fuses

Fuses are protective devices used in electrical circuits to prevent damage from overcurrents. They work by containing a conductive element that melts when excessive current flows, opening the circuit and stopping power to the protected load. The basic idea is to sacrifice a small component to prevent wires from overheating, fires, or damage to devices.

Fuses come in several forms. Cartridge fuses enclose a metal conductor in a glass or ceramic tube with end caps and are common in power supplies and industrial equipment. Blade or plug-in fuses are widely used in automotive and consumer electronics. Resettable fuses, including polymer positive temperature coefficient devices, rise in resistance as they heat and can return to a low-resistance state after a fault is removed, without replacement. Each type has specific voltage and current ratings and time‑current characteristics.

Operation and characteristics. Each fuse has a rated current, a voltage rating, and a characteristic that describes how quickly it will interrupt at a given overload. Fast-acting (fast-blow) fuses respond quickly to faults, while time-delay (slow-blow) fuses tolerate short surges. The actual blowing current is typically above the normal operating current, and the time to open depends on the magnitude and duration of the overcurrent.

Applications and safety. Fuses are placed in series with the protected circuit and are intended to be replaced after blowing with an identical fuse of the same rating and type. Bypassing a fuse or using a higher-rated conductor removes protection and creates safety risks. Standards bodies such as IEC and UL establish specifications for design, performance, and testing of fuses to ensure safe operation in electrical products.