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60-425: Rewiring is work done by an electrician. Rewire , Rewired and variants may also refer to: Rewiring Electrical wiring is an electrical installation of cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure. Wiring is subject to safety standards for design and installation. Allowable wire and cable types and sizes are specified according to

120-504: A brass or lead-coated iron sheet tube, with a crimped seam. The enclosure could also be used as a return conductor. Kuhlo wire could be run exposed on surfaces and painted, or embedded in plaster. Special outlet and junction boxes were made for lamps and switches, made either of porcelain or sheet steel. The crimped seam was not considered as watertight as the Stannos wire used in England, which had

180-514: A cable is permitted to carry. Because multiple conductors bundled in a cable cannot dissipate heat as easily as single insulated conductors, those circuits are always rated at a lower ampacity . Tables in electrical safety codes give the maximum allowable current based on size of conductor, voltage potential, insulation type and thickness, and the temperature rating of the cable itself. The allowable current will also be different for wet or dry locations, for hot (attic) or cool (underground) locations. In

240-430: A constant multiple, diameters vary geometrically . Any two successive gauges (e.g., A and B ) have diameters whose ratio (dia. B ÷ dia. A ) is 92 39 {\displaystyle {\sqrt[{39}]{92}}} (approximately 1.12293), while for gauges two steps apart (e.g., A , B , and C ), the ratio of the C to A is about 1.12293 ≈ 1.26098. Similarly for gauges n steps apart

300-468: A copper conductor with plastic insulation. The diameter information in the table applies to solid wires. Stranded wires are calculated by calculating the equivalent cross sectional copper area . Fusing current (melting wire) is estimated based on 25 °C (77 °F) ambient temperature. The table below assumes DC , or AC frequencies equal to or less than 60 Hz, and does not take skin effect into account. "Turns of wire per unit length"

360-410: A copper tube and the space filled with magnesium oxide powder. The whole assembly is drawn down to smaller sizes, thereby compressing the powder. Such cables have a certified fire resistance rating and are more costly than non–fire-rated cable. They have little flexibility and behave more like rigid conduit rather than flexible cables. The environment of the installed wires determine how much current

420-408: A cross section of 250 kcmil. A circular mil is the area of a wire one mil in diameter. One million circular mils is the area of a circle with 1,000 mil (1 inch) diameter. An older abbreviation for one thousand circular mils is MCM . AWG can also be used to describe stranded wire. The AWG of a stranded wire represents the sum of the cross-sectional diameter of the individual strands;

480-662: A flexible plastic jacket. In North America and the UK this conductor is usually bare wire but in the UK it is required that this bare Protective Earth (PE) conductor be sheathed in Green/Yellow insulating tubing where the Cable Sheathing has been removed. Most other jurisdictions now require the Protective Earth conductor to be insulated to the same standard as the current carrying conductors with Green/Yellow insulation. With some cables

540-412: A grounded barrier from the adjacent phases (segregated bus). For conducting large currents between devices, a cable bus is used. For very large currents in generating stations or substations, where it is difficult to provide circuit protection, an isolated-phase bus is used. Each phase of the circuit is run in a separate grounded metal enclosure. The only fault possible is a phase-to-ground fault, since

600-432: A light commercial environment, more frequent wiring changes can be expected, large apparatus may be installed and special conditions of heat or moisture may apply. Heavy industries have more demanding wiring requirements, such as very large currents and higher voltages, frequent changes of equipment layout, corrosive, or wet or explosive atmospheres. In facilities that handle flammable gases or liquids, special rules may govern

660-434: A quantifiable impact upon the ampacity derating, because the thermal insulation properties needed for fire resistance also inhibit air cooling of power conductors. Cable trays are used in industrial areas where many insulated cables are run together. Individual cables can exit the tray at any point, simplifying the wiring installation and reducing the labour cost for installing new cables. Power cables may have fittings in

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720-490: A run of cable through several areas, the part with the lowest rating becomes the rating of the overall run. Cables usually are secured with special fittings where they enter electrical apparatus; this may be a simple screw clamp for jacketed cables in a dry location, or a polymer-gasketed cable connector that mechanically engages the armour of an armoured cable and provides a water-resistant connection. Special cable fittings may be applied to prevent explosive gases from flowing in

780-567: A slash. For example, a 22   AWG 7/30 stranded wire is a 22   AWG wire made from seven strands of 30   AWG wire. As indicated in the Formulas and Rules of Thumb sections above, differences in AWG translate directly into ratios of diameter or area. This property can be employed to easily find the AWG of a stranded bundle by measuring the diameter and count of its strands. (This only applies to bundles with circular strands of identical size.) To find

840-482: A soldered sheath. A somewhat similar system called "concentric wiring" was introduced in the United States around 1905. In this system, an insulated electrical wire was wrapped with copper tape which was then soldered, forming the grounded (return) conductor of the wiring system. The bare metal sheath, at earth potential, was considered safe to touch. While companies such as General Electric manufactured fittings for

900-494: Is accomplished through the use of thicker, specially constructed jackets, and by tinning the individual wire stands. In North American practice, for residential and light commercial buildings fed with a single-phase split 120/240 service , an overhead cable from a transformer on a power pole is run to the service entrance point. The cable is a three conductor twisted "triplex" cable with a bare neutral and two insulated conductors, with no overall cable jacket. The neutral conductor

960-490: Is attempting to harmonise wiring standards among member countries, but significant variations in design and installation requirements still exist. Materials for wiring interior electrical systems in buildings vary depending on: Wiring systems in a single family home or duplex, for example, are simple, with relatively low power requirements, infrequent changes to the building structure and layout, usually with dry, moderate temperature and non-corrosive environmental conditions. In

1020-496: Is often a supporting "messenger" steel wire, which is used to support the insulated line conductors. Electrical devices often use copper conductors because of their properties, including their high electrical conductivity , tensile strength , ductility , creep resistance, corrosion resistance , thermal conductivity , coefficient of thermal expansion , solderability , resistance to electrical overloads , compatibility with electrical insulators , and ease of installation. Copper

1080-489: Is permitted, unless the fitting is rated or listed for multiple cables. Special cable constructions and termination techniques are required for cables installed in ships. Such assemblies are subjected to environmental and mechanical extremes. Therefore, in addition to electrical and fire safety concerns, such cables may also be required to be pressure-resistant where they penetrate a vessel's bulkheads. They must also resist corrosion caused by salt water or salt spray , which

1140-417: Is similar to many other non-metric gauging systems such as British Standard Wire Gauge (SWG). However, AWG is dissimilar to IEC 60228 , the metric wire-size standard used in most parts of the world, based directly on the wire cross-section area (in square millimetres, mm ). The AWG tables are for a single, solid and round conductor. The AWG of a stranded wire is determined by the cross-sectional area of

1200-799: Is solid wire, since the wiring is not required to be very flexible. Building wire conductors larger than 10 AWG (or about 5 mm ) are stranded for flexibility during installation, but are not sufficiently pliable to use as appliance cord. Cables for industrial, commercial and apartment buildings may contain many insulated conductors in an overall jacket, with helical tape steel or aluminium armour, or steel wire armour, and perhaps as well an overall PVC or lead jacket for protection from moisture and physical damage. Cables intended for very flexible service or in marine applications may be protected by woven bronze wires. Power or communications cables (e.g., computer networking) that are routed in or through air-handling spaces (plenums) of office buildings are required under

1260-457: Is the reciprocal of the conductor diameter; it is therefore an upper limit for wire wound in the form of a helix (see solenoid ), based on uninsulated wire. In the North American electrical industry, conductors thicker than 4/0   AWG are generally identified by the area in thousands of circular mils (kcmil), where 1 kcmil = 0.5067 mm . The next wire size thicker than 4/0 has

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1320-455: Is used in industrial cables and power cables installed underground because of its superior moisture resistance. Insulated cables are rated by their allowable operating voltage and their maximum operating temperature at the conductor surface. A cable may carry multiple usage ratings for applications, for example, one rating for dry installations and another when exposed to moisture or oil. Generally, single conductor building wire in small sizes

1380-512: Is used in many types of electrical wiring. Aluminium wire was common in North American residential wiring from the late 1960s to mid-1970s due to the rising cost of copper. Because of its greater resistivity , aluminium wiring requires larger conductors than copper. For instance, instead of 14 AWG ( American wire gauge ) copper wire, aluminium wiring would need to be 12 AWG on a typical 15 ampere lighting circuit, though local building codes vary. Solid aluminium conductors were originally made in

1440-427: Is used to distribute power down the length of a building; it is constructed to allow tap-off switches or motor controllers to be installed at designated places along the bus. The big advantage of this scheme is the ability to remove or add a branch circuit without removing voltage from the whole duct. Bus ducts may have all phase conductors in the same enclosure (non-isolated bus), or may have each conductor separated by

1500-485: The CO/ALR "copper-aluminium-revised" designation) were developed to reduce these problems. While larger sizes are still used to feed power to electrical panels and large devices, aluminium wiring for residential use has acquired a poor reputation and has fallen out of favour. Aluminium conductors are still heavily used for bulk power transmission , power distribution , and large feeder circuits with heavy current loads, due to

1560-525: The 1930s, was knob and tube (K&T) wiring: single conductors were run through cavities between the structural members in walls and ceilings, with ceramic tubes forming protective channels through joists and ceramic knobs attached to the structural members to provide air between the wire and the lumber and to support the wires. Since air was free to circulate over the wires, smaller conductors could be used than required in cables. By arranging wires on opposite sides of building structural members, some protection

1620-457: The 1960s from a utility-grade aluminium alloy that had undesirable properties for a building wire, and were used with wiring devices intended for copper conductors. These practices were found to cause defective connections and fire hazards. In the early 1970s new aluminium wire made from one of several special alloys was introduced, and all devices – breakers, switches, receptacles, splice connectors , wire nuts , etc. — were specially designed for

1680-407: The AWG of 7-strand wire with equal strands, subtract 8.4 from the AWG of a strand. Similarly, for 19-strand subtract 12.7, and for 37 subtract 15.6. Measuring strand diameter is often easier and more accurate than attempting to measure bundle diameter and packing ratio. Such measurement can be done with a wire gauge go-no-go tool or with a caliper or micrometer. Alternative ways are commonly used in

1740-399: The above formulas. For instance, for 0000 AWG or 4/0 AWG, use n = −3 . The sixth power of √ 92 is very close to 2, which leads to the following rules of thumb: Convenient coincidences result in the following rules of thumb for resistances: The table below shows various data including both the resistance of the various wire gauges and the allowable current ( ampacity ) based on

1800-423: The benefit of air cooling. A variation is to use heavy cables, especially where it is desirable to transpose or "roll" phases. In industrial applications, conductor bars are often pre-assembled with insulators in grounded enclosures. This assembly, known as bus duct or busway, can be used for connections to large switchgear or for bringing the main power feed into a building. A form of bus duct known as "plug-in bus"

1860-494: The circuit operating voltage and electric current capability, with further restrictions on the environmental conditions, such as ambient temperature range, moisture levels, and exposure to sunlight and chemicals. Associated circuit protection, control, and distribution devices within a building's wiring system are subject to voltage, current, and functional specifications. Wiring safety codes vary by locality, country, or region. The International Electrotechnical Commission (IEC)

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1920-455: The conductors. Rubber insulation further inside the cable often is in better condition than the insulation exposed at connections, due to reduced exposure to oxygen. The sulfur in vulcanized rubber insulation attacked bare copper wire so the conductors were tinned to prevent this. The conductors reverted to being bare when rubber ceased to be used. About 1950, PVC insulation and jackets were introduced, especially for residential wiring. About

1980-685: The contact surface does not oxidise. Insulated wires may be run in one of several forms between electrical devices. This may be a specialised bendable pipe, called a conduit , or one of several varieties of metal (rigid steel or aluminium) or non-metallic ( PVC or HDPE ) tubing. Rectangular cross-section metal or PVC wire troughs (North America) or trunking (UK) may be used if many circuits are required. Wires run underground may be run in plastic tubing encased in concrete, but metal elbows may be used in severe pulls. Wiring in exposed areas, for example factory floors, may be run in cable trays or rectangular raceways having lids. Where wiring, or raceways that hold

2040-675: The current capacity (ampacity). Special sealed fittings are used for wiring routed through potentially explosive atmospheres. For very high currents in electrical apparatus, and for high currents distributed through a building, bus bars can be used. (The term "bus" is a contraction of the Latin omnibus – meaning "for all".) Each live ("hot") conductor of such a system is a rigid piece of copper or aluminium, usually in flat bars (but sometimes as tubing or other shapes). Open bus bars are never used in publicly accessible areas, although they are used in manufacturing plants and power company switch yards to gain

2100-603: The development of standardized wire gauges rationalized selection of wire for a particular purpose. While the AWG is essentially identical to the Brown & Sharpe (B&S) sheet metal gauge, the B&;S gauge was designed for use with sheet metals as its name suggests. These are functionally interchangeable but the use of B&S in relation to wire gauges, rather than sheet metal gauges, is technically improper. Increasing gauge numbers denote logarithmically decreasing wire diameters, which

2160-464: The electrical industry to specify wire sizes as AWG. AWG is colloquially referred to as gauge and the zeros in thick wire sizes are referred to as aught / ˈ ɔː t / . Wire sized 1 AWG is referred to as "one gauge" or "No. 1" wire; similarly, thinner sizes are pronounced " x  gauge" or "No.  x " wire, where x is the positive-integer AWG number. Consecutive AWG wire sizes thicker than No. 1 wire are designated by

2220-458: The enclosures are separated. This type of bus can be rated up to 50,000 amperes and up to hundreds of kilovolts (during normal service, not just for faults), but is not used for building wiring in the conventional sense. Electrical panels are easily accessible junction boxes used to reroute and switch electrical services . The term is often used to refer to circuit breaker panels or fuseboxes. Local codes can specify physical clearance around

2280-461: The equivalent solid conductor. Because there are also small gaps between the strands, a stranded wire will always have a slightly larger overall diameter than a solid wire with the same AWG. By definition, 36 AWG is 0.005 inches in diameter, and 0000 AWG is 0.46 inches in diameter. The ratio of these diameters is 1:92, and there are 40 gauge sizes from 36 to 0000, or 39 steps. Because each successive gauge number increases cross sectional area by

2340-437: The framing of the building or on running boards. Where conductors went through walls, they were protected with cloth tape. Splices were done similarly to telegraph connections, and soldered for security. Underground conductors were insulated with wrappings of cloth tape soaked in pitch, and laid in wooden troughs which were then buried. Such wiring systems were unsatisfactory because of the danger of electrocution and fire, plus

2400-411: The gaps between strands are not counted. When made with circular strands, these gaps occupy about 25% of the wire area , thus requiring the overall bundle diameter to be about 13% larger than a solid wire of equal gauge. Stranded wires are specified with three numbers, the overall AWG size, the number of strands, and the AWG size of a strand. The number of strands and the AWG of a strand are separated by

2460-510: The high labour cost for such installations. The first electrical codes arose in the 1880s with the commercial introduction of electrical power; however, many conflicting standards existed for the selection of wire sizes and other design rules for electrical installations, and a need was seen to introduce uniformity on the grounds of safety. The earliest standardized method of wiring in buildings, in common use in North America from about 1880 to

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2520-514: The individual conductors are wrapped in paper before the plastic jacket is applied. Special versions of non-metallic sheathed cables, such as US Type UF, are designed for direct underground burial (often with separate mechanical protection) or exterior use where exposure to ultraviolet radiation (UV) is a possibility. These cables differ in having a moisture-resistant construction, lacking paper or other absorbent fillers, and being formulated for UV resistance. Rubber-like synthetic polymer insulation

2580-406: The installation and wiring of electrical equipment in hazardous areas . Wires and cables are rated by the circuit voltage, temperature rating and environmental conditions (moisture, sunlight, oil, chemicals) in which they can be used. A wire or cable has a voltage (to neutral) rating and a maximum conductor surface temperature rating. The amount of current a cable or wire can safely carry depends on

2640-651: The installation conditions. The international standard wire sizes are given in the IEC 60228 standard of the International Electrotechnical Commission . In North America, the American Wire Gauge standard for wire sizes is used. Modern non-metallic sheathed cables, such as (US and Canadian) Types NMB and NMC, consist of two to four wires covered with thermoplastic insulation, plus a wire for Protective Earthing/Grounding (bonding), surrounded by

2700-471: The insulation, with an overall woven jacket, usually impregnated with tar as a protection from moisture. Waxed paper was used as a filler and separator. Over time, rubber-insulated cables become brittle because of exposure to atmospheric oxygen, so they must be handled with care and are usually replaced during renovations. When switches, socket outlets or light fixtures are replaced, the mere act of tightening connections may cause hardened insulation to flake off

2760-419: The interior of jacketed cables, where the cable passes through areas where flammable gases are present. To prevent loosening of the connections of individual conductors of a cable, cables must be supported near their entrance to devices and at regular intervals along their runs. In tall buildings, special designs are required to support the conductors of vertical runs of cable. Generally, only one cable per fitting

2820-404: The model building code to be either encased in metal conduit, or rated for low flame and smoke production. For some industrial uses in steel mills and similar hot environments, no organic material gives satisfactory service. Cables insulated with compressed mica flakes are sometimes used. Another form of high-temperature cable is mineral-insulated cable , with individual conductors placed within

2880-434: The panels. Squirrels , rats, and other rodents may gnaw on unprotected wiring, causing fire and shock hazards. This is especially true of PVC-insulated telephone and computer network cables. Several techniques have been developed to deter these pests, including insulation loaded with pepper dust. The first interior power wiring systems used conductors that were bare or covered with cloth, which were secured by staples to

2940-592: The purpose. These newer aluminium wires and special designs address problems with junctions between dissimilar metals, oxidation on metal surfaces, and mechanical effects that occur as different metals expand at different rates with increases in temperature. Unlike copper, aluminium has a tendency to creep or cold-flow under pressure, so older plain steel screw clamped connections could become loose over time. Newer electrical devices designed for aluminium conductors have features intended to compensate for this effect. Unlike copper, aluminium forms an insulating oxide layer on

3000-594: The ratio between successive sizes to be the 39th root of 92, or approximately 1.1229322. ASTM B258-02 also dictates that wire diameters should be tabulated with no more than 4 significant figures, with a resolution of no more than 0.0001 inches (0.1 mils) for wires thicker than 44 AWG, and 0.00001 inches (0.01 mils) for wires 45 AWG and thinner. Sizes with multiple zeros are successively thicker than 0 AWG and can be denoted using " number of zeros /0", for example 4/0 AWG for 0000 AWG. For an m /0   AWG wire, use n = −( m − 1) = 1 − m in

3060-583: The ratio of the first to last gauges is about 1.12293 . The diameter of an AWG wire is determined according to the following formula: (where n is the AWG size for gauges from 36 to 0, n = −1 for 00, n = −2 for 000, and n = −3 for 0000. See below for rule.) or equivalently: The gauge can be calculated from the diameter using  and the cross-section area is The standard ASTM B258-02 (2008), Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors , defines

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3120-447: The same time, single conductors with a thinner PVC insulation and a thin nylon jacket (e.g. US Type THN, THHN, etc.) became common. American wire gauge The AWG originated in the number of drawing operations used to produce a given gauge of wire. Very fine wire (for example, 30 gauge) required more passes through the drawing dies than 0 gauge wire did. Manufacturers of wire formerly had proprietary wire gauge systems;

3180-499: The surface. This is sometimes addressed by coating aluminium conductors with an antioxidant paste (containing zinc dust in a low-residue polybutene base ) at joints, or by applying a mechanical termination designed to break through the oxide layer during installation. Some terminations on wiring devices designed only for copper wire would overheat under heavy current load and cause fires when used with aluminium conductors. Revised standards for wire materials and wiring devices (such as

3240-477: The system and a few buildings were wired with it, it was never adopted into the US National Electrical Code. Drawbacks of the system were that special fittings were required, and that any defect in the connection of the sheath would result in the sheath becoming energised. Armored cables with two rubber-insulated conductors in a flexible metal sheath were used as early as 1906, and were considered at

3300-503: The time a better method than open knob-and-tube wiring, although much more expensive. The first rubber-insulated cables for US building wiring were introduced in 1922 with US patent 1458803 , Burley, Harry & Rooney, Henry, "Insulated electric wire", issued 1923-06-12, assigned to Boston Insulated Wire and Cable   . These were two or more solid copper electrical wires with rubber insulation, plus woven cotton cloth over each conductor for protection of

3360-559: The time. Paper-insulated cables proved unsuitable for interior wiring installations because very careful workmanship was required on the lead sheaths to ensure moisture did not affect the insulation. A system later invented in the UK in 1908 employed vulcanised-rubber insulated wire enclosed in a strip metal sheath. The metal sheath was bonded to each metal wiring device to ensure earthing continuity. A system developed in Germany called "Kuhlo wire" used one, two, or three rubber-insulated wires in

3420-656: The tray to maintain clearance between the conductors, but small control wiring is often installed without any intentional spacing between cables. Local electrical regulations may restrict or place special requirements on mixing of voltage levels within one cable tray. Good design practices may segregate, for example, low level measurement or signal cables from trays carrying high power branch circuits, to prevent induction of noise into sensitive circuits. Since wires run in conduits or underground cannot dissipate heat as easily as in open air, and since adjacent circuits contribute induced currents, wiring regulations give rules to establish

3480-510: The various advantages they offer over copper wiring. Aluminium conductors both cost and weigh less than copper conductors, so a much larger cross sectional area can be used for the same weight and price. This can compensate for the higher resistance and lower mechanical strength of aluminium, meaning the larger cross sectional area is needed to achieve comparable current capacity and other features. Aluminium conductors must be installed with compatible connectors and special care must be taken to ensure

3540-475: The wiring, must traverse fire-resistance rated walls and floors, the openings are required by local building codes to be firestopped . In cases where safety-critical wiring must be kept operational during an accidental fire, fireproofing must be applied to maintain circuit integrity in a manner to comply with a product's certification listing . The nature and thickness of any passive fire protection materials used in conjunction with wiring and raceways has

3600-805: Was afforded against short-circuits that can be caused by driving a nail into both conductors simultaneously. By the 1940s, the labor cost of installing two conductors rather than one cable resulted in a decline in new knob-and-tube installations. However, the US code still allows new K&T wiring installations in special situations (some rural and industrial applications). In the United Kingdom, an early form of insulated cable, introduced in 1896, consisted of two impregnated-paper-insulated conductors in an overall lead sheath. Joints were soldered, and special fittings were used for lamp holders and switches. These cables were similar to underground telegraph and telephone cables of

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