The Impact of the New IEEE 1584-2018 Standard on Arc Flash Studies
In late 2018, the main standard that defines the arc flash equations, the “IEEE 1584 : Guide for Performing Arc-Flash Hazard Calculations” standard, was updated for the first time since 2002. This new version of the standard brought many changes with regard to arc flash studies. For example, the 125 kVA transformer limit was removed and the electrode configurations and enclosure sizes were added as new parameters in the equations. This webinar, presented by Simon Giard-Leroux, PE at CIMA+, will be an in-depth presentation about the new 2018 version of the standard and its impact on arc flash studies.
Simon's Presentation (PDF)
Answers to Q&A Following Live Webinar
|Question||Answer (Simon Giard-Leroux, P.Eng.)|
|You mentioned using a 2s assumption for the main service entrance equipment due to assumption the utility can change their upstream protective device without notice. Is this assumption stated in the standard or a practice you're recommending?||This is a recommended practice.|
|When barrier dimensions can't be practically measured (maybe due to lack of access) would there be some conservative assumptions for measurements based on configuration/voltage level/etc.? Or would the differences in sizes necessitate accurate measurements of enclosure?||Worst-case results are obtained with smaller enclosure sizes. For conservative assumptions, use small enclosure sizes. Typical dimensions can be found in IEEE 1584-2018 tables or in the EasyPower default library.|
|What is the electrode configuration if it is fuses?||In most cases, HCB.|
|What Cal and AF boundary shall be label equipment that is 240v nominal or less with less than 2000a short circuit current?||Since there is no arc flash danger at this level, no cal or af boundary needs be specified. There is not enough energy to sustain an arc.|
|Are there many changes in incident energy or is it roughly the same?||The energy changes alot when compared to the 2002 version. See the sensitivity analyses in the presentation PDF.|
|The arc flash study could be applied to SF6 panel enclosed?||If there is voltage above 240 V present in the cabinet, yes. If there is voltage below or equal to 240 V present in the cabinet and the available short-circuit current is equal or above 2 kA, yes. Otherwise, no.|
|How are you addressing labelling of empty MCC spare bucket sections which are larger than a single bucket?||Use the enclosure size of the smallest bucket in the arc flash equations & put an identical label on each column of the MCC, depending on the client.|
|For less than 2kA and 240V buses, what stickers do you put? 0 PPE ?||Sticker with shock hazard information only.|
|Just to be sure: a fused switch panel will be VCB?||HCB should be used in most cases.|
|Is the shallow vs typical cutoff voltage less than 600V or less than or equal to 600V?||Less than 600 V.|
|IEEE anex also shows HCB is possible in a 600V MCCB...this is very confusing. Do you have recommendations on how electrode configuration is determined?||True, but an arc flash is very unlikely to occur in the HCB (fig. G.43) configuration on a MCCB and much more likely to uccur in the VCB (fig. G.40) or VCBB (fig. G.41) configurations . It is up to sound engineering judgement to choose reasonable assumptions that represent reality.|
|How will tables in 70E be affected by the new calculation method, particularly for troubleshooting equipment under 600V?||NFPA 70E tables should be updated in the future to updated PPE categories based on the new IEEE 1584-2018 results.|
|How are the AF results comparing with the new standard in comparison to the old one?||It is hard to predict and depends on many factors. In general, the energy is much higher for medium voltage and for equipment with HCB configurations when compared to the 2002 results.|
|Which is the method to work over 15kV from point of view of the snatdard and from EasyPower.||EasyPower has a built-in module to calculate arc flash energy above 15 kV based on ArcPro curves. Lee Method is too conservative for very high voltage values, but could also be used in the 15-25 kV range.|
|Have you performed a case study on an actual facility using both the old method and the new method, and if yes, how different were the results?||Yes, for example for a 300 bus industrial factory with 13.8 kV, 4.16 kV and 600 V equipment, 65% of the PPE categories stayed the same, 34% PPE categories increased with the new 2018 standard and 1% showed a decreased PPE category.|
|For enclosure size, do you mean circuit breaker enclosure size?||Enclosure size represents the size of the panel or mcc/switchgear cell in which the arc flash can occur (metal box).|
|For areas where I am contracted to perform an arc-flash, but I do not know the electrode configuration or the enclosure size, what would you recommend as a default?||Choose a reasonable worst case electrode configuration based on your equipment type (if fuses VS breakers), then enclosure size based on typical values from IEEE 1584 or EasyPower library. Mention to your client that the values were assumed.|
|Example 1 it was stated that the 2 second rule should always be applied at the utility incoming location due to relay times possibly changing by the serving utility. Is the 2 second time to be used on utility incoming locatio when below 15kv? For example, at a 600V switchgear location.||Yes, for all voltage levels.|
|Electrode configuration - so in a bus plug, fuses and on bottom VCB but on top HCB for the bus stabs? = also mccb breaker in 480V switchgear, horizontal yet it's horizontal left and right as worker stands in front so that would be VCBB?||Bus stabs would be HCB.
Yes, for MCCB in 480V switchgear, VCBB if there are no busbars to act as HCB electrodes.
|Don't most of the changes allow for a lower cal rating? In most cases, isn't EasyPower's default settings the most conservative? From a company liabilty aspect and personnel safety, why would we not just use the most conservative values? Example: If the defualt results in 13 cals, and by changing the electrode configuration it results in lower than 12 cals, why would we not just use the 13 cal value?||EasyPower default setting is the least conservative : VCB.
Sound engineering judgment needs to be applied to find values that represent reality. Reasonable worst case assumptions must be used. Using too conservative results would result in asking the client to buy expensive arc flash suits and burden the workers with excessive PPE and lower their dexterity, increasing the risk of accidental short circuits.
|Considering electrical distribution that is not barriered between sections, when calculating the incident energy at the line-side of the main, do you use the main cubicle dimensions or the dimensions of the entire line-up?||If it's not barriered, use the entire line-up dimension.|
|Can you please explain more about Grounding as per IEEE 1584-2018?||Grounding type (wye, delta, etc.) is not a parameter anymore in the new IEEE 1584-2018.|
|Can VCB and VBB appear in a single bucket f an MCC ?||Yes, multiple electrode configuration may be present in a single bucket or switchgear enclosure.|
|A typical single phase 240/120V system is in fact a totally different type of system then a single-phase line which is feed from a three phase 208/120V system. How can you state that we can assume to use a single-phase line to ground fault arc flash value and it will be the same as a single-phase system?||As per IEEE 1584-2018 : "This model does not cover single-phase systems. Arc-flash incident energy testing for single-phase systems has not been searched with enough detail to determine a method for estimating the incident energy. Single-phase systems can be analyzed by using the single-phase bolted fault current to determine the single-phase arcing current (using the equations provided in 4.4 and 4.10). The voltage of the single-phase system (line-to-line, line-to-ground, center tap voltage, etc.) can be used to determine the arcing current. The arcing current can then be used to fnd the protective device opening time and incident energy by using the three-phase equations provided in this guide. The incident Energy result is expected to be conservative."|
|Can you explain how to consider electrode configuration for a fusible disconnect switch with fuse in an MCC bucket? Is that VCBB or HCB at incomer ?||With fuses, it would be HCB, since there is no insulating barrier on a fuse.|
|In the VCBB electrode is there any value of adding non-conductive barriers around the line side of the breaker and then conclude no hazard to person?||I would be careful with this practice. On the label, it should be clear that there is a risk of arc flash when the non-conductive barrier is removed. The barrier can help to avoid accidental contact or short-circuit but labels should still show the energy without the barrier.|
|Single phase system, 2400single phase system 2400v, 2500kva, It appears that I can model this and perform AF calculation using the 3ph formulas from what you say. Not sure I am comfortable with this. My guess is that you are typically looking at 120/240V panelboards with much lower KVA transformers. Any thought on dealing with large single phase systems?||As per IEEE 1584-2018 : "This model does not cover single-phase systems. Arc-flash incident energy testing for single-phase systems has not been searched with enough detail to determine a method for estimating the incident energy. Single-phase systems can be analyzed by using the single-phase bolted fault current to determine the single-phase arcing current (using the equations provided in 4.4 and 4.10). The voltage of the single-phase system (line-to-line, line-to-ground, center tap voltage, etc.) can be used to determine the arcing current. The arcing current can then be used to fnd the protective device opening time and incident energy by using the three-phase equations provided in this guide. The incident Energy result is expected to be conservative."|
|For overhead equipment (utility equipment), is the new 2018 version correctly calculates the arc behavior? (instead of using ArcPro or other method to evaluate arc going up in the air). Older version seemed to be conservative for such cases.||Up to 15 kV, the model is valid for open-air equipment.|
|Does the Arc Flash Boundary goes through the wall?||If the arc flash boundary goes through the wall, then conclude that it is not possible to use and apply the arc flash boundary, which is the distance at which you need to move away from the equipment for the arc flash energy to drop to 1.2 calories/cm2, since there is a physical limitation in the space around the equipment.|
|Should the condition of the enclosure be taken into consideration, and if so how? e.g. A heavily rusted box vs a new one? Or a fiberglass switchgear enclosure vs steel?||Condition of enclosure is not considered in IEEE 1584, so the arc flash label is the same if the equipment is in good vs bad condition. However, for bad condition equipment, live work should be avoided since the arc flash risk is increased, but the energy still stays the same, only the risk of occurence would increase but that is not on the label.|
|For an MCC, is the depth, width or height affected by the fact that their are not necessarily physical barriers between MMC cells?||Yes, the enclosure is defined by the physical barriers.|