Fill in the blank. A new NEC requirement on arc energy reduction for fuses applies to fuses rated ____ amperes or higher. The fuses shall have a clearing time of _____ seconds or less at the available arcing current or one of the methods listed in this Sec. 240.67(B) shall be provided.
A) 1,000 / 0.33
B) 1,200 / 0.07
C) 1,600 / 0.004
D) 800 / 0.042
Find the Answer
Answer: B
As noted in Sec. 240.67, “Where fuses rated 1,200 A or higher are installed, 240.67(A) and (B) shall apply. This requirement shall become effective January 1, 2020.
Sec. 240.67(B) states: “A fuse shall have a clearing time of 0.07 seconds or less at the available arcing current, or one of the following shall be provided:
“(1) Differential relaying
“(2) Energy-reducing maintenance switching with local status Indicator
“(3) Energy-reducing active arc flash mitigation system
“(4) An approved equivalent means”
Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at [email protected].
