Integrated Arc Flash Software Suite
IEEE 15842018 Arc Flash Incident Energy Calculation
New Standard, New Method, New Learning Curve
IEEE 15842018
The new IEEE 15842018 arc flash model supersedes the IEEE 15842002 model. The development of this new edition of the standard has taken over fifteen years of work and is a result of thousands of hours of research, development and validation. The following sections provide a summary of the main changes of IEEE 1584. ETAP has actively participated in the development and validation of this model to ensure its correct application in power system analysis software.
Model Development
The new model was developed based on over 1800 tests to incorporate different electrode configurations which was much more extensive than the 300 tests used in 2002.
Summary of tests performed:
Electrode Configuration

Tests Performed

Voltage Range

Current Range

Gap Range

VCB

485

0.208 ~ 14.8 kV

0.5 ~ 80 kA

6 ~ 250 mm

VCBB

400

0.215 ~ 14.8 kV

0.5 ~ 65 kA

6 ~ 154 mm

HCB

460

0.215 ~ 14.8 kV

0.5 ~ 63 kA

10 ~ 254 mm

VOA

251

0.240 ~ 14.8 kV

0.5 ~ 65 kA

10 ~ 154 mm

HOA

259

0.240 ~ 14.8 kV

0.5 ~ 66 kA

10 ~ 154 mm

Electrode Configuration
The most important step in implementing the calculations based on the new IEEE 15842018 model, is to identify which one of the five electrode configurations are present in the equipment being analyzed, while also understanding that it is possible to have one or more electrode configurations present in a piece of equipment.
Table 9 of IEEE 15842018 is a good starting point for some guidelines on how to identify the potential electrode configuration(s) present in the equipment.
VOA
HOA
Range of the Model
The range of the voltage and shortcircuit current is similar to that of the previous model. The notable improvement is the range of the gap for mediumvoltage equipment, which has almost doubled.
Model voltage, shortcircuit current, gap and working distance range:
Voltage Range
(3P kV LL)

I_{bf}(kA)

Gap (mm)

WD (inch)

Fault Duration (cycles)

0.208 ≤ V ≤ 0.600

0.5 to 106

6.35 to 76.2

> 12

No Limit*

0.600 < V ≤ 15.0

0.2 to 65

19.05 to 254

> 12

No Limit

Recommended range of the enclosure dimensions:
Enclosure Dimension

Value

Height

14 to 49 (in)*

Width

(4 x Gap) to 49 (in)*

Opening Area

2401 (in2)

Parameters used in testing:
Parameter

Value

Frequency

50 ~ 60 Hz

Phases

3Phase

Configurations

VCB, VCBB, HCB, VOA, HOA

*Larger opening sizes may be modeled but the correction factor is calculated at 49 (in).
IEEE 15842018, Section 4.11 still recommends that the model can be used for singlephase systems and expects the results to be conservative.
Summary of the actual sizes of the test enclosures used to develop the model range:
Equipment Class

Height (mm)

Width (mm)

Depth (mm)

15 kV Switchgear
5 kV Switchgear

1143*

762*

462*

15 kV MCC
5 kV Switchgear

914.4

914.4

914.4

5 kV MCC

660.4

660.4

660.4

LowVoltage Switchgear

508

508

508

Shallow LowVoltage MCCs and Panelboards
Cable Junction Box

355.6*

304.8*

≤ 203.2*

Deep LowVoltage MCCs and Panelboards
Cable Junction Box

355.6*

304.8*

> 203.2*

*Based on IEEE 15842002 enclosure sizes
Voltage Levels
The voltage range applicable to IEEE 1584 remains unchanged at 208V through 15kV.
Low voltage range is now 208V through 600V.
In previous versions of IEEE 1584 (2002) a reference to the Ralph Lee method allowed the possibility to use this method for this condition, yet its results were found to be totally unrealistic. Also, the physical behavior of the arcs and the mode of failure are totally different for overhead openair equipment. The following table presents a concise view of the application of different models across voltage levels between 0.208 kV to 15 kV and higher.
Method 
208 V to 600 V 
601 V to 15 kV 
15.1 kV to 38 kV 
> 38 kV 
Phases1 
3ɸa 
3ɸb 
1ɸa 
1ɸb 
3ɸa 
3ɸb 
1ɸa 
1ɸb 
3ɸa 
3ɸb 
1ɸa 
3ɸa 
3ɸb 
1ɸa 
IEEE 15842002 
G 
G 
Y 
Y 
G 
G 
Y 
Y 
Y 
Y 




IEEE 15842018 
G 
G 
Y 
Y 
G 
G 
Y 
Y 






*ArcFault™ 






G 
Y 
Y 
Y 
G 
Y 

G 
Green (G) – Directly Applicable / Yellow (Y) – Extended with Engineering Assumptions
NonShaded – Not Applicable
Note that the Ralph Lee method should not be used at all for voltages above 15 kV, however, since it was previously applied by ETAP as an alternative to the IEEE 15842002 method, ETAP still has this option available but with a warning.
Arc Current Model (0.208 kV to 0.6 kV)
Perhaps the greatest improvement to the IEEE 15842018 model is its capability to model five different electrode configurations and their effect on the arc current. The main areas of improvement are its improved expected arc physical behavior, its increased sensitivity to gap variation, the correction of inconsistencies (such as cases when Ia > Ibf), etc. Please refer to Annex G.5.5 of IEEE 15842018 for more details on the improvements to the arc current model. The following plot shows a comparative analysis of the arc current predictions of the new model vs. the IEEE 15842002 model.
Arc Current Model (0.6 kV to 15 kV)
Similar to the 2002 method, IEEE 15842018 has two different models for arc current. The mediumvoltage part of the model is described in section 4.4 and 4.9 of IEEE 15842018. The model uses an interpolation approach to apply the effect of the voltage on the arc current. The effect of voltage on the predicted arc current becomes less dominant as the voltage increases.
The new model centers around the calculation of the arc current at three different voltages which are 600, 2700 and 14300 Volts AC. The following plot shows the results of a parameter sweep for shortcircuit current for the mediumvoltage arc current model.
Arc Current Variation Correction Factor
The arc current is the most important factor to determine the operation time of overcurrent protective devices. This is the reason why the new IEEE 15842018 model applied an enhanced arc current model. The arc current predicted by the model is considered to be the average arc current for the duration of the arc. In reality, the arc current can experience variations caused by the ac and dc components of the shortcircuit current. Also, the magnitude of the arc current can vary as the arc ignites, persists and extinguishes. The average current model in 2002 does not include the arc current measured during ignition or extinguishing periods of the arc. It includes only the average of all threephase arc currents.
The physical concept of arc current variation is not changed, however, it was improved. Based on the analysis done during the new arc flash model development phase, it was found that the variation in the arc current was higher at voltages below 480 Volts and far less at voltages such as 600 Volts and 2700 Volts ac.
The value of the arc current variation is no longer fixed to 15% but calculated continuously based on the equations provided in section 4.5 of IEEE 15842018.
The arc current variation was determined from the median of the measured variation at each voltage level. The plot below shows the median arc current variation in percent for each of the five electrode configurations.
Low Voltage Arc Sustainability Limit
The reason the limits were revised is because additional electrode configurations such as VCBB used in the testing revealed that arcs can sustain at much lower shortcircuit currents than previously presented in the 2002 standard.
Previous versions of IEEE 1584 suggested a limit for sustainability at around 240 Volts ac with approximately 125 kVA (or 10 kA with a 3.5% impedance transformer). This left a substantial amount of equipment out of the scope of incident energy calculations. However, since the limit has been lowered to 240 Volt ac with 2.0 kA of shortcircuit current, it means that more systems had to be analyzed. An overlyconservative incident energy correction factor was removed from the lowvoltage model for IEEE 15842018 as shown in the plot below:
As can be observed in this plot, the incident energy results of the new IEEE 15842018 model are more accurate and also less over conservative.
Incident Energy Model – (0.208 kV to 0.6 kV)
The incident energy model is described in great detail in sections 4.3, 4.6, 4.9 and 4.10 of IEEE 15842018. The overall incident energy model is different from that of the 2002 model because it includes the additional three electrode configurations. In addition, for enclosed configurations VCB, VCBB and HCB, an enclosure sizecorrection factor is applied.
The incident energy model follows the same principle as the arc current. An interpolation process is done to determine the incident energy. The interpolation takes place by obtaining intermediate incident energy values at 600, 2700 and 14300 Volts ac.
Incident Energy Model – (0.6 kV to 15 kV)
The plot below shows a comparison of the incident energy for both IEEE 15842018 and 2002 models. The results reveal consistently that if the equipment is determined to now be HCB configuration that the incident energy can be significantly more. In the plot below the incident energy for a VCB configuration, using the 2002 model is 20 cal/cm^{2} while it is predicted to be over 45 cal/cm^{2} using the 2018 model if the HCB electrode configuration is used.
ArcFlash Boundary Model (0.208 to 0.6 kV)
The testing methods used allow the new model to predict shorter boundary distances. The testing and data processing used to develop the new arcflash boundary model reveal a gain in margin which becomes evident when comparing the results of both methods (2002 and 2018).
ArcFlash Boundary Model (0.6 to 15 kV)
Similar to the lowvoltage model, there is a notable reduction in the predicted arcflash boundary. The overly conservative IEEE 15842002 result consistently produces the highest AFB for similar incident energy values.
The plot below shows the arcflash boundary vs the arc duration and compares the 2018 AFB vs the 2002 AFB results. This comparison was made for a system voltage of 2700 Volts ac.
Effect of Grounding on the Incident Energy
Based on the findings of the development group of the new IEEE 15842018 model, the effect of grounding is no longer considered.
Additional Resources