An electrical component designed to act as a failsafe device when conditions of excessive current flow are detected in a circuit. Fuses are typically used in situations where circuit breakers are either too expensive to install or where system faults are likely to be rare. When a fuse blows, or burns through, it must be replaced, so circuit breakers are frequently less expensive alternatives for circuits which may suffer many overloads over a long service life.

Household and automotive fuses are typically made of thin strips of metal, and the metal will literally melt or burn from heat buildup when too much energy is passed through it. Once it melts or burns through, no more energy can pass along the circuit, and any components on the circuit beyond the point where the fuse is installed should be protected from damage. Industrial fuses designed to handle higher voltages can be constructed of paper or paper-like fiber, carbon, or other material that melts or burns easily when exposed to energy levels above a certain threshold.

Most fuses are designed to blow within fractions of a second. Some circuits require temporary current levels substantially higher than normal current levels, but only require high current flow for very brief periods. These circuits use a special type of fuse called a slow-blow or slo-blo fuse which will only blow if excess current levels are prolonged. Musical instrument amplifiers and circuits in public address systems can require very high current flow for fractions of seconds, for example in the first hundredths of a second after a guitar string is plucked by a pick or a drum skin is struck by a drumstick.

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