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In Electronics and Electrical Engineering a fuse, short for 'fusible link', is a type of overcurrent protection device. It has as its critical component a metal wire or strip that will melt when heated by a prescribed electric current, opening the Circuit of which it is a part, and so protecting the circuit from an overcurrent condition. A practical fuse was one of the essential features of Edison 's Electrical Power distribution system. An early fuse was said to have successfully protected an Edison installation from tampering by a rival from a gas-lighting concern. Properly-selected fuses (or other overcurrent devices) are an essential part of a power distribution system to prevent Fire or damage due to overload or short-circuits. Usually the maximum size of the overcurrent device for a circuit is regulated by law. For example, the Canadian Electrical Code, the United States National Electrical Code, and the UK Wiring Regulations provide limits for overcurrent device ampere rating for a given conductor, insulation material and installation conditions. Local authorities will incorporate these national codes as part of law. An overcurrent device should normally be selected with a rating just over the normal operating current of the downstream wiring or equipment which it is to protect. FUSE CHARACTERISTICS Each type of fuse (and all other overcurrent devices) has a time-current characteristic which shows the time required to melt the fuse and the time required to clear the circuit for any given level of overload current. Where the fuses in a system are of similar types, simple ratios between ratings of the fuse closest to the load and the next fuse towards the source can be used, so that only the affected circuit is interrupted after a fault. In power system design, main and branch circuit overcurrent devices can be co-ordinated for best protection by plotting the time-current characteristics on a consistent scale, making sure that the source curve never crosses that of any of the branch circuits. To prevent damage to utilization devices, both "maximum clearing" and "minimum melting" fuse curves are plotted. | ||
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