What is an arc flash study?

An arc flash study calculates the incident energy (cal/cm2) at each piece of electrical equipment in a facility using IEEE 1584-2018 methodology. The study determines PPE requirements, arc flash boundaries, and equipment label data. It requires short-circuit analysis, protective device coordination data, and equipment configuration details. Results identify high-hazard equipment and guide engineering mitigation strategies.

How can arc flash incident energy be reduced?

The most effective arc flash mitigation reduces fault clearing time through bus differential protection (87B), arc flash detection relays (clearing in 2 cycles), zone-selective interlocking (ZSI), and maintenance mode relay settings. Additional strategies include current-limiting fuses, high-resistance grounding to limit ground fault current, and increasing working distance through remote racking and operation. These engineering controls can reduce incident energy by 80-90%.

When should an arc flash study be updated?

Arc flash studies should be updated whenever the power system changes: utility fault current modifications, transformer additions or replacements, protective device setting changes, switchgear modifications, or new load additions. NFPA 70E recommends reviewing the study for accuracy whenever changes occur that could affect arc flash hazard levels. Many facilities establish a 5-year review cycle as a maximum interval.

Arc Flash Analysis and Mitigation

Understanding Arc Flash Hazards

An arc flash is a violent electrical discharge through air that occurs during a short circuit or fault condition in electrical equipment. The arc generates temperatures exceeding 35,000 degrees Fahrenheit (four times the surface temperature of the sun), producing an explosive blast of superheated plasma, molten metal, shrapnel, and intense light. Arc flash events cause severe burns, blindness, hearing damage, and fatalities. OSHA and NFPA 70E require employers to perform arc flash risk assessments and implement protective measures for workers who interact with energized electrical equipment.

NFM Consulting performs comprehensive arc flash studies compliant with IEEE 1584-2018 and NFPA 70E-2024. Our analysis identifies high-hazard equipment, quantifies incident energy levels, specifies PPE requirements, and recommends engineering controls to reduce arc flash risk to the lowest practicable level.

IEEE 1584 Arc Flash Calculations

IEEE 1584-2018 (Guide for Performing Arc-Flash Hazard Calculations) provides the empirical equations for calculating incident energy based on:

Arcing current: Calculated from the bolted fault current, system voltage, electrode configuration, and gap between conductors
Arc duration: Determined by the operating time of the upstream protective device at the calculated arcing current (the most significant variable in incident energy calculation)
Working distance: The distance from the arc source to the worker's face and chest, typically 18 inches for panelboards and 24-36 inches for switchgear
Electrode configuration: The physical arrangement of conductors (VCB = vertical conductors in a box, VCBB = vertical conductors terminated in a barrier, HCB = horizontal conductors in a box, VOA = vertical conductors in open air, HOA = horizontal conductors in open air)
Enclosure dimensions: Width, height, and depth of the equipment enclosure, which affects arc energy concentration

NFPA 70E PPE Categories

NFPA 70E defines PPE categories based on incident energy levels:

PPE Category 1 (4 cal/cm2): Arc-rated long sleeve shirt, pants, safety glasses, hearing protection, leather gloves
PPE Category 2 (8 cal/cm2): Arc-rated shirt, pants, arc-rated face shield with balaclava, hearing protection, leather gloves
PPE Category 3 (25 cal/cm2): Arc flash suit hood, arc-rated jacket, pants, arc-rated gloves, hearing protection
PPE Category 4 (40 cal/cm2): Multi-layer arc flash suit, arc-rated hood with face shield, arc-rated gloves, hearing protection

Equipment with incident energy exceeding 40 cal/cm2 is considered too dangerous for any PPE-based approach. Engineering controls must be implemented to reduce incident energy below 40 cal/cm2 before energized work is permitted.

Arc Flash Mitigation Strategies

Reducing Arc Duration

Since arc duration is the most significant factor in incident energy, the most effective mitigation strategies focus on clearing faults faster:

Bus differential protection (87B): Detects bus faults in 1-2 cycles and trips the source breaker with minimal time delay. Reduces arc flash incident energy by 80-90% compared to time-overcurrent protection alone.
Arc flash detection relays: Light-sensing relays (such as SEL-751A or ABB REA) detect the intense light from an arc flash and trip the source breaker within 35 milliseconds (approximately 2 cycles), dramatically reducing incident energy
Zone-selective interlocking (ZSI): A communication scheme between series overcurrent devices where a downstream device sends a restraint signal to the upstream device. If no restraint signal is received, the upstream device trips instantaneously rather than waiting for its time delay.
Maintenance mode settings: Temporarily lowering relay pickup settings or enabling instantaneous trip elements during maintenance activities to reduce arc duration. Settings are returned to normal after maintenance.

Reducing Fault Current

Reducing the magnitude of arcing current also reduces incident energy, though less effectively than reducing duration:

Current-limiting fuses: Fuses that clear faults in less than one-half cycle, limiting the let-through current and energy
Current-limiting reactors: Series reactors that limit fault current contribution from specific sources
High-resistance grounding: Limits ground fault current to 5-10 amperes, effectively eliminating arc flash hazard from single-line-to-ground faults (which represent 95% of all faults)

Increasing Working Distance

Remote racking devices, remote breaker operation, and infrared viewing ports allow workers to perform tasks from a greater distance, reducing incident energy exposure. A 36-inch working distance versus 18 inches reduces incident energy by approximately 75%.

Arc Flash Study Deliverables

NFM Consulting delivers comprehensive arc flash study reports including:

Short-circuit analysis at every bus in the system
Incident energy calculations per IEEE 1584-2018 for each piece of equipment
Arc flash boundary calculations (the distance at which incident energy equals 1.2 cal/cm2)
Equipment labeling data including incident energy, PPE category, arc flash boundary, limited and restricted approach boundaries, and available fault current
Recommendations for engineering controls to reduce incident energy at high-hazard locations

Equipment Labeling

NEC 110.16 requires arc flash warning labels on electrical equipment likely to be examined, adjusted, serviced, or maintained while energized. NFPA 70E 130.5(H) specifies the label content: nominal system voltage, arc flash boundary, available incident energy at the working distance, corresponding PPE category, date of analysis, and limited/restricted approach boundaries. NFM Consulting provides label data in formats compatible with Brady, DuraLabel, and other label printing systems for efficient facility-wide labeling programs.

Ongoing Compliance

Arc flash conditions change whenever the power system is modified: new equipment additions, transformer replacements, utility fault current changes, or protective device setting modifications all affect incident energy levels. NFPA 70E recommends updating arc flash studies whenever significant modifications occur. NFM Consulting maintains power system models for our clients and provides efficient study updates as systems evolve.