Arc flash analysis is the engineering calculation that produces incident energy values, arc flash boundaries, and PPE requirements for specific electrical equipment. It is the technical core of an arc flash study. You feed in system parameters, the model calculates arcing current and incident energy, and the output tells you what PPE a worker needs and how far away they must stay.
The standard method is IEEE 1584, an empirical model developed from laboratory arc flash testing. Understanding what the analysis requires, and what it produces, helps engineers and contractors plan the work correctly and avoid the data gaps that make results unreliable.
Arc flash analysis vs. arc flash risk assessment
These two terms get used interchangeably, but they are not the same thing. The arc flash risk assessment is the broader compliance process NFPA 70E 130.5 requires. It has three components: identifying arc flash hazards, estimating likelihood and severity, and determining required controls.
Arc flash analysis addresses the severity component. It gives you a number: this piece of equipment has an incident energy of X cal/cm² at an 18-inch working distance with a 36-inch arc flash boundary. That number feeds into the risk assessment and determines the PPE selection.
The risk assessment without an analysis is still valid. NFPA 70E allows the PPE category method as an alternative. But the analysis is how facilities get equipment-specific, accurate incident energy values rather than conservative table-based estimates.
Two calculation methods
Incident energy analysis method
The incident energy analysis method uses IEEE 1584 engineering calculations to model the electrical system and compute incident energy at each bus or equipment location. The worker's PPE must have an arc thermal performance value (ATPV) equal to or greater than the calculated incident energy at the specified working distance.
This method requires a power system model built in engineering software. The model must accurately represent transformer impedances, protective device settings, cable data, and available fault current before calculations can run. The output is equipment-specific and accounts for the actual clearing time of the protective device upstream of each piece of equipment.
PPE category method
NFPA 70E Table 130.5(G) assigns PPE categories based on the task being performed and the type of equipment. Category 1 covers tasks with lower arc flash exposure; Category 4 covers the highest hazard level. Each category specifies minimum arc ratings and required PPE items.
No engineering calculations are required for the PPE category method. But the method is conservative by design. It assumes conditions that may not reflect the actual system. For equipment where the real incident energy is low, the table may require heavier PPE than the hazard warrants. For equipment where conditions fall outside the table assumptions, the table method cannot be used at all.
Most industrial facilities commission a formal incident energy analysis. The additional precision has real value when workers wear arc flash PPE regularly in warm environments, and when the analysis result justifies lighter gear than the table would assign.
Required inputs for IEEE 1584 analysis
The accuracy of arc flash analysis results depends entirely on the quality of the input data. Every parameter in the table below affects the output. Missing or wrong values at this stage produce wrong incident energy values downstream.
| Input parameter | Description | Typical source |
|---|---|---|
| Available bolted fault current | Maximum prospective fault current at each bus (kA) | Short circuit study, utility data |
| System voltage | Nominal operating voltage at the point of analysis | Equipment nameplate, one-line diagram |
| Equipment configuration | Open air, VCB, VCBB, HCB, or cable (IEEE 1584 categories) | Field observation |
| Electrode gap | Distance between conductors; varies by voltage class | IEEE 1584 Table 1 defaults or measurement |
| Protective device type and setting | Breaker, fuse, relay; trip curves and setting values | Field data collection, device trip curves |
| Clearing time | Time from fault initiation to current interruption (seconds) | TCC analysis, device trip curves |
| Working distance | Distance from worker's face to the potential arc source (mm or inches) | NFPA 70E Table 130.5(C) or field measurement |
| Grounding type | Solidly grounded, ungrounded, or high-resistance grounded | System documentation, one-line diagram |
Download the free arc flash field data collection checklist covering every data point by equipment type, formatted for field use.
The IEEE 1584 2018 model
IEEE 1584-2018 replaced the original 2002 standard with a substantially revised empirical model based on more than 1,800 arc flash tests conducted across a range of voltages, current levels, and equipment configurations. The 2018 model is more accurate than the 2002 version for most equipment types and voltage levels.
Key differences from the 2002 model:
- Five distinct equipment configurations, each producing different results
- Electrode gap is now an explicit input parameter
- Grounding type affects the arcing current calculation
- Voltage range: 208V to 15kV (the 2002 model was validated for 208V to 15kV but less reliably so)
- Enclosure dimensions affect incident energy in enclosed equipment configurations
Systems outside the 208V to 15kV range require engineering judgment and may need methods beyond IEEE 1584 or careful extrapolation.
Equipment configurations in IEEE 1584
Equipment configuration is one of the most significant variables in arc flash analysis. The same fault current at the same voltage produces different incident energy depending on whether the equipment is open air or enclosed, and how the conductors are oriented inside an enclosure.
Open air (OA)
Arc energy dissipates in all directions. Open air typically produces lower incident energy than enclosed equipment at the same fault current and clearing time. Substations, aerial conductors, and exposed bus work fall into this category.
Vertical conductors or buses in a box (VCB)
The enclosure focuses arc energy toward the worker. This configuration is common in switchgear with vertical bus sections. Incident energy is typically higher than open air for the same parameters.
Vertical conductors or buses in a box with insulating barrier (VCBB)
Similar to VCB but with an insulating barrier that changes arc behavior. The barrier redirects some arc energy and typically results in lower incident energy than a standard VCB configuration.
Horizontal conductors or buses in a box (HCB)
Common in panelboards and some MCCs with horizontal bus arrangement. Arc behavior in this configuration differs from vertical bus configurations.
Cable systems
The cable configuration applies to cable terminations in trays or conduit. Arc behavior in cable systems is distinct from bus-based equipment.
Selecting the wrong configuration during analysis produces wrong incident energy results. This requires a field engineer who understands both the software model and the actual equipment construction.
What arc flash analysis produces
For each equipment location analyzed, the output includes four primary values:
- Arcing current: The current that actually flows through an arcing fault, calculated as a function of bolted fault current, voltage, and electrode gap. Arcing current is lower than bolted fault current because arc impedance limits current flow. IEEE 1584 calculates both a maximum and minimum arcing current to account for the range of protective device response.
- Incident energy: The thermal energy in cal/cm² that a worker at the specified working distance would receive if an arc flash event occurred. This drives the PPE arc rating requirement.
- Arc flash boundary: The distance from the potential arc source at which incident energy equals 1.2 cal/cm². Workers inside this distance require arc-rated PPE.
- Required PPE arc rating: The minimum ATPV or Ebt in cal/cm² that PPE must meet to protect a worker at the working distance. This comes directly from the incident energy result.
The analysis also feeds equipment labels. NFPA 70E 130.5(H)(1) requires labels to show nominal system voltage, arc flash boundary, and the incident energy with working distance or the PPE category.
Who performs arc flash analysis
Arc flash analysis requires power system engineering expertise. The short circuit study, coordination study, and arc flash calculations are performed by a licensed professional engineer or an engineering firm with qualified power system engineers.
The software platforms used for these calculations are SKM PowerTools, ETAP, and EasyPower. Each platform performs the full sequence: load flow, short circuit, protective device coordination, and arc flash analysis. The final report and equipment labels carry the engineer's seal.
The field work, collecting nameplate data and documenting the electrical system, can be performed by qualified technicians under engineering direction. But building the model, running the calculations, and interpreting the results are engineering tasks. See the broader arc flash study overview for how all the phases fit together.
Why data accuracy determines result quality
The IEEE 1584 model is only as accurate as what you put into it. The field data collection phase is where arc flash studies most often produce unreliable results.
A wrong transformer impedance value shifts fault current calculations at every downstream bus. Incorrect breaker trip settings change clearing times and therefore incident energy at every piece of equipment that breaker protects. Missing cable data affects impedance values throughout the model. Each error compounds as it flows through the calculation sequence.
These errors are easy to make during traditional field data collection. Nameplates are dirty. Equipment is in tight spaces with poor lighting. A technician hand-writing data from a nameplate in an MCC room at the end of a long shift misses a digit. That digit ends up in the model. The analysis runs. The result looks reasonable. But the label on the equipment understates the actual hazard.
70Ez was built for this problem. Field technicians photograph equipment nameplates. The AI reads nameplate data and populates project records. The team verifies. The data exports directly to SKM PowerTools, ETAP, or EasyPower, organized by equipment type and project. Manual transcription is eliminated as a step. See how arc flash data collection works with modern tools, and start a free trial to see the workflow.
Common arc flash analysis errors
Field engineers and quality reviewers should watch for these issues when auditing arc flash study results:
- One-line diagram that does not reflect current equipment configuration
- Transformer impedance taken from nameplate rather than tested values (these can differ by 10% or more)
- Instantaneous trip settings that have been changed but not updated in the model
- Wrong equipment configuration selected in the software (VCB vs. HCB vs. open air)
- Working distances that do not match actual field conditions for the tasks being performed
- Missing contributions from motors, which affect available fault current at bus locations
The short circuit and coordination study is always performed first. The arc flash analysis depends on fault current values and clearing times from those studies. Errors there propagate directly into arc flash results.
Frequently asked questions
How long does arc flash analysis take?
The engineering analysis phase, once the power system model is built and validated, typically takes two to five days for most facilities. Building the model from field data adds time, particularly if the facility does not have a current one-line diagram. The full study process from start to final report ranges from two to eight weeks depending on facility size and complexity. See our arc flash study cost guide for a breakdown of time and cost by facility type.
Can arc flash analysis be performed on a system that has not been updated in years?
Yes, but the engineer must first verify that the model reflects current conditions. Equipment added or replaced since the last study must be incorporated. Protective device settings must be confirmed against current configurations. NFPA 70E 130.5(G)(1)(d) requires review of the incident energy analysis at intervals not to exceed five years precisely because systems change over time.
Does arc flash analysis cover DC systems?
IEEE 1584 covers three-phase AC systems. DC arc flash is a separate calculation with different methodology. NFPA 70E does address DC systems, but IEEE 1584 does not apply. DC arc flash calculations use methods from other references, and the results differ significantly from AC arc flash behavior at the same voltage and current level.
What software is used for arc flash analysis?
The major platforms are SKM PowerTools, ETAP, and EasyPower. All three perform short circuit studies, coordination studies, and IEEE 1584 arc flash calculations. The choice often comes down to what the engineer's firm uses or what the existing power system model was built in. See our arc flash study software guide for a comparison.
What is the relationship between arc flash analysis and the short circuit study?
The short circuit study calculates available fault current at each bus in the electrical system. Arc flash analysis uses those fault current values, along with protective device clearing times from the coordination study, to calculate incident energy. The three studies are performed in sequence as part of a complete power system study. Running arc flash calculations without first completing a short circuit study produces incorrect results.