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Fuses

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A fuse is simply an electrical conductor that is designed to fail when the current passing through it exceeds a certain threshold value. Most fuses comprise a thin wire conductor fixed inside a glass or ceramic tube and terminated at each end by caps which provide an effective electrical connection with the associated fuse-holder.

The basic principle behind the fuse is simply that, by making the fuse the weakest link in the current path, it will fail before anything else does. This is, unfortunately sometimes NOT the case - simply because the action of rupturing (i.e., literally melting) even the thinnest of wire conductors takes a finite time. Other components can, and often do, fail much more rapidly. If a circuit is not fitted with a fuse, and a serious fault does arise, one or more other devices (often considerably more expensive) will usually fail.

Various types of fuse and fusible device are fitted to modern electronic equipment. The main types are as follows:

1. Fuses designed for fitting into mains plugs (e.g. the 13A domestic plug universally found in the UK which may be fitted with 1A, 3A, 5A and 13A cartridge fuses).
2. 'Quick-blow' fuses (types F and FF).
3. 'Medium-blow' fuses (type M).
4. 'Slow-blow' (or 'time delay') fuses (types T and TT).
5. Electronic (or 'solid-state') resettable fuses.
6. Thermal fuses.

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