Arc Flash PPE Selector (IEEE 1584-2018)
Required PPE
Category 1: Arc-rated FR shirt and pants (min 4 cal/cm²), hard hat, safety glasses, hearing protection, leather gloves
Arc Flash Label
ARC FLASH HAZARD Incident Energy: 1.6 cal/cm² at 18" Arc Flash Boundary: 21" PPE 1 Voltage: 480V Fault Current: 25 kA
An arc flash is an explosive release of energy from an electrical fault, and the incident energy it delivers to a worker drives the protective clothing they must wear. This tool follows the IEEE 1584-2018 methodology to estimate arcing current, incident energy in cal/cm², and the arc flash boundary, then maps the result to an NFPA 70E PPE category so you can build a compliant warning label.
Formula
E = 4.184 × 0.24 × Kf × Iarc^1.081 × t × (61 / D)^1.641
- E
- Incident energy at the working distance (cal/cm²)
- Kf
- Electrode-configuration energy factor (1.00 for VCB down to 0.55 for HOA)
- Iarc
- Arcing current (kA), derived from the bolted fault current and voltage
- t
- Arc duration in seconds (arc cycles ÷ 60 at 60 Hz)
- D
- Working distance converted to centimetres (inches × 2.54)
How it works
- Enter the system voltage, the bolted (three-phase) fault current in kA, the working distance in inches, the conductor gap in mm, and pick the electrode configuration (VCB, VCBB, HCB, VOA, or HOA).
- The engine first computes arcing current. For systems at 600 V or below it uses a logarithmic regression of the bolted fault current, voltage, and gap; above 600 V the arcing current is taken as a fixed fraction (85-98%) of the bolted fault current.
- Incident energy is then scaled by the arc duration (cycles divided by 60 for 60 Hz) and the inverse-square-style distance term, the arc flash boundary is solved for the 1.2 cal/cm² burn-onset threshold, and the energy is binned into PPE category 0 through 4.
Worked example
A 480 V switchboard with 25 kA bolted fault current, an 18-inch working distance, a 32 mm gap, VCB electrodes, and a 6-cycle clearing time.
- Arc duration: 6 cycles ÷ 60 = 0.1 s.
- Low-voltage arcing current model gives Iarc ≈ 8.11 kA (about 32% of the 25 kA bolted fault current after the gap and config factors).
- Incident energy: 4.184 × 0.24 × 1.00 × 8.11^1.081 × 0.1 × (61 / 45.72)^1.641 ≈ 1.55 cal/cm².
- Solving the same equation for E = 1.2 cal/cm² gives an arc flash boundary of about 21 inches.
Incident energy ≈ 1.55 cal/cm², arc flash boundary ≈ 21 inches, PPE Category 1 (arc-rated shirt and pants rated at least 4 cal/cm²).
Frequently asked questions
- What is the difference between bolted fault current and arcing current?
- Bolted fault current is the maximum short-circuit current if conductors were solidly connected with no arc. Arcing current is the lower current that actually flows through the plasma of an arc, and it is what determines incident energy. At low voltage the arcing current can be well under half of the bolted value.
- Why does the electrode configuration matter?
- Geometry controls how the arc plasma and pressure wave are directed toward the worker. Vertical conductors in a box (VCB) focus energy outward and are treated as the worst case, while horizontal conductors in open air (HOA) disperse energy and produce roughly half the incident energy for the same fault.
- What does the PPE category tell me?
- NFPA 70E maps incident energy to a category of arc-rated clothing: Category 1 needs at least 4 cal/cm², Category 2 at least 8 cal/cm², Category 3 at least 25 cal/cm², and Category 4 at least 40 cal/cm². Above 40 cal/cm² no PPE is considered adequate and the equipment must be de-energized.
- Is this calculator a substitute for a full arc flash study?
- No. It uses the IEEE 1584-2018 framework for screening and training, but a code-compliant study requires a complete short-circuit and protective-device coordination analysis, often performed by a professional engineer with verified utility and equipment data.