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

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

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

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

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

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

Moisture Content in Electrical Cabinet



At one facility I find that the condensation gathers on the inside surface of an enclosure, which can cause the rusting, short circuits, and breakdowns in electric and electronic equipment that is housed in enclosures. And one short circuit is already happened in the same cabinet.
One more critical problem in the same panel, the cable insulation is fell apart in pieces near the cable lugs. Same cable connected in else panels but didn’t find any such problem there.
So what will be the reason for the cable insulation breaking and what will be the preventive measures for the condensations??



If you have mild overloading/overheating, especially if the overload protection isn’t set up correctly, the highest resistance connections are at the lugs/joints and damage from overheating will start there and then work progressively back up into the cable body. After this occurs the first couple feet or so of insulation will lose it’s flexibility and either crack on its own or if you so much as touch it, it will crack and fall apart in your hands. If you catch it in the act, it will be literally smoking but won’t actually burst into flames or anything like that. This can occur without seeing any ongoing temperature issues and without discoloration occurring at the lugs and the flaking insulation might be your one and only sign that overload protection isn’t set up right.

This doesn’t mean you have an ongoing problem. Although all standards and manufacturers specifications say that you need to change the cable and/or remove the obviously defective portions, the reality is that this usually takes a lot of labor to remove and replace cable so it doesn’t get done…after all, the insulation is clearly obviously still there. And many times it gets overlooked since it just looks like the black rubber/plastic stuff is on the cable like it always is and cracks on something black are hard to see unless you are looking for it. I don’t condone the practice of leaving it when it is obviously defective but I definitely understand the reasons that this becomes a problem that may take years to address even if maintenance departments know about it and are truly committed to trying to do something about it. As a field service engineer I’ll point it out and document it which often gives the maintenance department ammunition to try to justify replacement but often the fact is that it’s hard to convince someone that it is important. They don’t recognize how much cables will actually jump during a fault and that all that insulation will fling off as the cable suddenly flexes.

It’s also definitely possible to find corrosion or similar damage occurring from other sources but the difference is usually obvious because you’ll see a whole lot more than just damaged cable if it’s a corrosion issue due to corrosive atmospheres.

As to the moisture problem…first off the anti-condensate heater idea works well IF you have a reliable source of power and if you are going to PM the heaters once in a while. There are two versions of these. One is a strip heater that is literally exactly what it sounds like and constantly puts out heat. A local motor vendor should easily be able to put you onto a source because they use them for customers that request them in motors, especially medium voltage motors. Second type are the ones that have a small thermostat that turns on and off as required and might even have a small circulation fan depending on the power output. Pretty much any MCC or switchgear catalog will list these in the “accessories” section. Obviously the reliability of a device that has more than just a strip of metal will be less…so along with the strip heater you will be committing yourself to regular PM’s to check them. In today’s paranoid world of so much as opening a cabinet, you can see the obvious issue. Many plants get along just fine with a simple small DIN rail circuit breaker and the previously mentioned “dumb” strip heaters, turning them on in Autumn and turning them off again in the Spring. READ MORE

AF label on Service Disconnect and ATS in same Enclosure

With the awareness of arc flash, many giant manufacturers do not manufacture the Service Disconnect and the Automatic Transfer Switch located in the same section or enclosure. However, this practice can be seen in the field for switchboards rated as high as 600 Amps.
The dangerous part is the upstream of service disconnect is like a blind spot as the only protective device is the utility’s fuse on the primary side of the transformer and often result in high incident energy (greater than 40 Cal/cm2 in most of the cases) at the service disconnect. But because of service disconnect as protective device, in the downstream the incident energy on the ATS(normal-utility side) gets reduced to for instance less than 4 cal/cm2. The problem is although ATS has lower incident energy, it is located right below the Service Disconnect in the same section (enclosure). This is a arc flash hazard and I affix the conservative label (service disconnect) on the section that has service disconnect on the top and ATS at the bottom. So please share your thoughts on how you affix labels:
1. When the Service Disconnect & ATS is located in the same section (enclosure)
2. When there is a barrier between Service Disconnect and ATS located in the same section (enclosure).


IEEE 1584.1-2013


Hello, good afternoon.

Does the standard contain new information to consider for arc flash analysis?

Thank you



No because we’re still on the 2002 edition. The new edition won’t get released until probably next year at the earliest.

As to answering your question, sort of yes and no. Three areas I know will change somewhat:
1. The “lower cutoff” (the old 125 kVA comment/rule) will likely change, probably downward in terms of what is “covered” under this exception but also it sounds like the “1 transformer” part may change to something a little more flexible such as a simple bolted fault cutoff.
2. They have a lot more data to work with. It is my understanding that the 2002 equations are within about 10-15% of the new equations. I’ve seen 3 possible new equations. The first is that EPRI and others have expanded into other areas for “device specific” equations so even though that’s the section that sees little attention, it might change. Second there’s the Wilkins simplified as well as the Wilkins time-domain models. In the past IEEE 1584 kind of covered everything out there and I wouldn’t be surprised if this one does something similar so both get honorable mentions. Both models fit the data a little better. The time domain model is the best but computationally complex to use. Finally I’ve heard that they are getting away from the “jump” that occurs at 1 kV due to the implementation differences between the medium voltage and low voltage models in terms of having a single empirical calculation or at least one that passes through the same point at 1 kV.
3. There has been a lot of discussion and rumbling about a lot more conditons/situations such as having more than just the existing 3 box cases and including electrode orientation which accounts for very problematic situations such as some switchgear. I’d expect that this is where the data gathering is going to have to increase substantially. Everything else just revises the model a bit. READ MORE

Liability and Legal Action

It’s no secret that the United States is a very litigious country.

Sometimes the more “interesting” interpretations that people use regarding codes, standards, design etc. tend to be more influenced by fear of lawsuits. I have had this conversation with many people over the years.

There are many reasons that legal action may be taken but this week’s question is very specific. It refers to: Liability from accident, injury, death, equipment failure. It applies to both the Plaintiff and Defendant.

Since this can be a sensitive topic, one of the answers is “can not answer”
Here it is:

Have you or your company/client ever been involved in legal action involving liability?
Can not answer

Stories are welcome if you are able to comment. ANSWER

Evaluation of Onset to Second Degree Burn Energy in Arc Flash

Our interest in determining accurate onset to second degree burn energy and its significance in computing the arc flash boundary is focused on the prevention of injury to the skin of a human who might be exposed to an arc-flash. During the last two decades different formulas have been proposed to calculate incident energy at an assumed working distance, and the arc flash boundary in order to determine arc rated personal protective equipment for Qualified Electrical Workers. Among others, the IEEE Standard P1584 Guide for Performing Arc-Flash Hazard Calculations [1584 IEEE Guide for Performing Arc-Flash Hazard Calculations. IEEE Industry Applications Society. September 2002] and formulas provided in Annex D of NFPA 70E [NFPA 70E Standard for Electrical Safety in the Workplace. 2012.] and CSA Z462 [ CSA Z462 Workplace electrical safety Standards. 2012.] Workplace Electrical Safety Standard are the most often utilized in the industry to perform arc flash hazard analysis. The formulas are based on incident energy testing performed and calculations conducted for selected range of prospective fault currents, system voltages, physical configurations etc.

Use of Incident Energy as a Measure of Burn Severity in Arc Flash Boundary Calculations
The IEEE P1584 Standard was developed by having incident energy testing performed based on methodology described in the ASTM F1959-99 standard. The incident energy to which the worker’s face and chest could be exposed at working distance during an electrical arc event was selected as a measure for determining hazard risk category and calculating the arc flash boundary. The incident energy of 1.2 cal/cm2 ( 5.0 J/cm2 ) for bare skinwas selected in solving the equation for the arc flash boundary in IEEE P1584 [1584 IEEE Guide for Performing Arc-Flash Hazard Calculations. IEEE Industry Applications Society. September 2002. page 41]. Also, NFPA 70E [NFPA 70E Standard for Electrical Safety in the Workplace. 2012. page 10] states that “a second degree burn is possible by an exposure of unprotected skin to an electric arc flash above the incident energy level of 1.2 cal/cm2 ( 5.0 J/cm2 )” and assumes 1.2 cal/cm2 as a threshold incident energy level for a second degree burn for systems 50 Volts and greater [NFPA 70E Standard for Electrical Safety in the Workplace. 2012. page 26].The IEEE 1584 Guidestates that “the incident energy that will cause a just curable burn or a second degree burn is 1.2 cal/cm2 (5.0 J/cm2 )” [1584 IEEE Guide for Performing Arc-Flash Hazard Calculations. IEEE Industry Applications Society. September 2002. page 96]. To better understand these units, IEEE P1584 refers to an example of a butane lighter. Quote: “if a butane lighter is held 1 cm away from a person’s finger for one second and the finger is in the blue flame, a square centimeter area of the finger will be exposed to about 5.0 J/cm2 or 1.2 cal/cm2 “. However IEEE P1584 equations (5.8) and (5.9) for determining the arc flash boundary can also be solved with other incident energy levels as well such as the rating of proposed personal protective equipment (PPE). The important point to note here is that threshold incident energy level for a second degree burn or onset to second degree burn energy on a bare skin is considered constant value equal to 1.2 cal/cm2 (5.0 J/cm2) in IEEE P1584 Standard.

Flash Fire Burn Experimentations and Observations

Much of the research which led to equations to predict skin burns was started during or immediately after World War II. In order to protect people from fires, atomic bomb blasts and other thermal threats it was first necessary to understand the effects of thermal trauma on the skin. To name the few, are the works done by Alice M. Stoll, J.B.Perkins, H.E.Pease, H.D.Kingsley and Wordie H. Parr. Tests were performed on a large number of anaesthetized pigs and rats exposed directly to fire. Some tests were also performed on human volunteers on the fronts of the thorax and forearms. A variety of studies on thermal effects have been performed and thermal thresholds were identified for different degree burns. We will focus on second degree burn as this is the kind of burn used to determine the arc flash boundary in engineering arc flash analysis studies.

Alice Stoll pursued the basic concept that burn injury is ultimately related to skin tissue temperature elevation for a sufficient time. Stoll and associates performed experimental research to determine the time it takes for second degree burn damage to occur for a given heat flux exposure. Stoll showed that regardless of the mode of application of heat, the temperature rise and therefore the tolerance time is related to heat absorbed by the skin[Stoll, A.M., Chianta M.A, Heat Transfer Through Fabrics. Naval Air Development Center. Sept. 1970]. Results of this study are represented in Figure 1 line (A) along with other studies discussed below. READ MORE

Time To Second Degree Burn Graph

Include Date on Arc Flash Label?

According to the 2015 Edition of NFPA 70E 130.5(2), The arc flash risk assessment “…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.”

According to 130.5(D) Equipment Labeling, the date is not listed as a requirement for including on the label. However, many believe the date is an important aspect of the label in order to keep track of the “5 years” time limit.

Here is this week’s question:

Do you feel the date should be included on the arc flash label?


Adjusted Pickup Method – Shift Factor

I have been looking into the adjusted pickup method and associated shift factors used when multiple source bus configurations are being coordinated [ex. parallel generator systems two or more] and was hoping someone could point me to an IEEE standard or some industry articles on this to better understand this on shifting TCC’s around a specific location or device. On one example where two different sized generators were modeled it shifted the smaller units beyond the TCC of the larger unit indicating a longer trip time for that device for a downstream fault condition. It looks that the shift factor calculation looks at the generator current to the fault / the fault current at the location specified, assuming that larger gen breaker sees more current and trips faster than the smaller unit, this is what I am seeing and was looking for some backup information but searching around it appeared the information was pretty scarce and was hoping someone could point me toward some. THANKS. READ MORE

Non-melting clothing

Our company in the past 2 years has implemented an electrical safety and control of hazardous energy program for employees world-wide. Our daily work-wear clothing minimum requirement is non-melting clothing, except in US and Canada for which our AFHA’s determine minimum PPE requirements. Unfortunately, many countries have yet to recognize arc flash is a real threat to people and arc flash isn’t isolated to just North America. (Good news is they are beginning to wake up!)

As the implementation project manager I have not been able to find non-melting clothing for our Chinese colleagues that can be sourced in China. We can get clothing items from other countries but at a higher costs, shipping delays, etc.

Anyone have any experience in this area or have any suggestions? READ MORE

Behavior of Apparel Fabrics During Convective and Radiant Heating

Personal protective equipment (PPE) recommended for arc flash is not always designed for arc flash exposure. The purpose of this paper is to warn of the dangers posed by using the improper materials in arc flash exposures until standards have caught up on this issue.

The table below shows a representative range of everyday textiles along with some of the measurements of importance in establishing their response towards convective and radiant heating[1]:

Properties of Fabric Table


Times to ignition or melting of the 20 fabrics in Table above were reported by Wulff[2], [3] for different incident heat fluxes. The Wulff’s data have been used to develop a methodology by which ignition and melting times may be forecast. A semi-empirical relationship between ignition/melting time and radiative heat flux has been derived[1]:

[NF0] = -1 / NBi * ln(1 – NBi / [qxrad]) + a * [qxrad]^b * (1 – NBi / [qxrad])^-1, Equation 1
where [NF0] is the non-dimensional destruction time of the fabric (that is, time to ignition or melting) and is given by:

[NF0] = (k/l) * t / (pl * c), Equation 2



(k/l) – average thermal conductance, W / (m^2 * C);
t – ignition/melting time, sec;
pl – mass/unit area, kg / m^2;
c – average specific heat, W * sec / (kg * C).

NBi is the Biot number which is defined as the ratio of the average convective heat transfer coefficient of the fabric to the average thermal conductance of the fabric. It is obtained experimentally for each fabric.

The non-dimensional radiative heat flux [qxrad] is given by:

[qxrad] = ads * W0 / (k/l) / (Tim – T0), Equation 3 READ MORE

Safe Return-to-Service Following a Maintenance Outage

Best Practices for a Safe Return-to-Service Following a Maintenance Outage
Charles M. McClung, MarTek Limited
Russell R. Safreed, PE, MarTek Limited


Returning electrical equipment to service after a planned maintenance outage creates a unique set of hazards. Facility managers are under stringent time constraints for taking the system out of service, performing necessary maintenance tasks (as well as making un-anticipated repairs) and returning the system to service by the appointed time. These common, real-world factors may create circumstances that place workers at great risk as the system is returned to service. This paper seeks to identify those initiating factors and develop logical and practical ways to lessen or eliminate risks.

It’s all a setup, with good intentions.

Most well-run, progressive-minded companies readily accept the fact that their electrical distribution system is fundamental to the operation of their facilities. Maintaining the electrical is not an option—it is a ‘must’, not merely from a continuity of operations perspective, but also from a loss prevention perspective. Delaying the restart of a manufacturing process after a planned maintenance outage because of ‘schedule creep’ or ‘scope creep’ can be costly. Extended outages caused by major equipment failure can be devastating.

As important as these economic factors are, the prevention of a life-altering injury or death trumps all economic incentives. However, few would disagree that protecting people is also another form of loss prevention. Aside from the moral responsibility that is incumbent on employers to protect their workers, the failure to adequately protect people will likely result in significant economic losses in the form of OSHA fines, medical payments, higher worker’s compensation premiums and litigation.

Electrical maintenance outages are high-stress for everyone concerned. The Plant Manager just wants it to be over so operations may be returned to normal as soon as possible. The Electrical Distribution Engineer wants the greatest amount of work possible to be done in the allotted time to help ensure he never has to answer to the Plant Manager for an unplanned outage. The Maintenance Crew wants to be thorough and do a good job, but they also know the criteria for deeming the job ‘well done’—returning the system to operation on-time and with just enough ‘bad news’ about the condition of the equipment to justify the expense of the outage, but with not so much ‘bad news’ that a re-start is delayed or that significant repairs would be necessary.

All of these real-world pressures and sometimes competing objectives can produce a high-risk condition when the time comes to re-energize the electrical system following a planned maintenance outage.

Three major categories of risk-creating scenarios will now be explored. READ MORE

2015 NFPA 70E Changes

The following is an article that I wrote a few years ago listing the major changes for the 2015 edition. It was originally published in the May 2014 issue of Electrical Contractor Magazine and is provided here as a resource for your use.

Change Is On The Way! 2015 NFPA 70E
Published: May 2014 – Electrical Contractor Magazine
By Jim Phillips

Deja vu?

Déjà vu is that feeling you get when you think you have seen or done something before. NFPA 70E is giving us all déjà vu since it was just three short years ago, in 2011, that we were analyzing changes for the upcoming 2012 edition (see “It’s Almost Here, ”May 2011 Electrical Contractor Magazine. It’s time for that feeling once again as we move toward completion of the 2015 edition.

What’s new?

Some of the terminology used during this revision cycle has changed. Request for Proposals are now called Public Input (PI), and this revision cycle had 448 PIs. The Report on Proposals (ROP) is now called the First Draft, and what was previously called the Report on Comments (ROC) is referred to as the Second Draft.

The changes this article outlines are based on what was known at the time of writing. It does not include every change made, and much of the language is paraphrased due to space limitations. Since the NFPA Standards Council has not formally approved the final document, there is always the possibility of additional changes. Therefore, always refer to the final approved version when it is published.

Global changes

Several terms used throughout NFPA 70E have been changed for the 2015 edition. The left column in the terms table above refers to the term used in the 2012 edition and the right column lists the new corresponding term for 2015.

Please note: all references to hazard/risk category (HRC) have been deleted throughout the standard. Arc flash PPE category is the revised term.


How Many Arc Flash Labels on Equipment?

Question of the Week

Some equipment may have multiple arc flash labels for a variety of reasons.

  • Different operating configurations
  • Equipment is long/large – including busway
  • Equipment has different incident energy for main/feeders such as some switchgear.

There may be other reasons as well.

This week’s question:

What is the greatest number of arc flash labels you have seen/used on electrical equipment?
More than 3 (how many?) ANSWER

Medium or high voltage training in U.S.

Recently a Fortune 500 company called asking if service technicians were “certified” to work on 4160 V equipment. This isn’t in the context of say the New Brunswick province where they actaully require such things at the unusual voltage of 750 V but rather this is in the U.S. in the Southeast. It smells like some training company is managing to hock something.

Has anyone heard of this? Does it even make any sense?

Granted there are 3 different major OSHA electrical work sections (30 CFR 1910.269, 30 CFR 1926, and 30 CFR 1910.3xx aka Subchapter S). There are a handful of major differences and the terminology is very different accounting for the origins in NFPA vs. IEEE committees, but that’s largely the differences.

Technically there are definitely differences that are voltage dependent such as the requirement for shielded cable and cabinetry that is designed to limit access as you get into the 5 kV range so there is definitely some merit to the idea of training based on voltage but most of the training programs out there either don’t address these kinds of issues or do it with a pretty broad brushed approach. Somehow I don’t see training involving this level of detail being part of the requirement. READ MORE

Face equipment or face away during switching?

Weekly Question:

This week’s question was submitted from one of our forum members. I will post it here

When locking out or resetting a tripped breaker on a CAT 4 system (actually extreme danger), I have one electrician that says he feels more comfortable facing the distribution than facing away. He argues that the shield will protect him better than the Balaclava. He also says that the force needed to reset a tripped (1200 Amp) breaker is easier when facing the breaker. Our lockout rules say to face away, close your eyes and hold your breath (and pray), using your left hand. Which is safer?

To summarize, here is this week’s question:

When switching equipment, do you believe it better to face the equipment or face away.
Face equipment
Face away
Doesn’t matter
Something else


If you have a question you would like to see submitted as a “Question of the Week” pass it along to me and I’ll get it posted! – Jim

ATS Protection and UL

In looking at the latest edition [7th] of UL 1008 for transfer switches I came across the following:
“The circuit breaker must include an instantaneous trip response and shall not include a sort time trip response” as it relates to switches tested per &

It seems different manufactures have different interpretations. So does this disqualify any breaker with an adjustable STPU / STD setting from protecting a 3-cycle [0.05sec] any breaker rated switch, even if the breaker has an instantaneous override less than the interrupting kA of the switch? It seems counterproductive because if I have a LSI MCCB I can almost always provide better protection in the instantaneous and in the short time than with a standard thermal mag. C/B. For low level arcing / fault currents, that sometimes extend into the LTD portion of the T/M I can adjust the STD down to pick up these currents faster providing better equipment and personal protection? One manufacture I talked to indicated that if the breaker has an adjustable short time ahead of the switch the switch is misapplied, even though the TCC’s show different? Then what about the specific breaker ratings, many breakers on the “Specific Breaker” list can be provided with a myriad of trip units types and styles from your standard TM, to LI, LSI, LSIG. So does this restrict the specific breaker to the T/M? The literature does not differentiate. Just curious if anyone else has run into this and other thought and opinions… READ MORE.

Hot Stick Testing

Question: Everyone, I got this question from a client. He asked if it’s necessary to have their hot sticks tested? Understand this company has nothing higher than 480 volts on site and only uses these hot sticks to switch on and off 480 volt 30- to 200 amp bus duct fused disconnect switches.

The bus in this factory is hanging well above the floor. If an employee needs to reach a bus plug, he uses a hot stick to access the handle from the floor. I can’t see any reason to get the hot sticks tested, but wanted to get your views. I’d think they’d want to put some sort of notice on each stick that indicates the stick is not to be used for real hot work, or words to that effect. What’s your take on this?

Answers: If insulation isn’t required, my first thought is why not use conductive pipe instead. I suspect the answer is to be safe from inadvertent movement and contact. So if insulation is needed for this aspect, I suggest testing the insulation. READ MORE.

Regenerative Drive Contributions to Upstream Fault

Is there any information on what a regenerative drive will allow a motor to contribute to an upstream fault? I know ANSI has some standards for motor contributions based on <50HP or >50HP for across the line starters. We have some DC motors with regen drives connected to a 480VAC system and I want to model the contributions of the motors on the upstream switchgear. A few of these motors are 500HP or bigger.

We used to use Easypower and I remember that had an option for selecting if your drive was Regen or Non-Regen, and that would affect the contributions. But the contributions of a regen drive was less than across-the-line for the same size motor.

We’ve since switched to etap, and their drive model doesn’t have a re-gen option. Not to mention they don’t have a real clean way to model a DC drive on an AC system.

I’m thinking there’s a way I can model the load and the short circuit calculations if there’s some sort of impedance multiplier for re-gen drives for the 1/2 cycle or 5 cycle short circuit. READ MORE.

Arc Flash Labels-PPE Category

In the NFPA 70E-2015 Handbook, page 122, 130.5(D) states incident energy or PPE category shall be on the equipment arc flash label, but not both. Yet when reviewing Annex H in the NFPA 70E-2015 handbook, on page 279 it states “Arcflash PPE categories may be applicable when using incident energy method to perform an arc flash risk assessment. When performing an incident energy analysis, the arc flash labels created may include an arc flash category”. Am I missing something or is this a mis-print?? READ MORE.

Reducing Arc Flash I/E At Fire Pump Controllers

Question: What are you guys recommending to reduce incident energy levels on fire pump controllers fed directly from the secondary side of utility transformers?

Answer: Can’t be done. This is a common practice but is very illegal in most cases. NEC is very specific in that overload protection (ie, overload relay) is eliminated and short circuit protection only remains. I have no idea why and I’ve had multiple fire marshals actually try to tell me that fire pumps get ZERO protection which is utterly false. In most cases the short circuit protection on the primary side is NOT sufficient to protect the branch circuit on the secondary side. And that’s the answer to your problem…short circuit protection (e.g. a MCP aka magnetic-only circuit breaker or simply a fuse) with the instantaneous trip point set below the arcing current fixes the problem and is 100% legal, and in most cases such as what you describe where it’s a huge Code violation, it also fixes that issue. READ MORE.

Work on an energized disconnect

Recently, a client asked if there was something I could point to in the NFPA 70E Standard that specifically prevented a qualified electrician from working on a disconnect after it was shut off, but with the line side left energized?

I asked exactly what he meant? He said our electricians sometimes need to disconnect one of our 480 volt welders for repair or to be serviced. We sometimes have more than one welder on a circuit, so shutting off the breaker to disconnect a welder affects other welders or machines. So, my question is this: is there a specific section in NFPA 70E that prevents the above described activity? Please remember, the electrician has verified that the load side of the disconnect is off. However, he’s left the line side energized. READ MORE

120 Volt Arc Flash

Download FREE Arc Flash Calculations

I believe it to physically impossible to sustain an arc flash at 120 V but can someone point me to the proof? Can someone indicate where a code specifically states no arc flash PPE is required at 120 VAC? READ MORE.






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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Arc Flash Label Updating – How Many Times?

NFPA 70E requires that an Arc Flash Risk Assessment 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. Countries outside of the US that do not use NFPA 70E may have a similar label review/updating requirement.

NFPA 70E further states that where the review of the arc flash hazard risk assessment identifies a change that renders the label inaccurate, the label shall be updated.

What is the maximum number of times you have updated any arc flash label since first applied?
-Still have original labels
-Updated once
-Updated twice
-Updated more than twice
-No labels yet
-I don’t do labeling


Picture of the Week


Chimpanzee Screams on Power Line


Hopefully you’ll never have to experience this on the job!

Male chimpanzee Chacha screams after escaping from nearby Yagiyama Zoological Park as a man tries to capture him on the power lines at a residential area in Sendai, northern Japan, in this photo taken by Kyodo, April 14, 2016. The chimp was eventually caught after being shot with a tranquilizer gun and falling from the power lines, Kyodo news reported. REUTERS/Kyodo

Maximum Short Circuit Current

The intensity of an arc flash is dependent on the magnitude of short circuit current. Lower voltage systems (less than 600 volts) tend to have the highest short circuit currents. Here is this weeks question:

What is the maximum short circuit current that you have seen?

less than 50 kA
greater than 50 kA
greater than 100 kA
greater than 150 kA


Using gloves with a stick

1910.269 requires arc flash protection for hands with exceptions when wearing leather protectors over rubber gloves, and when wearing heavy duty work gloves. The workers state that sticks should be used bare handed, and that work gloves will contaminate the stick. Any advice on this topic?
Leather gloves aren’t going to contaminate a hot stick unless for instance they get saturated in creosote or other materials. Granted there are tons of nasty, sticky materials in the utility work site and if the gloves get soaked with the more flammable ones, their “fire retardant” properties disappear.

It has been shown that up to 12 cal/cm2, leather gloves are sufficient.

You can’t use gloves realistically at high voltage and above (as per IEEE 516) because the voltage across the gloves might exceed their ratings. Since it is so hard to find class 3 or 4 gloves I kind of disagree with the current version of IEEE 516 cutting off the “no gloves” limit at 40 kV and I think it is more realistic to do this above 15 kV.

Finally with the hot stick method the intent is that some current flows through the worker’s body. Wearing gloves with hot sticks interferes with this. You are basically mixing work methods, the insulated tool method and the rubber glove method. READ MORE

100A panel with 200A “gutter mounted” main. WTF??

Came across this today while surveying. The original drawing shows this panel with a 100A branch mounted main. Well, someone needed that breaker for another panel and removed it and installed this instead.

Not in the photo: 4/0 feeder spliced inside an adjacent panel with #2. #2 goes through wireway to this 200A “gutter mounted” MCB which had been removed from the adjacent panel. Adjacent panel was re-fed from a different source. Sheesh!

Oh, and the 4/0 feeder (and the #2 splice, and the 200A gutter main and the 100A panel) are protected with 200A fuses. READ MORE

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


Maintenance of LV components inside HV cabinet

Good Morning All,

I am from the Safety Office and our organization prohibits working on electrical components/systems above 600V. I have a situation that I need advice on. Here is the background:

There is a group of Electronics Technicians/Engineers who believes they are responsible of an electrical system just because it resides in their occupied building. Inside this building is an 15kV CB which disconnects a transformer bank 11.5kV:570V, 540V and an 8.32kV harmonic filter (in a cabinet) from the substation (11.5kV). In this cabinet, there are LV fans and pressure sensors that they guys want to maintain and do housekeeping such as dusting. The management is fully supportive of getting contractors to do this work for them but they are very much adamant that they can do this work since they will be in an electrically safe condition utilizing LOTO (their LOTO procedure was not approved).

Our office has told them they cannot access this cabinet and the lead engineer is very persistent and insisting that they are only working on the LV side inside the HV cabinet. ANY THOUGHTS? READ MORE.

RELT or ARM Arc Flash Labels

It always seems as if we are kicking the dead horse on arc flash labels but I was just interested in your opinion of how to label a piece of equipment which is fed from a circuit breaker with an Arc Flash Reduction Switch (ARMS) or Reduced Energy Let-thru (RELT) switch.

We are currently performing a project with several new circuit breakers using the RELT switch.

Install two labels on the equipment? One with ARMS and one without?

To avoid confusion, how to distinguish between the two.

Wording on the label?

Any opinions welcome. READ MORE.

Maximum distance where arc flash label is still readable

This week’s question is very subjective and is based on all kinds of variables such as lighting, eye sight etc. For an average person under normal conditions:

What is the MAXIMUM distance where the typical arc flash label details are still readable?

Less than 4 ft. (1.2 M)
Between 4 and 8 ft. (1.2 to 2.4 M)
Between 8 and 12 ft. (2.4 to 3.7 M)
Something greater than 12 ft. (3.7 M)
It depends


I wonder what the withstand rating is on these?

I’ve known about these switches in this old house for at least 15 years but never took any pics. I was over there today and thought I would share to see if they are common in other parts of the country. Out east maybe? I’ve only seen these switches in this one house here in Indiana. The house was built in 1931. I assume these are original to the building but don’t know for sure.

Yes, they are manufactured by the same company you’re thinking of. READ MORE.

2017 NEC 240.87 Instantaneous Trip

Download FREE Arc Flash Calculations

The NEC requires that where a circuit breaker’s highest continuous current trip setting is rated or can be adjusted to 1200 Amps or higher, a method for reducing the arc energy must be provided.

The 2014 Edition of the NEC provided a list of methods which included: zone-selective interlocking, differential relaying, energy-reducing maintenance switching and energy-reducing active mitigation systems or an approved equivalent means. The device’s instantaneous trip function was excluded from the list.

The 2017 Edition of the NEC now permits the use of the device’s instantaneous trip unit or instantaneous override as long as there is sufficient arcing short circuit current for it to trip. IEEE 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations is referenced in this section as a method for calculating the arcing short circuit current.

Since the National Electrical Code (NEC) is a U.S. based standard, this requirement may not be applicable to those in other countries. It would be interesting to hear the different views.

With that long introduction, here is this week’s question:

Will you/your clients begin using the instantaneous to reduce arc flash energy for breakers 1200A and greater?

Doesn’t apply
We were using it anyway/already


About Jim Phillips: 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.

NFPA70E 2018 Update video by Jim PhillipsJim is Vice Chair of IEEE 1584, International Chairman of IEC TC78 Live Working and Steering Committee Member – IEEE/NFPA Arc Flash Collaborative Research Project. He has developed a reputation for being one of the best trainers in the electric power industry.  Learn More

Arc Flash & Electrical Power Training Classes
 by Jim Phillips Click Here

Arc Flash & Electrical Power Training Products by Jim Phillips Click Here

Sign-up for my monthly publication “Grey Matter” which contains news about new standards, conferences, technical articles, Electrical Engineering news and more! Click Here

Low Fault Current on Utility System

Here is the situation:

It is a municipal system, very rural, and has long single phase runs with low fault current. For example: 2400 delta single phase lateral ends up with about 92A fault current at the end of the run. The run is 7.5 miles with AAAC Ames and a 40K fuse on the txf secondary. The only fusing is on the secondary side of a stepdown transformer (13.2kv primary). Trying to use ArcPro and the fault current is too low (<200A lower limit). IEEE 1584 is for 3 phase faults but did try it and got an absurd value.

Any ideas on how to figure the incident energy? READ MORE


Easy way to get a series combo rating – sometimes??? Maybe?

Hi all. As I continue to slog through my list of 104 buildings on campus I need to do studies on I discovered yet another over-dutied situation yesterday. Common scenario, 208Y/120V “service” with 15-ish kA available at the main panel and a 100A MLO branch panel right next to it (very short feeder) with 14-ish kA available. Square D QOB (10KAIC) branch breakers. No main breaker. The main panel is Cutler Hammer so no series ratings exist between CH and SQ D.

I’ve come across this several times over the course of the first 50 buildings’ studies and have been changing the breakers out to 22KAIC rated, QOB-VH (or whatever, brand specific) breakers to solve it if no series ratings exist already (existing or easily replaceable feeder breaker or fuse in combo with the branch panel breakers).

I was looking at the Square D series chart and it appears to me there is a series rating of 22KAIC available with a QOB-VH main and QOB branches.

Hmmm. Just move the feeder conductors from the main lugs over to a new 3P80 or 3P90 or 3P100 branch mounted QOB-VH breaker. Simple and easy enough if the feeder reaches. If not, it is only about 4′ long to start with so it is easy to replace.

Not sure why it never occurred to me before now to look for a branch mounted main solution for situation like this, Square D or Siemens or GE or Cutler Hammer or otherwise.

Probably commonly done by others on here but if not, now you have another weapon in your arsenal to consider in certain situations. If you have, say, an existing 42 ckt panel with 30+ circuits in-use to deal with adding a branch mounted main like this should be a lot easier and cheaper with less down time than replacing all the breakers. READ MORE

Do you use equipment/methods based on IEC Standards?

This week’s “Question of the week” is coming from Frankfurt, Germany. This week I have the privilege of attending the International Electrotechincal Commission’s 80th General Meeting as the International Chairman of IEC TC78 Live-Working which has 35 standards/publications including Arc Flash Protection.

The IEC prepares and publishes International Standards for all electrical, electronic and related technologies. Since the Arc Flash Forum is an international community, here is this week’s question:

Do you (your company) use any electrical equipment/methods based on IEC standards?
Not sure


Arc Rated Clothing Causing Health Effects

We have gone to wearing cotton HRC2 (8.6 cal/cm2) uniforms and about 10% of the employees have found the clothing to cause burning and itching with at least one case of dermatitis. This seems to be happening in hot locations and when the employee works hard enough to work up a sweat. Our company has taken the approach that we are to wear arc flash protection at all times even there is no risk of danger (sitting in a control room entering data into a computer).I was wondering if others have found some of their employees also have had adverse reactions to wearing PPE’s and how it was dealt with. We are going into our cooling season and a few more people are complaining about the uniforms. READ MORE.


Air Conditioner Motor Contribution

I’d like to hear how some of you are handling Air Conditioner motor contributions in your models. I’m working off a one-line to build the model (while the site is under construction!). I’m wondering if most people model the various motors separately (compressor, fan, other?), or do you leave them modeled as one.

Also, as some of the motors may be buried in the equipment, do you always verify RPM, service factor, FLA, and other motor nameplate data?
I’m not sure some of this data will even be available as these motors may or may not be NEMA standard motors… READ MORE.

Lock Out / Tag Out Simple vs. Complex

BUY NOW: 2018 NFPA 70E Changes Part 1

OSHA and NFPA 70E refer to a Simple LOTO as involving only one person/conductors/circuit part(s). A Complex LOTO is when there are conditions such as more than one person/circuit/shift/source involved – A complex LOTO has significantly more requirements.

Here is this week’s question:

Have you ever performed a complex LOTO?



About Jim Phillips: 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.

NFPA70E 2018 Update video by Jim PhillipsJim is Vice Chair of IEEE 1584, International Chairman of IEC TC78 Live Working and Steering Committee Member – IEEE/NFPA Arc Flash Collaborative Research Project. He has developed a reputation for being one of the best trainers in the electric power industry.  Learn More

Arc Flash & Electrical Power Training Classes
 by Jim Phillips Click Here

Arc Flash & Electrical Power Training Products by Jim Phillips Click Here

Sign-up for my monthly publication “Grey Matter” which contains news about new standards, conferences, technical articles, Electrical Engineering news and more! Click Here

Replacing AF Labels

I will be updating arc flash labels on numerous working locations which means the old label has to be removed and a new one applied. By design these labels are very rugged and difficult to peel off. Anyone have experience with tools or techniques that make the old label removal more time efficient?I’m not a huge fan of sticking new labels on old labels unless it’s unavoidable, I think it looks sloppy unless the two labels were perfectly lined up. READ MORE.

Aluminum vs. Copper IE differences

I’m pushing through the brilliant book “Industrial Power System Grounding Design Handbook” by Dunki-Jacobs and Co. In it, the authors indicate that copper is endothermic (absorbs energy when converting from solid to liquid) and aluminum is exothermic (releases energy when converting from solid to liquid).

They claim that due to these differences equipment with internal aluminum construction has a much greater potential for destructive energy release during an arc fault vs. copper construction. Does anyone account for this difference in their analysis of systems? The program I use for arc flash evaluation does not give me an option for copper vs. aluminum windings in the distribution transformers so I can’t compare & contrast material types for IE levels. For panelboards I do have the ability to adjust for material type but it doesn’t appear to make a difference for IE levels based on a quick sample study I just did.

Thoughts? Is material type a consideration that needs to be addressed? I believe the answer is no but wanted the groups opinion.



How far would you go?

All – I found this installation the other day while in an area I am not officially in charge of. I called the person in charge and recommended he have it removed form service that day before something bad happened. Obviously that didn’t happen. If your electrician installed this would he still be working for you? How about his supervisor who did not have it removed? The other option would be I’m the crazy one and it’s no big deal. After all it’s a welding plug…………………….  :D READ MORE.

Falsified Arc Flash Study

As a electrical engineer who performs arc flash studies and investigates electrical accidents I have come across a company who is faking their arc flash studies. They go into companies and collect a little data such as the number of electrical panels then go back and print labels with made up numbers. I have proven that this particular study was totally fabricated. This false study resulted in three maintenance personnel being burned with two having very serious injuries. There is presently a civil case against the company who performed the study and additional action is anticipated such as criminal action.

MY question is how do we prevent such these bogus studies? I will be publishing information of the accident and the arc flash company as soon as I can but that is not enough. There could be many companies with arc flash studies out there where the information on the labels that are wrong. READ MORE.

AF Boundary Marking

As per NFPA 70E, we have 3 boundaries to mark(AFB, limited and restricted). It is easy to mark and follow only one boundary which is greater than two. Sometimes AFB is more than limited approach boundary, so we marked the AFB and follow that.

But sometimes AFB is very less for lighting boards and power distribution boards. Also it is not feasible to mark limited boundary as it is very big for small board placed in normal working area and not even AFB because it is too small to mark.

I need some suggestions on it, that whether to mark boundary to LDB & PDB’s. If yes, which boundary need to mark? READ MORE.

Short sleeves versus long sleeves

The industrial plant I work in has a policy that you must have long sleeves when inside an electrical room. Yesterday we had our annual “cold day”, where all turbine generators are offline and we are disconnected from the electric utility. During that period it is common practice for electricians to where short sleeves only. However, there doesn’t appear to be a facility policy to that effect, so someone made a fuss and we are having to clarify the policy.

The first part of the discussion is is that an appropriate practice? The proposed policy would be that you can have short sleeves as long as you have all power sources to the room locked out.

The second part of the discussion is does it really matter if you have long sleeves or short sleeves? To my thinking if you aren’t wearing a full set of arc flash hazard equipment (e.g. 4 cal, 8 cal, 40 cal, etc) then it doesn’t really matter what you are wearing, except that it not be flammable. READ MORE.

IEEE 1814 – Have you heard of it?

IEEE 1814 Recommended Practice for Electrical System Design Techniques to Improve Electrical Safety

The overview of this standard is that the Recommended Practice will communicate “electrical safety by design” concepts and their benefits. Current standards and codes place minimum requirements on electrical system designers and manufacturers that yield functional, reasonably safe electrical installations. The final product of this working group will capture, in one location, a wealth of “electrical safety by design” concepts that have been published in recent IEEE papers and in other industry sources. Visit IEEE 1814.

Here is this week’s question:

Until reading it here, have you heard of IEEE 1814?


Application range of methods in IEEE1584

Hello everyone,

The application range for the empirical method is clearly defined : 208V to 15kV and a bolted fault current between 700A and 106kA.

But for the theoretical method, what is the applicable bolted fault current range?
Can it be used for any voltage?

The position about the type of bolted fault current is also not clear. Is it only for 3-phase fault? Or 1-phase fault can be treated?

How do you understand those? Do you use another standard in case of you’re out of one of the above range? READ MORE.

Arc flash detection relay

What is the practice for the use of arc detection relay trip time in the arc incident energy calculations? NFPA-70E recognized arc detection relay but kept under “Other Methods” as opposed to “Incident Energy Reduction Method”. Does this means the arc flash relay tripping time should not be used for the arc incident energy calculations? READ MORE.

IEEE 1584 Equations – Your Thoughts?

When an arc flash study is performed, most rely on software that is built around the equations from IEEE 1584. This week’s question focuses on performing arc flash calculations by hand – either as an exercise or for an actual analysis.

What are your thoughts about the existing IEEE 1584 equations?

Too complex / Too much detail
Too simple / Not enough detail
Seems to be OK as is.
I’ve Never performed calculations manually

Click to ANSWER

Underrated/Over dutied panels in an old building…..WWYD?

We’ll call this a hypothetical question. Say you are running a short circuit and arc flash study on a 50 year old building as part of a multi-building study. You discover you have about a half dozen branch panelboards that are over-dutied in this building. These are all 225A rated, 208Y/120V. Some are flush in block walls in finished areas. Breakers in these panels are 50 year old, long discontinued 10KAIC rated. The feeders are all protected with FRN or LPN fuses with no published series ratings available and no higher rated replacement breakers located. Artificially adding feeder length and/or reducing feeder sizes and fuses to reduce available fault current is possible but just as costly as changing the panels out.

You learn this building is supposed to be torn down within the next 5 years.

Now then switch hats, you’re the Owner and aware of the issue. Would you:

1. Do nothing other than proceed with arc flash labeling the building since the study is practically done. Afterall, this building is 50 years old and nothing has failed in all that time plus the feeders are protected with current limiting fuses so “‘yer’ prolly good. Yeehaw!”
2. Replace the panels with new with 22KAIC breakers even though some of them will be a bear and new guts and covers won’t fit in the old tubs and you’re tearing down the building in a few years. READ MORE

Bus Duct and Arc Flash Hazard?

I was asked to evaluate some “newer” bus duct technology that are finger safe, use a turn and lock connection or similar methods without turning off the power. It seems to do a great job at significantly reducing if not outright eliminating the shock hazard. It also looks like the risk of causing a fault when installing or removing a module is reduced (eliminated?) as it seems it would be very difficult to short line to line or line to ground. Therefore the arc flash risk greatly reduced (eliminated?). Assuming there is > 1.2 cal/cm2 energy available, is there still a arc flash hazard here? Comments on Labeling? PPE?
For example only as there are other manufactures with similar technology.


Adding fuses or a CB in a pad mount transformer secondary

Hi All.

I know I’ve seen a picture or two of your typical oil filled pad mounted transformer that had fuses or a breaker installed right off the paddles on the secondary compartment. I tried googling it and could not find any.

I’ve asked our ABB and Cooper reps if they offer and factory installed breakers or fuses and they both said “no”.

Has anyone come across anything like this? I realize on the bigger sizes it may be very difficult to do and be able to get several sets of parallel 500’s landed due to limited room but there would be some instances where it could be an advantage to “move the problem” from the line side of the switchboard main out to the transformer. READ MORE



Looking at the IE calculation there is a variable for grounding depending on what type system you have installed, and noticed that the grounding type can have a significant effect on the calculated IE energy on ungrounded vs grounded systems. Just curious if anyone can shed some light or point me in the direction of some literature that would better explain the cause of increased IE on ungrounded systems. I see the variable change in the calculations and there is a brief statement about this and found some articles that discuss the grounding types etc. but could not find any technical literature on the “why’s” any information is greatly appreciated. Thanks… READ MORE.

Using Grounding Resistors

One of the forum member’s posts prompted this weeks question of the week. It is about grounding, more specifically – high and low resistance grounding. (some may use reactance grounding). Rather than having a solidly grounded system or a delta connected system, some will use a grounding resistor to limit the line-to-ground short circuit current that flows during a fault.

This week’s question:
Does your company (or clients) use grounding resistors anywhere in the power distribution system?

Hi Resistance Grounding
Low Resistance Grounding
Both Hi and Low
It depends – Many locations/clients
Doesn’t apply to me


Preload indicating washers

Anyone ever heard of a preload indicating washer?

Looks very simple. It’s a washer that crushes when the fastener reaches 80% of yield. According to Sandia Report SAND2008-0771 they are accurate to +/-10% of clamping force compared to +/-35% for a torque wrench and it directly measures clamping force unlike a torque wrench that is mostly measuring the friction being overcome by the nut heat and the threads.

It appears that there are 3 versions. One has slots where you can stick something and attempt to turn it. When it won’t turn, the preload has been reached. With the second type, you measure the gap (see if you can stick feeler gauge in it). When the gap is gone, preload has been reached. The third type loads the gaps with RTV. When the RTV squirts out of the joint, preload has been reached.

Sounds like a good, cheap solution to ensure proper clamping force at least with bolted joints. I love the fact that since it measures clamping force directly it avoids issues with damaged/galled/contaminated threads that can fool you into thinking the joint is tightened properly even with a torque wrench. They also look relatively inexpensive. But frankly I’ve never seen these in use anywhere except for critical connections on steel structures. Has anyone used these before? Care to share any experiences? CLICK to answer.

Using the series rating charts – real example

Don’t mean to beat this topic to death. Well, yeah, I guess I do, but since I had another example of being over dutied/under rated come up today I thought I would share it.

Scenario: Fairly low impedance (2.9%) 300 kva dry transformer originally feeding a large dimmer rack. Over the years someone added a panelboard off the secondary of this transformer plus a cam-lock quick hookup for a mobile TV broadcast truck.

The branch panel is a Siemens S1 with a 125A type ED4 main breaker and a bunch of 1P20A type BL branch breakers. Voltage is 208Y/120V.

SKM model tells me I have a little over 10KA available at this panel. The BL breakers are only good for 10KAIC. Hmmm. What to do.

1. Replace the breakers with BLH’s or other 22KAIC rated breakers.
2. Artificially increase the feeder length until we get below 10KA available.
3. See if there is a tested series combination rated high enough.

See attached 3 page PDF for the solution. CLICK to get PDF and read more.

NFPA 70E and Improved Electrical Maintenance

The duration of an arc flash can be greatly affected by the condition of electrical protective devices – i.e. circuit breakers, relays etc. NFPA 70E has been placing an increased emphasis on equipment being properly maintained.

Has your company/client increased the emphasis on electrical maintenance as a result of 70E?

Many clients – it depends

CLICK to answer.

SKM PTW Viewer – can you build a one-line with this

Hi all.

I use SKM PTW on a daily basis but only have a single user license with a hardware key. I have a student worker (I work at a university) who mostly spends his time pulling old drawings and product data from our archives for me to work from. He also does some measuring of feeders and records them on the one-line and also goes out and applies the arc flash labels after I’ve done the study and printed them.

It would be nice if the student could start drawing models by at least getting the basic outline in place (utility, transformers, ATS’s busses, PD’s, cables, motors etc.) but without the data populated. That would save me some time and get this basic stuff done at a far lower cost that paying me for essentially drafting. I would then verify the basic model and modify as needed, fill in the data and do the analyses etc.

The problem is I can’t give up my hardware key for him to draft and can’t afford a second 1000 bus license for this. Someone mentioned to me once their company has a “lite” version of PTW that allows the very things I’m talking about. In looking at SKM’s site all I see is the PTW Viewer. Specs on it say:

Key Features:
Open, view, print, and export all study results from any project without a full version of PTW.
Create new one-lines from existing components and expand the one-lines.
Modify or create new datablocks and apply them to any one-line and TCC.
Adjust component position in existing one-lines and add annotations.
View different scenarios created from the base project and compare the results of multiple scenarios in the Data Visualizer.
Create customized Arc Flash labels, print Warning Labels and Work Permits.
Access to the Component Editor to view specifications of each component for all designs and projects.
View tabular and graphical representations of completed studies.

Does anyone know if “Create new one-lines from existing components and expand the one-lines.” means you can draw a one-line from scratch or do you have to have a project already created with devices already in the one-line that one can then modify? Does anyone here use the Viewer and are able to shed some light on its capabilities or if there is another option you know of?


Circuit Breaker Maintenance

Apologizes if this topic is covered elsewhere in the forum. If so, please point me in the right direction.

We are having some arc flash studies completed for buildings across our campus. The consultant is recommending that fuses be replaced with current limiting type fuses and also that breaker settings be dialed down to be more conservative. Adjusting our old breakers is something that we are nervous about doing and so I wanted some reactions from this group.

I know NFPA 70B has guidelines about exercising/cleaning breakers every couple of years but of course we, like every other building owner I have ever ran across, don’t regularly maintain our low voltage circuit breakers. We are not staffed to regularly clean & exercise the plethora of breakers across of 100+ buildings, nor do we have funds lying around to replace the vintage to middle aged breakers should they be discovered as prone to failure.

We are worried that by adjusting the breakers as recommended by the studies that we are asking for them to nuisance trip or perhaps malfunction in some unforeseeable way, causing widespread building outage or expensive parts replacements. Of course, if we run across breakers that are clearly on the their last leg or are an immediate threat to personnel they should be addressed right away. It’s those “dark horse” breakers that concern us.

Do folks have recommendations for what to do or have similar situations? Are there simple ways to inspect breakers to see if they appear to have useful service life remaining / can be exercised or adjusted without worry of problems in doing so? Any tips and tricks that don’t involve a lengthy outage to building power? What are your other large campus type clients doing in regards to maintenance and testing of breakers? Is this something anyone does that you are aware of?

Any feedback is appreciated. READ MORE

Tested vs. Engineered Series Ratings

One more question about series ratings. NEC 240.86 addresses series ratings “Selected Under Engineering Supervision in Existing Systems” and “Tested Combinations” Please refer to last week’s post and NEC 240.86 for specific application details.

Do you use “Engineered/Selected under engineering supervision” or “Tested Combinations” series ratings

– Engineered/Selected under engineering supervision
– Tested combinations
– Both
– None


Racking in medium voltage breakers – does this exist?

The question of the week on racking in medium voltage breakers got me thinking about this video:

and what else could be done to prevent it from happening again. Yes, I know the guy was wearing insufficient PPE and should have had the door closed. I also know that in our newer gear where I work we have remote remote racking operators, fiber optic flash detection and tripping and the gear is designed differently to contain or re-direct an arcing fault.

All that said, I expect events like this mostly occur while racking the breakers in and out. What if there was a quick connect gas hose port in each cubicle with a nozzle inside to flood the stabs with SF6 or some other gas while racking? If there were a fault the gas should help knock it way down I would think and help to save the equipment even if you were using remote racking.

Maybe it already exists and I’m not aware or maybe it’s not feasible due to not being enclosed would keep you from achieving a high enough concentration of gas, or the EPA wouldn’t like it, or it would be too expensive. It is just a thought I had if there are any manufacturers reading this.

I also thought about compressed bottled gasses inside the gear with quick acting firing could possible serve a similar function but those would likely never fire fast enough and never be tested or maintained. READ MORE.

Series Ratings NEC 240.86

The National Electrical Code article 240.86 addresses series ratings with the following:

Where a circuit breaker is used on a circuit having an available fault current higher than the marked interrupting rating by being connected on the load side of an acceptable overcurrent protective device having a higher rating, the circuit breaker shall meet the requirements specified in (A) or (B), and (C).

(A) Selected Under Engineering Supervision in Existing Installations. The series rated combination devices shall be selected by a licensed professional engineer engaged primarily in the design or maintenance of electrical installations. The selection shall be documented and stamped by the professional engineer. This documentation shall be available to those authorized to design, install, inspect, maintain, and operate the system. This series combination rating, including identification of the upstream device, shall be field marked on the end use equipment. For calculated applications, the engineer shall ensure that the downstream circuit breaker(s) that are part of the series combination remain passive during the interruption period of the line side fully rated, current-limiting device.

During the early 1980’s there were some problems with series ratings and tested combinations were introduced. Series rated test standards in accordance with U.L were developed and circuit breaker manufacturers begin to provide tables with their listed series ratings like we see today. 240.87(B) states

(B) Tested Combinations. The combination of line-side overcurrent device and load-side circuit breaker(s) is tested and marked on the end use equipment, such as switchboards and panelboards.
Informational Note to (A) and (B): See 110.22 for marking of series combination systems.

240.87 (C) addresses the situation where short circuit contribution from motor’s a.k.a. “motor contribution” may occur between the line side and load side devices that make up a series rating. The consideration is as follows:

(C) Motor Contribution. Series ratings shall not be used where (1) Motors are connected on the load side of the higher rated overcurrent device and on the line side of the lower-rated overcurrent device, and
(2) The sum of the motor full-load currents exceeds 1 percent of the interrupting rating of the lower-rated circuit breaker.

An example of a series rating may be a breaker that normally has an interrupting rating of 22,000 Amps but when protected with upstream fuses of a specific size and class, may have a series rating of 100,000 Amps. This must be either a listed combination or determined under engineering supervision as stated above in 240.86 (A)

Those that consider using series ratings should thoroughly review the requirements of 240.87.

With all of that information, here is this week’s question.

Does your facility/client’s facility use series ratings?
– Yes
– No
– Multiple sites – some do
– Don’t know
– Doesn’t apply to me

CLICK to answer and review discussion.

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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IEEE 1584 – Required Certification for Products/Services?

I have heard a rumour that IEEE1584 are up to their old tricks again.
Back in 2012 it was to introduce royalties for use of the equations. This time I understand that the IEEE Standards Association are planning to require certification for the use of the next edition of IEEE 1584 in products and services with that Certification commanding an not unsubstantial fee for the certification.
I have a number of issues with all of this. Technical Standards are firstly produced by a number of experts including those who actively participate in the development of the standard at meetings etc. but also third parties who comment at all stages through to the ballot stage.
IEEE1584 is not the culmination of the work of a single person neither is it the work of only those members of the TC but it is the work of many people over many years some of whom, like Ernie Jones, are no longer with us. They’ll be wanting to copyright Ohms Law next!
To even consider a system of Certification of persons would be full of holes and the only benefit would be to those who certify and this is erroneous in itself. Who certifies and what qualifies them to certify? I started in this field in 1993. I’m a Fellow of the IET; Senior Member of the IEEE; Chair the European Cenelec TC responsible for this field of activity and contribute on the IEC Committees – etc. etc. I resent someone believing they have the authority to certify me or others like me.
This would be a very dangerous precedent. The IEEE need to be reminded of their roots and why the Institution was founded back in 1884 and be aware of a potential backlash if they allow a minority to capitalise on others work.
From the point of my National Committee we would be requesting to IEC to develop its own information for distribution on a global platform; to drop the official Liaison with IEEE; and basically suggesting to the UK and European industry not to reference IEEE 1584.
I would be interested if there is any substance in this rumour and will anyone be at the September meeting in Philadelphia.

New to Arc Flash, Short Circuit and Coordination studies

Hi. I currently work as an Engineer in the energy management field. I would like to branch off in to doing Arc Flash, Short Circuit and Coordination Studies. How would I go about doing this. I have been exposed to these reports but have never done them before. Would any of you happen to have any training material on how to get started? From what I’ve read I should learn how to do these reports manually then look in to getting software to aid with the reports. Not sure if it matters or not but I’m located in Canada. Thanks. READ MORE

ArcPro and Windows 10

Has anyone found a way to run ArcPro on Windows 10? I cannot even install it on Windows 10. Not sure about any 3rd party programs that could emulate a earlier Windows version. FYI: I have sent 3 emails to the creators of ArcPro (Kinectics) specifically to Stephen Cress and it has been 6 weeks since the initial email with followups sent but I have not received a response. READ MORE

X factor for Disconnect switches

Hello What is the optimal X factor for disconnect switches. I assumed it is 2 because that’s the default value that ETAP gives you. Am I correct for assuming this? Furthermore, It falls under the low voltage category (0.208-1), so it can be the value for MCC’s and panels which is 1.473. Which value is optimal for Arc Flash calculations? Thanks READ MORE

PE/Certification (moved from IEEE 1584 Certification thread)

There is a long and well documented fight between the NSPE as the “political arm” of professional engineering and various industry groups which have all but made “industrial exemption” here to stay. And speaking from the other side, guess how much support there is in industry for getting that PE? Is there a pay increase or even funding (and time allotted) for taking classes? I’ll give you a hint…been there, done that. Furthermore, does hiring an engineering firm versus a “consultant” have any merit to it whatsoever? I’ll give you a hint…been there, done that. And doesn’t an engineering firm by itself since they are third-party in nature and independent because of the NCEES ethics requirements guarantee that the workmanship is a cut above others? Again, been there, done that.

The answers at least from my point of view are that none of this is any kind of litmus test. In fact someitmes it seems to be almost the direct opposite of a litmus test…those without certification recognize the bigger hurdle to cross and put more effort into producing a good work product. If some kind of license or certification narrows the field of potential bidders significantly it tends to turn into a “good old boys club” and the quality goes totally out the window very quickly with no performance incentives.

And I agree with rubber stamping as far as certification goes, that’s very true. However even if the certification process of choice is possessing a PE, in itself that means nothing as well. As a simple practical matter you can’t get a license unless you’ve worked as an engineer to meet the on-the-job requirements. You can’t get that unless you work under the “industrial exemption” clause or under another PE’s license. Even then if you’ve ever worked with engineering firms then you know that there is a certain approach to doing business with them. They are used to an environment where you produce paper to fulfill a contract. As long as the paper quality is good enough to pass muster and get another contract, that is the minimum quality standard. Many companies insist on outside engineering groups or don’t have engineers on staff and hire whatever they can get, so the quality standard is extremely low. So this is how it played out for me. We hire an engineering firm to do the engineering for a project. The firm comes to me and gets me to do all their research for them. They write it all up and pass it back to us for “checking”. They did a crap job so I spend so much time getting them to do it correctly that it’s easier to just do it myself. So the end result is that hiring an outside engineering firm which is supposed to reduce my workload actually triples it since instead I’m doing all the engineering and I’m doing all the documentation and I’m also spending all kinds of time in meetings, writing E-mails, etc., so that the engineering firm gets credit for my work. Mind you it’s not the 3% of good engineering firms that I have a problem with. It’s the 97% that do the crap jobs that actually cost me time and money. The problem of course is that this gets results and time and again, “engineering managers” and “purchasing managers” buy into this crap. So time and again I get shafted with dealing with these idiots. Unlike the engineering firm, I am the one responsible for ensuring that we get a quality work product out. If it doesn’t work, I’m answering for it. If it doesn’t work, I’m the one spending my midnights and weekends away from my family (and bed) in the trenches with the maintenance guys getting it up and running. I’m the guy that has to work with production training them how to work around the design defects and having to explain why we can’t spend an more money to fix it right. They’re just responsible for generating billable hours and once the dollars are exhausted, they move on and never get called to the job again.

One of the qualifications I use for engineering firms by the way is that I read their resumes. If I get 3 pages of contract after contract and the person has not had one shred of experience working outside of an engineering firm, the resume goes to the trash can. There is no reason to even bother interviewing them. They have never, ever had any experience with taking ownership of anything and never will, so there is no incentive for them to do anything other than bill hours to a job. They got the PE by virtue of how much money they brought in for the engineering firm, not b virtue of workmanship. And who knows how many of those contracts on their resume resulted in dissatisfied customers. READ MORE

Arc Flash Shields in disconnect boxes

I repair UL listed appliances that are sometimes directly wired into a fused or unfused disconnect box if they exceed 50A.

Sometimes I need to test the voltage on both sides of the knife switch. The new boxes seem to come with shields on the “hot” side, with little holes so that I don’t accidentally short things out with my probes. That would be okay except that my probes are not long enough to make contact with anything when I insert them in the holes.

So I have to remove the shield (usually very easy to thwart) and test as if it didn’t exist. I’m using a fluke meter with probes about 1.5″ long, so there is nothing wrong with my meter or probes. I was working with an electrician today and pointed this out and he said “Do not adjust your set. You are not doing anything wrong.”

And then he pointed out the obvious way to thwart the shielding.

So what gives? READ MORE

Existing Overdutied Equipment

This week’s question is a continuation of last week’s topic regarding overcurrent devices that do not have an adequate interrupting rating. When the calculated short circuit current is greater than the device’s short circuit interrupting or withstand rating, the device is often referred to as “overdutied”. (X/R can play a role too but we’ll save that for another day) This week’s question: Do you/client presently have any overdutied devices? Yes No Not Sure Rather Not Say READ MORE

PPE Selection when Interacting with non-labeled Equipment

Hi All, To put my question in context, I train Industrial Maintenance and Construction Electricians at a Community College. Some of the students are new to the field and are receiving training to gain employment. Many of the students are already employed and are taking classes to enhance their skill set. Many of these folks are involved with service work that takes them to a variety of locations from 7-11s to industrial sites. Where I am troubled is how to advise them about what PPE to wear in READ MORE

Fiber Optic Arc Flash Detection Modeling

I will start by stating that I am not 100% familiar with these types of systems [Fiber Optic Light Detecting]. In recent MV switchgear submittal the manufacturer [I assume at the recommendation of the engineer of record and or the owner] included a fiber optic light detection system for arc flash mitigation. This included “point source detection” at the terminations in addition to “linear fiber optic detection” in the breaker cubicles at the runbacks / breaker connections. In discussing with multiple manufactures of these types of systems and colleges. The way I understand is that when the fiber optic system detects the light emitted during the early stages of an event and triggers the relay trip circuit to operate the breaker. Most of the literature from manufactures indicates a lower category of PPE required due to the increased / early detection and interruption however I have not found any literature or testing that quantifies what level of light [lumens?] is required in order to operate the trip signal, and at what level of arcing current this is correlated to? So all this leads to how is this type of detection system typically modeled in the different AF software’s if there is no testing to correlate the arcing current to emitted light? Has IEEE reviewed this? How can the manufactures claim or “guarantee” two levels lower of PPE? Is it based purely on testing by the manufacturer? I understand that these types of systems are recognized by the IEC [62271-200]. Has anyone on the forum installed, started up or familiar with these types of systems I would like to get your feedback on their reliability, and if there is a industry standard [ANSI/IEEE/UL] on how these types of systems are manufactured / installed /etc.. Thanks in advance. READ MORE

Arc Flash Boundary – Calculated, Larger, Something Else?

It has been a while since a question of the week was asked about the Arc Flash Boundary. This is the distance from a prospective arc flash where the incident energy is 1.2 cal/cm^2 which is the generally accepted value for the onset of a second degree burn. IEEE 1584 has a method for calculating this distance.

Since electrical safety practices continue to evolve, this week’s question is about the Arc Flash Boundary. Although the AFB is required to be on the warning label and is a calculated value, many are opting to keep unprotected/unqualified workers further away from a possible arc flash during live work (which should be kept to a minimum). This week’s question:

For your (client’s) electrical safety practices, do you use:
Select up to 2 answers

Calculated AFB
Something larger (please explain)
Keep unprotected people out of the electrical room
It depends

Please feel free to elaborate READ MORE

Non Specific incident energy

I have started working at a manufacturing plant where the past practice is to put <1.2 cal on their arc flash labels. The thought being that any run less than several hundred feet fed from bus duct with LPS-RK1 fuses will be less than 1.2 cals. This turns out to be true based on my calculations. Even with the maximum motor contributions the calculations hold. Does anyone consider this to be in compliance with 70E? Does anyone else do this? READ ANSWER

Short Circuit Calculations and Conduit Material

I recently came across a previous study that was completed for a facility that assumed a specific type of conduit [non-metallic/magnetic; PVC] vs what was actually installed [Rigid Meal Conduit], in digging into this deeper and looking at some of the short circuit calculations information available to me it appears that in the calculation they type of conduit [magnetic vs non-magnetic] can play a role in the amount of available fault current. When doing some quick simplistic calculations it appears that the conduit material does play a role and in larger systems could make a difference. I did some digging in my software’s reference material and some other material but could not find adequate explanation / technical data.

I was hoping someone could share or point me to some additional resources on how conduit material affects available fault current? It appears there are different constants for conductors based on the type of installation [conduit type for systems of .208-13.2kV] also what if you have conductors installed in tray [3-1/C cables] does the spacing and configuration of how the cables are installed come into play and where could I find some information on this. Thanks in advance. READ MORE.

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.

Click here for upcoming Arc Flash Safety Training

Click here for all scheduled Electrical Safety Training

Click here to request an Onsite Training

Sign-up for my monthly publication “Grey Matter” which contains news about new standards, conferences, technical articles, Electrical Engineering news and more!


Need some TCC curves for two fuses – can’t find them

Hi all. I have a pad mounted transformer with internal primary side 15KV rated fuses. There are two types in series. One is an expulsion fuse GE# 9F54WLD303 and one is an oil submersible protector (OSP) GE # 9F59TCD150.

I don’t have them in my SKM library. I asked SKM for them and they sent me new .lib files for these but would not guarantee them. After merging them into my library and adding them to the model I don’t think the curves are correct. I questioned SKM about them and they said they did not have the curves to double check against and that the file they sent me was one someone put together a long time ago and they said they did not know if they were accurate or not.

I’ve searched the web but cannot find the data sheets or curves on these fuses. I did find one reference to one of the fuse types in ETAP but don’t know if maybe ETAP has them in their library.

I have attempted to upload a little info on these fuses from 1986 when we bought this transformer. It is 2 pages, one file. READ MORE

Overdutied Protective Devices and Catastrophic Failures

People seem to love to watch videos of electrical explosions. One type of failure is when a protective device is applied beyond its interrupting rating and catastrophically fails (explodes) when it has to interrupt a short circuit. Although this does not happen for every overdutied device, it could happen. That is the main reason for performing a short circuit study – to identify these types of deficiencies so they can be corrected.

So with that intro, here is this week’s question.

Have you/clients ever had an overcurrent device catastrophically fail when it interrupted a fault?