An over-current protective device, which consists of a mechanical switching device, that automatically switches off when the current exceeds a certain ampere value for a certain duration. Circuit breakers can be designed to have a long or short trip time depending on how critical small overloads are to a circuit. The trip time on a direct short circuit is almost instantaneous. Circuit breakers have an ampere trip rating for normal overload protection and a maximum magnetic ampere interrupting capacity (AIC) for short circuit protection. (see: Fuse)