Since the second edition of IEEE 1584—IEEE Guide for Performing Arc Flash Hazard Calculations was published in 2018, many questions concerning the changes and additions have arisen. In particular, many people have wondered how to determine the electrode configuration.
The 2002 edition was based on arc flash tests performed with vertically configured electrodes. At the time, when performing an arc flash study, only two options were available: either an arc flash in an enclosure or an arc flash in open air.
Since the 2002 edition, additional research has shown the electrode configuration can influence incident energy, arc flash boundary and arcing short-circuit current. As a result, many new tests were conducted using additional electrode configurations. In addition to the vertical configuration, the new tests include vertical electrodes that terminate into an enclosure’s insulating barrier and horizontal electrodes in an open air enclosure. The new configurations and resulting calculation methods make providing more detailed modeling of electrical equipment possible.
The 2018 Edition of IEEE 1584 includes five different electrode/bus configurations and new acronyms (see figure above):
1. VCB—Vertical conductors/electrodes in a metal box/enclosure (also in 2002 Edition). With the original vertical electrode configuration, when an arc flash occurs in an enclosure, the arc is driven away from the source, down the electrodes, toward the bottom of the enclosure and out of the front.
2. VCBB—Vertical conductors/electrodes terminated in a metal box/enclosure’s insulating barrier. If vertical electrodes are terminated into an insulating barrier, research has demonstrated the arc hits the barrier, and the plasma cloud is directed more toward the enclosure opening.
3. HCB—Horizontal conductors/electrodes in a metal box/enclosure. When the electrodes are placed horizontally, the arc plasma is directed from the electrode ends outward.
4. VOA—Vertical conductors/electrodes in open air (also in 2002 Edition). Tests were conducted in open air using the original vertical configuration in open air.
5. HOA—Horizontal conductors/electrodes in open air. Tests were conducted in open air using a new configuration with horizontal electrodes in open air.
Confusion and uncertainty—deja vu
The second edition is only a few months old, and people are trying to decide what to make of it. Something similar occurred when the original 2002 edition was published. An arc flash calculation standard was a new concept, so people back then struggled to sort out the details. Some of the initial uncertainty and confusion from the 2002 edition led to questions such as: Do you measure the actual bus gaps or use the default values from IEEE 1584? Do you dare cut off the arc duration at 2 seconds? How do you model switchgear? What information goes on the label? How much detail was really necessary? The list went on.
These questions seem trivial today, but when the 2002 edition was published, they were considered quite significant. Over time, the industry converged into a more standardized practice for arc flash studies, but it took a while.
History is repeating itself as arc flash studies and software transition from the 2002 edition to the 2018 edition. The electrode configuration is a brand-new concept, and questions and second guessing come with anything new.
Electrode configuration—what people are doing
For over a decade, I have conducted a “Question of the Week” survey at ArcFlashForum.com to gauge the electrical safety industry’s views of various topics. Recently I asked, “How will you address electrode configurations?”
Although not a scientific survey, the results so far are as follows:
- Use VCB/VOA for now (same as 2002 edition): 16 percent
- Review actual equipment bus/conductor configuration and decide: 36 percent
- Use the configuration that provides the highest incident energy: 8 percent
- Not sure yet: 40 percent
It is a close race between “Not sure yet” and “Review actual equipment bus/conductor configuration.” The “not sure yet” crowd is simply 2002 repeating itself, and I am sure, in the not-too-distant future, we will look back at this and wonder what was so confusing.
In my next article, I will explore specific examples of electrode configurations.