An old Grateful Dead lyric sums up the last 16 years of developing the next edition of IEEE 1584, IEEE Guide for Performing Arc-Flash Hazard Calculations: “What a long, strange trip it’s been.” Truer words have never been spoken. Although at the time of this writing in late August, the next edition of IEEE 1584 has not been officially approved or published, but it is finally very close to the finish line.
Note: Since I am vice-chair of IEEE 1584 and Steering Committee Member of the IEEE/NFPA Arc Flash Collaborative Research Project, I’m required to state that this article is from my view and may not necessarily represent any official position of IEEE or NFPA.
The (not so short) history
IEEE 1584 was first published on Sept. 23, 2002, and at the time, it was a highly celebrated standard. This was the first time an internationally recognized standard provided a method to calculate the arcing short-circuit current, incident energy and arc flash boundary. The results of the incident energy and arc flash boundary calculations are often listed on arc flash/equipment labels and used as part of an arc flash risk assessment.
The celebration was short-lived, however, as several global experts began the discussion of what comes next. Attention shifted away from what was done and toward what else should be done.
The list of what came next was becoming quite formidable. It was obvious that the next edition of IEEE 1584 would be a project of epic proportions, requiring significant financial and technical resources. To move on to the next level, a different approach would be necessary, so a collaboration between IEEE and NFPA was created.
From 2003 to 2006, the collaboration was established, a test plan was developed, and a project team and project manager were selected. The estimated cost of this undertaking was projected to be $6.5 million. Of course, neither IEEE nor NFPA had those resources just lying around, so an aggressive fundraising effort began involving many major contributors. The fundraising was going relatively well until the Great Recession, and then it came to a grinding halt.
Armed with a little more than half of the estimated project funds, preliminary work finally began on the next generation of arc flash testing. The research and testing by the collaboration project moved into high gear from 2009 to 2012. In 2013, the test results, preliminary model and new equations were handed off to the IEEE 1584 working group.
A small task group was formed to review and refine the new arc flash model from 2013 to 2016. During 2016 and 2017, the next stage was to bring the new model and new text together as a complete draft of the second edition.
Heading into the final stages was going to be another challenge: voting and approval. This was done in two phases. The first phase was voting and approval by the members of the working group—known as a consensus ballot—so the draft could move on to the next phase.
Once the working group achieved consensus, the draft moved to the second phase—known as Sponsor Ballot. This involves a separate group that joins a ballot pool to participate in the standard’s formal voting and approval. More than 160 people registered to vote on the draft.
The draft was approved on the first round of balloting, which was a major accomplishment. However, more than 1,000 submitted comments needed to be addressed. To more efficiently resolve so many comments and prepare the next draft for reballoting, a ballot resolution committee was formed. It was made up of nine people representing a cross section of the working group.
As one of the nine, I found myself holed up in conference rooms over weekends in various locations working to address the comments and develop subsequent drafts of the standard. This was in addition to the literally thousands of emails, countless conference calls and many weekends on the phone discussing various issues attempting to move IEEE 1584 toward the finish line.
The current (and hopefully final) version at this moment is the sixth draft. It was just recently sent to the IEEE Standards Association for the next steps in the process.
I am often asked what has changed from the 2002 edition to the next edition of IEEE 1584. Perhaps an easier question to answer is what hasn’t changed. Well, at least the next edition still has the same title!
The 2002 edition was based on more than 300 arc flash tests used to develop empirically derived equations. The range of validity is from 208 volts (V) to 15,000V, three-phase and for bolted short-circuit currents from 700 amperes (A) to 106,000A.
The new edition is based on almost 2,000 additional tests spanning a wide range of voltages, configurations and parameters. Let’s take a look at the major changes as of draft six.
Range of model
Voltage range (unchanged):
208V to 15,000V, three-phase
Range of bolted short-circuit current:
208V–600V: 500A to 106,000A
600V–15,000V: 200A to 65,000A
208V–600V: ¼ inch to 3 inches
601V–15,000 V: ¾ inch to 10 inches
Working distance: 12 inches or larger
New electrode/bus configuration
The 2002 edition was based on arc flash tests with electrodes in a vertical orientation as shown in Figure 1. When an arc flash occurs using the original model, the arc plasma is driven toward the bottom of the box and often spills out of the front.
Subsequent research has shown that incident energy can be influenced by the electrode orientation. As a result, the project team conducted many new tests using electrode orientations that include both a horizontal configuration and vertical electrodes that terminate into an insulating barrier. These additional configurations may be possible with some types of electrical equipment as shown in Figure 2.
When the electrodes are placed horizontally, the arc plasma is directed from the ends of the electrodes outward. Research has also indicated that, if vertical electrodes are terminated into an insulating barrier as shown in Figure 3, the arc hits the barrier and the plasma cloud is directed more toward the enclosure opening.
In addition, tests were conducted in open air and included the original vertical configuration in open air and a new configuration with the electrodes oriented horizontally.
To provide greater modeling flexibility for equipment, five different electrode/bus configurations have been included in the testing program and subsequent model development which include:
- Vertical electrodes in a metal box/enclosure—VCB (also in 2002 edition)
- Vertical electrodes terminated in an insulating barrier in a metal box/enclosure—VCCB
- Horizontal electrodes in a metal box/enclosure—HCB
- Vertical electrodes in open air—VOA (also in 2002 edition)
- Horizontal electrodes in open air—HOA
125-kVA transformer exception
The 2002 edition contained language that many refer to as the “125 kVA [kilovolt- ampere] transformer exception.” This language states: “Equipment below 240V need not be considered unless it involves at least one 125 kVA or larger low-impedance transformer in its immediate power supply.”
This language was based on a few tests that indicated lower short-circuit currents at lower voltages may be less likely to sustain an arc flash resulting in a lower incident energy.
However, subsequent IEEE 1584 testing has demonstrated that, although not very common, it may be possible to sustain arcs briefly at lower levels of short-circuit current resulting in a greater incident energy. Based on the results of additional testing, the 125-kVA language has been deleted.
Instead, new language states: “Sustainable arcs are possible but less likely in three-phase systems operating at 240V nominal or less with an available short- circuit current below 2,000 Amps.”
Although the 2002 edition is valid for voltages from 208V to 15,000V, only two different equations were provided for the arcing short-circuit current: One for systems operating from 208V up to 1,000V and one for 1,000V to 15,000V. This left a discontinuity at 1,000V and further refinements were needed. In addition, the 2002 edition required a calculation factor (Cf) for incident energy calculations at voltages less than 1,000V. The next edition uses three voltages and also includes interpolation for other voltages for greater accuracy. The three voltages are 600V, 2,700V and 14,300V.
The 2002 edition made a distinction in the results based on whether a power system is grounded or ungrounded/impedance grounded. During the arc initiation stage when the fuse wire is melting, the arc can be very erratic, i.e., unbalanced. The erratic arcing created a difference in the arcing current and incident energy during this very brief period that could be influenced by how the system is grounded. The new model is based on the more stable arc so there is no difference in the calculations based on grounding.
Arcing current variation correction factor
The first addendum for the 2002 edition of IEEE 1584 was published in 2004. Known simply as IEEE 1584a, this addendum added an 85 percent factor for reducing the calculated arcing short-circuit current for systems up to 1 kilovolt. The reduction was to account for variations that may occur in the actual arcing current, which could affect how fast a protective device may operate. If the reduced arcing current resulted in a longer clearing time and larger incident energy, results based on the adjusted current would be used.
Instead of a fixed 85 percent factor, the next edition includes an “Arcing Current Variation Correction Factor” based on using a new equation. This represents a more accurate arcing current variation based on the electrode configuration as well as other factors and applies for all voltages.
Enclosure size correction factor
The enclosure size can have a significant impact on the arc flash energy being expelled and reaching a worker. To address this, additional enclosure sizes were included in the test program. An enclosure size correction factor has also been introduced to adjust the incident energy for smaller and larger enclosures. For equipment operating at voltages less than 1,000V, the next edition now makes a distinction between “shallow” enclosures which are less than eight inches in depth and “typical” enclosures that are greater than eight inches in depth.
There is language in the 2002 edition that suggests the arc duration may be capped at 2 seconds if calculations indicate that a protective device may take an unusually long time to operate. Judgment must be used to evaluate if a person would have room to react and jump out of the way within 2 seconds.
This leads to another question: Will the 2 second rule remain? The simple answer: Yes!
When will the next edition be issued?
The burning question (pun intended): When will the next edition of IEEE 1584 finally be published? Over the years, some people have been overly optimistic, proclaiming the next edition is about to be published. I first heard this back in 2012 and have heard it a few more times since then.
When it is finally approved, the three IEEE 1584 working group officers will hear the news first from the IEEE Standards Association. Then we will spread the news rapidly to the working group and beyond. I hesitate to guess on a final date because there are a few hurdles yet to cross. The best-case scenario is hopefully before the end of the year.
Just because the IEEE 1584 standard is finally about ready to be published doesn’t mean arc flash research and standards development is finished. Quite the opposite! After 16 long years, there will undoubtedly be celebration—but then we will once again begin looking at what’s next!
I will continue exploring the details of the next edition of IEEE 1584 in future articles.