kAIC...
kilo Amps Interrupting Current...
A fuse rating ( to a voltage limit ) of blocking/ stopping power against over current flow.
Obviously, this is in reference to A/C systems with infinite bus character.
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kASC
kilo Amps Short Circuit
This is a metric related to the inverse impedance of a system.
It is calculated based upon what current can flow through from the Poco side into a shorted distribution system PLUS the instantaneous back EMF available from induction elements ( motors, chiefly ) and capacitive elements ( pf correction capacitor banks, chiefly ) when a 'bolted' short circuit occurs across a customer's main bus.
Because the system has a shifting impedance throughout and back-EMF changes with motor state the typical calculations are done WRT worst case fault energy thresholds.
A classic would be catastrophic transformer failure due to physical impact. Marc once related such a fiasco: a load shifted while on a massive forklift. Both load and lift tumbled into a rack of massive XFMRS. They went off like bombs. In a bolted short mode EMF from all associated systems drained into the short producing a plasma explosion, followed by a nasty fire.
Months later the rebuilt, redesigned system used COORDINATED fuses to protect against both Poco side energy and back-EMF coming back from all of the rotary loads.
They even threw in some bollards!
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For most situations rotating loads are trivial ( homes, small businesses ) but it gets interesting in industries that have the works.
Naturally, no electrician's calculations are going to satisfy: the insurance company will insist on an EE -- who carries a nice E & O Policy.
( E & O = Errors & Omissions = professional screw-up insurance )
