Electrical Equipment Protection
There are are three basic approaches protection.
Protection by a fuse - Short circuit,Earth faults, and overloads.
Protection using releases integrated with circuit breakers - Short circuits,overloads and earth faults.
Protection using relays and circuits.
Steady loads - Normally protect against over load as well as short circuit.
Fluctuating load - Eg: DOL motors with high inrush compared to normal rating. Here fuses generally protect against short circuit only.
Fuses act as fault current sensors and interrupters.
Other approaches use a circuit breaker to interrupt short circuit/earth fault.
Circuit Breaker with Release
Basic Types of relay