Arc-Flash Incident Energy and Boundary (IEEE 1584-2018)

Empirical model of IEEE Std 1584-2018 for three-phase 208 V to 15 kV equipment, 50 or 60 Hz.

Steps

1. Intermediate arcing currents, Equation (1), at 600, 2700 and 14300 V:

2. Final arcing current. Above 600 V the three values are interpolated, Equations (16)-(18); up to 600 V Equation (25) is used.
3. Arcing current variation, Equation (2): $I_{arc,min} = I_{arc}(1 - 0.5\,VarC_f)$, applied to the intermediate currents above 600 V and to the final current up to 600 V.
4. Arc duration is read by the user from the time-current curve of the protective device at $I_{arc}$ and at $I_{arc,min}$ (6.9).
5. Enclosure correction factor CF from the equivalent enclosure size, Table 6, Equations (11)-(15) and Table 7 (CF = 1 for open air).
6. Incident energy, Equations (3)-(6):

Above 600 V it is evaluated at 600, 2700 and 14300 V and interpolated, Equations (19)-(21). Up to 600 V, Equation (6) takes $I_{arc,600}$ in the $k_3$ term and the final $I_{arc}$ in the $k_{13}$ term.

7. Arc-flash boundary, Equations (7)-(10): the distance at which the incident energy is 5.0 J/cm2 (1.2 cal/cm2); interpolated like E.
8. Both cases (average and reduced arcing current) are calculated; the final E and AFB are the higher of the two (4.5).

Incident energy in cal/cm2 is E in J/cm2 divided by 4.184.

The results depend on the input data, above all on the protective device clearing times and the equipment data, which the user must verify. The model has a stated range and uncertainty, and real events can differ from it. The author and the publisher accept no liability for decisions made on these results.

• The model and all coefficients are taken from IEEE Std 1584-2018 (Tables 1 to 7, Equations (1) to (25)); they were transcribed from the standard, not derived here.
• The arc duration is an input: it comes from the protective device curves and is not calculated here. Use the longest time of a band, the total clearing time of fuses, and add the breaker opening time where the curves do not include it (6.9).
• Voc is taken equal to the system nominal voltage (allowed by 4.2).
• Enclosure sizes above 1244.6 mm are treated as 1244.6 mm; the depth only decides shallow or typical (4.8).
• The result is the incident energy at the working distance for a worker's face and chest; it is not a PPE category. Choosing PPE follows another standard (for example NFPA 70E) and is not part of IEEE 1584.
• Single-phase and dc systems are outside the model; the special models for current-limiting fuses (Annex H) and circuit breakers (Annex I) are not included.
• The diagram is a section through the arc drawn to scale: the arc is taken at the centre of the enclosure, the boundary is a circle around it, and the electrodes are not drawn.
• Not verified here: the protective device times you enter, and the enclosure and electrode data of your equipment.

• Voltage 208 V to 15 000 V, three-phase, 50 or 60 Hz.
• Bolted fault current: 0.5 to 106 kA (208-600 V), 0.2 to 65 kA (601-15 000 V).
• Gap: 6.35 to 76.2 mm (208-600 V), 19.05 to 254 mm (601-15 000 V).
• Working distance 305 mm or more.
• Enclosure: largest side up to 1244.6 mm, opening area up to 1.549 m2, width more than four times the gap.
• Outside these ranges the tool shows a warning and the result is an extrapolation.
• Sustained arcs are possible but unlikely at 240 V or less with a bolted fault current below 2 kA.