Arc Flash Calculator

Parameters

Eleven inputs feed the model. Three are required, the rest carry defaults and can be filled in for you by the equipment class selector. This is what each one means, what it is measured in, the range it accepts, and how much it actually moves the answer in this implementation.

Equipment class

A shortcut that fills the conductor gap, working distance, enclosure dimensions, electrode configuration, and enclosure type with the typical values for that kind of equipment. The options are LV switchgear and switchboards, LV motor control centre or panelboard, MV switchgear to 5 kV, MV switchgear to 15 kV, open air conductors and bus work, and custom.

Default. Custom, which fills nothing. Picking any other class writes its typical values into the form, and every field stays editable afterwards.

Gotcha. The class is also passed to the engine, so if you override the working distance or the gap the calculator warns you that the value differs from the class typical. That warning is informational, not a failure.

System voltage (kilovolts)

The nominal system voltage at the equipment. Enter 0.4 for a 400 V board, 0.415 for 415 V, 11 for an 11 kV switchboard.

Valid range. The engine validator accepts 0.208 to 15 kV.

Gotcha. Voltage is used only to pick a band of coefficients: at or below 0.6 kV, 0.6 to 1.0 kV, 1.0 to 5.0 kV, and above 5 kV. Every low-voltage system from 230 V to 600 V therefore returns identical coefficients, and the result changes in steps at the band edges rather than smoothly.

Bolted fault current (kiloamperes)

The prospective three-phase short-circuit current at the equipment terminals, taken from a fault study or from the transformer impedance and cable impedances back to the source.

Typical range. 10 to 50 kA at a low-voltage main switchboard fed by a distribution transformer, lower at a subboard down a long cable run.

Gotcha. Incident energy rises with roughly the square of the arcing current at low voltage, so this input dominates the output. The simplified model used here overstates energy badly at high fault currents, which is covered under assumptions below.

Arc duration (seconds)

How long the arc burns before the upstream device clears it. That is the protective device operating time at the arcing current, plus the breaker opening time.

Typical range. 0.05 to 0.1 s behind a current-limiting fuse, 0.2 to 0.5 s behind a graded relay, up to 2 s where an upstream device is slow. The form accepts 0.01 to 10 s and the validator rejects anything above 30 s.

Gotcha. Incident energy is directly proportional to this value. Double the clearing time and you double the energy. It is the cheapest lever you have, which is why protection settings and arc flash risk are the same conversation.

Working distance (millimetres)

Distance from the prospective arc source to the worker face and chest, not to their hands.

Typical values. The IEEE 1584 standard distances are 455 mm for low-voltage switchgear, 610 mm for medium voltage, and 910 mm for high voltage. The form accepts 100 to 3000 mm and the validator rejects anything above 5000 mm.

Gotcha. At and below 5 kV the model divides by distance squared, so energy falls off very fast with distance. Going from 450 mm to 900 mm cuts the calculated energy to a quarter.

Electrode configuration (VCB, VCBB, HCB, VOA, HOA)

The geometry of the conductors at the arc point: vertical or horizontal, in a box or in open air. Most low-voltage switchboards are VCB or VCBB, and open outdoor bus work is VOA or HOA.

What it does. The selection applies two factors, both normalised so that VCB is 1.000. The arcing current factor is 1.00 for VCB, 1.03 for VCBB, 0.99 for HCB, 0.93 for VOA, and 0.91 for HOA. The incident energy factor is 1.00 for VCB, 1.28 for VCBB, 1.12 for HCB, 0.60 for VOA, and 0.52 for HOA. Running the same figures as VCB and as HOA now returns roughly half the incident energy and a smaller boundary.

Gotcha. A full IEEE 1584:2018 study uses a separate published coefficient set per configuration rather than a single relative factor. These factors are indicative and pending verification, so read them as the shape of the effect, not its exact size.

Gap between conductors (millimetres)

The physical arc gap between phases at the fault point. The dropdown offers 25, 32, 50, 104, and 152 mm, with 32 mm the usual low-voltage switchboard value and 104 or 152 mm typical for medium-voltage switchgear.

Gotcha. At or below 0.6 kV the gap coefficient is zero, so on a low-voltage system the gap has no effect on the result at all. Above 0.6 kV it increases the calculated arcing current. The dropdown values now match the 25 to 152 mm range the engine validator expects.

Enclosure type (open air or enclosed box)

Whether the arc is inside an enclosure that channels the plasma toward the worker, or in free air. Sits under advanced options.

What it does. Enclosed box switches on the enclosure size correction described below and adds a compliance check that the enclosure sits inside the modelled size range. Open air sets the correction factor to exactly 1.000 and ignores the three dimension fields entirely. If you leave a box electrode configuration selected while choosing open air, the calculator warns about the mismatch.

Enclosure height, width, and depth (millimetres)

The internal dimensions of the enclosure the arc occurs in. Under advanced options, and only used when the enclosure type is enclosed box.

Defaults. A 508 by 508 by 508 mm box, the nominal 20 inch cube the IEEE 1584 box tests are built around. That reference box returns a correction factor of exactly 1.000, so the default result is unchanged from before these inputs existed.

What it does. Height and width give an equivalent enclosure size, the mean of the two. The size factor is 508 divided by that mean, raised to 0.35 at low voltage, 0.30 to 5 kV, and 0.25 above. A smaller box concentrates the plasma toward the opening and raises incident energy; a larger box lowers it. Depth below 203.2 mm marks a shallow box and adds up to a further 10 percent. The two factors multiply into a single correction factor, clamped to 0.70 to 1.75, that scales both incident energy and the boundary.

Gotcha. The equivalent size is clamped to 100 to 1244 mm, roughly the 4 inch to 49 inch span of the box model. Outside that the correction is capped, a warning appears, and the enclosure size check fails.

Assumptions and limits

Read this section before you use any number from this page. The arc flash engine is the most heavily simplified calculator on the site, and the gap between what it returns and what a compliant study returns is large.

The model actually used

Arcing current is calculated as the base-10 logarithm of the bolted fault current plus a voltage-band coefficient K1, plus a second coefficient K2 multiplied by the base-10 logarithm of the gap, then multiplied by an electrode configuration factor. Incident energy is then an effective constant multiplied by arc duration, multiplied by arcing current raised to an exponent x, divided by working distance in metres raised to an exponent y. The effective constant is the voltage-band constant C multiplied by the electrode configuration energy factor and by the enclosure correction factor. At or below 0.6 kV the constants are K1 equals minus 0.097, K2 equals 0, C equals 2.331, x equals 1.966, and y equals 2.0.

Both the electrode configuration factors and the enclosure correction are normalised so that the defaults, VCB in a 508 by 508 by 508 mm box, return factors of exactly 1.000. Leaving every optional input alone therefore reproduces the earlier, simpler model figure for figure.

Known limitations

• These are linearised placeholder coefficients, not the published IEEE 1584:2018 table coefficients. The electrode configuration factors and the enclosure size correction are indicative relative factors rather than the per-configuration coefficient sets published in the standard, and there is none of the interpolation between the 600 V, 2700 V, and 14300 V model points that the standard requires.
• The divergence from a real study grows quickly with fault current and duration. At 20 kA and 0.5 seconds at 450 mm the model returns about 1,340 calories per square centimetre, far above what a compliant IEEE 1584:2018 study produces for the same switchboard. Treat results at high fault current as order-of-magnitude nonsense rather than a conservative estimate.
• Above 0.6 kV with a large gap the arcing current formula can return a value greater than the bolted fault current, which is not physically possible. Real arcing current is always a fraction of bolted fault current. The calculator now flags this in the notes panel when it happens, but it does not correct it.
• The check labelled working distance against arc flash boundary passes when your working distance is inside the boundary. Read it as a statement of where the boundary sits relative to you, not as a safety verdict. The first check compares incident energy against 1.2 calories per square centimetre and will fail for almost any real fault, because 1.2 is the second-degree burn threshold, not a pass mark.
• PPE categories are assigned at 4, 8, 25, and 40 calories per square centimetre. That means category 1 here covers everything up to 4, which is wider than the NFPA 70E category 1 band that ends at 1.2. Do not read the returned category straight onto a PPE schedule.
• There is no arc sustainability check at low voltage, no minimum-arcing-current sensitivity run at 85 percent, no DC arc flash model, and no credit for current-limiting devices, arc quenching systems, or maintenance switching modes.

What this must not be used for

• Producing or updating an arc flash hazard label for a switchboard.
• Selecting the arc rating of PPE for a work party, or deciding that live work is acceptable.
• Serving as the record of an arc flash study, or as evidence in a safe work method statement.
• Setting an arc duration figure for insurance, audit, or regulatory purposes.

What it is genuinely useful for is intuition: seeing how halving the clearing time halves the energy, and how doubling the working distance quarters it. An arc flash study for an Australian installation must be carried out to IEEE 1584:2018 by a competent engineer, checked against the current edition of the standard and AS/NZS 4836, reviewed whenever protection settings or system topology change, and signed off by the person responsible for the installation. Nothing on this page has been validated or certified.

Worked examples

Four runs through the equations exactly as the calculator implements them. The figures below are what the tool returns, not what a compliant IEEE 1584:2018 study would return. Examples 1 to 3 leave the advanced options at their defaults, so the electrode factor and the enclosure correction are both 1.000.

Arc Flash Analysis for IEEE 1584:2018

Arc flash is the sudden release of thermal and radiant energy during an electrical fault. It can reach temperatures of 19,000 °C in milliseconds and produce pressure waves strong enough to throw a worker across a switch room. This calculator implements the IEEE 1584:2018 model to determine the incident energy at a defined working distance, the arc flash boundary, and the corresponding PPE category required to keep a worker survivable.

Arc flash calculation walkthrough

A typical analysis follows six steps:

1. Bolted fault current. The prospective short-circuit current at the equipment, calculated from source impedance, transformer impedance, and cable impedances.
2. Arc duration. The time the upstream protective device takes to clear the fault, looked up from its operating curve at the bolted fault current.
3. Electrode configuration. VCB, VCBB, HCB, VOA, or HOA. Matches your equipment geometry.
4. Gap between conductors. Typically 32 mm for LV switchgear, larger for MV.
5. Working distance. 455 mm for LV per IEEE 1584 Table 9, longer for higher voltages.
6. Solve. The calculator applies the IEEE 1584 model and returns incident energy, boundary, and PPE category.

Electrode configurations explained

• VCB. Vertical Conductors in a Box. Most common for LV switchboards. Plasma jet directs out of the box toward the worker.
• VCBB. Vertical Conductors in a Box with Barrier. Same as VCB but with an insulating barrier; reduces incident energy 5 to 20%.
• HCB. Horizontal Conductors in a Box. Used when bus bars run horizontally inside enclosed switchgear.
• VOA. Vertical Open Air. Outdoor bus bar arrangements. Lower incident energy than enclosed for the same fault current.
• HOA. Horizontal Open Air. Outdoor horizontal conductors. Lowest incident energy of the five.

PPE category selection (NFPA 70E)

The calculated incident energy maps to one of four categories:

• Category 1 (≤ 1.2 cal/cm²): arc-rated long- sleeve shirt + pants, safety glasses, hard hat, hearing protection, leather gloves.
• Category 2 (1.2 to 8 cal/cm²): arc-rated shirt + pants OR coverall, arc-rated face shield with balaclava OR hood, hearing protection.
• Category 3 (8 to 25 cal/cm²): multi-layer arc flash suit, hood, gloves; total system rating ≥ incident energy.
• Category 4 (> 25 cal/cm²): full hazmat-style arc suit + SCBA. Consider de-energising before any work at this level.

How to reduce arc flash hazard

Three levers, in order of effectiveness:

1. De-energise before work. Always the first option per AS/NZS 4836.
2. Lower the arc duration by reducing upstream relay settings, within selectivity constraints. Halving arc time roughly halves incident energy.
3. Increase working distance via remote racking, live-line tools, or insulating barriers. Incident energy falls with the square of distance.