Fuses provide protection against short-circuits, by rapidly interrupting the circuit when the current exceeds the rated value. However, fuses do not provide protection against overloads, which are sustained currents that exceed the current-carrying capacity of the circuit conductors. Overloads can cause overheating and damage to the conductors and devices in the circuit, but will not cause a fuse to blow unless they also lead to a short-circuit.
2). Earth faults
Fuses also don't provide protection against earth faults, which occur when the live conductor comes into contact with an earthed surface or another conductor connected to earth. Earth faults do not necessarily cause a high current flow, and may not be sufficient to blow a fuse. Earth faults can be dangerous because they can create a voltage potential on metal surfaces and enclosures, and can cause electric shocks.
To provide protection against overloads and earth faults, additional protective devices such as circuit breakers, earth leakage circuit breakers (ELCBs) or residual current devices (RCDs) are used in electrical installations.