Arc Flash Hazard Analysis: IEEE 1584-2018 Methodology and NFPA 70E-2024 Compliance

Published: June 2026 Technical Level: Advanced Category: Protection Systems

Abstract

Arc flash hazard analysis is the engineering study that quantifies the incident energy a worker may be exposed to during an electrical arc flash event and determines the personal protective equipment (PPE) required to limit the worker's exposure to a survivable level. IEEE Standard 1584-2018, Guide for Performing Arc-Flash Hazard Calculations, establishes the empirically derived equations that relate arc flash incident energy to the available fault current, the equipment configuration, the working distance, and the protective device clearing time. NFPA 70E-2024, Standard for Electrical Safety in the Workplace, establishes the risk assessment procedure, the PPE selection requirements, and the arc flash labeling requirements that implement the IEEE 1584-2018 calculations in a workplace safety program. This paper develops the complete arc flash analysis methodology: the data collection requirements, the IEEE 1584-2018 calculation procedure for the five electrode configurations, the NFPA 70E-2024 PPE selection from the incident energy result, and the arc flash label content that communicates the hazard to workers.

1. Introduction

The IEEE 1584-2018 standard replaced the 2002 edition with an empirical model derived from more than 1,800 arc flash tests across equipment configurations, voltages and current levels. The 2018 model uses five electrode configurations: vertical conductors in a box (VCB), vertical conductors terminating in an insulating barrier in a box (VCBB), horizontal conductors in a box (HCB), vertical conductors in open air (VOA) and horizontal conductors in open air (HOA). They represent the physical arrangements found in switchgear, motor control centers, panelboards, cable junction boxes and open-air equipment. The 2002 model used a single configuration for all enclosed equipment and a grounding distinction the 2018 tests did not support; the 2018 model drops grounding as an input, adds the electrode configuration and an enclosure size correction, and replaces the fixed 85 percent arcing-current reduction with a voltage- and configuration-dependent variation factor.

The engineering significance is that the configuration and the enclosure now change the result materially: the same bolted fault current and clearing time give different incident energies for VCB, VCBB and HCB electrodes, and a shallow enclosure is not treated like a deep one. Studies performed under the 2002 edition should be redone under the 2018 method.

2. IEEE 1584-2018 Calculation Procedure

2.1 Data Collection

The arc flash analysis requires the following input data for each equipment location where workers may perform energized electrical work: the available bolted three-phase fault current at the equipment bus (from the short-circuit study), the electrode configuration (VCB, VCBB, HCB, VOA or HOA), the gap between the electrodes and the enclosure dimensions (Table 8 typical values for standard equipment: 32 mm and a 508 mm cube for low-voltage switchgear, 25 mm for low-voltage MCCs and panelboards, 104 mm for 5 kV and 152 mm for 15 kV switchgear), the working distance from the arc to the worker's face and chest (Table 10 typical values: 609.6 mm for low-voltage switchgear, 457.2 mm for MCCs and panelboards, 914.4 mm for medium-voltage switchgear), and the clearing time of the upstream overcurrent protective device at the arcing current and at the reduced arcing current.

2.2 Arcing Current Calculation

The IEEE 1584-2018 model calculates the arcing current from the bolted fault current, the electrode gap, and the equipment voltage. The arcing current is less than the bolted fault current because the arc itself has finite impedance; the standard provides equations for arcing current as a function of these parameters for each electrode configuration. Because the arcing current is lower than the bolted fault current, the overcurrent protective device may operate on a slower portion of its time-current curve, which increases the arc duration and can substantially increase the incident energy relative to what would be calculated using the bolted fault current as the device lookup value.

The standard requires a second evaluation at a reduced arcing current, $I_{arc,min} = I_{arc}(1 - 0.5\,VarC_f)$ , where the variation correction factor $VarC_f$ of Equation 2 depends on the electrode configuration and the system voltage (about 0.25 for VCB at 480 V, so the reduced current is about 88 percent of the nominal; much smaller at medium voltage). The clearing time is read from the device curve at each current, the incident energy is calculated for both, and the higher result is used. The fixed 85 percent factor of the 2002 edition is gone.

2.3 Incident Energy Calculation

The incident energy at the working distance is, for each voltage level (Equations 3 to 6, coefficients of Tables 3 to 5):

$E = \frac{12.552}{50}\, T \cdot 10^{\left(k_1 + k_2 \lg G + \frac{k_3 I_{arc}}{k_4 I_{bf}^7 + \dots + k_{10} I_{bf}} + k_{11} \lg I_{bf} + k_{12} \lg D + k_{13} \lg I_{arc} + \lg \frac{1}{CF}\right)}$

Where: $E$ is the incident energy in J/cm² (1 cal/cm² = 4.184 J/cm²).

$T$ is the arc duration in milliseconds, from the protective device clearing time at the arcing current.

$I_{arc}$ and $I_{bf}$ are the arcing and bolted fault currents in kA.

$G$ is the electrode gap in mm and $D$ the working distance in mm.

$CF$ is the enclosure size correction factor of clause 4.8 (Tables 6 and 7, Equations 11 to 15), 1 for open-air configurations.

At 600 V and below the 600 V coefficient set applies; above 600 V the result is interpolated between the 600 V, 2700 V and 14,300 V sets (Equations 19 to 24). The 2002 edition's normalized energy $E_n$ , its calculation factor $C_f$ and its distance exponent $x$ do not appear in the 2018 model.

2.4 Worked Example: 600 V Switchgear

Consider a 600 V class metal-enclosed switchgear lineup (low-voltage switchgear preset: VCB configuration, 32 mm gap, 508 x 508 x 508 mm enclosure, 609.6 mm working distance) with a 30 kA bolted fault current, protected by a low-voltage power circuit breaker that clears the arcing fault in 0.10 seconds at both arcing currents. The ZinaVee implementation of the 2018 model gives:

Quantity	Value
Arcing current, nominal	23.634 kA
Arcing current, reduced	20.868 kA
Incident energy at 609.6 mm, nominal case (governs)	16.238 J/cm² = 3.881 cal/cm²
Arc flash boundary	1,271 mm (50 in)
Minimum arc rating of the PPE (NFPA 70E 130.5(G))	3.9 cal/cm²

The result of 3.881 cal/cm² exceeds the 1.2 cal/cm² threshold at which arc-rated PPE is required and sits in the 1.2 to 12 cal/cm² band of Table 130.5(G): arc-rated shirt and pants or coverall with an arc-rated face shield and balaclava or hood, each with an arc rating of at least 3.9 cal/cm². The label for this equipment states 3.9 cal/cm² at 609.6 mm and the 1,271 mm boundary. The example also shows the leverage of clearing time: had the breaker cleared in 0.20 seconds rather than 0.10, the linear dependence on $T$ would double the incident energy to about 7.76 cal/cm², which is why reducing the protective device's operating time at the arcing current is the single most effective engineering control for incident energy.

The dominant influence of clearing time on incident energy is shown in Figure 1, which plots incident energy against protective device clearing time for a fixed available fault current and working distance.

Incident energy as a function of protective device clearing time at fixed arcing current and working distance. The horizontal axis is clearing time in cycles and the vertical axis is incident energy in cal/cm². Because incident energy.

Figure 1. Incident energy as a function of protective device clearing time at fixed arcing current and working distance. The horizontal axis is clearing time in cycles and the vertical axis is incident energy in cal/cm². Because incident energy scales linearly with arc duration, the relationship is a straight line through the origin; the engineer should observe that halving the clearing time halves the incident energy, which is why reducing the upstream device's operating time is the single most effective means of lowering the arc flash hazard.

3. NFPA 70E-2024 PPE Selection

NFPA 70E-2024 130.5(G), the incident energy analysis method, selects PPE directly from the calculated incident energy: arc-rated clothing and equipment with an arc rating (ATPV or EBT) at or above the incident energy at the working distance. Table 130.5(G) lists the equipment in two bands, 1.2 to 12 cal/cm² (arc-rated shirt and pants or coverall, arc-rated face shield and balaclava or hood, hard hat, safety glasses, hearing protection, leather or arc-rated gloves, leather footwear) and greater than 12 cal/cm² (arc-rated clothing with an arc flash suit, suit hood and arc-rated gloves, with the same hard hat, eye, hearing and foot protection). The arc rating applies to the arc-rated items; the hard hat, glasses, hearing protection and footwear are required by their own standards. No PPE category is derived from a calculated incident energy (130.5(G) Informational Note No. 1); the category method of Table 130.7(C)(15) is a separate method, chosen by equipment and task, and the two are not mixed on one piece of equipment. Incident energy above 40 cal/cm² is an extreme hazard: arc-rated PPE at that rating exists, but the arc blast is not addressed by it, and NFPA 70E directs that engineering controls to reduce the incident energy (current-limiting fuses, instantaneous override, shorter clearing time) or de-energized work be applied before energized tasks are permitted.

4. Arc Flash Label Requirements

NFPA 70E-2024 Section 130.5(H) requires that arc flash labels be applied to all electrical equipment where arc flash hazard analysis has been performed. The label must include: the nominal system voltage, the arc flash boundary (the working distance at which the incident energy equals 1.2 cal/cm², the onset of a second-degree burn), the working distance used in the calculation, the available incident energy at the working distance, and the minimum required PPE arc rating. Labels must be updated whenever a modification to the electrical system changes the fault current, clearing time, or equipment configuration at the labeled location.

Conclusion

Arc flash hazard analysis under IEEE 1584-2018 and NFPA 70E-2024 is a deterministic engineering calculation whose result, the incident energy at the working distance and the corresponding PPE requirement, directly governs worker survivability, and the worked 600 V switchgear example developed in this paper demonstrates that the controlling variable is almost always the protective device clearing time rather than the available fault current. Because incident energy scales linearly with arc duration, a reduction in clearing time through faster relay settings, current-limiting devices, or an arc-energy-reduction maintenance switch is the most effective single intervention an engineer can apply to bring the incident energy, and the arc rating the PPE must carry, down to a manageable level. The conclusion for practice is that the arc flash study is not a one-time compliance document but a living analysis that must be revised whenever the upstream protective settings, the available fault current, or the equipment configuration changes, because each of those changes propagates directly into the incident energy result. The label requirements of NFPA 70E-2024 then translate the calculation into the field information that protects the worker at the point of work.

References

[1] IEEE Standard 1584-2018, Guide for Performing Arc-Flash Hazard Calculations, IEEE, 2018.

[2] NFPA 70E, Standard for Electrical Safety in the Workplace, 2024 edition, NFPA, 2024.

[3] NFPA 70, National Electrical Code, 2023 edition, NFPA, 2023.

[4] OSHA Standard 29 CFR 1910.269, Electric Power Generation, Transmission, and Distribution, OSHA, 2014 (updated 2023).

[5] IEEE Standard C37.010-2016, Application Guide for AC High-Voltage Circuit Breakers, IEEE, 2016.

[6] J. C. Das, Arc Flash Hazard Analysis and Mitigation, IEEE Press/Wiley, 2012.

[7] ASTM F1506-22, Standard Performance Specification for Flame Resistant and Arc Rated Textile Materials, ASTM, 2022.

[8] IEEE Standard 242-2001, Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems, IEEE, 2001.