A short is a closed circuit without a load. A dead short... I dunno throw some chains onto the bus bars. Well don't really.
Use a water analogy to understand a breakers AIC. Let's pretend a river is the conductor and a circuit breaker is a gate allowing the water to flow. Under normal circumstances the proper flow is allowed to pass. If a huge surge of water flows through that gate, how long will it take to close the gate and how much is too large a surge of water before it blows the gate open and destroys it?
How about bouncer at a club. The bouncers job is to only let one person in at a time. The bouncer is strong enough to stop ten guys. If one person at a time is coming through the door then great. If two, sorry not allowed. If 12 guys come through all at once, the bouncer gets trampled.
Sccr is similar but with no means of stopping the flow. It must only be able to maintain the flow without being destroyed until the Ocpd can do its job.
I think the thing to realize here is that just because a breaker says 30A does not mean it will only allow 30A and no more. It is more complex than that. It is designed to limit current to 30A but it must take into account time. It's OK to exceed 30A for a short time. Such as motor inrush current. There is a trip curve where generally the higher the current the shorter time before trip. As said before there is always some amount of time before tripping. During this time large amounts of current can flow before the breaker is able to trip. The breaker should be able to clear the maximum available current, and the downstream components should be able to maintain that current for the short time until the breaker opens the circuit.
