Arc Flash Calculator — IEEE 1584-2018 Incident Energy, Boundary & Arcing Current

Arc flash incident energy under IEEE 1584-2018 — a practical guide

What the IEEE 1584-2018 arc flash model calculates

IEEE 1584-2018 (the IEEE Guide for Performing Arc-Flash Hazard Calculations) is the empirical model used worldwide to quantify the thermal hazard of an arcing fault. From the open-circuit voltage, the available three-phase bolted fault current, the electrode gap, the working distance, the arc duration and the electrode configuration, it predicts three numbers: the average arcing current (the current that actually flows in the arc, always lower than the bolted fault current), the incident energy at the working distance (in cal/cm² and J/cm²), and the arc flash boundary (the distance at which the incident energy falls to 1.2 cal/cm², the onset of a second-degree burn).

The 2018 edition replaced the single 2002 equation with a set of configuration-specific models evaluated at three model voltages — 600 V, 2700 V and 14 300 V — and interpolated to the actual system voltage. The ElecAS arc flash calculator implements that full model, including the enclosure size correction factor and the arcing current variation correction factor, and reproduces the IEEE 1584-2018 Annex D worked examples exactly.

What is arc flash incident energy?

Arc flash incident energy is the amount of thermal energy received on a surface (such as exposed skin) at a given working distance during an arcing fault, measured in calories per square centimetre (cal/cm²) or joules per square centimetre (J/cm², where 1 cal/cm² = 4.184 J/cm²). It is the single number that determines the arc-rated PPE required: the PPE arc rating must equal or exceed the calculated incident energy at the working distance.

The reference threshold is 1.2 cal/cm² (5.0 J/cm²) — the incident energy at which a person receives the onset of a second-degree burn. Incident energy rises with the available fault current, the arc duration and a shorter working distance, and it varies strongly with the electrode configuration. IEEE 1584-2018 is valid for incident energy driven by three-phase arcs from 0.208 kV to 15 kV.

What is the arc flash boundary?

The arc flash boundary is the distance from the prospective arc source at which the incident energy falls to 1.2 cal/cm² (5.0 J/cm²). Anyone closer than the arc flash boundary during an arcing fault could receive at least a second-degree burn, so arc-rated PPE is required inside it. IEEE 1584-2018 derives the boundary by solving the incident energy equation for the distance at which the energy equals that threshold.

The arc flash boundary and the incident energy at the working distance together define the arc flash hazard printed on equipment labels: the boundary tells workers where protection begins, and the incident energy at the working distance tells them what arc rating that protection must have.

What inputs does an IEEE 1584-2018 arc flash calculation need?

The IEEE 1584-2018 model needs six inputs: the electrode configuration (VCB, VCBB, HCB, VOA or HOA), the open-circuit system voltage (kV), the three-phase bolted fault current (kA), the conductor gap between electrodes (mm), the working distance from the arc to the worker (mm) and the arc duration (ms, the protective-device clearing time). Enclosed configurations also need the enclosure height, width and depth.

Each input has a validity range: voltage 0.208–15 kV; bolted fault current 0.5–106 kA below 600 V and 0.2–65 kA from 601 V to 15 kV; conductor gap 6.35–76.2 mm below 600 V and 19.05–254 mm from 601 V to 15 kV; a minimum working distance of 305 mm (12 inches); and an enclosure width of at least four times the conductor gap. Applying the model outside these ranges gives unreliable results, so the ElecAS calculator flags any out-of-range input.

What changed from IEEE 1584-2002 to IEEE 1584-2018?

IEEE 1584-2002 used a single incident-energy equation with an open-air correction. IEEE 1584-2018 replaced it with five electrode-configuration-specific models (three enclosed, two open-air), evaluated at three model voltages (600 V, 2700 V, 14 300 V) and interpolated to the actual voltage. The 2018 edition added an enclosure size correction factor that adjusts the result for enclosures larger or smaller than a 508 mm reference box, and an arcing-current variation correction factor for a mandatory second, lower-bound scenario.

Because electrode configuration and enclosure size now change the answer materially, an arc flash study redone to IEEE 1584-2018 can differ substantially from a 2002 result for the same equipment — often higher for horizontal-electrode and barrier configurations. The ElecAS calculator uses the 2018 model throughout.

Electrode configuration is the most important input

IEEE 1584-2018 defines five electrode configurations, each with its own coefficient set: VCB (vertical electrodes in a metal box), VCBB (vertical electrodes terminated in an insulating barrier in a box), HCB (horizontal electrodes in a box), VOA (vertical electrodes in open air) and HOA (horizontal electrodes in open air). The configuration captures how the arc plasma is directed — a barrier or horizontal geometry pushes more energy toward the worker, so VCBB and HCB generally yield higher incident energy than VCB for the same fault.

Box configurations (VCB, VCBB, HCB) apply the enclosure size correction factor, which adjusts the result for enclosures larger or smaller than the 508 mm × 508 mm × 508 mm reference box, and classify shallow enclosures (below 600 V, height and width under 508 mm, depth ≤ 203.2 mm) separately. Open-air configurations (VOA, HOA) take no enclosure correction. Choosing the configuration that matches the real equipment is the single biggest driver of an accurate result.

Why arcing current and arc duration matter together

The arcing current is not just an output — it is the current at which you read the upstream protective device to find the clearing time. IEEE 1584-2018 arcing current is typically 40–90% of the bolted fault current depending on voltage and configuration, and a lower arcing current can mean a longer clearing time on an inverse-time device, which increases incident energy. Because incident energy scales linearly with arc duration, an accurate clearing time matters as much as the current.

IEEE 1584-2018 also requires a second scenario using a reduced arcing current (via the arcing current variation correction factor) to account for arc current variability — at the reduced current the device may clear more slowly, and the worst-case incident energy of the two scenarios governs. The ElecAS calculator reports both the average and the reduced arcing current so the two clearing times can be checked against the protective device curve.

From incident energy to PPE and labels

The incident energy in cal/cm² at the working distance is the number that drives arc-rated PPE selection — the PPE arc rating (ATPV or EBT) must equal or exceed it. The arc flash boundary defines where arc-rated protection becomes necessary. Common thresholds of 1.2, 4, 8, 25 and 40 cal/cm² band the result, and above 40 cal/cm² the blast hazard is severe enough that energised work should be avoided and the equipment de-energised.

The incident energy result feeds the arc flash risk assessment and the equipment arc flash label. IEEE 1584-2018 gives the incident energy; the arc flash risk assessment, PPE program and labelling are governed by the applicable safety standard (such as NFPA 70E). This calculator is an engineering estimate to support that assessment — it does not replace it, and the results must be confirmed by a competent engineer against the actual protective-device coordination and site conditions.