Information about Maximum Prospective Short Circuit Current
The maximum prospective short circuit current is the maximum electrical current which can flow in a particular electrical system under short circuit conditions. It is determined by the voltage and impedance of the supply system. It is of the order of a few thousand amperes for a standard domestic mains electrical installation in the UK, but may be as low as a few milliamperes in a SELV (Safety Extra Low Voltage or, occasionally, Separated Extra Low Voltage) system or as high as hundreds of thousands of amps in large industrial power systems.
In domestic power installations in European countries (230 V 50 Hz AC single phase power) the short circuit current available on the electrical outlets needs to be taken into account when designing electrical power wiring. The short circuit current should not be too high or too low. The effect of too high short circuit current is discussed in the previous paragraph. The short circuit current should be of the order of around 200 A or higher for normal 10 A or 16 A outlet to guarantee that the normal wire protecting fuse or breaker will quickly disconnect the supply in case of short circuit. Quick disconnecting is needed, because in live-ground short circuit the grounding pin potential on the power outlet can rise compared to the local earth (concrete floor, water pipe etc.) during short circuit to a dangerous voltage, which needs to be shut down quickly for safety. If the short circuit current is lower than this figure, special precautions needs to be taken to make sure that the system is safe; those usually include using a residual current device for extra protection.
The short circuit current available on the electrical outlets is often measured with a suitable instrument when examining electrical installations to make sure that the short circuit current is within reasonable limits. Having a high enough short circuit current on the outlet will also tell that the resistance from the electrical panel to the outlet is reasonably low, so there will not be too high voltage losses on the wires when outlets are loaded normally.
Importance
It is of particular interest when designing an electrical installation because fuses and circuit breakers must be capable of safely breaking the flow of current in the event of a short circuit. When a large electrical current is interrupted an arc may form and if the breaking capacity of a fuse or circuit breaker is exceeded then it may not be able to extinguish this arc meaning that the flow of current will continue, possibly resulting in a fire or explosion.In domestic power installations in European countries (230 V 50 Hz AC single phase power) the short circuit current available on the electrical outlets needs to be taken into account when designing electrical power wiring. The short circuit current should not be too high or too low. The effect of too high short circuit current is discussed in the previous paragraph. The short circuit current should be of the order of around 200 A or higher for normal 10 A or 16 A outlet to guarantee that the normal wire protecting fuse or breaker will quickly disconnect the supply in case of short circuit. Quick disconnecting is needed, because in live-ground short circuit the grounding pin potential on the power outlet can rise compared to the local earth (concrete floor, water pipe etc.) during short circuit to a dangerous voltage, which needs to be shut down quickly for safety. If the short circuit current is lower than this figure, special precautions needs to be taken to make sure that the system is safe; those usually include using a residual current device for extra protection.
The short circuit current available on the electrical outlets is often measured with a suitable instrument when examining electrical installations to make sure that the short circuit current is within reasonable limits. Having a high enough short circuit current on the outlet will also tell that the resistance from the electrical panel to the outlet is reasonably low, so there will not be too high voltage losses on the wires when outlets are loaded normally.
See also
Electric current is the flow (movement) of electric charge. The SI unit of electric current is the ampere (A), which is equal to a flow of one coulomb of charge per second.
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Definition
The amount of electric current (measured in amperes) through some surface, e.g...... Click the link for more information.
A short circuit (sometimes abbreviated to short or s/c) allows a charge to flow along a different path from the one intended. The electrical opposite of a short circuit is an open circuit, which is infinite resistance between two nodes.
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Voltage (sometimes also called electric potential difference or electrical tension) is the potential similarity of electrical potential between two points of an electrical or electronic circuit, expressed in volts.
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Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal alternating current (AC). Electrical impedance extends the concept of resistance to AC circuits, describing not only the relative magnitudes of the voltage and current, but also the
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An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. The ratio most commonly used is 10.
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ampere, in practice often shortened to amp, (symbol: A) is a unit of electric current, or amount of electric charge per second. The ampere is an SI base unit, and is named after André-Marie Ampère, one of the main discoverers of electromagnetism.
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mains usually refers to the general purpose alternating current (AC) electrical power supply (as in “I've connected the appliance to the mains”). The term is not usually used in the United States and Canada.
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fuse, short for 'fusible link', is a type of overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows. When the metal strip melts, it opens the circuit of which it's a part, and so protects the circuit from excessive
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A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or
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electric arc is an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. The phenomenon was first described by Vasily V.
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The breaking capacity gives the current that a fuse is able to interrupt without being destroyed or causing an electric arc. The maximum short circuit current which can occur under fault conditions should not exceed the rated breaking capacity of the fuse.
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Fire is an oxidation process that releases energy in varying intensities in the form of light (with wavelengths also outside the visual spectrum) and heat and often creates smoke. It is commonly used to describe either a fuel in a state of combustion (e.g.
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explosion is a sudden increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases.
The most common artificial explosives are chemical explosives, usually involving a rapid and violent oxidation
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The most common artificial explosives are chemical explosives, usually involving a rapid and violent oxidation
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Voltage (sometimes also called electric potential difference or electrical tension) is the potential similarity of electrical potential between two points of an electrical or electronic circuit, expressed in volts.
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hertz (symbol: Hz) is the SI unit of frequency. Its base unit is cycle/s or s-1 (also called inverse seconds, reciprocal seconds). In English, hertz is used as both singular and plural.
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alternating current (AC) is an electrical current whose magnitude and direction vary cyclically, as opposed to direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of
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ampere, in practice often shortened to amp, (symbol: A) is a unit of electric current, or amount of electric charge per second. The ampere is an SI base unit, and is named after André-Marie Ampère, one of the main discoverers of electromagnetism.
..... Click the link for more information.
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The breaking capacity gives the current that a fuse is able to interrupt without being destroyed or causing an electric arc. The maximum short circuit current which can occur under fault conditions should not exceed the rated breaking capacity of the fuse.
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