When we define ratings of a CB SHORT TIME CURRENT RATING & SHORT TIME BREAKING CAPACITIES to be mentioned .So what o we mean by them??

Circuit breakers are rated for current and current at time. In order to avoid trips for transient events, the circuit breaker might be rated to break at Current A for 1 Sec, but at a higher current, current B, it might break at 100 mSec.

Hello swa

Perito's answer is correct. The higher the voltage or the current, the faster the switching has to go, to shorten arcing and resulting damage.

By means of short time current rating of acb, we understand that the circuit breaker will withstand up to that peak current for specified / designed time duration say 1 second or 3 seconds without any damages caused to the cb.