In electronics and electrical engineering, fuses are electrical safety devices that are designed to provide overcurrent protection of an electrical circuit. The most essential component is a metal strip or wire that melts when too much current flows through it, and therefore interrupts the current. Fuses are sacrificial devices, meaning that once a fuse has operated, it must be replaced or rewired.
Fuses have been used since the early days of electrical engineering, with the first examples of expendable wiring being used to protect electrical devices dating back to 1864 and Thomas Edison patented the first true fuse in 1890. There are now thousands of fuse designs, each with their own specific current and voltage ratings, breaking capacity, and response times. Time and current operating characteristics are especially important for providing adequate protection without needless interruption. Properly wired, fuses can prevent short circuits, overloads, mismatched loads, and device failure.
Fuses consist of the aforementioned metal strip or wire fuse, mounted between a pair of electrical terminals, and are usually enclosed by a non-combustible housing. The fuse is arranged in a series to carry all of the current passing through the protected circuit. The resistance of the element generates heat due to the current flow and influences the size and construction of the element; however, the heat produced cannot cause the element to reach an unsafely high temperature. The fuse element is made from aluminum, copper, silver, zinc, or alloys to provide stable and predictable characteristics. Ideally, a fuse can carry its rated current indefinitely, and melt quickly with little to no excess. A fuse element cannot be damaged by minor current surges and cannot oxidize or change its behavior after years of service.
Fuses have several parameters they must operate under. The rated current is the maximum current that the fuse can continuously conduct without interrupting the circuit. The speed at which a fuse blows depends on how much current flows through it, and the material the fuse is made of; it is not a fixed interval but decreases as the current increases. The breaking capacity is the maximum current that can be safely interrupted by the fuse. This should be higher than the prospective short-circuit current. For example, fuses for small, low-voltage residential wiring systems are commonly rated to interrupt 10,000 amps, while fuses for commercial or industrial power systems are rated for 300,000 amps.
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