The purpose of using Miniature Circuit Breaker (MCB) are Overload Protection and Short Circuit.
MCB protects electrical circuits from failure.
Short Circuit is an electrical failure.
A short circuit is an accidental or intentional conductive path between two or more conductive parts.
The over current is a multiple of the rated current.If too many devices are connected to one line and consume more energy than the line can carry,it is called overload.All components are fine,they just consume too much.