#Add a fuse series#

The operating time is not a fixed interval but decreases as the current increases. Manufacturers can provide a plot of current vs time, often plotted on logarithmic scales, to characterize the device and to allow comparison with the characteristics of protective devices upstream and downstream of the fuse. The speed at which a fuse blows depends on how much current flows through it and the material of which the fuse is made. Silica sand or non-conducting liquids may be used.Ĭharacteristics Rated current I N Ī maximum current that the fuse can continuously conduct without interrupting the circuit. The fuse element may be surrounded by air, or by materials intended to speed the quenching of the arc. Fuse elements may be supported by steel or nichrome wires, so that no strain is placed on the element, but a spring may be included to increase the speed of parting of the element fragments. A dual-element fuse may contain a metal strip that melts instantly on a short circuit, and also contain a low-melting solder joint that responds to long-term overload of low values compared to a short circuit. In large fuses, current may be divided between multiple strips of metal. The fuse elements may be shaped to increase heating effect. The element must not be damaged by minor harmless surges of current, and must not oxidize or change its behavior after possibly years of service. The fuse ideally would carry its rated current indefinitely, and melt quickly on a small excess. The fuse element is made of zinc, copper, silver, aluminum, or alloys among these or other various metals to provide stable and predictable characteristics. If too high a current flows, the element rises to a higher temperature and either directly melts, or else melts a soldered joint within the fuse, opening the circuit. The size and construction of the element is (empirically) determined so that the heat produced for a normal current does not cause the element to attain a high temperature. The resistance of the element generates heat due to the current flow.

#Add a fuse series#

The fuse is arranged in series to carry all the charge passing through the protected circuit. Construction Ī fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a non-combustible housing. Ī fuse was patented by Thomas Edison in 1890 as part of his electric distribution system. A variety of wire or foil fusible elements were in use to protect telegraph cables and lighting installations as early as 1864. Circuit breakers can be used as an alternative to fuses, but have significantly different characteristics.īreguet recommended the use of reduced-section conductors to protect telegraph stations from lightning strikes by melting, the smaller wires would protect apparatus and wiring inside the building. When a damaged live wire makes contact with a metal case that is connected to ground, a short circuit will form and the fuse will melt.Ī fuse is an automatic means of removing power from a faulty system often abbreviated to ADS (Automatic Disconnection of Supply).

Short circuits, overloading, mismatched loads, or device failure are the prime or some of the reasons for fuse operation. Wiring regulations usually define a maximum fuse current rating for particular circuits. The time and current operating characteristics of fuses are chosen to provide adequate protection without needless interruption. Today there are thousands of different fuse designs which have specific current and voltage ratings, breaking capacity, and response times, depending on the application. It is a sacrificial device once a fuse has operated it is an open circuit, and must be replaced or rewired, depending on its type.įuses have been used as essential safety devices from the early days of electrical engineering. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit.

Melting of internal conductor due to heat generated by excessive current flow A miniature time-delay 250 V fuse that will interrupt a 0.3 A current at after 100 s, or a 15 A current in 0.1 s.