Arc Flash Calculator

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.