What is incident energy?

Incident energy is the thermal energy radiated by an electric arc that strikes a surface at a working distance. It is measured in calories per square centimeter (cal/cm²) and determines the minimum PPE arc rating a worker must wear.

What IEEE standard does this calculator use?

This calculator applies the legacy empirical equations from IEEE 1584-2002. The current IEEE 1584-2018 model is substantially different and requires additional inputs. This educational implementation covers the 2002 model range of 208 V to 15 kV and 0.7 kA to 106 kA.

What is the arc flash protection boundary?

The arc flash protection boundary (AFB) is the distance from the arc source at which a worker would receive a just-curable burn — 1.2 cal/cm² of incident energy. Unprotected workers must stay beyond this boundary.

Why does working distance matter?

Incident energy decreases with working distance raised to the equipment-specific exponent x. IEEE 1584-2002 uses x = 1.473 for low-voltage switchgear, 1.641 for MCCs/panelboards, 0.973 for medium-voltage switchgear, and 2.000 for open-air/cable configurations.

Which constants are used?

For arcing current at or below 1 kV, K is −0.097 for enclosed equipment and −0.153 for open air. For normalized energy, k1 is −0.555 enclosed or −0.792 open, while k2 is −0.113 for grounded systems and 0 for ungrounded or high-resistance-grounded systems. Cf is 1.5 at or below 1 kV and 1.0 above 1 kV.

What PPE arc rating do I need?

PPE must have an arc rating equal to or greater than the calculated incident energy. NFPA 70E Table 130.5(G) maps cal/cm² ranges to PPE categories (Cat 1: 1.2–4, Cat 2: 4–8, Cat 3: 8–25, Cat 4: 25–40). Above 40 cal/cm², additional engineering controls are needed.

How accurate is this tool?

The IEEE 1584-2002 empirical model carries a ±20–30% uncertainty band. This tool is intended for preliminary assessment and training. A formal arc flash study by a qualified electrical engineer using power-system software is required for compliance labeling.

Arc Flash Incident Energy Calculator

Enter voltage, fault current, enclosure, grounding, gap, distance, and duration to estimate incident energy and boundary with the IEEE 1584-2002 model.

System Parameters

System Voltage (V)

Range: 208 V – 15,000 V (IEEE 1584 scope)

Equipment Type

System Grounding

Bolted Fault Current (kA)

Three-phase bolted short-circuit current (0.7 – 106 kA)

Arcing Gap (mm)

Typical: 25 mm (LV switchgear), 102 mm (5 kV), 152 mm (15 kV)

Working Distance (in)

Typical: 18 in (LV panelboard), 24 in (switchgear), 36 in (MV)

Arc Duration (seconds)

Upstream protective device clearing time (e.g. 0.05 s for 3-cycle breaker)

Results

Arc Current

—

Incident Energy

—

cal/cm²

AFB

—

inches

Intermediate Values

Enter parameters and click Calculate

Disclaimer: Results are based on the IEEE 1584-2002 empirical model (±20–30% uncertainty). This tool is for preliminary assessment and training only. Formal arc flash labels and PPE requirements must be determined by a qualified electrical engineer using validated power-system software per NFPA 70E and applicable OSHA regulations.

Summary

Enter voltage, fault current, enclosure, grounding, gap, distance, and duration to estimate incident energy and boundary with the IEEE 1584-2002 model.

How it works

Enter the system voltage (0.208–15 kV), equipment enclosure, and grounding type.
Enter the bolted three-phase fault current at the point of work.
Set the arcing gap distance (mm) based on equipment voltage class.
Enter the working distance in inches from the arc source to the worker.
Enter the arc duration (trip time of the upstream overcurrent device).
Results show arc current, incident energy in cal/cm², and the arc flash protection boundary.

Use cases

Perform arc flash studies on low-voltage switchgear and panelboards.
Determine the correct PPE category for a live-work task.
Verify the arc flash protection boundary before approach.
Calculate incident energy for medium-voltage (up to 15 kV) equipment.
Support NFPA 70E and OSHA 1910.333 hazard assessments.
Estimate impact of reducing arc duration by selecting a faster upstream breaker.
Compare incident energy at different working distances.
Train electrical workers on how system parameters affect arc flash risk.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu