Made up scenario for this discussion: SCCR of a chiller is lower than the available short-circuit current. example: AIC at chiller is calculated at 30kAIC, Chiller is rated for 10kSCCR. What to do? (don't get hung up on this question though, the real question is below)

I have been reading a lot of posts that really suggest that installing current limiting fuses in a circuit to limit KAIC downstream doesn't work. Fingers point to IEEE Buff Book 242-1986 article 2.3.6 which states that over current protection devices shouldn't be factored in to short-circuit calculations, unless a manufacturer has tested it as part of their system to reduce the KAIC to their equipment or to give them a higher SCCR value for their equipment. SKM models for short-circuit won't include over-current protection devices for this reason.

NEC says that a current-limiting device can be used in the circuit per designed and approved by a protection engineer. What software would do this, and if IEEE 242-1986 says this is not kosher, why does NEC say it is OK? A lot of posts I have read state that engineers would have to be nuts to put their license on the line to do such a thing, but is it really that complicated?

Then to add another twist, how is adding a current limiting fuse to reduce the KAIC upstream of a piece of equipment any different from putting in a fuse upstream to reduce available energy for arc-flash. Adding current-limiting fuses to reduce available current is completely OK with IEEE 1584 in determining incident energy. I just can't wrap my mind around how this would be any different at all?

I really need someone to explain to me what is OK, what isn't, why, what is different, and where should I be looking for more info?

https://www.electricallicenserenewal.co ... ee%20image).

Arc Flash does not care how long fault a fault lasts and is usually not a bolted fault value, while an AIC and SCCR rating is extremely time sensitive These values are typically determined by the manufacturer there is nothing you can do, in the field, to change them. The only thing you can do is lower the available fault current.

Fuses must be operating within their limiting region or they do nothing for downstream equipment. for example, say your equipment is rated for 5kA, but you have only 7kA od arcing current available. A 200A current limiting fuse would not likely do anything to reduce the current at the equipment.