240.67

[infinity]

Someone asked me to explain what this meant. Rather than butcher an explanation I figured I would first ask the people who are more familiar with this requirement. What exactly is the label saying?

 

[dkidd]

This is sort off an explanation.


Arc energy reduction is critical for electrical safety in the
workplace. NEC 2011 introduced an Arc Energy Reduction
requirement for circuit breakers (NEC 240.87) rated 1200 A
and higher. The added circuit breaker requirement has
reduced arc-flash injuries since being introduced by
lowering fault clearing times. The value of 0.07 s for the
new fuse clearing time requirement was chosen to align
with circuit breakers using zone selective interlocking.

However, it should be reinforced that additional
arc energy reduction methods ONLY need to be
implemented if the specified fuse is greater than 1200 A
AND cannot clear the minimum arcing current in less
than 0.07 s.

https://m.littelfuse.com/~/media/protection-relays/technical-papers/littelfuse-nec-240-67-arc-energy-reduction-technical-paper.pdf

 

[jim dungar]

Remember you likely need to perform an arc flash study to confirm the opening time. The .07sec is based on arcing current not the bolted fault current.

Also these arc reductions methods cannot protect themselves nor the equipment they are mounted in. They can be very useful for mitigating arc flash incident energy at downstream equipment.