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In
physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Physical scie ...

physics
and
electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics The field of electronics is a branch of physics and electrical enginee ...

electrical engineering
, a conductor is an object or type of
material Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and t ...

material
that allows the flow of
charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * Charge (David Ford album), ''Charge'' (David Ford album) * Charge (Machel Montano album), ''Charge'' (Mac ...
(
electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, ...
) in one or more directions. Materials made of
metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
are common electrical conductors. Electric current is generated by the flow of negatively charged
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
s, positively charged
holes A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of engin ...
, and positive or negative
ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
s in some cases. In order for current to flow within a closed
electrical circuit An electrical network is an interconnection of electrical component An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic component ...
, it is not necessary for one charged particle to travel from the component producing the current (the
current source A current source is an electronic circuit that delivers or absorbs an electric current which is independent of the voltage across it. A current source is the duality (electrical circuits), dual of a voltage source. The term ''current sink'' is so ...

current source
) to those consuming it (the
load Load or LOAD may refer to: Aeronautics and transportation *Load factor (aeronautics), the ratio of the lift of an aircraft to its weight *Passenger load factor, the ratio of revenue passenger miles to available seat miles of a particular transpor ...
s). Instead, the charged particle simply needs to nudge its neighbor a finite amount, who will nudge ''its'' neighbor, and on and on until a particle is nudged into the consumer, thus powering it. Essentially what is occurring is a long chain of
momentum In Newtonian mechanics, linear momentum, translational momentum, or simply momentum is the product of the mass Mass is the quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinui ...

momentum
transfer between mobile
charge carriers In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior through Sp ...
; the
Drude model The Drude model of electrical conduction Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that quantifies how strongly it resists electric current. Its inverse, ...
of conduction describes this process more rigorously. This momentum transfer model makes metal an ideal choice for a conductor; metals, characteristically, possess a delocalized
sea of electrons Metallic bonding is a type of chemical bond A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the Coulomb's law, electrostatic force of att ...
which gives the electrons enough mobility to collide and thus affect a momentum transfer. As discussed above, electrons are the primary mover in metals; however, other devices such as the cationic
electrolyte An electrolyte is a medium containing ions that is electrically conducting Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that quantifies how strongly it resist ...

electrolyte
(s) of a
battery Battery may refer to: Energy source * Electric battery, an electrochemical device to provide electrical power ** Automotive battery, a device to provide power to certain functions of an automobile ** List of battery types * Energy storage, inclu ...
, or the mobile protons of the
proton conductor A proton conductor is an electrolyte An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separates into cations and anions, which disperse uni ...
of a fuel cell rely on positive charge carriers.
Insulator Insulator may refer to: * Insulator (electricity), a substance that resists electricity ** Pin insulator, a device that isolates a wire from a physical support such as a pin on a utility pole ** Strain insulator, a device that is designed to work i ...
s are non-conducting materials with few mobile charges that support only insignificant electric currents.


Resistance and conductance

The
resistance Resistance may refer to: Arts, entertainment, and media Comics * Either of two similarly named but otherwise unrelated comic book series, both published by Wildstorm: ** ''Resistance'' (comics), based on the video game of the same title ** ''Th ...
of a given conductor depends on the material it is made of, and on its dimensions. For a given material, the resistance is inversely proportional to the cross-sectional area. For example, a thick copper
wire A wire is a single usually cylindrical A cylinder (from ) has traditionally been a Solid geometry, three-dimensional solid, one of the most basic of curvilinear geometric shapes. Geometrically, it can be considered as a Prism (geometry), p ...

wire
has lower resistance than an otherwise-identical thin copper wire. Also, for a given material, the resistance is proportional to the length; for example, a long copper wire has higher resistance than an otherwise-identical short copper wire. The resistance and conductance of a conductor of uniform cross section, therefore, can be computed as : \begin R & = \rho \frac \ell A, \\G & = \sigma \frac A \ell. \end where \ell is the length of the conductor, measured in
metre The metre ( Commonwealth spelling) or meter (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English ...
s ''A'' is the cross-section area of the conductor measured in
square metre The square metre ( international spelling as used by the International Bureau of Weights and Measures The International Bureau of Weights and Measures (french: Bureau international des poids et mesures, BIPM) is an intergovernmental organi ...
s 2 σ (
sigma Sigma (uppercase Letter case is the distinction between the letters Letter, letters, or literature may refer to: Characters typeface * Letter (alphabet) A letter is a segmental symbol A symbol is a mark, sign, or word that ind ...
) is the
electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current An electric current is a stream of charged particle In p ...
measured in
siemens Siemens AG ( ) is a German multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, ...
per meter (S·m−1), and ρ (
rho Rho (uppercase Ρ, lowercase ρ or ; el, ῥῶ) is the 17th letter of the Greek alphabet The Greek alphabet has been used to write the Greek language since the late ninth or early eighth century BC. It is derived from the earlier Phoenician ...
) is the
electrical resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current An electric current is a stream of charged particle In p ...
(also called ''specific electrical resistance'') of the material, measured in ohm-metres (Ω·m). The resistivity and conductivity are proportionality constants, and therefore depend only on the material the wire is made of, not the geometry of the wire. Resistivity and conductivity are : \rho=1/\sigma. Resistivity is a measure of the material's ability to oppose electric current. This formula is not exact: It assumes the
current density In electromagnetism Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electric charge, electrically charged particles. The electromagnetic force is c ...

current density
is totally uniform in the conductor, which is not always true in practical situation. However, this formula still provides a good approximation for long thin conductors such as wires. Another situation this formula is not exact for is with
alternating current Alternating current (AC) is an electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'natu ...
(AC), because the
skin effect Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble like, for example, an or ...

skin effect
inhibits current flow near the center of the conductor. Then, the ''geometrical'' cross-section is different from the ''effective'' cross-section in which current actually flows, so the resistance is higher than expected. Similarly, if two conductors are near each other carrying AC current, their resistances increase due to the proximity effect. At commercial power frequency, these effects are significant for large conductors carrying large currents, such as
busbar In , a busbar (also bus bar) is a metallic strip or bar, typically housed inside , , and for local high current power distribution. They are also used to connect high voltage equipment at electrical switchyards, and low voltage equipment i ...

busbar
s in an
electrical substation A substation is a part of an electrical Electricity generation, generation, electric power transmission, transmission, and electric power distribution, distribution system. Substations transform voltage from high to low, or the reverse, or per ...

electrical substation
, or large power cables carrying more than a few hundred amperes. Aside from the geometry of the wire, temperature also has a significant effect on the efficacy of conductors. Temperature affects conductors in two main ways, the first is that materials may expand under the application of heat. The amount that the material will expand is governed by the
thermal expansion coefficient Thermal expansion is the tendency of matter to change its shape A shape or figure is the form of an object or its external boundary, outline, or external Surface (mathematics), surface, as opposed to other properties such as color, Surface ...
specific to the material. Such an expansion (or contraction) will change the geometry of the conductor and therefore its characteristic resistance. However, this effect is generally small, on the order of 10−6. An increase in temperature will also increase the number of phonons generated within the material. A
phonon In , a phonon is a in a periodic, arrangement of s or s in , specifically in s and some s. Often referred to as a , it is an in the of the for elastic structures of interacting particles. Phonons can be thought of as quantized , similar to ...
is essentially a lattice vibration, or rather a small, harmonic kinetic movement of the atoms of the material. Much like the shaking of a pinball machine, phonons serve to disrupt the path of electrons, causing them to scatter. This electron scattering will decrease the number of electron collisions and therefore will decrease the total amount of current transferred.


Conductor materials

Conduction materials include
metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
s,
electrolyte An electrolyte is a medium containing ions that is electrically conducting Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that quantifies how strongly it resist ...

electrolyte
s, s,
semiconductor A semiconductor material has an electrical conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric curre ...
s,
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood plasma ...
s and some nonmetallic conductors such as
graphite Graphite (), archaically referred to as plumbago, is a Crystallinity, crystalline form of the element carbon with its atoms arranged in a Hexagonal crystal system, hexagonal structure. It occurs naturally in this form and is the most stable for ...

graphite
and
conductive polymer Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are organic polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Po ...
s.
Copper Copper is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

Copper
has a high conductivity. Annealed copper is the international standard to which all other electrical conductors are compared; the
International Annealed Copper StandardThe International Annealed Copper Standard (IACS) is a standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metro ...
conductivity is , although ultra-pure copper can slightly exceed 101% IACS. The main grade of copper used for electrical applications, such as building wire,
motor An engine or motor is a machine A machine is a man-made device that uses power to apply forces and control movement to perform an action. Machines can be driven by animals and people A people is a plurality of person A person ( ...

motor
windings, cables and
busbar In , a busbar (also bus bar) is a metallic strip or bar, typically housed inside , , and for local high current power distribution. They are also used to connect high voltage equipment at electrical switchyards, and low voltage equipment i ...

busbar
s, is electrolytic-tough pitch (ETP) copper (CW004A or
ASTM ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization A standards organization, standards body, standards developing organization (SDO), or standards setting organization ( ...
designation C100140). If high conductivity copper must be
welded Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing Fusion welding, fusion. Welding is distinct from lower ...

welded
or
brazed Brazing is a metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. ...
or used in a reducing atmosphere, then oxygen-free high conductivity copper (CW008A or ASTM designation C10100) may be used. Because of its ease of connection by
soldering Soldering (AmE American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. Currently, Ameri ...

soldering
or clamping, copper is still the most common choice for most light-gauge wires.
Silver Silver is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical ele ...

Silver
is 6% more conductive than copper, but due to cost it is not practical in most cases. However, it is used in specialized equipment, such as
satellite In the context of spaceflight Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either human spaceflight, with or uncrewed spaceflight, without humans on board. Most spaceflight ...

satellite
s, and as a thin plating to mitigate
skin effect Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor Conductor or conduction may refer to: Music * Conductor (music), a person who leads a musical ensemble like, for example, an or ...

skin effect
losses at high frequencies. Famously, of silver on loan from the
United States Treasury The Department of the Treasury (USDT) is the national treasury A treasury is either *A government department related to finance and taxation, a Finance minister, finance ministry. *A place or location where treasure, such as currency or preciou ...
were used in the making of the
calutron A calutron is a mass spectrometer Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-cha ...
magnets during World War II due to wartime shortages of copper.
Aluminum Aluminium (aluminum in American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the United States The United States of America (USA), commonly known as the Uni ...

Aluminum
wire is the most common metal in
electric power transmission Electric power transmission is the bulk movement of electrical energy Electrical energy is energy derived as a result of movement of electrically charged particles. When used loosely, ''electrical energy'' refers to energy that has been convert ...

electric power transmission
and
distributionDistribution may refer to: Mathematics *Distribution (mathematics) Distributions, also known as Schwartz distributions or generalized functions, are objects that generalize the classical notion of functions in mathematical analysis. Distr ...
. Although only 61% of the conductivity of copper by cross-sectional area, its lower density makes it twice as conductive by mass. As aluminum is roughly one-third the cost of copper by weight, the economic advantages are considerable when large conductors are required. The disadvantages of aluminum wiring lie in its mechanical and chemical properties. It readily forms an insulating oxide, making connections heat up. Its larger
coefficient of thermal expansion Thermal expansion is the tendency of matter to change its shape A shape or figure is the form of an object or its external boundary, outline, or external surface File:Water droplet lying on a damask.jpg, Water droplet lying on a damask ...
than the brass materials used for connectors causes connections to loosen. Aluminum can also "creep", slowly deforming under load, which also loosens connections. These effects can be mitigated with suitably designed connectors and extra care in installation, but they have made aluminum building wiring unpopular past the
service drop In electric power distribution Electric power distribution is the final stage in the delivery Delivery may refer to: *Delivery (commerce), of goods, e.g.: **Pizza delivery **Milk delivery Film and television *Delivering (film), ''Delivering'' ...

service drop
. Organic compounds such as octane, which has 8 carbon atoms and 18 hydrogen atoms, cannot conduct electricity. Oils are hydrocarbons, since carbon has the property of tetracovalency and forms covalent bonds with other elements such as hydrogen, since it does not lose or gain electrons, thus does not form ions. Covalent bonds are simply the sharing of electrons. Hence, there is no separation of ions when electricity is passed through it. Liquids made of compounds with only covalent bonds cannot conduct electricity. Certain organic
ionic liquid An ionic liquid (IL) is a salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure ...
s, by contrast, can conduct an electric current. While pure
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
is not an electrical conductor, even a small portion of ionic impurities, such as
salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure fo ...

salt
, can rapidly transform it into a conductor.


Wire size

Wires are measured by their cross sectional area. In many countries, the size is expressed in square millimetres. In North America, conductors are measured by American wire gauge for smaller ones, and circular mils for larger ones.


Conductor ampacity

The
ampacity Ampacity is a portmanteau A portmanteau (, ) or portmanteau word (from "Portmanteau (luggage), portmanteau") is a Blend word, blend of words
of a conductor, that is, the amount of
current Currents or The Current may refer to: Science and technology * Current (fluid) A current in a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. ...
it can carry, is related to its electrical resistance: a lower-resistance conductor can carry a larger value of current. The resistance, in turn, is determined by the material the conductor is made from (as described above) and the conductor's size. For a given material, conductors with a larger cross-sectional area have less resistance than conductors with a smaller cross-sectional area. For bare conductors, the ultimate limit is the point at which power lost to resistance causes the conductor to melt. Aside from fuses, most conductors in the real world are operated far below this limit, however. For example, household wiring is usually insulated with
PVC Polyvinyl chloride (colloquial Colloquialism or colloquial language is the style (sociolinguistics), linguistic style used for casual communication. It is the most common functional style of speech, the idiom normally employed in conversatio ...
insulation that is only rated to operate to about 60 °C, therefore, the current in such wires must be limited so that it never heats the copper conductor above 60 °C, causing a risk of
fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because the conversion of the weak double bond in molecula ...

fire
. Other, more expensive insulation such as
Teflon Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer A fluoropolymer is a fluorocarbon Fluorocarbons, sometimes referred to as perfluorocarbons or PFCs, are organofluorine B: isoflurane Isoflurane, sold under the brand name Foran ...

Teflon
or
fiberglass Fiberglass (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American Englis ...
may allow operation at much higher temperatures.


Isotropy

If an
electric field An electric field (sometimes E-field) is the physical field that surrounds electrically-charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' ' ...

electric field
is applied to a material, and the resulting induced
electric current An electric current is a stream of charged particle In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, ...
is in the same direction, the material is said to be an ''isotropic electrical conductor''. If the resulting electric current is in a different direction from the applied electric field, the material is said to be an ''anisotropic electrical conductor''.


See also

*
Bundle conductor An overhead power line is a structure used in electric power transmission and Electric power distribution, distribution to transmit electrical energy across large distances. It consists of one or more uninsulated electrical cables (commonly mu ...
*
Charge transfer complex A charge-transfer (CT) complex or electron-donor-acceptor complex is an association of two or more molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five ...
*
Electrical resistivity and conductivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current An electric current is a stream of charged particle In p ...
*
Fourth rail A railway electrification system supplies electric power Electric power is the rate, per unit time, at which electrical energy Electrical energy is energy derived as a result of movement of electrically charged particles. When used loos ...
*
Overhead line An overhead line or overhead wire is an electrical cable An electrical cable is an assembly of one or more wire A wire is a single usually cylindrical A cylinder (from Greek Greek may refer to: Greece Anything of, from, or related ...
* Stephen Gray, first to identify electrical conductors and insulators *
Superconductivity Superconductivity is a set of physical properties observed in certain materials where electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current An electric current is a st ...

Superconductivity
*
Third rail A third rail, also known as a live rail, electric rail or conductor rail, is a method of providing electric power Electric power is the rate, per unit time, at which electrical energy Electrical energy is energy derived from electric po ...


References


Further reading


Pioneering and historical books

* William Henry Preece. ''On Electrical Conductors''. 1883. * Oliver Heaviside. ''Electrical Papers''. Macmillan, 1894.


Reference books

* ''Annual Book of ASTM Standards: Electrical Conductors.'' American Society for Testing and Materials. (every year) * ''IET Wiring Regulations.'' Institution for Engineering and Technology
wiringregulations.net


External links


BBC: Key Stage 2 Bitesize: Electrical Conductors


{{DEFAULTSORT:Electrical Conductor Electricity