Arc-Flash Incident-Energy Screen (Lee 1982)
Simplified pre-IEEE-1584 incident-energy estimate and PPE band.
Example
You enter
- System voltage (V) 480
- Bolted-fault current (A) 25000
- Arc clearing time (s) 0.1
- Working distance (in) 18
- Equipment configuration open_air
You get
- Incident energy (cal/cm²) 2.94
- Arc-flash boundary (in) 28.2
Details, formula, and sources
Screen only; not an IEEE 1584 study.
E_lee (cal/cm^2 at distance D in inches) = (7.935e-4 * V * I_bf * t) / D^2, with V in volts, I_bf in amps. The 7.935e-4 coefficient is the Lee (IEEE 1584) constant 2.142e6 (stated for kV, kA, mm and J/cm^2) re-expressed for volts, amps, inches and cal/cm^2: 2.142e6 / (1000 * 1000 * 25.4^2 * 4.184). Boundary distance D_b = sqrt((7.935e-4 * V * I_bf * t) / 1.2). PPE category band looked up against the NFPA 70E Table 130.7(C)(15)(c) ranges (table cited by name only; not reproduced).
NFPA 70E-2024 §130.5 governs the arc-flash risk assessment. IEEE 1584-2018 is the study-grade method.
Free read-only access at nfpa.org/freeaccess. for NFPA 70E TOC and Annex D.
Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
Field names used by the API: voltage_V, bolted_fault_A, clearing_time_s, working_distance_in, equipment_config, incident_energy_cal_cm2, boundary_distance_in
- Equation source Ralph Lee 1982 closed-form, pre-IEEE-1584Lee, R.H., 'The Other Electrical Hazard: Electric Arc Blast Burns', IEEE Trans. on Industry Applications, 1982
- Second-degree threshold 1.2 cal/cm^2NFPA 70E hazard threshold
- Conservatism Lee is conservative below 600 V open-air but may be non-conservative for some 480 V box configurations covered by IEEE 1584engineering practice; IEEE 1584-2018 commentary
- PPE category bands 1.2 / 4 / 8 / 25 / 40 cal/cm^2 breakpointsNFPA 70E Table 130.7(C)(15)(c) ranges; table not reproduced