Overcurrent devices
Overcurrent devices limit the current that can flow through a circuit or electrical device. If current exceeds a given limit , the device shuts off power. Fuses and circuit breakers are two common overcurrent devices.
Fuses
When placed in a circuit and current in the circuit exceeds some limiting value, the material in a fuse(usually lead or a lead alloy) heats above its melting point and separates, thereby stopping the flow of current. If the overcurrent is very large, components of the circuit or equipment connected to it may be damaged, because the fuse heats and melts too slowly. Fuses come in various sizes and shapes for different purposes. They may protect very low current electrical circuits or large distribution lines. There are fast-acting and slow-acting fuses. Codes specify what type are to be used in specific application.