Arc flash calculator
Estimate the energy of an arc flash and its PPE category.
Reads IEEE 1584-2002 and 2018. Tables checked 1 Oct 2026.
Try a job 7
Each job fills in example values. Replace them with your values.
- Estimate arc flash energy at an MCCThe incident energy at 455 mm from a 25 kA MCC, cleared in 0.15 s.
- Estimate arc flash at a main switchboardThe incident energy at 40 kA cleared in 0.3 s.
- Estimate arc flash at a distribution boardThe incident energy at 10 kA cleared in 0.1 s.
- Estimate arc flash in open airThe incident energy with no enclosure.
- Estimate arc flash at 11 kV switchgearThe incident energy at 11 kV and 12 kA.
- Find the boundary at a longer reachThe incident energy and arc flash boundary at a 600 mm working distance.
- Compare a faster clearing timeThe incident energy of a 25 kA fault cleared in 0.05 s.
Inputs
A worked example with the default inputs.
- Model
- IEEE 1584-2018
- System voltage
- 0.4 kV
- Bolted fault current
- 20 kA
- Clearing time
- 0.2 s
- Clearing time at reduced current
- 0 s
- Equipment
- Switchgear
- Electrode configuration
- VCB: vertical conductors in a box
- Electrode gap
- 0 mm
- Enclosure height
- 0 mm
- Enclosure width
- 0 mm
- Enclosure depth
- 0 mm
- Working distance
- 455 mm
Incident energy
7.01cal/cm²
- Arcing current
- 13.64kA
- Reduced arcing current
- 11.9kA
- Arc flash boundary
- 1,373.09mm
- PPE category
- 2
This result is a design aid. Verify it against the current standard.
Calculation steps
- ModelIEEE 1584-2018
IEEE 1584-2018 Cl 4
- Arcing current at 600 V16.27kA
IEEE 1584-2018 Cl 4
- Electrode configurationVCB
IEEE 1584-2018 Cl 4
- Electrode gap32mm
IEEE 1584-2018 Cl 4
- Arcing current13.64kA
IEEE 1584-2018 Cl 4
- Equivalent enclosure size20
IEEE 1584-2018 Cl 4
- Enclosure size correction factor×1.00
IEEE 1584-2018 Cl 4
- Incident energy at the full arcing current7.01cal/cm²
IEEE 1584-2018 Cl 4
- Arcing current variation factor0.26
IEEE 1584-2018 Cl 4
- Reduced arcing current11.9kA
IEEE 1584-2018 Cl 4
- Incident energy at the reduced arcing current6.15cal/cm²
IEEE 1584-2018 Cl 4
- Incident energy, the higher passResult7.01cal/cm²
IEEE 1584-2018 Cl 4
- Arc flash boundary, the higher pass1,373.09mm
IEEE 1584-2018 Cl 4
About this calculator
How this is calculated
The tool estimates the incident energy of an arcing fault. It uses the IEEE 1584-2018 model. It can also run the 2002 model for older studies. IEEE 1584 is not an AS/NZS Standard, so the steps cite its clause only.
- Model. You pick the 2018 or the 2002 model. The 2018 model asks for the electrode configuration and the equipment. The 2002 model asks if the equipment is enclosed and earthed (Cl 4).
- Arcing current. The tool finds the arcing current at 600 V. It then corrects it to your voltage for the electrode gap.
- Enclosure. It works the equivalent enclosure size. It applies the enclosure size correction factor.
- Incident energy. It works the incident energy at the full arcing current. It uses your clearing time and working distance.
- Reduced current. It applies an arcing current variation factor. It works the incident energy again at that lower current.
- Result. The tool keeps the higher of the two passes. It gives the arc flash boundary and the PPE category.
| Step | Table or clause | What it decides |
|---|---|---|
| Arcing current | IEEE 1584-2018 Cl 4 | The current at your voltage and gap |
| Enclosure correction | IEEE 1584-2018 Cl 4 | The effect of the box size |
| Incident energy and boundary | IEEE 1584-2018 Cl 4 | The energy and the distance for the higher pass |
Worked example
- 400 V switchgear with a 20 kA bolted fault and a 0.2 s clearing time. The working distance is 455 mm. The tool gives an arcing current of 13.64 kA and an incident energy of 7.01 cal/cm². The boundary is 1,373.09 mm. The PPE category is 2.
Limits
- The 2018 model covers 208 V to 15 kV. Above 15 kV the tool uses the Lee model, which is a different method.
- The reduced current pass uses the same clearing time. Enter its own time from the device curve.
- The tool takes your bolted fault current and clearing time as given. Get them from a fault level study and the device curve.
- The result is an estimate. It is not a label and it is not a safe-work permit.
See also: Arc flash basics, Incident energy at a 400 V switchboard and Arc flash label for a commercial main switchboard.
Questions
The result is a design aid. Verify against the current standard.
What does the arc flash calculator do?
The tool estimates the arcing current, then the arc flash boundary. It also estimates the incident energy at your working distance, and reports a PPE category for that energy. The steps show each value the model used.
Which model does it use?
A new page uses the IEEE 1584-2018 model. Choose 2002 to match an older study. A link or save made before the 2018 model reads 2002, so its result does not change. Above 15 kV neither model applies, so the tool uses the Lee method and says so.
Which inputs matter most?
The bolted fault current and the clearing time drive the incident energy. The working distance also matters and defaults to 455 mm. In the 2018 model, the electrode configuration and the enclosure size change the energy. VCB, vertical conductors in a box, is the usual switchboard case. In the 2002 model, the enclosed and earthed settings matter.
Why does the 2018 model run twice?
The arcing current varies from test to test. So the tool also runs at a reduced arcing current, which can trip the device more slowly. It reports the higher energy and the larger boundary. Enter the clearing time at the reduced current if your device curve gives a different time.
How is the PPE category decided?
The tool sets the category from the incident energy. The band edges it uses are 1.2, 4, 8, 25 and 40 calories per square centimetre. Above 40 the result is reported as above category 4. Inputs sit in the page address, so a link reproduces the study case.
Worked examples
- IEEE 1584-2002: arc flash model and limitsWhat the IEEE 1584-2002 empirical model governs, where it stops applying, and a 400 V switchboard study that lands on 7.54 cal/cm² at 455 mm.
- Arc flash at a 48 V home batteryClass a 48 V lithium home battery with 6 kA at its terminals by AS/NZS 5139, find its arc flash energy and PPE level, then bring it down with fuses.
- Arc flash boundary at a motor control centreArcing current, incident energy and arc flash boundary for a 400 V MCC at 25 kA with a 0.1 s clearing time, and why the equipment type moves the result.
- Arc flash incident energy at a 400 V switchboardA 400 V board with 20 kA bolted fault and 0.2 s clearing gives 6.23 cal/cm² at 455 mm, an arcing current of 9.64 kA and a 1395.97 mm boundary.
Background
- Battery classes and arc flash in AS/NZS 5139How AS/NZS 5139 classes a battery system by hazard and decisive voltage class, works its arc flash energy, and sets the PPE, consequence and home limits.
- Arc flash basicsArcing current, incident energy, boundary and working distance explained, with three engine runs that show clearing time beating fault current every time.
Clauses and tables this tool reads
- IEEE 1584-2018 Cl 4Arc flash incident energy, 2018 model
- IEEE 1584-2002 Cl 5Arc flash incident energy
- IEEE 1584-2018 Table 1Coefficients for the intermediate average arcing current
- IEEE 1584-2018 Table 2Coefficients for the arcing current variation correction factor
- IEEE 1584-2018 Table 7Enclosure size correction factor coefficients
- IEEE 1584-2018 Tables 3 to 5Coefficients for the intermediate incident energy and arc-flash boundary
- IEEE 1584-2018 Tables 8 and 10Typical bus gaps, enclosure sizes and working distances by equipment class
- IEEE 1584-2002 Cl 5.2–5.6Arc flash incident energy model coefficients
Every clause and table, with how each was verified
Tables last checked on 1 Oct 2026.
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