An toànCâu 425 / 521
The arc flash boundary is best defined as the distance at which:
a.The electrician can no longer physically reach the equipment
b.The incident energy equals 1.2 cal/cm², the onset of a second-degree burn to bare skin
c.The voltage on the conductors drops to zero
d.The restricted approach boundary begins
Giải thích
The arc flash boundary is the distance from a potential arc source where incident energy is 1.2 cal/cm²—the level that would cause a second-degree burn to unprotected skin. It is a thermal (burn) boundary, not a reach limit or a shock (approach) boundary, and it has nothing to do with voltage reaching zero.
Trích dẫn luật: NFPA 70ELuyện miễn phí toàn bộ 521 câu hỏi — không cần đăng ký.
Câu hỏi liên quan cùng chủ đề
- On a construction site, which receptacles must have GFCI protection for personnel?
- A Class A GFCI intended to protect people trips at approximately what ground-fault current?
- What is the difference between a Class A (personnel) GFCI and a 30-milliampere 'equipment' ground-fault protection device?
- In NFPA 70E, the 'limited approach boundary' is best described as:
- Crossing the restricted approach boundary toward an exposed energized part requires:
- An arc-flash study shows an available incident energy of 8 cal/cm² at the working distance. The arc-rated clothing and PPE must have an arc rating of:
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