Fusibles

Fusibles, or fuses, are protective devices used in electrical circuits to prevent damage from overcurrent conditions. They consist of a conductive element—often a metal wire or strip—encased in a housing. When current exceeds its rated value, the heat generated by I^2R losses causes the element to melt, breaking the circuit and stopping the current flow. After operation, the device is single-use and must be replaced.

Fuses are characterized by their current rating (amps) and voltage rating, and by their time-current characteristic. Fast-acting or quick-blow fuses respond quickly to overloads, while slow-blow (time-delay) fuses tolerate short surges such as motor inrush without tripping. The choice depends on the load profile and the need to avoid nuisance tripping.

Common constructions include cartridge fuses (glass or ceramic tubes with end caps), and blade or plug fuses used in consumer and automotive applications. In electronics, small axial or radial lead fuses are used on printed circuit boards. There are also resettable fuses, known as polymer positive temperature coefficient (PTC) devices, which increase resistance with temperature and can be reused after cooling.

Fuses are widely used to protect wiring, motors, power supplies, and consumer electronics. They complement other protective devices such as circuit breakers. Standards and specifications vary by region; common references include IEC 60269 and UL 248 in North America. Safety considerations include proper rating, clear labeling, and compliance with applicable electrical codes.