Views: 3 Author: Site Editor Publish Time: 2023-04-25 Origin: Site
Copper has been used in wires since the invention of the electromagnet and the telegraph in the 1820s.The invention of the telephone in 1876 further fueled the need for copper wire as an electrical conductor.Copper is an electrical conductor in many classes of wire.Copper wire is used in the generation, transmission, distribution, telecommunications, electronic circuits, and countless types of electrical equipment.Copper and its alloys are also used to make electrical contacts.Wires in buildings are the most important market for the copper industry.About half of all mined copper is used to make wire and cable conductors.
Electrical conductivity measures the ability of a material to transport electrical charge.This is a fundamental property in electrical wiring systems.Copper has the highest conductivity of all non-noble metals: at 20 °C,copper resistivity = 16.78 nΩ•m.Solid metal theory helps to explain the unusually high electrical conductivity of copper.In copper atoms, the outermost 4s energy band, or conduction band, is only half filled, so many electrons are able to carry current.When an electric field is applied to the copper wire, the conduction of electrons to the positive terminal is accelerated, thereby generating an electric current.These electrons encounter resistance by colliding with impurity atoms, vacancies, lattice ions, and defects.The average distance traveled between collisions, defined as the "mean free path" is inversely proportional to the resistivity of the metal.Copper is unique in its long mean free path (approximately 100 atomic distances at room temperature).As the copper cools, this means that the free path increases rapidly.
Due to its excellent conductivity, annealed copper becomes the international standard for all other electrical conductors.In 1913, the International Electrotechnical Commission defined the conductivity of commercially pure copper in its International Standard for Annealed Copper as 100% IACS = 58.0 MS/m, with a drop of 0.393%/°C at 20 °C.As commercial purity has improved over the last century,copper conductors used in building electrical wiring generally exceed the 100% IACS standard by a little.
The primary copper grade used for electrical applications is Electrolytic Toughened (ETP) Copper (CW004A or ASTM No. C11040). This copper is at least 99.90% pure and has a conductivity of at least 101% IACS.ETP copper contains a small amount of oxygen (0.02 to 0.04%).If highly conductive copper is required for soldering or brazing or for use in reducing atmospheres, extra pure oxygen-free copper (CW008A or ASTM designation C10100) can be used;it increases conductivity by about 1% (i.e. to at least 101% IACS).
Several conductive metals have lower densities than copper,but require larger cross-sections to carry the same current, and may not be available when limited space is the primary requirement.The electrical conductivity of aluminum is 61% that of copper.For the same current carrying capacity, the cross-sectional area of aluminum conductors must be 56% larger than that of copper.The need to increase the thickness of aluminum wire limits its use in many applications,such as in small electric motors and automobiles. However,in some applications such as overhead power transmission cables, aluminum predominates while copper is rarely used.
Silver is a precious metal and the only metal with a higher conductivity than copper.The conductivity of silver is 106% of that of annealed copper on the IACS scale, and the resistivity of silver at 20 °C = 15.9 nΩ•m.The high cost of silver and its low tensile strength limit its use in special applications such as connection plating and sliding contact surfaces, and in high-quality coaxial cables for frequencies above 30 MHz. Conductor Plating.