (kV) level. Since arc flash calculations are based on a three-phase model, only the three-phase short-circuit calculations are used. Some of the values are slightly rounded.

Short-circuit ampere format
This is the simplest format because it defines the short-circuit current in terms of amperes at a specified location. As an example, the utility has provided the following information:

Short-circuit amperes three-phase = 6,000A
Voltage = 23 kV line-to-line

Since the data is already in terms of amperes, no additional calculations are necessary.

Short-circuit MVA format
Utility companies often provide short- circuit data in terms of short-circuit MVA. This format combines the short-circuit current with the voltage and the square root of 3 (for a three-phase representation) to provide the data in terms of short-circuit power. Below is an example of the MVA format.

Three-phase short-circuit MVA = 240 MVA
Voltage = 23 kV line-to-line

To convert three-phase short-circuit MVA to short-circuit current in amperes, use the following equations:

Short-circuit amperes = [MVA x 1,000] / [kV line-to-line x the square root of 3]

where 1,000 is the conversion from MVA to kVA

Short-circuit amperes = [240 MVA x 1,000] / [23 kV line-to-line x 1.732]
Short-circuit amperes = 6,000A


ANSI Z535 – Series of Standards for Safety Signs and Tags

Many safety labels use either Caution, Warning or Danger with a specific color associated with it.

The U.S. National Electrical Code and NFPA 70E both reference ANSI Z535 to provide guidance regarding effective words, colors and symbols for signs and labels that provide warning about electrical hazards.

Other countries may have a different standard for guidance.

Here is this week’s question:

How familiar are you with the ANSI Z535 Series of Standards for Safety Signs and Tags

Not in the U.S. / Doesn’t apply
Not Familiar
Know about it
I’ve read it


Utility Short Circuit Current Data, Arc Flash and Change

Webinar – Utility Short Circuit Current Data, Arc Flash Studies and Change
by Jim Phillips, P.E.

[See more about Jim Phillips]

Agua Caliente 1It goes up, it goes down, sometimes it is thought to be infinite (although it really isn’t!) and other times it seems impossible to find. “It” refers to the available short circuit current from the electric utility which is one of the more important pieces of information for an arc flash hazard calculation study. Used to help define the severity of an arc flash hazard, it represents the magnitude of current that could f
low from the electric utility during a short circuit. Continue reading

2015 NFPA 70E – 10 Item Check Up

With the 2015 Edition of NFPA 70E being published and all of the changes that it brings, it is time to review your arc flash study, labels and overall practices.  There are many key areas that should be evaluated.  Here ten of the more important areas to look at to give your site a check up. Continue reading

Specifying Arc Flash Studies and IEEE 1584.1

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

NFPA 70E – Qualified Workers

“Raise your right hand”  Pretty intimidating words – especially if they are said in a court room and the trial is about an injury or death.  –  and you are on the wrong side of what happened.  Let’s face it in the litigious society that we have in the United States, it seems anytime there is an accident where there is a significant economic loss, personal injury or worse – someone died, there will almost certainly be legal actions. Continue reading

NFPA 70E – 2015 Edition – Update of Changes

NFPA 70E – Standard for Electrical Safety in the Workplace, was first published in 1979 and consisted of only one part, The 2015 Edition marks the tenth edition to NFPA 70E and with it, many sweeping changes. This article provides a review of the major changes to the latest edition of this important electrical safety standard. Continue reading

Happy August 11! (and call before you dig)

Today is a special day.  August 11 – Also known as 8 11 (unless you use the format day/month) What is so special about 811?  8-1-1 is the telephone number that you use to find underground utilities before you dig.  Known as “Call Before You Dig” it is a nationwide network (in the U.S.) that is designed to assists in locating underground utilities. Continue reading

Arc Flash Labels – Simplified!

“What do you mean we need to relabel the electrical equipment? Didn’t we just do this a few years ago?”

This is a pretty common response when addressing the requirements of NFPA 70E 130.5(2), which necessitate that the arc-flash risk assessment shall, “be updated when a major modification or renovation takes place. It shall be reviewed periodically, at intervals not to exceed 5 years, to account for changes in the electrical distribution system that could affect the results of the arc-flash risk assessment.” Continue reading

Electric Shock – It CAN Happen to Anyone – Like Me!

Electric shock happens to more people than they care to admit. In almost every NFPA 70E / electrical safety training class that I conduct, I ask the group “how many of you have NEVER experienced an electric shock.” I have yet to see a hand go up. In today’s “Modern World” electricity is part of daily life and as a consequence, an electric shock can happen to anyone – Including Me! Continue reading

NFPA 70E Major Updates for the 2012 Edition – Part 2.

Although beginning with an erratic schedule with revisions to NFPA 70E being spaced anywhere from 2 to 5 years apart, this very important electrical safety standard is now on a regular 3 year revision cycle. In early 2011, I wrote an article about the significant changes that were about to be part of the 9th Edition, the 2012 Edition of NFPA 70E Standard for Electrical Safety in the Workplace. This article will take us a little further into the standard and address some changes that I was not able to include in the previous article. Continue reading

How to Perform an Arc Flash Study

Download FREE Arc Flash Calculations

What started as a slow drip a decade ago has turned into something more like a tidal wave. I’m not talking about a leaky faucet or a failing dam; I am referring to arc flash studies. Years ago, only a few mostly larger companies performed these complex studies. Then little by little, the “drip” of studies turned into a steady Continue reading

Arc Flash Hazard Calculation Studies

In the earlier years of NFPA 70E and the emergence of arc flash protection requirements, many people would use the NFPA 70E Hazard/Risk Tables to determine what arc rated PPE to wear. This approach continues to shift towards the use of arc flash studies involving incident energy and arc flash boundary calculations based on IEEE 1584. Continue reading

How to Perform an Arc Flash Calculation Study

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 Hazard Calculations Studies guide


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

Working Distance and Arc Flash Protection Boundary

Greater Distance = Greater Safety

Download FREE Arc Flash Calculations

When a bomb goes off, the further you are from the explosion, the safer you will be.  This same concept also applies to the arc flash hazard.  Whether you are a properly protected 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. Continue reading

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 down a low voltage problem and was conducting voltage measurements on a 4,160V to 480V dry type transformer on an upper level mezzanine. He Continue reading

NEC and Hazardous Locations

The NEC defines a “Hazardous Location” as a location “where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings.” There are 13 articles and 68 pages in the NEC regarding hazardous locations, installation practices and equipment requirements. Understanding what makes a location “hazardous” is the first step in providing a safer electrical system.

Materials that can cause a location to be classified as hazardous range from hydrogen, to grains, coal dust, petroleum products and many others.
Jim Phillips, P.E. – October 2005 – NEC Digest

Download Article: NEC Digest Hazardous Locations


Short Circuit Calculations – Infinite Bus Method

How to perform a short circuit study

Learn more about the Infinite Bus Method. BUY NOW

Have you wondered is there a simpler way to calculate short circuit currents without a computer program? A very simplified method known by many as the “infinite bus” calculation method is a good way to approximate short circuit calculations.  This article takes you thought the steps with an example of the infinite bus calculation process.  If you would like to know how to perform more detailed short calculations which include the source impedance, conductor impedance and motor contribution in addition to the transformer impedance, Jim has a 4 DVD series that takes you through the entire short circuit calculation process complete with many examples and calculation worksheets.  Now, on with the article…

Continue reading

X/R Ratio

Short Circuit Analysis on-demand classBackground of X/R
Short circuit calculations are actually just an elaborate version of Ohm’s Law. One of the key components in the calculation process is to determine the total impedance of the circuit from the utility/source, through the transmission system, transformers, conductors, down to the point in question such as a panel or switchboard location. The impedances of the various circuit elements, Continue reading

How to Perform a Power Factor Study – kVA Demand Rate

Jim Phillips, P.E.

DSC02142A power factor study is a key to properly determining a system’s power factor correction requirements. A study determines capacitor size and location as well as the number of steps and incremental sizes to be switched. A study also provides an economic analysis of the proposed installation based on the forecast reduction in electric utility bills. A power factor study can be divided into three major steps.

▪ Review of the electric utility company’s rate structure.

▪ Development of a graphical profile of the facilities kVA, kW and kvar.

▪ Determination of the required capacitor kvar additions for the desired power factor improvement level.

The power factor study begins with a utility rate structure review together with a historical sample (six to 24 months) of electric bills. This information is used to evaluate present use patterns and to determine the potential economic benefits of improving power factor. Utility rate structures usually provide significant economic incentives to reduce total kVA demand.

Typical demand charges can vary from minimal to $20 per demand kVA, so for reducing a demand by just 100 kVA with a demand charge of, let’s say, $10 per kVA could save $1,000 per month. It’s easy to see that larger demand reductions and higher demand charges could potentially large savings. After reviewing the rate structure and billing history, a detailed graphical profile of the facility’s use over typical 24 hour operating periods should be developed.

The profile could be created from recorded kW and kVA data and either calculated or recorded power factor and var data. This data is obtained from on –site monitoring over several 24 hour periods. Some utilities are prepared to provide this data. However, independent monitoring usually is necessary using a commercially available energy analyzer to record demand, power factor and total energy use. The data is used to develop the graphical profile which is plotted with respect to time to provide a representation of a complete operating cycle. This profile can then be used to determine the required kvar of capacitors necessary and the number of Switching steps to offset the inductive kvar.

The minimum reactive kvar determine the amount of capacitors that can be used without switching to provide close to 100 percent power factor during minimum load conditions. Additional capacitor requirements can be determined based on the profile and sized as needed. Capacitance is introduced into the facilities electrical distribution system to balance inductance due to equipment operation. When equipment load, and subsequently inductance decreases, capacitance also should be reduced. For more erratic demand patters, more switching steps may be required.

NFPA70E 2018 Update video by Jim PhillipsAbout Jim Phillips, P.E.: Electrical Power and Arc Flash Training Programs – For over 30 years, Jim Phillips has been helping tens of thousands of people around the world, understand electrical power system design, analysis, arc flash and electrical safety. Jim is Vice Chair of IEEE 1584 and International Chairman of IEC TC78 Live Working. He has developed a reputation for being one of the best trainers in the electric power industry, Learn More.

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