The IEEE 1584 Model
Inputs (V, Isc, gap, electrode, WD, clearing time) → IE / AFB / PPE.
IEEE 1584 is an empirical regression — not first-principles physics. Researchers ran hundreds of staged arcing tests inside representative enclosures with calibrated calorimeters at known distances. The resulting equations predict the median incident energy a worker absorbs, given the system parameters.
The 2002 version (used in this calculator) covers 208 V – 15 kV with seven coefficients. The 2018 version refines the model with electrode-specific coefficients (so VCB, VCBB, and HCB give different energies even for the same Ibf and gap) and an enclosure-size correction. Production studies should use the 2018 model with vendor software that licenses it; the 2002 model is plenty for teaching the shape of the result.
You’ll see a Model toggle in the calculator below offering both versions. The 2018 option is disabled here — the coefficient table is published only in the licensed standard, and we don’t ship fabricated numbers. For real 2018-model output, run the scenario in SKM, ETAP, or EasyPower. The 2002 numbers here land within ~10–20 % of 2018 for typical LV / VCB configurations: fine for understanding the model’s shape, not for printing a real arc-flash label.
The seven inputs
| Input | Why it matters |
|---|---|
| System voltage | Drives the arcing current and sets which coefficient block applies. Higher V → more energy released per cycle. |
| Bolted Isc | The bigger the available current, the bigger the arcing current that follows. |
| Conductor gap | Wider gap → longer arc → more voltage drop across the arc → more power. |
| Electrode configuration | VCB / VCBB / HCB / VOA / HOA. Affects how much energy is reflected back at the worker (vs scattered into the box, vs going into open air). |
| Working distance | Energy falls off with distance to some power x between 1.4 and 2.0. The exponent depends on equipment type. |
| Clearing time | The arc burns for as long as the upstream device takes to interrupt. Energy is roughly proportional to time. |
| System grounding | Solidly grounded systems tend to produce slightly less arcing-fault energy than ungrounded — the grounding path bleeds some current. |
Try the calculator
The starting state — 480 V / 25 kA / 32 mm / VCB / 24 in / 200 ms — lands around 5.8 cal/cm², which puts you in PPE Category 2 territory: an arc-rated shirt-and-pants (or coverall) ensemble rated ≥ 8 cal/cm², not yet a full flash suit.
Try this — push each input
Clearing time is the lever
Drag t from 200 ms down to 50 ms (3 cycles). Energy drops by 4×. This is the most direct lever an engineer has — and it’s the bridge to the TCC coordination tutorial. Every short-time-delay reduction or instantaneous-trip enable on the upstream device reduces the worker’s incident energy proportionally.
Now push t up to 1 s and the energy reaches ~29 cal/cm² — Cat 4, the top of the PPE scale. Push it on toward 1.5 s and you cross into DANGER territory — no PPE category exists at that level, and energized work isn’t permitted without engineering reduction.
A 1-second clearing time isn’t hypothetical. It’s what you get when:
- The upstream breaker is a service main with its instantaneous off for coordination,
- Its short-time pickup is set above the actual fault current at the bus, and
- Its long-time element takes ~1 s at the fault current it sees.
That combination, perfectly common in older industrial installations, produces lethal arc-flash energies at the bus.
Electrode geometry matters
Switch from VCB (vertical-in-box, like switchgear) to VOA (vertical open air). Energy at the worker drops a little — open-air arcs aren’t reflected back at you by the enclosure walls. But the arc-flash boundary distance grows, because energy radiates outward unimpeded. Open-air arcs are more dangerous to bystanders even though they’re slightly less dangerous to the worker right in front.
Working distance and the inverse-square (-ish)
Switch working distance from 18 in to 36 in. For switchgear, the distance exponent x is 1.473 — so doubling distance reduces energy by 2^1.473 ≈ 2.8×. Not quite inverse-square, but close.
The arc-flash boundary in the label answer is the distance at which incident energy drops to 1.2 cal/cm² — roughly the threshold for second-degree skin burns. If you can stand outside that boundary, you don’t need arc-rated clothing for the task.
Big current isn’t always the worst-case
Drop Ibf from 25 kA down to 5 kA. Counter-intuitively, energy doesn’t drop linearly — and the arcing current as a fraction of Ibf grows at low Ibf. A 5 kA fault with a slow clearing time can deliver as much energy as a 25 kA fault with a fast one. The relationship is nonlinear because:
- Arcing current drops sub-linearly with Ibf.
- The breaker’s clearing time often grows at lower Ibf (you’re walking down its time-current curve into the slow region).
Together these two effects can make moderate fault currents the worst-case for arc-flash, even though they’re not the worst case for breaker AIC or bus bracing. Many real coordination studies find their worst-case incident energy at a current 30–50 % of Ibf.
The two outputs that matter
The label answer has two numbers a worker actually uses:
- Incident energy at working distance (cal/cm²) — sets the arc-rating of the PPE the worker has to be wearing.
- Arc-flash boundary (in or mm) — sets the distance at which any other person needs the same PPE or needs to be physically excluded by barriers.
Once you’ve calculated the incident energy, NFPA 70E’s incident-energy analysis method (130.5(G)) has the worker wear clothing and PPE rated for at least that many cal/cm². The familiar PPE categories come from a separate method (Table 130.7(C)(15)) — the next lesson walks through both, and the rule that you don’t mix them.
What’s next
Lesson 5 turns the same calculator’s output into the label that goes on the equipment door. Categories, boundaries, working distance assumptions — and what to do when the answer is DANGER.