Which of the following best describes an arc flash boundary?

• A. The distance at which a person could receive a specified level of incident energy; beyond which protective measures required.
• B. The maximum reach of a worker's arm.
• C. The distance to keep from a crane.
• D. The physical fence around a substation.

Answer: (A)

Arc flash boundary is the distance from energized equipment inside which an arc flash could deliver a defined amount of incident energy to a worker, so protective measures and PPE are required. This boundary is set so that inside it, workers must use arc-rated clothing, face protection, and other safeguards to limit injury; beyond it, the exposure is considered low enough that standard precautions suffice. It’s determined by the equipment’s voltage and the available fault energy, not by how far a person can reach, how close you are to a crane, or where a fence sits around a substation.