What PPE is required within the arc flash boundary?

Per NFPA 70E, workers inside the boundary need arc-rated clothing and equipment selected either by the incident-energy method (PPE rated at or above the calculated cal/cm2) or the PPE category method.

How often should an arc flash study be updated?

NFPA 70E calls for reviewing the arc flash risk assessment at least every five years, or whenever a change to the electrical system could affect the results.

What Is the Arc Flash Boundary?

Q: What is the arc flash boundary?

The arc flash boundary is the distance from an energized part at which the incident energy equals 1.2 cal/cm2 - the threshold for a second-degree burn on bare skin. Anyone crossing it must wear arc-rated PPE.

Q: How is the arc flash boundary calculated?

It is derived in an arc flash (incident energy) study using the IEEE 1584 equations, based on available fault current, the protective device's arcing clearing time, working distance, electrode configuration, and system voltage.

The arc flash boundary is the distance from energized electrical equipment at which the incident energy drops to 1.2 cal/cm² - the level that can cause a second-degree burn on unprotected skin. Any worker crossing this boundary must wear arc-rated personal protective equipment (PPE).

Key terms

Incident energy - thermal energy at a given working distance during an arc flash, measured in cal/cm². It determines the required PPE.
Working distance - the distance from the arc source to a worker's face and torso (commonly 18 inches for low-voltage equipment).
Arc flash study - an engineering analysis (per IEEE 1584) that produces incident energy, boundaries, and PPE labels for each piece of equipment.

Frequently asked questions

How is the arc flash boundary calculated?

It comes out of an arc flash study using the IEEE 1584 equations: available fault current, the protective device's arcing clearing time, working distance, electrode configuration, and system voltage.

What PPE is required within the boundary?

Under NFPA 70E, arc-rated clothing and equipment selected by either the incident-energy method or the PPE category method.

How often should the study be updated?

NFPA 70E recommends a review at least every five years, or after any system change that affects the results.

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