IEEE 1584 -2018 changes offer a robust upgrade
Comprehensive standard review impacts arc flash analysis.
IEEE 1584 was a groundbreaking endeavor when it was originally published in 2002. Though it was soon recognized that there were limitations in the document, it refined previous work and finally gave the electrical industry a method to estimate the amount of incident energy exposure in an arc flash event. It also allowed the arc-flash boundary to be identified.
Throughout the next 16 years IEEE and NFPA committee members collaborated together to do additional testing and produce an update to this milestone document.
The calculations in IEEE 1584 are based upon empirical results from numerous tests. For this latest version of the document, the team completed more than six times the number of tests to refine the calculation methods. This has resulted in a more robust and complex solution. This solution however, sometimes results in lower calculated incident energy and sometimes higher calculated incident energy.
Summary of changes
IEEE 1584-2018 is a considerable rewrite of the 2002 document, but the major impact of the revisions can be summarized as the following items:
- Presents a more complex calculation method.
- The calculations are more robust, handling the full range of voltage from 208 to 15,000 volts.
- Identifies additional electrode configurations.
- Adjusts the results based upon enclosure size, and for systems less than 600 volts, the depth of the enclosure.
- Calculates an adjustment factor for variation of arc current.
- Refines how small, low voltage systems are addressed.
Each of these changes impacts the way that we analyze the arc flash risk in electrical systems.
Calculation methods and voltage range
The calculations are different with more variables. They allow the system to be analyzed based on the physical arrangement of the electrical components. These variables result in more complexity. The results will more accurately approximate the real world incident energy based upon the application of the proper variables.
The formulas are based upon a much wider range of test results. The higher number of tests allowed the document’s authors to more thoroughly model the system from 208-volts to 15,000-volts. This allows the results to be fine-tuned for any system voltage within this range.
The 2018 version of IEEE 1584 is now the current guide for performing arc-flash hazard calculations. Completing an analysis based upon the 2002 version and its associated errata provides out-of-date information.
The tools used to analyze electrical systems need to be updated to use the new calculation methods. Software companies that provide electrical system and arc flash analysis programs have upgraded their software to handle these new methods. The software users will have to upgrade their program licenses to be able to complete the arc-flash analysis based upon the IEEE 1584-2018 methods.
The 2002 document was published based upon data using what is defined as VCB and VOB electrode configurations. The 2018 document recognizes five different electrode configurations. The IEEE 1584-2018 definitions are as follows:
- VCB: Vertical conductors/electrodes inside a metal box/enclosure.
- VCBB: Vertical conductors/electrodes terminated in an insulating barrier inside a metal box/enclosure.
- HCB: Horizontal conductors/electrodes inside a metal box/enclosure.
- VOA: Vertical conductors/electrodes in open air.
- HOA: Horizontal conductors/electrodes in open air.
The HCB directs the arc flash directly out of the enclosure, while the VCBB directs the arc inside of the enclosure until it hits a barrier and then directs the energy out of the enclosure. The VCB directs the arc in the enclosure a further distance. An HCB may be found in a bucket with no breaker or with a fused switch, while a VCBB would be connections above a breaker within an enclosure. IEEE 1584 gives some guidance for classifying enclosure types which can vary for different equipment depending upon the device application within the equipment.
The testing found that the incident energy and resultant arc-flash boundary varied based upon each of the electrode configurations. A relative comparison of these configurations for one set of parameters generally finds: HCB produces the highest incident energy; VCBB and HOA are similar in incident energy and higher than the VCB values from 2002; the VCB results for 2018 are actually lower than 2002 especially as the fault current increases; and, VOA is the lowest but the 2018 values are slightly higher as the fault current increases.
The new version of IEEE 1584 recognizes that electrical equipment comes in various sizes. Because of the additional testing, the calculations are able to provide size adjustment factors that account for different enclosure sizes (height and width) and for certain enclosures in systems less than 600-volts, to account for shallow enclosures.
Variation of arc current
The 2002 version of IEEE 1584 recognized that there was some statistical deviation in the equations, therefore the worst-case incident energy was determined based upon the clearing time at 100% of the arcing current compared to that at 85% of the arcing current. Now the calculation is tightened up and an arcing current variation factor is calculated and applied to determine the lower end arcing current. This now applies to all voltages from 208-volts to 15,000-volts.
Small, low-voltage systems
There has been a long debate on how to handle small, low voltage systems. The information is being refined, but the debate is not resolved. This new standard indicates that “sustainable arcs are possible but less likely in three-phase systems at 240-volts or less when the available fault current is less than 2000A.” Based upon the maximum let through short circuit current of transformers this would apply to 45kVA transformers with impedance (%Z) greater than 6%, 30kVA with %Z greater than 4%, and 15kVA with %Z greater than 2%. In other words, the arc flash risk should be assessed for most 45kVA and larger transformers.
The results will vary as you compare the new calculated incident energy and arc flash boundaries in your system with the older values. Some will be lower. Some may be the same. Some will be higher. The total impact cannot be realized until the arc flash analysis has been updated.
Those responsible for analyzing the hazards in facilities will need to start preparing to implement the changes per the IEEE 1584-2018 guidelines. This will mean that:
- Software will need to be upgraded.
- Time will be needed to identify the enclosure types and sizes.
- Time will be needed to document more information on small, low voltage systems.
- Most system labels will change.
- The incident energy at some equipment may be different enough that the necessary PPE may change, so old habits will need to be changed.
IEEE 1584-2018 is now the current guide for calculating the arc flash hazard in your facility. There is nothing that says that you need to update your analysis immediately. NFPA 70E-2018 130.5(G) states, “The incident energy analysis shall be updated when changes occur in the electrical distribution system that could affect the results of the analysis. The incident energy analysis shall also be reviewed for accuracy at intervals not to exceed five years.” But there is a risk that the actual incident energy and resultant arc-flash boundary at some equipment may be higher than what has been calculated previously. This puts your employees and contractors at more risk than has been identified.
Look at your current results and the associated equipment. Equipment that now would be classified as enclosure type HCB is the most likely to be a higher risk. Equipment that would now be classified as enclosure type VCBB is the next level of risk. If you implement a two-level PPE system, it is likely that those HCB or VCBB enclosures with incident energy designated near your PPE upper limit should now be considered to be tasks requiring the next higher level of PPE, until you can have your arc-flash hazard analysis re-evaluated based upon the new guideline.
NFPA 70E guidelines recommend that your study be re-evaluated every five years unless there is a change to your system. If your study is three years old or older, consider updating your arc-flash hazard analysis now. If it is less than three years old, look at interim solutions and start budgeting for a system update. System updates will require additional field evaluation and modification of most equipment in the model. If you are in the midst of an evaluation now, determine what it will take to complete the study to comply with the new guidelines of IEEE 1584.
Original content can be found at Plant Engineering.