Which statement describes NFPA 70E's arc flash boundary for low voltage?

• A. The default is 2 feet.
• B. The default is 4 feet.
• C. The default is 6 feet.
• D. The default is 8 feet.

Answer: (B)

Arc flash boundary is the distance from the arc source within which incident energy could be high enough to require protective PPE, based on a chosen energy threshold (commonly around 1.0 cal/cm2) in NFPA 70E. For low-voltage systems, the standard uses a conservative default boundary of four feet. This four-foot rule gives a practical, safe guideline for most typical low-voltage installations, so workers outside that distance are not exposed to the higher energy levels that would necessitate arc-rated gear. The actual boundary can be longer or shorter depending on specific factors like available fault current and enclosure design, but four feet is the baseline used in general practice and training.