In electronics and electrical engineering, fuses are used to prevent an overcurrent condition from damaging the circuit that it is designed to protect. Fuses come in many shapes, sizes, current limits, and operational voltages. The primary component in the fuse it usually a metal wire whose length, diameter, and alloy composition is tailored to melt (fuse) at a precise current value.
Two basic types of fuses are available - fast reaction and slow reaction. Fast reaction fuses are used to protect circuit that cannot tolerate even a small amount of excessive current. The sensitive gate of a semiconductor device is an example. Slow reaction (slow-blow) fuses are used for circuits where a higher than normal current condition can be survived for a short time, such as a motor when it first starts (inrush current can be many times greater than the normal run current).
The fuse cases shown here (full-size) are commonly found in electronic circuits and may either be in fuse holders that allow easy replacement, or soldered in place. Fuses can also be found in surface mount form factors.
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