In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. It is a sacrificial device; once a fuse has operated, it is an open circuit, and must be replaced or rewired, depending on its type.
 A miniature time-delay 250 V fuse that will interrupt a 0.3 A current at after 100 s, or a 15 A current in 0.1 s. 32 mm (1+1⁄4 in) long. | |
| Component type | Passive |
|---|---|
| Working principle | Melting of internal conductor due to heat generated by excessive current flow |
| Electronic symbol | |
 Electronic symbols for a fuse | |
Fuses have been used as essential safety devices from the early days of electrical engineering. Today there are thousands of different fuse designs which have specific current and voltage ratings, breaking capacity, and response times, depending on the application. The time and current operating characteristics of fuses are chosen to provide adequate protection without needless interruption. Wiring regulations usually define a maximum fuse current rating for particular circuits. A fuse can be used to mitigate short circuits, overloading, mismatched loads, or device failure. When a damaged live wire makes contact with a metal case that is connected to ground, a short circuit will form and the fuse will melt.
A fuse is an automatic means of removing power from a faulty system, often abbreviated to ADS (automatic disconnection of supply). Circuit breakers have replaced fuses in many contexts, but have significantly different characteristics, and fuses are still used when space, resiliency or cost are significant factors.