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Encyclopedia > Power cable

A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power. In science and engineering, conductors are materials that contain movable charges of electricity. ...

Contents

History

Early telegraph systems were the first forms of electrical cabling but transmitted only small amounts of power. Gutta-percha insulation used for the first transatlantic cables was unsuitable for building wiring use since gutta-percha deteriorated rapidly when exposed to air. The first power distribution system developed by Thomas Edison used copper rods, wrapped in jute and placed in rigid pipes filled with a bituminous compound. Although vulcanized rubber had been patented by Charles Goodyear in 1844, it was not applied to cable insulation until the 1880s, when it was used for lighting circuits. Rubber-insulated cable was used for 11,000 volt circuits in 1897 installed for the Niagara Falls power project. Oil-impregenated paper-insulated high voltage cables were commercially practical by 1895. During World War II several varieties of synthetic rubber, and polyethylene insulation was applied to cables. Telegraphy (from the Greek words tele = far away and grapho = write) is the long distance transmission of written messages without physical transport of letters, originally over wire. ... Species About 100-120 species, including: Palaquium amboinense Palaquium barnesii Palaquium bataanense Palaquium beccarianum Palaquium borneense Palaquium burckii Palaquium clarkeanum Palaquium cochleariifolium Palaquium dasyphyllum Palaquium ellipticum Palaquium formosanum Palaquium galactoxylum Palaquium gutta Palaquium herveyi Palaquium hexandrum Palaquium hispidum Palaquium hornei Palaquium impressinervium Palaquium kinabaluense Palaquium lanceolatum Palaquium leiocarpum Palaquium lobbianum... A transatlantic telephone cable is a submarine communications cable that carries telephone traffic under the Atlantic Ocean between North America and Europe. ... Thomas Alva Edison (February 11, 1847 – October 18, 1931) was an American inventor and businessman who developed many devices which greatly influenced life in the 20th century. ... Combatants Major Allied powers: United Kingdom Soviet Union United States Republic of China and others Major Axis powers: Nazi Germany Italy Japan and others Commanders Winston Churchill Joseph Stalin Franklin Roosevelt Harry Truman Chiang Kai-Shek Adolf Hitler Benito Mussolini Hideki Tojo Casualties Military dead: 17,000,000 Civilian dead... This article or section does not cite its references or sources. ...


Construction

Modern power cables come in a variety of sizes, materials, and types, each particularly adapted to its uses. Large single insulated conductors are also called power cables in the trade.


Conductors are usually made of copper or aluminum wires, or may be composite conductors with steel strands at their core. Conductors are usually stranded for flexibility, but small cables may use solid conductors.


Conductors in a cable may be different sizes. Each conductor has its own electrical insulation. The cable may include uninsulated conductors used for the circuit neutral or for ground (earth) connection.


The overall assembly may be round or flat. Filler strands may be added to the assembly to maintain its shape. Special purpose power cables for overhead or vertical use may have additional elements such as steel or Kevlar structural supports. Kevlar is DuPont Companys brand name for a particular light but very strong aramid fibre. ...


For circuits operating at 2400 volts between conductors or more, a conductive shield surrounds each conductor. This equalizes electrical stress on the cable insulation. This technique was patented by Martin Hochstadter in 1916, and so the shield is sometimes called a Hochstadter shield. The individual conductor shields of a cable are connected to earth ground at one or both ends of each length of cable.


Some power cables for outdoor overhead use may have no overall sheath. Other cables may have a plastic or metal sheath enclosing all the conductors. The materials for the sheath will be selected for the intended application, and may be specially resistant to water, oil, sunlight, underground conditions, chemical vapors, impact, or high temperatures. Cables intended for underground use or direct burial in earth will have heavy plastic sheaths, or may be protected by a lead sheath. Where cables must run where exposed to impact damage, they are protected with flexible steel tape or wire armor, which may also be covered by a water resistant jacket.


Cables for high-voltage (more than 65,000 volts) power distribution may be insulated with oil and paper, and are run in a rigid steel pipe, semi-rigid aluminium or lead jacket/sheath. The oil is kept under pressure to prevent formation of voids that would allow partial discharges within the cable insulation. In electrical engineering, a partial discharge (PD) is a localised dielectric breakdown of a small portion of a solid or liquid electrical insulation system under high voltage stress. ...


A hybrid cable will include conductors for control signals or may also include optical fibers for data. Besides data transmission, these optical fibres are used for distributed temperature monitoring in order to optimize the load/ampacity of the cable. Fiber Optic strands An optical fiber in American English or fibre in British English is a transparent thin fiber for transmitting light. ... Distributed temperature sensing systems (DTS) are optoelectronic devices which measure temperatures by means of optical fibres functioning as linear sensors. ...


Named cable types

Common types of general-purpose cables used by electricians are defined by national or international regulations or codes. Commonly-used types of power cables are often known by a "shorthand" name. For example, NEC type NM-B (Non-Metallic, variant B), often referred to as RomexTM (named by the Rome Wire Company, now a trademark of Southwire Company [1]), is a cable with a nonmetallic jacket. UF (underground feeder) is also nonmetallic but uses a moisture- and sunlight-resistant construction suitable for direct burial in the earth or where exposed to sunlight, or in wet, dry, or corrosive locations. Type AC is a fabricated assembly of insulated conductors in a flexible metallic armor, made by twisting an interlocking metal strip around the conductors. BX, an early genericized trademark of the General Electric company was used before and during WWII, designating a particular design of armored cable. An electrician is a tradesman specializing in electrical wiring of buildings and related equipment. ... The National Electric Code manual, 2005 edition The National Electrical Code, NFPA 70 is part of the National Fire Codes published by the National Fire Protection Association (NFPA). ... A genericized trademark (Commonwealth English genericised trade mark), sometimes known as a generic trade mark, generic descriptor or proprietary eponym, is a trademark or brand name which is often used as the colloquial description for a particular type of product or service as a result of widespread popular or cultural... GE redirects here. ...


In Canada, type TECK cable, with a flexible aluminum or steel armour and overall flame-retardent PVC jacket, is used in industry for wet or dry locations, run in trays or attached to building structure, above grade or buried in earth. A similar type of cable is designated type MC in the United States. Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... The old Steel cable of a colliery winding tower Steel is a metal alloy whose major component is iron, with carbon content between 0. ... Polyvinyl chloride Polyvinyl chloride, (IUPAC über Polychloroethene) commonly abbreviated PVC, is a widely used thermoplastic polymer. ...


Electrical power cables are often installed in raceways including electrical conduit, and cable trays, which may contain one or more conductors. Conduit may also be rigid or flexible, metallic or nonmetallic, and differentiation from cable may require some investigation of the contents at their termination.


Mineral Insulated Copper Clad cable (type MI) is a fire-resistant cable using magnesium oxide as an insulator. It is used in demanding applications such as fire alarms and oil refineries. PVC-sheathed MICC cable. ... Magnesium oxide Magnesium oxide is a white solid mineral that occurs naturally as periclase and is a source of magnesium. ... A Wheelock MT-24-LSM fire alarm horn and strobe. ... View of Shell Oil Refinery in Martinez, California. ...


Ampacity and ampacity derating

moved to ampacity


Flexible cables

All cables are flexible, which allows them to be shipped to installation sites on reels or drums. Where applications require a cable to be moved repeatedly, more flexible cables are used. Small cables are called "cords" or "flex". Flexible cords contain finer stranded conductors, rather than solid, and have insulation and sheaths that are engineered to withstand the forces of repeated flexing. Heavy duty flexible power cords such as feeding a mine face cutting machine are carefully engineered -- since their life is measurable in (6) weeks! See "Power cord" and "Extension cable" for further description of flexible power cables. Other types of flexible cable include twisted pair, extensible, coaxial, shielded, and communication cable. A power cord or mains cable is a cable that temporarily connects an electrical appliance to an electrical power source. ... An extension cord (also known as a power extender or an extension lead) is a length of flexible electrical cable (flex) with a plug on one end and one or more sockets on the other end (usually of the same type as the plug). ... 25 Pair Color Code Chart 10BASE-T UTP Cable Twisted pair cabling is a common form of wiring in which two conductors are wound around each other for the purposes of cancelling out electromagnetic interference known as crosstalk. ... Coaxial cable is an electrical cable consisting of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath, usually surrounded by a final insulating layer. ... Four-conductor shielded cable with metal foil shield and drain wire A shielded cable is a simple insulated cable with a braided shield of strands of copper(or other metal), a non braided(solid) shield, or a winding of metal tape completely enclosing this insulation. ...


See also

Electrical wiring in general refers to conductors used to carry electricity, and their accessories. ... American wire gauge (AWG), also known as the Brown and Sharpe wire gauge, is used in the United States and other countries as a standard method of denoting wire diameter, especially for nonferrous, electrically conducting wire. ... Ampacity is the rms current which a device can carry within specified temperature limitations in a specified environment dependent upon: a) temperature rating, b) power loss, c) heat dissipation. ... Voltage drop is the reduction in voltage in an electrical circuit between the source and utilitization device. ... XLPE (Cross-linked polyethylene) is a kind of insulator which is used as insulation layer in underground power cables. ... Ethylene propylene rubber also known as EPR is an insulation used for high voltage cables. ...

References

Underground Systems Reference Book , Edison Electric Institute, New York, 1957, no ISBN


  Results from FactBites:
 
Power cable - Wikipedia, the free encyclopedia (1004 words)
Cables for high-voltage (more than 65,000 volts) power distribution may be insulated with oil and paper, and are run in a rigid steel pipe, semi-rigid aluminium or lead jacket/sheath.
In Canada, type TECK cable, with a flexible aluminum or steel armour and overall flame-retardent PVC jacket, is used in industry for wet or dry locations, run in trays or attached to building structure, above grade or buried in earth.
Electrical power cables are often installed in raceways including electrical conduit, and cable trays, which may contain one or more conductors.
  More results at FactBites »

 
 

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