Guest contributor: Kevin J. Lippert, manager, codes & standards, Eaton
An arc flash analysis quantifies incident energy to better protect against an arc flash hazard. The latest updates to the Institute of Electrical and Electronics Engineers (IEEE) Std 1584TM 2018 Guide for Performing Arc Flash Calculations have made significant strides toward furthering electrical safety. The Guide, a widely accepted method for performing arc flash hazard calculations, is now backed by nearly 2000 additional tests — more than any other method — to provide the information necessary to complete an arc flash risk assessment.
Of course, arc flash analysis is never an exact science and, the use of IEEE 1584 is not mandatory. But I strongly recommend electrical engineers embrace the new version of IEEE 1584, as its formulas and mathematical models are based on a multitude of varied field conditions and the most up-to-date science.
New requirements lead to new questions
Consultants and electrical engineers have been using IEEE 1584 to calculate incident energy since the Guide’s inception in 2002. Many engineers have a comfort level with the 2002 version of the Guide and are very accustomed to its calculation methodologies, so they may have reservations about the 2018 version. Further, some professionals are beginning to raise questions as they apply the 2018 version in real-world scenarios.
Let’s take the new addition of electrode configuration as an example. Engineers have begun applying this aspect of the Guide on new projects, as data and equipment details are more likely available to meet the parameter needs of equations. However, these professionals question whether they have the same level of clarity for older systems and existing projects. In these cases, electrode configurations and box dimensions may be unclear or very difficult to ascertain, making the implementation of the 2018 version questionable for existing systems. Some engineers have indicated they would revert to the 2002 version in such instances.
Situations vary, so toggling between the 2002 and 2018 calculations may sometimes seem logical, but in practice, doing so creates confusion. At Eaton, we think it is important to eliminate that confusion.
Clarifying requirements through independent studies
Our mission is to help professionals adopt the 2018 Guide and increase confidence in their data and calculation results. Today, my engineering colleagues at Eaton use updated IEEE 1584 equations to model electrical systems and perform sample calculations to define the differences between the 2002 and 2018 versions.
Our mission is to help consultants and electrical engineers understand and adopt the 2018 Guide and increase confidence in their data and calculation results.
With each new power distribution system model, we gain a better understanding of the increases and decreases of incident energy value applications calculated from the 2002 version and recommend how to apply the updated Guide moving forward.
Our preliminary findings suggest:
- Three additional electrode configurations — vertical electrodes (metal box with an insulating barrier (VCBB)), horizontal electrodes (metal box (HCB)) and horizontal electrodes (open air (HOA)) — represent perhaps the most significant changes to the Guide. Generally, the horizontal electrode configurations result in higher calculated incident energy than the vertical configurations.
- The Guide now accounts for engineered electrical assemblies and tests to North American ANSI/IEEE Standards and those in other world regions thanks to higher calculated arcing current values in the 2018 version. We also see an increase in incident energy values. We believe one of the reasons this occurs is because the 2018 update offers more selection options for phase conductor spacing.
- Additional options for enclosure size are now available, allowing for more accurate modeling based on actual equipment conditions. In most cases, larger enclosures result in slightly lower incident energies as plasma arc events partially dissipate in voluminous enclosures.
How to account for real-world applications
While preliminary, I expect our findings to impact many field applications. Topping the list is additional training that may be required to perform surveys, collect data and complete accurate calculations due to the sheer number of alternatives and variables to consider. In my opinion, consultants and electrical engineers should prepare for significant procedural changes:
- Higher arcing currents calculated using the 2018 Guide could be offset by faster clearing times of the overcurrent protective device (OCPD). Higher currents mean a better chance that protective devices will operate in the instantaneous region and result in faster clearing times. This may offer lower calculated incident energies than the 2002 version, which has a lower arcing current but a longer clearing time.
- Engineers should pay close attention to time-current characteristic (TCC) curves and work to understand relationships between arcing currents and clearing times based on protective device selection and the many settings available.
- The 2018 Guide is not definitive in suggesting a 240V low-end threshold for system analysis, stating only that sustainable arcs are less likely but possible in systems with available short circuit currents of 2000A or less. The former Guide defined a low-end for analysis stating that equipment below 240V not be considered unless it involves at least one 125kVA transformer or larger.
- There is a gap in the methodology used to establish bus configurations for equipment. Clarity and direction should be provided in an application-style guide to help manufacturers and power system engineers understand configurations that apply to diverse electrical components and assemblies.
Implement IEEE 1584 across all systems
I believe consultants and electrical engineers should embrace and begin using the 2018 edition of IEEE 1584 moving forward. As with any new change in engineering practice, I expect an adjustment period during which professionals will acclimate to the Guide’s new calculations. Further, while IEEE 1584 is not a mandatory requirement, I believe more users will accept how the updated Guide enhances safety across all electrical systems, both existing and new:
If you’ve changed your OCPD, its settings, or are approaching the five-year update threshold mandated by National Fire Protection Association (NFPA) 70E Section 130.5(G), calculating incident energy based on IEEE 1584 makes great sense because its models are based on the most current data available.
Higher incident energy calculations should cause users to look for alternative methods of reducing arc flash risk. We’ve determined that some IEEE 1584 calculated incident energies are higher. As a result, engineering controls such as arc reduction maintenance switches and arc quenching technologies will mitigate the risk of increased arc flash energies. Design engineers should take it upon themselves to understand the options of engineering controls to reduce or eliminate the risk of arc flash events.
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