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51-478: A short circuit is an electrical circuit that allows a current to travel along an unintended path with no or a very low electrical impedance. Short Circuit may also refer to: Short circuit A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at different voltages. This results in an electric current limited only by the Thévenin equivalent resistance of

102-466: A virtual ground because its potential is (ideally) identical to that of the ground. An ideal operational amplifier also has infinite input impedance , so unlike a real short circuit, no current flows between the terminals of the virtual short. Fuse (electrical) In electronics and electrical engineering , a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component

153-411: A channel of hot ionized plasma , is highly conductive and can persist even after significant amounts of original material from the conductors has evaporated. Surface erosion is a typical sign of electric arc damage. Even short arcs can remove significant amounts of material from the electrodes. The temperature of the resulting electrical arc is very high (tens of thousands of degrees), causing the metal on

204-640: A circuit intended for a lower rating. Glass cartridge and plug fuses allow direct inspection of the fusible element. Other fuses have other indication methods including: Some fuses allow a special purpose micro switch or relay unit to be fixed to the fuse body. When the fuse element blows, the indicating pin extends to activate the micro switch or relay, which, in turn, triggers an event. Some fuses for medium-voltage applications use two or three separate barrels and two or three fuse elements in parallel. The International Electrotechnical Commission publishes standard 60269 for low-voltage power fuses. The standard

255-413: A circuit presumed to be isolated. To help reduce the negative effects of short circuits, power distribution transformers are deliberately designed to have a certain amount of leakage reactance . The leakage reactance (usually about 5 to 10% of the full load impedance) helps limit both the magnitude and rate of rise of the fault current . A short circuit may lead to formation of an electric arc . The arc,

306-403: A dual 12/42 V DC electrical system that will require a fuse rated at 58 V DC. Fuses are used on power systems up to 115,000 volts AC. High-voltage fuses are used to protect instrument transformers used for electricity metering, or for small power transformers where the expense of a circuit breaker is not warranted. A circuit breaker at 115 kV may cost up to five times as much as

357-709: A fault end. The breaking capacity is the maximum current that can safely be interrupted by the fuse. This should be higher than the prospective short-circuit current . Miniature fuses may have an interrupting rating only 10 times their rated current. Fuses for small, low-voltage , usually residential, wiring systems are commonly rated, in North American practice, to interrupt 10,000 amperes. Fuses for commercial or industrial power systems must have higher interrupting ratings, with some low-voltage current-limiting high interrupting fuses rated for 300,000 amperes. Fuses for high-voltage equipment, up to 115,000 volts, are rated by

408-431: A high temperature. 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 fuse element is made of zinc, copper, silver, aluminum, or alloys among these or other various metals to provide stable and predictable characteristics. The fuse ideally would carry its rated current indefinitely, and melt quickly on

459-454: A low resistance in the connection, a high current will flow, causing the delivery of a large amount of energy in a short period of time. A high current flowing through a battery can cause a rapid increase of temperature, potentially resulting in an explosion with the release of hydrogen gas and electrolyte (an acid or a base ), which can burn tissue and cause blindness or even death. Overloaded wires will also overheat causing damage to

510-479: A low-melting solder joint that responds to long-term overload of low values compared to a short circuit. 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. The fuse element may be surrounded by air, or by materials intended to speed the quenching of the arc. Silica sand or non-conducting liquids may be used. A maximum current that

561-403: A pair of electrical terminals, and (usually) enclosed by a non-combustible housing. The fuse is arranged in series to carry all the charge passing through the protected circuit. The resistance of the element generates heat due to the current flow. 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

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612-544: A particular type: Fuses come in a vast array of sizes and styles to serve in many applications, manufactured in standardised package layouts to make them easily interchangeable. Fuse bodies may be made of ceramic , glass , plastic , fiberglass , molded mica laminates , or molded compressed fibre depending on application and voltage class. Cartridge ( ferrule ) fuses have a cylindrical body terminated with metal end caps. Some cartridge fuses are manufactured with end caps of different sizes to prevent accidental insertion of

663-521: A pin that prevents installation of similar-appearing class H fuses, which have a much lower breaking capacity and a solid blade terminal that lacks the slot of the RK type. Fuses can be built with different sized enclosures to prevent interchange of different ratings of fuse. For example, bottle style fuses distinguish between ratings with different cap diameters. Automotive glass fuses were made in different lengths, to prevent high-rated fuses being installed in

714-714: A set of power fuses, so the resulting saving can be tens of thousands of dollars. In medium-voltage distribution systems, a power fuse may be used to protect a transformer serving 1–3 houses. Pole-mounted distribution transformers are nearly always protected by a fusible cutout , which can have the fuse element replaced using live-line maintenance tools. Medium-voltage fuses are also used to protect motors, capacitor banks and transformers and may be mounted in metal enclosed switchgear, or (rarely in new designs) on open switchboards. Large power fuses use fusible elements made of silver , copper or tin to provide stable and predictable performance. High voltage expulsion fuses surround

765-444: A short circuit will form and the fuse will melt. A fuse is an automatic means of removing power from a faulty system, often abbreviated to ADS (automatic disconnection of supply). Circuit breakers can be used as an alternative to fuses, but have significantly different characteristics. Louis Clément François Breguet recommended the use of reduced-section conductors to protect telegraph stations from lightning strikes ; by melting,

816-400: A small excess. 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 elements may be shaped to increase heating effect. In large fuses, current may be divided between multiple strips of metal. A dual-element fuse may contain a metal strip that melts instantly on a short circuit, and also contain

867-421: A very high current and therefore quickly trigger an overcurrent protection device. However, it is possible for short circuits to arise between neutral and earth conductors and between two conductors of the same phase. Such short circuits can be dangerous, particularly as they may not immediately result in a large current and are therefore less likely to be detected. Possible effects include unexpected energisation of

918-507: Is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. 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. Fuses have been used as essential safety devices from the early days of electrical engineering. Today there are thousands of different fuse designs which have specific current and voltage ratings, breaking capacity, and response times, depending on

969-628: Is dependent upon the specific application, voltage, and current demands of the electrical circuit. Automotive fuses can be mounted in fuse blocks, inline fuse holders, or fuse clips. Some automotive fuses are occasionally used in non-automotive electrical applications. Standards for automotive fuses are published by SAE International (formerly known as the Society of Automotive Engineers). Automotive fuses can be classified into four distinct categories: Most automotive fuses rated at 32 volts are used on circuits rated 24 volts DC and below. Some vehicles use

1020-418: Is designed to allow a current which is above the rated value of the fuse to flow for a short period of time without the fuse blowing. These types of fuse are used on equipment such as motors, which can draw larger than normal currents for up to several seconds while coming up to speed. The I t rating is related to the amount of energy let through by the fuse element when it clears the electrical fault. This term

1071-472: Is in four volumes, which describe general requirements, fuses for industrial and commercial applications, fuses for residential applications, and fuses to protect semiconductor devices. The IEC standard unifies several national standards, thereby improving the interchangeability of fuses in international trade. All fuses of different technologies tested to meet IEC standards will have similar time-current characteristics, which simplifies design and maintenance. In

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1122-411: Is no resistance and thus no voltage drop across the connection. In real circuits, the result is a connection with almost no resistance. In such a case, the current is limited only by the resistance of the rest of the circuit. A common type of short circuit occurs when the positive and negative terminals of a battery or a capacitor are connected with a low- resistance conductor , like a wire . With

1173-416: Is normally used in short circuit conditions and the values are used to perform co-ordination studies in electrical networks. I t parameters are provided by charts in manufacturer data sheets for each fuse family. For coordination of fuse operation with upstream or downstream devices, both melting I t and clearing I t are specified. The melting I t is proportional to the amount of energy required to begin melting

1224-483: Is not significant in more traditional wire type fuses, but can be significant in other technologies such as resettable (PPTC) type fuses. Ambient temperature will change a fuse's operational parameters. A fuse rated for 1 A at 25 °C may conduct up to 10% or 20% more current at −40 °C and may open at 80% of its rated value at 100 °C. Operating values will vary with each fuse family and are provided in manufacturer data sheets. Most fuses are marked on

1275-589: The National Electrical Code , NFPA 70 (NEC). The standard ampere ratings for fuses (and circuit breakers ) in USA/Canada are considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses are 1, 3, 6, 10, and 601. UL 248 currently has 19 "parts". UL 248-1 sets

1326-465: The arc and increases the breaking capacity of the fuse. Medium-voltage fuses may have liquid-filled envelopes to assist in the extinguishing of the arc . Some types of distribution switchgear use fuse links immersed in the oil that fills the equipment. Fuse packages may include a rejection feature such as a pin, slot, or tab, which prevents interchange of otherwise similar appearing fuses. For example, fuse holders for North American class RK fuses have

1377-490: The United States and Canada, low-voltage fuses to 1 kV AC rating are made in accordance with Underwriters Laboratories standard UL 248 or the harmonized Canadian Standards Association standard C22.2 No. 248. This standard applies to fuses rated 1 kV or less, AC or DC, and with breaking capacity up to 200 kA. These fuses are intended for installations following Canadian Electrical Code, Part I (CEC), or

1428-401: The advantage of a fuse element visible for inspection purposes, they have a low breaking capacity (interrupting rating), which generally restricts them to applications of 15 A or less at 250 V AC . Ceramic fuses have the advantage of a higher breaking capacity, facilitating their use in circuits with higher current and voltage . Filling a fuse body with sand provides additional cooling of

1479-419: The application. The time and current operating characteristics of fuses are chosen to provide adequate protection without needless interruption. Wiring regulations usually define a maximum fuse current rating for particular circuits. A fuse can be used to mitigate short circuits , overloading, mismatched loads, or device failure. When a damaged live wire makes contact with a metal case that is connected to ground,

1530-422: The body or end caps with markings that indicate their ratings. Surface-mount technology "chip type" fuses feature few or no markings, making identification very difficult. Similar appearing fuses may have significantly different properties, identified by their markings. Fuse markings will generally convey the following information, either explicitly as text, or else implicit with the approval agency marking for

1581-412: The contact surfaces to melt, pool and migrate with the current, as well as to escape into the air as fine particulate matter. A short circuit fault current can, within milliseconds, be thousands of times larger than the normal operating current of the system. Damage from short circuits can be reduced or prevented by employing fuses , circuit breakers , or other overload protection , which disconnect

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1632-406: The forces generated in a short circuit. In electronics , the ideal model (infinite gain ) of an operational amplifier is said to produce a virtual short circuit between its input terminals because no matter what the output voltage is, the difference of potential between its input terminals is zero. If one of the input terminals is connected to the ground, then the other one is said to provide

1683-426: The fuse at rated current. There is a direct relationship between a fuse's cold resistance and its voltage drop value. Once current is applied, resistance and voltage drop of a fuse will constantly grow with the rise of its operating temperature until the fuse finally reaches thermal equilibrium. The voltage drop should be taken into account, particularly when using a fuse in low-voltage applications. Voltage drop often

1734-436: The fuse body and terminals to be reused if not damaged after a fuse operation. Fuses designed for soldering to a printed circuit board have radial or axial wire leads . Surface mount fuses have solder pads instead of leads. High-voltage fuses of the expulsion type have fiber or glass-reinforced plastic tubes and an open end, and can have the fuse element replaced. Semi-enclosed fuses are fuse wire carriers in which

1785-405: 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 of which the fuse is made. 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

1836-412: The fuse element. The clearing I t is proportional to the total energy let through by the fuse when clearing a fault. The energy is mainly dependent on current and time for fuses as well as the available fault level and system voltage. Since the I t rating of the fuse is proportional to the energy it lets through, it is a measure of the thermal damage from the heat and magnetic forces that will be produced by

1887-453: The fuse. The operating time is not a fixed interval but decreases as the current increases. Fuses are designed to have particular characteristics of operating time compared to current. A standard fuse may require twice its rated current to open in one second, a fast-blow fuse may require twice its rated current to blow in 0.1 seconds, and a slow-blow fuse may require twice its rated current for tens of seconds to blow. Fuse selection depends on

1938-403: The fusible wire itself can be replaced. The exact fusing current is not as well controlled as an enclosed fuse, and it is extremely important to use the correct diameter and material when replacing the fuse wire, and for these reasons these fuses are slowly falling from favour. These are still used in consumer units in some parts of the world, but are becoming less common. While glass fuses have

1989-459: The general requirements for fuses, while the latter parts are dedicated to specific fuses sizes (ex: 248-8 for Class J, 248-10 for Class L), or for categories of fuses with unique properties (ex: 248-13 for semiconductor fuses, 248-19 for photovoltaic fuses). The general requirements (248-1) apply except as modified by the supplemental part (240-x). For example, UL 248-19 allows photovoltaic fuses to be rated up to 1500 volts, DC, versus 1000 volts under

2040-478: The general requirements. IEC and UL nomenclature varies slightly. IEC standards refer to a "fuse" as the assembly of a fusible link and a fuse holder . In North American standards, the fuse is the replaceable portion of the assembly, and a fuse link would be a bare metal element for installation in a fuse. Automotive fuses are used to protect the wiring and electrical equipment for vehicles. There are several different types of automotive fuses and their usage

2091-434: The load's characteristics. Semiconductor devices may use a fast or ultrafast fuse as semiconductor devices heat rapidly when excess current flows. The fastest blowing fuses are designed for the most sensitive electrical equipment, where even a short exposure to an overload current could be damaging. Normal fast-blow fuses are the most general purpose fuses. A time-delay fuse (also known as an anti-surge or slow-blow fuse)

Short circuit (disambiguation) - Misplaced Pages Continue

2142-673: The maximum prospective short-circuit current . In an improper installation, the overcurrent from a short circuit may cause ohmic heating of the circuit parts with poor conductivity (faulty joints in wiring, faulty contacts in power sockets, or even the site of the short circuit itself). Such overheating is a common cause of fires . An electric arc, if it forms during the short circuit, produces high amount of heat and can cause ignition of combustible substances as well. In industrial and utility distribution systems, dynamic forces generated by high short-circuit currents cause conductors to spread apart. Busbars, cables, and apparatus can be damaged by

2193-421: The maximum voltage source it would have to disconnect. Connecting fuses in series does not increase the rated voltage of the combination, nor of any one fuse. Medium-voltage fuses rated for a few thousand volts are never used on low voltage circuits, because of their cost and because they cannot properly clear the circuit when operating at very low voltages. The manufacturer may specify the voltage drop across

2244-431: The open-circuit voltage. For example, a glass tube fuse rated at 32 volts would not reliably interrupt current from a voltage source of 120 or 230 V. If a 32 V fuse attempts to interrupt the 120 or 230 V source, an arc may result. Plasma inside the glass tube may continue to conduct current until the current diminishes to the point where the plasma becomes a non-conducting gas. Rated voltage should be higher than

2295-457: The power in reaction to excessive current. Overload protection must be chosen according to the current rating of the circuit. Circuits for large home appliances require protective devices set or rated for higher currents than lighting circuits. Wire gauges specified in building and electrical codes are chosen to ensure safe operation in conjunction with the overload protection. An overcurrent protection device must be rated to safely interrupt

2346-444: The public power grid, e.g. in transformer stations, main distribution boards, or in building junction boxes and as meter fuses. In some countries, because of the high fault current available where these fuses are used, local regulations may permit only trained personnel to change these fuses. Some varieties of HRC fuse include special handling features. The voltage rating of the fuse must be equal to or, greater than, what would become

2397-454: The rest of the network which can cause circuit damage, overheating , fire or explosion . Although usually the result of a fault , there are cases where short circuits are caused intentionally, for example, for the purpose of voltage-sensing crowbar circuit protectors . In circuit analysis , a short circuit is defined as a connection between two nodes that forces them to be at the same voltage. In an 'ideal' short circuit, this means there

2448-430: The smaller wires would protect apparatus and wiring inside the building. A variety of wire or foil fusible elements were in use to protect telegraph cables and lighting installations as early as 1864. A fuse was patented by Thomas Edison in 1890 as part of his electric distribution system. A fuse consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors, mounted between

2499-650: The total apparent power (megavolt-amperes, MVA ) of the fault level on the circuit. Some fuses are designated high rupture capacity (HRC) or high breaking capacity (HBC) and are usually filled with sand or a similar material. Low-voltage high rupture capacity (HRC) fuses are used in the area of main distribution boards in low-voltage networks where there is a high prospective short circuit current. They are generally larger than screw-type fuses, and have ferrule cap or blade contacts. High rupture capacity fuses may be rated to interrupt current of 120 kA. HRC fuses are widely used in industrial installations and are also used in

2550-463: The wire's insulation, or starting a fire. In electrical devices, unintentional short circuits are usually caused when a wire's insulation breaks down, or when another conducting material is introduced, allowing charge to flow along a different path than the one intended. In mains circuits, short circuits may occur between two phases , between a phase and neutral or between a phase and earth (ground). Such short circuits are likely to result in

2601-412: The wrong fuse rating in a holder, giving them a bottle shape. Fuses for low voltage power circuits may have bolted blade or tag terminals which are secured by screws to a fuseholder. Some blade-type terminals are held by spring clips. Blade type fuses often require the use of a special purpose extractor tool to remove them from the fuse holder. Renewable fuses have replaceable fuse elements, allowing

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