Copper wire and cable
Encyclopedia
Copper
has been used in electric wiring since the invention of the electromagnet
and the telegraph in the 1820s. The invention of the telephone
in 1876 proved to be another early boon for copper wire.
Today, despite competition from other materials, copper remains the preferred electrical conductor
in nearly all categories of electrical wiring. For example, copper is used to conduct electricity in high, medium and low volt
age power networks, including power generation, power transmission
, power distribution, telecommunications, electronics
circuitry, data processing
, instrumentation
, appliances, entertainment systems, motors, transformers
, heavy industrial machinery, and countless other types of electrical equipment
. Aside from electrical conductors, other important electrical applications for copper include electrical contacts and resistors.
Electrical wiring is the most important market for the copper industry. Roughly half of all copper mined is used to manufacture electrical wire and cable conductors.
. This is an essential property in electrical wiring systems. Copper has the highest electrical conductivity rating of all non-precious metals (electrical conductivity of copper = 101% IACS (International Annealed Copper Standard); electrical resistivity of copper = 16.78 nΩ•m at 20 °C). Oxygen-Free Electronic (OFE) copper
achieves a minimum of 101% IACS.
The solid state theory of metals helps to explain the unusually high electrical conductivity of copper. In a copper atom
, the outermost 4s energy zone, or conduction band
, is only half filled, so many electron
s are able to carry electric current
. When an electric field
is applied to a copper wire, the conduction of electrons accelerates towards the electropositive end, thereby creating a current. These electrons encounter resistance to their passage by colliding with impurity atoms, vacancies, lattice ions, and imperfections. The average distance travelled between collisions, defined as the “mean free path
,” is inversely proportional to the resistivity of the metal. What is unique about copper is its long mean free path (approximately 100 atomic spacings at room temperature). Furthermore, this mean free path increases rapidly as copper is chilled.
Silver, an expensive precious metal
, is the only metal with a higher electrical conductivity rating than copper (i.e., electrical conductivity of silver = 106% IACS, electrical resistivity of silver = 15.9 nΩ•m at 20°C). The high cost of silver combined with its low tensile strength
limits its use to special applications, such as joint plating and sliding contact surfaces. With the exception of silver, copper conducts electricity with less resistance than any other metallic material.
Because of its superior conductivity, annealed copper became the international standard to which all other electrical conductors are compared. In 1913, the International Electrotechnical Commission
set the conductivity of copper in its International Annealed Copper Standard (IACS) to 100%. Today, copper conductors used in building wire often exceed the 100% IACS standard.
The main grade of copper used for electrical applications, such as building wire, motor
windings, cables and busbar
s, is electrolytic-tough pitch (ETP) copper (CW004A or ASTM designation C100140). This copper is at least 99.90% pure and has an electrical conductivity of at least 101% IACS. ETP copper contains a small percentage of oxygen
(0.02 to 0.04%). If high conductivity copper needs to be welded
or brazed or used in a reducing atmosphere, then oxygen-free high conductivity copper
(CW008A or ASTM designation C10100) may be used.
Several electrically conductive metals are lighter than copper, but since they require larger cross sections to carry the same current, they are unacceptable when limited space is a major requirement.
Aluminium has 61% of the conductivity of copper. The cross sectional area of an aluminium conductor must be 56% larger than copper for the same current carrying capability. The need to increase the thickness of aluminium wire
restricts its use in several applications, such as in small motors and automobiles. In some applications such as aerial electric power transmission
cables, thickness is an advantage and copper is rare.
measures the force required to pull an object such as rope, wire, or a structural beam to the point where it breaks. The tensile strength of a material is the maximum amount of tensile stress it can take before breaking.
Copper’s higher tensile strength (200-250 N/nm2 annealed) compared to aluminium is another reason why copper is used extensively in the building industry. Copper’s high strength resists stretching, neck-down, creep, nicks and breaks, and thereby also prevents failures and service interruptions.
In equipment installations and machinery using non-copper wiring, nicks and scratches due to vibration and flexing can deteriorate into large breaks in the wiring and lead to failure and long-term service interruptions. For example, when long runs of aluminium are pulled through conduit and cable trays, they can stretch and neck-down. These effects reduce current carrying capacity, wastes energy, and can cause overheating. Because of copper’s higher tensile strength, these problems are minimized in copper wire.
is a material's ability to deform under tensile stress. This is often characterized by the material's ability to be stretched into a wire
. Ductility is especially important in metalworking
because materials that crack or break under stress cannot be hammered, rolled, or drawn (drawing is a process that uses tensile forces to stretch metal).
Copper has a higher ductility than alternate metal conductors with the exception of gold and silver, both expensive precious metals reserved for highly specialized wiring applications. Because of copper’s high ductility, it is easy to draw down to diameters with very close tolerances.
is the gradual deformation of a material from constant expansions and contractions under “load, no-load” conditions. This process has adverse effects on electrical systems: terminations can become loose, causing connections to heat up or create dangerous arcing.
Copper does not creep or loosen at its connections. For other metal conductors that creep, extra maintenance is required to check terminals periodically and ensure that screws remain tightened to prevent arcing and overheating. These extra measures can be avoided with the use of copper wire.
is the unwanted breakdown and weakening of a material due to chemical reactions. Copper resists corrosion from moisture, humidity, industrial pollution, and other atmospheric influences. However, any corrosion oxides, chlorides, and sulfides that do form on copper are conductive, not resistive. Therefore, copper connections and terminations will not overheat from corrosion. Aluminium corrosion products, on the other hand, are resistive and therefore can cause unwanted heat. To prevent corrosion and protect joints, special surface preparations or oxide-inhibiting pastes are applied to aluminium. Copper connections do not require these preparations and their associated additional costs.
Electrolytic-tough pitch (ETP) copper, which is used in building wire, is a noble metal. It is not subject to galvanic corrosion when connected to other, less noble metals and alloys.
for an electrical conducting material. Aluminium, an alternate common conductor, expands nearly one third more than copper under increasing temperatures. This higher degree of expansion, along with aluminium’s lower ductility can cause electrical problems when bolted connections are improperly installed. By using proper hardware, such as spring pressure connections and cupped or split washers at the joint, it may be possible to create aluminium joints that compare in quality to copper joints.
is the ability of a material to conduct heat. In electrical systems, high thermal conductivity is important for dissipating waste heat, particularly at terminations and connections. It is also important for reducing energy consumption due to the generation of waste heat.
Copper has a 60% better thermal conductivity rating than aluminium, so it is better able to reduce thermal hot spots in electrical wiring systems.
is a process whereby two or more metals are joined together by a heating process. This is a desirable property in electrical systems. Some electrical codes require soldered joints. Copper is readily soldered to make durable connections when necessary.
Copper has a melting point of 1083°C. Because of its high melting point, copper conductors can take heavy overloads or current surges without melting. Of all wiring materials, copper is best able to withstand electrical overloads. Also, due to copper’s creep resistance as described previously, electrical overloads will not loosen copper joints.
and polyethylene
.
line cords for appliances, musical instrument cables, computer mouse cables, connections between circuit boards in multi-printed circuit-board devices, welding electrode cables, control cables connecting moving machine parts, mining machine cables, and trailing machine cables.
A stranded copper wire is more flexible and easier to install than a single-strand copper wire. Stranding also improves wire longevity for applications with moderate to high vibration. A particular cross-section of a stranded conductor gives it essentially the same resistance characteristics as a single-strand conductor, but with added flexibility.
Copper wires in a cable may be bare or they may be plated to reduce oxidation with a thin layer of another metal, most often tin
but sometimes gold
or silver
. Plating may lengthen wire life and makes soldering
easier.
Cables can be made with one or two different types of wire. For example, all-copper cables are used in a wide range of applications, including telecommunications and power distribution. Combination conductor cables, such as copper and steel
, are used when increased strength with high conductivity is required over long distances (e.g., several hundred-meter spans), such as for telephone cables or for thin hookups, such as CATV cable.
Some cables are designed to be multi-functional, such as those installed in residences to carry power, telephone, video, and control/communications signals. They are usually made from copper.
Current-carrying cables radiate an electromagnetic field
. Cables also pick up energy from any existing electromagnetic fields that are around it. These effects are often undesirable, in the first case amounting to unwanted transmission of energy which may adversely affect nearby equipment or other parts of the same piece of equipment; and in the second case, unwanted pickup of noise which may mask the desired signal being carried by the cable, or, if the cable is carrying power supply or control voltages, cause equipment malfunctions.
Three principal cable designs (shielding, twisted-pair geometry, and coaxial geometry) help to minimize electromagnetic pickup and transmission.
s. Simple shielding is not too effective against low-frequency magnetic field
s, resulting, for example, in a magnetic "hum" from a nearby power transformer.
cabling is a type of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together to cancel out electromagnetic interference (EMI) from external sources and reduce signal loss. This is why twisted pairs have been used in telephone communications for many decades. For further information regarding the application of twisted pair cables in communication wire, see: Copper wire and cable#Twisted pair cable.
s reduce low-frequency magnetic transmission and pickup. They consist of two or more wires that are wrapped concentric
ally and separated by a dielectric
insulation material. The term, coaxial, was coined because the center conductor and the outer conductor, or shield, form concentric cylinder
s (i.e., co-axial). This causes voltage
s induced by a magnetic field between the shield and the core conductor to consist of two nearly equal magnitudes which cancel out each other. The center conductor of a coaxial cable may be a single strand or it may be stranded.
Common conductor materials used in coaxial cables include copper, tinned or silver plated copper, copper-clad steel, and copper-clad aluminium. Less frequently, aluminium is used as an alternate inner conductor. The outer conductor is typically made from a woven copper wire mesh braid shield layer, or less frequently, aluminium foil. This layer also gives the wire protection from interference. The cables are insulated with a flexible, tubular insulating layer made from polyethylene
(PE), polypropylene
(PP), fluorinated ethylene propylene
(FEP) or polytetrafluoroethylene
(PTFE). This is surrounded by a tubular conducting shield (i.e., the dielectric
, normally made from foam
).
The advantage of coaxial design is that the electric and magnetic fields are confined to the dielectric
with little leakage outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from causing interference to signals inside the cable. This property makes coaxial cable a good choice for carrying weak signals that cannot tolerate interference from the environment or for higher power signals that must not be allowed to radiate or couple into adjacent structures or circuits.
For further information about coaxial cable in communications wire applications, see: Copper wire and cable#Coaxial cable.
as an alloy
ing agent, represents the bulk of electrical conductor
applications because of its high electrical conductivity and improved annealability. ETP copper is used for power transmission
, power distribution, and telecommunications. Common applications include building wire, motor windings, cables, and busbars. Oxygen-free copper
s are used to resist hydrogen embrittlement
when extensive amounts of cold work is needed, and for applications requiring higher ductility
(e.g., telecommunications cable
). When hydrogen embrittlement is a concern and low electrical resistivity is not required, phosphorous may be added to copper.
For certain applications, copper alloy conductors are preferred instead of pure copper, especially when higher strengths and/or improved abrasion
and corrosion
resistance properties are required. An example of a copper alloy conductor is cadmium
copper trolley wire, which is used for railroad electrification
in North America. However, relative to pure copper, the higher strength and corrosion resistance benefits that are offered by copper alloys are offset by their lower electrical conductivities. Design engineers weigh the advantages and disadvantages of the various types of copper and copper alloy conductors when determining which type to specify for a specific electrical application.
Some of the major application markets for copper wire and cable are summarized below.
s up to 600V. The thickness of the wire is based on ampacity requirements in conjunction with safe operating temperatures. Solid wire is used for smaller diameters; thicker diameters are stranded to provide flexibility. Conductor types include non-metallic/non-metallic corrosion-resistant cable (two or more insulated conductors with a nonmetallic outer sheath), armored or BX cable (cables are surrounded by a flexible metal enclosure), metal clad cable, service entrance cable, underground feeder cable, TC cable, fire resistant cable, and mineral insulated cable, including mineral-insulated copper-clad cable
.
Copper is considered the material of choice for building wire because of its conductivity, strength, and reliability. Over the life of a building wire system, copper can also be the most economical conductor.
Copper used in building wire has a conductivity rating of 100% IACS or better. Copper building wire requires less insulation and can be installed in smaller conduits than when lower-conductivity conductors are used. Also, comparatively, more copper wire can fit in a given conduit than conductors with lower conductivities. This greater “wire fill” is a special advantage when a system is rewired or expanded.
Copper building wire is compatible with brass and quality plated screws. The wire provides connections that will not corrode or creep. It is not, however, compatible with aluminium wire or connectors. If the two metals are joined, a galvanic reaction can occur. Anodic
corrosion
during the reaction can disintegrate the aluminium. This is why most appliance and electrical equipment manufacturers use copper lead wires for connections to building wiring systems.
"All-copper" building wiring is a term that refers to homes where the inside electrical service is carried exclusively over copper wiring. In all-copper homes, copper conductors are used in circuit breaker
panels, branch circuit wiring (to outlets, switches, lighting fixtures and the like), and in dedicated branches serving heavy-load appliances (such as ranges, ovens, clothes dryers and air conditioners).
Attempts to replace copper with aluminium in building wire were curtailed in most countries when it was found that aluminium connections gradually loosened due to their inherent slow relaxation process (i.e., creep), combined with the fact that aluminium oxidation products are resistive (i.e., generate heat). Spring-loaded contacts have largely alleviated this problem with aluminium conductors in building wire, but some building codes still forbid the use of aluminium.
For branch-circuit sizes, virtually all basic wiring for lights, outlets and switches is made from copper. The market for aluminium building wire today is mostly confined to larger gauge sizes used in supply circuits.
cabling, the most popular network cable today, is often used in data networks for short and medium length connections (up to 100 meters or 328 feet). This is due to its relatively lower costs compared to optical fiber and coaxial cable.
Twisted pair cables can be shielded or unshielded.
Shielded twisted pair (STP) cables are made from copper braid, aluminium braid, or aluminium foil surrounding the conductors, giving it greater resistance to electrical interference than the unshielded twisted pair cable and enabling it to be used in much longer lengths. However, since STP is much heavier than unshielded twisted pair (UTP), is harder to work with, and has a different impedance
rating, it is not used for the Ethernet
.
Unshielded twisted pair (UTP) cables are the primary cable type for telephone usage. In recent years, UTPs have emerged as the most common cable in computer networking Category cables, especially as patch cables or temporary network connections. They are increasingly used in video applications, primarily in security cameras.
UTP plenum cable
s (i.e., cables that run above ceilings and inside walls) use a solid copper core for each conductor, which enables the cable to hold its shape when bent. Patch cables, which connect computers to wall plates, use stranded copper wire because they are expected to be flexed during their lifetimes.
UTPs are the best balanced line wires (i.e., they reject noise) available. However, they are also the most prone to interference and the easiest to tap into. When interference and security are concerns, shielded cable or fiber optic cable is often considered.
UTP cables include: Category 3 cable
, now the minimum requirement by the FCC (USA) for every telephone connection; Category 5e cable, 100-MHz enhanced pairs for running Gigabit Ethernet (1000Base-T); and Category 6 cable
, where each pair runs 250 MHz for improved 1000Base-T performance.
The most modern practice today is to wire buildings with Category 5e UTP cables, which are suitable for transmission up to 100Mbit/s.
Some Category cables use bonded pairs where the two wires in each pair are joined without glue. This dramatically improves impedance variations, especially after installation, where bending and twisting the cable tend to make a pair open. Cables with individual pairs in their own channel allow tight control of spacing and crosstalk between pairs. Most Category cables require a minimum bend radius of "four times the diameter" when installed.
s were extensively used in mainframe computer
systems and were the first type of major cable used for Local Area Networks (LAN
). Common applications for coaxial cable today include computer network (Internet) and instrumentation data connections, video and CATV distribution, RF and microwave transmission, and feedlines connecting radio transmitters and receivers with their antenna
s.
Most coaxial cables have a characteristic impedance
of 50 Ω, 52 Ω, 75 Ω, or 93 Ω. The RF industry uses standard type-names for coaxial cables. Thanks to television, RG-6
is the most commonly used coaxial cable for home use, and the majority of connections outside Europe are by F connectors.
Coaxial cables differ from other shielded cables used for carrying lower frequency signals, such as audio signals, in that the dimensions of the cables are controlled to give a precise, constant conductor spacing, which is needed to function efficiently as a radio frequency transmission line.
Coaxial cables operate at much higher frequencies than UTPs. While 600 MHz might be cutting edge for a twisted pair, a coaxial cable can handle this frequency easily.
While coaxial cables can go longer distances and have better protection from EMI than twisted pairs, coaxial cables are harder to work with and more difficult to run from offices to the wiring closet. For these reasons, it is now generally being replaced with lesser expensive UTP cables for long distances (less than 100 meters or 328 feet) or by fiber optic cables for more capacity.
Limitations in the performance of copper cables are dependent upon size of the cable (e.g., smaller coaxials work better at high frequencies) and size of the wires (e.g., smaller wires have higher losses). Therefore, there are theoretical limitations to both coaxial cables and twisted pairs. Coaxial performance is being approached with new developments in twisted pairs.
Today, many CATV companies still use high performance coaxial cables into homes. These cables, however, are increasingly connected to a fiber optic data communications system outside of the home. Debates ensue regarding copper vs. fiber vs. wireless on premises cabling. This is especially true for Local Area Network
(LAN) cabling where both fiber and copper may be viable options.
Most building management systems use proprietary copper cabling (e.g., thermostat wiring), as do paging/audio speaker systems. Security monitoring and entry systems, certainly the lower cost ones, still depend on copper, although higher-security facilities, like government and military installations, use fiber, which is more expensive and more secure.
“Structured wiring
” is the general term for today's high-capacity telephone, video, data-transmission, security, control, and entertainment wiring systems. Installations usually include a central distribution panel where all connections are made, as well as outlets with dedicated connections for phone, data, TV and audio jacks.
Structured wiring enables computers to communicate with each other error-free and at high speeds while simultaneously resisting interference among various electrical sources, such as household appliances (e.g., microwave oven
s, vacuum cleaner
s, etc.), fluorescent lights, power tools, and external communications signals. Networked computers are able to share high-speed Internet connections simultaneously. Structured wiring can also connect computers with printer
s, scanner
s, telephone
s, fax
machines, and even home security systems and home entertainment equipment.
Copper Category 5
unshielded twisted pair (UTP) wires (i.e., four twisted wire pairs, or eight color coded wires) is the standard for carrying Internet, computer communications, and telephone signals. Category 5 has an approved bandwidth (i.e., information-carrying capacity) of 100 MHz (megahertz), which is many orders of magnitude greater than a modern 56 Kb (kilobits) per second modem
. Category 5 is increasingly being supplanted by a higher-speed version, known as Category 5e ("e" for enhanced). Category 6, which will likely accommodate at least twice the bandwidth of Category 5, will be able to carry at least 1 gigabit
(billion bits) per second. This equates to about 50,000 pages of text per second.
Quad-shielded RG-6
can service a large number of TV channels at the same time.
A star wiring pattern, where the wiring to each jack extends to a central distribution device, facilitates flexibility of services, problem identification, and better signal quality. This pattern has advantages to daisy chain loops. Installation tools, tips, and techniques for networked wiring systems using twisted pairs, coaxial cables, and connectors for each are available.
Structured wiring competes with wireless systems (e.g., wireless telephones), single-channel video transmitters, and wireless computer networks in homes. While wireless systems certainly have convenience advantages, they also have drawbacks over copper-wired systems: the higher bandwidth of systems using Category 5e wiring typically support more than ten times the speeds of wireless systems for faster data applications and more channels for video applications. Alternatively, wireless systems are a security risk as they can easily and unintentionally transmit sensitive information to unintended users over similar receiver devices. Also, wireless systems are more susceptible to interference from other devices and systems, which can compromise performance. And certain geographic areas and some buildings may be unsuitable for wireless installations. Incompatibilities exist among wireless systems, thereby making managing these systems more complicated.
Power cables are used for the transmission and distribution of electric power, either outdoors or inside buildings. Details on the various types of power cables are available.
Copper is the preferred conductor material for underground transmission lines operating at high and ultra-high voltages (64V to 400 kV). The predominance of copper underground systems stems from its higher volumetric electrical and thermal conductivities compared to other conductors. These beneficial properties for copper conductors conserve space, minimize power loss, and maintain lower cable temperatures.
Aluminium may be used for medium-voltage underground transmission cables, but these usually contain as much as 50% copper. Copper continues to dominate low-voltage lines in mines and underwater applications, as well as in electric railroads, hoists, and other outdoor services.
Aluminium is the preferred conductor for overhead transmission lines in many countries due to its lighter weight. Copper is, however, used for overhead transmission lines in some regions. Medium- and low-voltage overhead systems in some countries are being converted to copper underground cables.
is used in windings of electric motor
s, transformer
s, inductor
s, generator
s, headphones, loudspeaker
coils, hard drive head positioners, potentiometers, electromagnet
s, and other devices.
The most suitable materials for magnet wire applications are unalloyed pure metals, particularly copper and aluminium. When factors such as chemical, physical, and mechanical property requirements are considered, copper is considered the first choice conductor for magnet wire.
Most often, magnetic wire is composed of fully annealed, electrolytically refined copper to allow closer winding when making electromagnetic coils. The wire is coated with a range of polymer
ic insulations, including varnish
, rather than the thicker plastic or other types of insulation commonly used on electrical wire.
Aluminium magnet wire is sometimes used as an alternative for large transformers and motors. Because of its lower electrical conductivity, aluminium wire requires a 1.6-times larger cross sectional area than a copper wire to achieve comparable DC resistance.
High-purity oxygen-free copper
grades are used for high-temperature applications in reducing atmospheres or in motors or generators cooled by hydrogen gas.
s convert electrical energy into mechanical motion, usually through the interaction of magnetic field
s and current-carrying conductors. Electric motors are found in numerous diverse applications, such as fans, blowers, pumps, machines, household appliances, power tools, and disk drives. The very largest electric motors with ratings in the thousands of kilowatts are used in such applications as the propulsion of large ships. The smallest motors move the dials in electric wristwatches.
One of the essential components of electric motors is the coil
, which is made from a wound conductor. Electrical conductivity is a key operating parameter in determining which type of material to use in a motor’s coil. Wires made from better electrical conductors result in more efficient transfers of electrical energy into mechanical energy. Poorer conductors generate more waste heat when transferring electrical energy into kinetic energy.
Because of its high electrical conductivity, copper is commonly used in coil windings, bearings, collectors, brushes, and connectors of motors, including the highest quality motors. Copper’s greater conductivity versus other materials enhances the electrical energy efficiency of motors. For example, to reduce load losses in continuous-use induction-type motors above 1 horsepower
, manufacturers invariably use copper as the conducting material in windings. Aluminium is an alternate material in smaller horsepower motors, especially when motors are not used continuously.
One of the design elements of premium motors is the reduction of heat losses due to the electrical resistance of conductors. To improve the electrical energy efficiencies of induction-type motors, load loss can be reduced by increasing the cross section of copper coils. A high efficiency motor will usually have 20% more copper in the stator winding than its standard counterpart.
Early developments in motor efficiency focused on reducing electrical losses by increasing the packing weight of stator
windings. This made sense since electrical losses typically account for more than half of all energy losses, and stator losses account for approximately two‐thirds of electrical losses.
There are, however, disadvantages in increasing the electrical efficiency of motors through higher packing densities. This invariably results in an increase in motor size which may not be desirable in certain applications, especially in consumer appliances and in the automotive market.
is a device that transfers electrical energy from one circuit to another through its coils (windings). The properties needed for motor windings are similar to those needed for transformers, but with the additional requirement to withstand mechanical vibration and centrifugal forces at operating temperatures.
Transformer windings are normally made from electrolytic-tough pitch (ETP) copper but aluminium is a suitable competitor where weight and first cost are decisive factors.
In North America, aluminium is the predominant choice of winding material for low-voltage, dry-type transformers larger than 15 kilovolt-amperes (kVA). In most other areas of the world, copper is the predominant winding material. Purchasing decisions are generally a function of loss valuations expressed in currency per kilowatt.
Copper used for the manufacture of transformer windings is in the form of wire for small products and strip for larger equipment. For small products, the wire must be strong enough to be wound without breakage, yet flexible enough to provide close-packed windings. Strip products must be of good surface quality so that insulating enamels do not break down under voltage. Good ductility is essential for the strip to be formed and packed while good strength is needed to withstand the high electro-mechanical stresses set up under occasional short-circuit conditions. Copper winding wires in transformers are compatible with all modern insulation materials, such as lacquer
and enamel
. Lacquers permit the close spacing of windings to give best efficiency in the coils.
A major engineering reason to choose copper windings over aluminium is space considerations. This is because a copper-wound transformer can be made smaller than aluminium transformers. To obtain equal ratings in aluminium transformers, a 66% larger cross-sectional area is required than for copper conductors. However, the use of larger-sized conductors results in aluminium winding strength nearly equivalent to copper windings.
Connectivity is another important benefit of copper-wound transformers. Cleaning and brushing with a quality joint compound to prevent oxidation is not necessary with copper.
for field bars and magnetic wire in place of formerly used deoxidized copper.
Due to the need to increase the transmission of high-speed voice and data signals, the surface quality of copper wire is expected to continue to improve. Demands for better drawability and movement towards “zero” defects in copper conductors are expected to continue.
A minimum strength requirement for magnet wire may evolve in order to improve formability and prevent excessive stretching of wire during high speed coiling operations.
It does not seem likely that standards for copper wire will increase beyond the current minimum value of 101% IACS. Although 6-nines copper (99.9999% pure) has been produced in small quantities, it is extremely expensive and probably unnecessary for most commercial applications such as magnet, telecommunications, and building wire. The electrical conductivity of 6-nines copper and 4-nines copper (99.99% pure) is nearly the same at ambient temperature, although the higher-purity copper has a higher conductivity at cryogenic temperatures. Therefore, for non-cryogenic temperatures, 4-nines copper will probably remain the dominant material for most commercial wire applications.
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
has been used in electric wiring since the invention of the electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
and the telegraph in the 1820s. The invention of the telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
in 1876 proved to be another early boon for copper wire.
Today, despite competition from other materials, copper remains the preferred electrical conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
in nearly all categories of electrical wiring. For example, copper is used to conduct electricity in high, medium and low volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
age power networks, including power generation, power transmission
Power transmission
Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work.Power is defined formally as units of energy per unit time...
, power distribution, telecommunications, electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
circuitry, data processing
Data processing
Computer data processing is any process that a computer program does to enter data and summarise, analyse or otherwise convert data into usable information. The process may be automated and run on a computer. It involves recording, analysing, sorting, summarising, calculating, disseminating and...
, instrumentation
Instrumentation
Instrumentation is defined as the art and science of measurement and control of process variables within a production, or manufacturing area....
, appliances, entertainment systems, motors, transformers
Transformers
A transformer is a device that transfers electrical energy from one circuit to another by magnetic coupling.Transformer may also refer to:* ASUS Eee Pad Transformer, an Android 3.2 Honeycomb tablet computer manufacturer by Asus...
, heavy industrial machinery, and countless other types of electrical equipment
Electrical equipment
Electrical equipment includes any machine powered by electricity. They usually consists of an enclosure, a variety of electrical components, and often a power switch...
. Aside from electrical conductors, other important electrical applications for copper include electrical contacts and resistors.
Electrical wiring is the most important market for the copper industry. Roughly half of all copper mined is used to manufacture electrical wire and cable conductors.
Beneficial properties of copper for electrical wire and cable
Nearly all electrical devices rely on copper wiring because of its multitude of inherent beneficial properties. The most useful beneficial properties for electrical applications are summarized here.Electrical Conductivity
Electrical conductivity is a measure of how well a material transports an electric chargeElectric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
. This is an essential property in electrical wiring systems. Copper has the highest electrical conductivity rating of all non-precious metals (electrical conductivity of copper = 101% IACS (International Annealed Copper Standard); electrical resistivity of copper = 16.78 nΩ•m at 20 °C). Oxygen-Free Electronic (OFE) copper
Oxygen-free copper
Oxygen-free copper or Oxygen-free high thermal conductivity copper generally refers to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below....
achieves a minimum of 101% IACS.
The solid state theory of metals helps to explain the unusually high electrical conductivity of copper. In a copper atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
, the outermost 4s energy zone, or conduction band
Conduction band
In the solid-state physics field of semiconductors and insulators, the conduction band is the range of electron energies, higher than that of the valence band, sufficient to free an electron from binding with its individual atom and allow it to move freely within the atomic lattice of the material...
, is only half filled, so many electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s are able to carry electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
. When an electric field
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
is applied to a copper wire, the conduction of electrons accelerates towards the electropositive end, thereby creating a current. These electrons encounter resistance to their passage by colliding with impurity atoms, vacancies, lattice ions, and imperfections. The average distance travelled between collisions, defined as the “mean free path
Mean free path
In physics, the mean free path is the average distance covered by a moving particle between successive impacts which modify its direction or energy or other particle properties.-Derivation:...
,” is inversely proportional to the resistivity of the metal. What is unique about copper is its long mean free path (approximately 100 atomic spacings at room temperature). Furthermore, this mean free path increases rapidly as copper is chilled.
Silver, an expensive precious metal
Precious metal
A precious metal is a rare, naturally occurring metallic chemical element of high economic value.Chemically, the precious metals are less reactive than most elements, have high lustre, are softer or more ductile, and have higher melting points than other metals...
, is the only metal with a higher electrical conductivity rating than copper (i.e., electrical conductivity of silver = 106% IACS, electrical resistivity of silver = 15.9 nΩ•m at 20°C). The high cost of silver combined with its low tensile strength
Tensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
limits its use to special applications, such as joint plating and sliding contact surfaces. With the exception of silver, copper conducts electricity with less resistance than any other metallic material.
Because of its superior conductivity, annealed copper became the international standard to which all other electrical conductors are compared. In 1913, the International Electrotechnical Commission
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
set the conductivity of copper in its International Annealed Copper Standard (IACS) to 100%. Today, copper conductors used in building wire often exceed the 100% IACS standard.
The main grade of copper used for electrical applications, such as building wire, motor
Motor
Motor is a device that creates motion. It usually refers to an engine of some kind. It may also specifically refer to:*Electric motor, a machine that converts electricity into a mechanical motion...
windings, cables and busbar
Busbar
In electrical power distribution, a bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus....
s, is electrolytic-tough pitch (ETP) copper (CW004A or ASTM designation C100140). This copper is at least 99.90% pure and has an electrical conductivity of at least 101% IACS. ETP copper contains a small percentage of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
(0.02 to 0.04%). If high conductivity copper needs to be welded
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
or brazed or used in a reducing atmosphere, then oxygen-free high conductivity copper
Oxygen-free copper
Oxygen-free copper or Oxygen-free high thermal conductivity copper generally refers to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below....
(CW008A or ASTM designation C10100) may be used.
Several electrically conductive metals are lighter than copper, but since they require larger cross sections to carry the same current, they are unacceptable when limited space is a major requirement.
Aluminium has 61% of the conductivity of copper. The cross sectional area of an aluminium conductor must be 56% larger than copper for the same current carrying capability. The need to increase the thickness of aluminium wire
Aluminium wire
Aluminum wire is a type of wiring used in houses, power grids, and airplanes. Aluminum provides a much better conductivity to weight ratio than copper, and therefore is used in power wiring of some aircraft....
restricts its use in several applications, such as in small motors and automobiles. In some applications such as aerial electric power transmission
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
cables, thickness is an advantage and copper is rare.
Tensile Strength
Tensile strengthTensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
measures the force required to pull an object such as rope, wire, or a structural beam to the point where it breaks. The tensile strength of a material is the maximum amount of tensile stress it can take before breaking.
Copper’s higher tensile strength (200-250 N/nm2 annealed) compared to aluminium is another reason why copper is used extensively in the building industry. Copper’s high strength resists stretching, neck-down, creep, nicks and breaks, and thereby also prevents failures and service interruptions.
In equipment installations and machinery using non-copper wiring, nicks and scratches due to vibration and flexing can deteriorate into large breaks in the wiring and lead to failure and long-term service interruptions. For example, when long runs of aluminium are pulled through conduit and cable trays, they can stretch and neck-down. These effects reduce current carrying capacity, wastes energy, and can cause overheating. Because of copper’s higher tensile strength, these problems are minimized in copper wire.
Ductility
DuctilityDuctility
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...
is a material's ability to deform under tensile stress. This is often characterized by the material's ability to be stretched into a wire
Wire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...
. Ductility is especially important in metalworking
Metalworking
Metalworking is the process of working with metals to create individual parts, assemblies, or large scale structures. The term covers a wide range of work from large ships and bridges to precise engine parts and delicate jewelry. It therefore includes a correspondingly wide range of skills,...
because materials that crack or break under stress cannot be hammered, rolled, or drawn (drawing is a process that uses tensile forces to stretch metal).
Copper has a higher ductility than alternate metal conductors with the exception of gold and silver, both expensive precious metals reserved for highly specialized wiring applications. Because of copper’s high ductility, it is easy to draw down to diameters with very close tolerances.
Strength and ductility combination
Usually, the stronger a metal is, the less pliable it is. This is not the case with copper. A unique combination of high strength and high ductility makes copper ideal for wiring systems. At junction boxes and at terminations, for example, copper can be bent, twisted, and pulled without stretching or breaking.Creep resistance
CreepCreep (deformation)
In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material....
is the gradual deformation of a material from constant expansions and contractions under “load, no-load” conditions. This process has adverse effects on electrical systems: terminations can become loose, causing connections to heat up or create dangerous arcing.
Copper does not creep or loosen at its connections. For other metal conductors that creep, extra maintenance is required to check terminals periodically and ensure that screws remain tightened to prevent arcing and overheating. These extra measures can be avoided with the use of copper wire.
Corrosion resistance
CorrosionCorrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
is the unwanted breakdown and weakening of a material due to chemical reactions. Copper resists corrosion from moisture, humidity, industrial pollution, and other atmospheric influences. However, any corrosion oxides, chlorides, and sulfides that do form on copper are conductive, not resistive. Therefore, copper connections and terminations will not overheat from corrosion. Aluminium corrosion products, on the other hand, are resistive and therefore can cause unwanted heat. To prevent corrosion and protect joints, special surface preparations or oxide-inhibiting pastes are applied to aluminium. Copper connections do not require these preparations and their associated additional costs.
Electrolytic-tough pitch (ETP) copper, which is used in building wire, is a noble metal. It is not subject to galvanic corrosion when connected to other, less noble metals and alloys.
Coefficient of thermal expansion
Metals and other solid materials expand upon heating and contract upon cooling. This is an undesirable occurrence in electrical systems. Copper has a low coefficient of thermal expansionThermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
for an electrical conducting material. Aluminium, an alternate common conductor, expands nearly one third more than copper under increasing temperatures. This higher degree of expansion, along with aluminium’s lower ductility can cause electrical problems when bolted connections are improperly installed. By using proper hardware, such as spring pressure connections and cupped or split washers at the joint, it may be possible to create aluminium joints that compare in quality to copper joints.
Thermal conductivity
Thermal conductivityThermal conductivity
In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
is the ability of a material to conduct heat. In electrical systems, high thermal conductivity is important for dissipating waste heat, particularly at terminations and connections. It is also important for reducing energy consumption due to the generation of waste heat.
Copper has a 60% better thermal conductivity rating than aluminium, so it is better able to reduce thermal hot spots in electrical wiring systems.
Solderability
SolderingSoldering
Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece...
is a process whereby two or more metals are joined together by a heating process. This is a desirable property in electrical systems. Some electrical codes require soldered joints. Copper is readily soldered to make durable connections when necessary.
Resistance to electrical overloads
Electrical overloads are sudden unexpected surges that produce unwanted I2r (current2 x resistance) heating. These surges can melt conducting materials with low melting points and create operational or safety problems in electrical systems. Therefore, to withstand electrical overloads, it is important that an electrical conductor have a high melting point.Copper has a melting point of 1083°C. Because of its high melting point, copper conductors can take heavy overloads or current surges without melting. Of all wiring materials, copper is best able to withstand electrical overloads. Also, due to copper’s creep resistance as described previously, electrical overloads will not loosen copper joints.
Compatibility with electrical insulators
Electrical insulators reduce the flow of electricity. Hence, an insulator on an electric cord prevents electricity from injuring a person who touches the cord. Copper is compatible with all common insulation materials, such as PVCPVC
Polyvinyl chloride is a plastic.PVC may also refer to:*Param Vir Chakra, India's highest military honor*Peripheral venous catheter, a small, flexible tube placed into a peripheral vein in order to administer medication or fluids...
and polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
.
Ease of installation
The inherent strength, hardness, and flexibility of copper building wire make it very easy to work with. Copper wiring can be installed simply and easily with no special tools, washers, pigtails, or joint compounds. Its flexibility makes it easy to join, while its hardness helps keep connections securely in place. It has good strength for pulling wire through tight places (“pull-through”), including conduits. It can be bent or twisted easily without breaking. It can be stripped and terminated during installation or service with far less danger of nicks or breaks. And it can be connected without the use of special lugs and fittings. The combination of all of these factors makes it easy for electricians to install copper wire.Meets electrical codes
Copper wiring, the industry standard, complies with codes, ordinances, and regulations for electrical conductors.Single wire
Single-strand copper wire, also called solid wire or solid-core wire, consists of one piece of copper metal wire surrounded by an insulator. Single-strand copper conductors are typically used as magnet wire in motors and transformers. They are relatively rigid, do not bend easily, and are typically installed in permanent, infrequently handled, and low flex applications. Single strand copper wires also provide mechanical ruggedness and good protection against the environment.Stranded wire
A stranded copper wire refers to a group of copper wires that are braided or twisted together. Examples include alternating currentAlternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
line cords for appliances, musical instrument cables, computer mouse cables, connections between circuit boards in multi-printed circuit-board devices, welding electrode cables, control cables connecting moving machine parts, mining machine cables, and trailing machine cables.
A stranded copper wire is more flexible and easier to install than a single-strand copper wire. Stranding also improves wire longevity for applications with moderate to high vibration. A particular cross-section of a stranded conductor gives it essentially the same resistance characteristics as a single-strand conductor, but with added flexibility.
Cable
A copper cable consists of two or more copper wires running side by side and bonded, twisted or braided together to form a single assembly. Electrical cables may be made more flexible by stranding the wires.Copper wires in a cable may be bare or they may be plated to reduce oxidation with a thin layer of another metal, most often tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
but sometimes gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
or silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
. Plating may lengthen wire life and makes soldering
Soldering
Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece...
easier.
Cables can be made with one or two different types of wire. For example, all-copper cables are used in a wide range of applications, including telecommunications and power distribution. Combination conductor cables, such as copper and steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, are used when increased strength with high conductivity is required over long distances (e.g., several hundred-meter spans), such as for telephone cables or for thin hookups, such as CATV cable.
Some cables are designed to be multi-functional, such as those installed in residences to carry power, telephone, video, and control/communications signals. They are usually made from copper.
Current-carrying cables radiate an electromagnetic field
Electromagnetic field
An electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...
. Cables also pick up energy from any existing electromagnetic fields that are around it. These effects are often undesirable, in the first case amounting to unwanted transmission of energy which may adversely affect nearby equipment or other parts of the same piece of equipment; and in the second case, unwanted pickup of noise which may mask the desired signal being carried by the cable, or, if the cable is carrying power supply or control voltages, cause equipment malfunctions.
Three principal cable designs (shielding, twisted-pair geometry, and coaxial geometry) help to minimize electromagnetic pickup and transmission.
Shielding cables
Shielding cables are encased in foil or wire mesh. The wires inside the shielding are mostly decoupled from external electric fieldElectric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
s. Simple shielding is not too effective against low-frequency magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s, resulting, for example, in a magnetic "hum" from a nearby power transformer.
Twisted pair cables
Twisted pairTwisted pair
Twisted pair cabling is a type of wiring in which two conductors are twisted together for the purposes of canceling out electromagnetic interference from external sources; for instance, electromagnetic radiation from unshielded twisted pair cables, and crosstalk between neighboring pairs...
cabling is a type of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together to cancel out electromagnetic interference (EMI) from external sources and reduce signal loss. This is why twisted pairs have been used in telephone communications for many decades. For further information regarding the application of twisted pair cables in communication wire, see: Copper wire and cable#Twisted pair cable.
Coaxial cables
Coaxial cableCoaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
s reduce low-frequency magnetic transmission and pickup. They consist of two or more wires that are wrapped concentric
Concentric
Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another...
ally and separated by a dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
insulation material. The term, coaxial, was coined because the center conductor and the outer conductor, or shield, form concentric cylinder
Cylinder
Cylinder most commonly refers to:* Cylinder , a three-dimensional geometric shapeCylinder may also refer to:-Science and technology:* Cylinder , the space in which a piston travels in an engine...
s (i.e., co-axial). This causes voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
s induced by a magnetic field between the shield and the core conductor to consist of two nearly equal magnitudes which cancel out each other. The center conductor of a coaxial cable may be a single strand or it may be stranded.
Common conductor materials used in coaxial cables include copper, tinned or silver plated copper, copper-clad steel, and copper-clad aluminium. Less frequently, aluminium is used as an alternate inner conductor. The outer conductor is typically made from a woven copper wire mesh braid shield layer, or less frequently, aluminium foil. This layer also gives the wire protection from interference. The cables are insulated with a flexible, tubular insulating layer made from polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
(PE), polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...
(PP), fluorinated ethylene propylene
Fluorinated ethylene propylene
Fluorinated ethylene propylene or FEP is a copolymer of hexafluoropropylene and tetrafluoroethylene. It differs from the PTFE resins in that it is melt-processible using conventional injection molding and screw extrusion techniques. Fluorinated ethylene propylene was invented by DuPont and is sold...
(FEP) or polytetrafluoroethylene
Polytetrafluoroethylene
Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....
(PTFE). This is surrounded by a tubular conducting shield (i.e., the dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
, normally made from foam
Foam
-Definition:A foam is a substance that is formed by trapping gas in a liquid or solid in a divided form, i.e. by forming gas regions inside liquid regions, leading to different kinds of dispersed media...
).
The advantage of coaxial design is that the electric and magnetic fields are confined to the dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
with little leakage outside the shield. Conversely, electric and magnetic fields outside the cable are largely kept from causing interference to signals inside the cable. This property makes coaxial cable a good choice for carrying weak signals that cannot tolerate interference from the environment or for higher power signals that must not be allowed to radiate or couple into adjacent structures or circuits.
For further information about coaxial cable in communications wire applications, see: Copper wire and cable#Coaxial cable.
Applications for copper wire and cable
Electrolytic-tough pitch (ETP) copper, a high-purity copper that contains oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
as an alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
ing agent, represents the bulk of electrical conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
applications because of its high electrical conductivity and improved annealability. ETP copper is used for power transmission
Power transmission
Power transmission is the movement of energy from its place of generation to a location where it is applied to performing useful work.Power is defined formally as units of energy per unit time...
, power distribution, and telecommunications. Common applications include building wire, motor windings, cables, and busbars. Oxygen-free copper
Oxygen-free copper
Oxygen-free copper or Oxygen-free high thermal conductivity copper generally refers to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below....
s are used to resist hydrogen embrittlement
Hydrogen embrittlement
Hydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen...
when extensive amounts of cold work is needed, and for applications requiring higher ductility
Ductility
In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized...
(e.g., telecommunications cable
Telecommunications cable
Telecommunication cables are a type of guided transmission mediums. Cables are usually known to transmit electric energy but in telecommunications fields, cables are used to transmit electromagnetic waves, they are called electromagnetic wave guides....
). When hydrogen embrittlement is a concern and low electrical resistivity is not required, phosphorous may be added to copper.
For certain applications, copper alloy conductors are preferred instead of pure copper, especially when higher strengths and/or improved abrasion
Abrasion
In dermatology, an abrasion is a wound caused by superficial damage to the skin, no deeper than the epidermis. It is less severe than a laceration, and bleeding, if present, is minimal. Mild abrasions, also known as grazes or scrapes, do not scar or bleed, but deep abrasions may lead to the...
and corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
resistance properties are required. An example of a copper alloy conductor is cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
copper trolley wire, which is used for railroad electrification
Electrification
Electrification originally referred to the build out of the electrical generating and distribution systems which occurred in the United States, England and other countries from the mid 1880's until around 1940 and is in progress in developing countries. This also included the change over from line...
in North America. However, relative to pure copper, the higher strength and corrosion resistance benefits that are offered by copper alloys are offset by their lower electrical conductivities. Design engineers weigh the advantages and disadvantages of the various types of copper and copper alloy conductors when determining which type to specify for a specific electrical application.
Some of the major application markets for copper wire and cable are summarized below.
Building wire
Building wire distributes electric power inside residential, commercial, or industrial buildings, mobile homes, recreational vehicles, boats, and substations at voltageVoltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
s up to 600V. The thickness of the wire is based on ampacity requirements in conjunction with safe operating temperatures. Solid wire is used for smaller diameters; thicker diameters are stranded to provide flexibility. Conductor types include non-metallic/non-metallic corrosion-resistant cable (two or more insulated conductors with a nonmetallic outer sheath), armored or BX cable (cables are surrounded by a flexible metal enclosure), metal clad cable, service entrance cable, underground feeder cable, TC cable, fire resistant cable, and mineral insulated cable, including mineral-insulated copper-clad cable
Mineral-insulated copper-clad cable
Mineral-insulated copper-clad cable is a variety of electrical cable made from copper conductors inside a copper sheath, insulated by inorganic magnesium oxide powder. The name is often abbreviated to MICC or MI cable, and colloquially known as pyro...
.
Copper is considered the material of choice for building wire because of its conductivity, strength, and reliability. Over the life of a building wire system, copper can also be the most economical conductor.
Copper used in building wire has a conductivity rating of 100% IACS or better. Copper building wire requires less insulation and can be installed in smaller conduits than when lower-conductivity conductors are used. Also, comparatively, more copper wire can fit in a given conduit than conductors with lower conductivities. This greater “wire fill” is a special advantage when a system is rewired or expanded.
Copper building wire is compatible with brass and quality plated screws. The wire provides connections that will not corrode or creep. It is not, however, compatible with aluminium wire or connectors. If the two metals are joined, a galvanic reaction can occur. Anodic
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
during the reaction can disintegrate the aluminium. This is why most appliance and electrical equipment manufacturers use copper lead wires for connections to building wiring systems.
"All-copper" building wiring is a term that refers to homes where the inside electrical service is carried exclusively over copper wiring. In all-copper homes, copper conductors are used in circuit breaker
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
panels, branch circuit wiring (to outlets, switches, lighting fixtures and the like), and in dedicated branches serving heavy-load appliances (such as ranges, ovens, clothes dryers and air conditioners).
Attempts to replace copper with aluminium in building wire were curtailed in most countries when it was found that aluminium connections gradually loosened due to their inherent slow relaxation process (i.e., creep), combined with the fact that aluminium oxidation products are resistive (i.e., generate heat). Spring-loaded contacts have largely alleviated this problem with aluminium conductors in building wire, but some building codes still forbid the use of aluminium.
For branch-circuit sizes, virtually all basic wiring for lights, outlets and switches is made from copper. The market for aluminium building wire today is mostly confined to larger gauge sizes used in supply circuits.
Twisted pair cable
Since the dawn of telephony, telephones have relied on wire pairs. Twisted pairTwisted pair
Twisted pair cabling is a type of wiring in which two conductors are twisted together for the purposes of canceling out electromagnetic interference from external sources; for instance, electromagnetic radiation from unshielded twisted pair cables, and crosstalk between neighboring pairs...
cabling, the most popular network cable today, is often used in data networks for short and medium length connections (up to 100 meters or 328 feet). This is due to its relatively lower costs compared to optical fiber and coaxial cable.
Twisted pair cables can be shielded or unshielded.
Shielded twisted pair (STP) cables are made from copper braid, aluminium braid, or aluminium foil surrounding the conductors, giving it greater resistance to electrical interference than the unshielded twisted pair cable and enabling it to be used in much longer lengths. However, since STP is much heavier than unshielded twisted pair (UTP), is harder to work with, and has a different impedance
Impedance
Impedance may refer to:*Electrical impedance, the ratio of the voltage phasor to the electric current phasor, a measure of the opposition to time-varying electric current in an electric circuit**Characteristic impedance of a transmission line...
rating, it is not used for the Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
.
Unshielded twisted pair (UTP) cables are the primary cable type for telephone usage. In recent years, UTPs have emerged as the most common cable in computer networking Category cables, especially as patch cables or temporary network connections. They are increasingly used in video applications, primarily in security cameras.
UTP plenum cable
Plenum cable
Plenum cable is cable that is laid in the plenum spaces of buildings. The plenum is the space that can facilitate air circulation for heating and air conditioning systems, by providing pathways for either heated/conditioned or return airflows...
s (i.e., cables that run above ceilings and inside walls) use a solid copper core for each conductor, which enables the cable to hold its shape when bent. Patch cables, which connect computers to wall plates, use stranded copper wire because they are expected to be flexed during their lifetimes.
UTPs are the best balanced line wires (i.e., they reject noise) available. However, they are also the most prone to interference and the easiest to tap into. When interference and security are concerns, shielded cable or fiber optic cable is often considered.
UTP cables include: Category 3 cable
Category 3 cable
Category 3 cable, commonly known as Cat 3 or station wire, is an unshielded twisted pair cable designed to reliably carry data up to 10 Mbit/s, with a possible bandwidth of 16 MHz...
, now the minimum requirement by the FCC (USA) for every telephone connection; Category 5e cable, 100-MHz enhanced pairs for running Gigabit Ethernet (1000Base-T); and Category 6 cable
Category 6 cable
Category 6 cable, commonly referred to as Cat 6, is a cable standard for Gigabit Ethernet and other network physical layers that is backward compatible with the Category 5/5e and Category 3 cable standards. Compared with Cat 5 and Cat 5e, Cat 6 features more stringent specifications for crosstalk...
, where each pair runs 250 MHz for improved 1000Base-T performance.
The most modern practice today is to wire buildings with Category 5e UTP cables, which are suitable for transmission up to 100Mbit/s.
Some Category cables use bonded pairs where the two wires in each pair are joined without glue. This dramatically improves impedance variations, especially after installation, where bending and twisting the cable tend to make a pair open. Cables with individual pairs in their own channel allow tight control of spacing and crosstalk between pairs. Most Category cables require a minimum bend radius of "four times the diameter" when installed.
Coaxial cable
Coaxial cableCoaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
s were extensively used in mainframe computer
Mainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...
systems and were the first type of major cable used for Local Area Networks (LAN
Län
Län and lääni refer to the administrative divisions used in Sweden and previously in Finland. The provinces of Finland were abolished on January 1, 2010....
). Common applications for coaxial cable today include computer network (Internet) and instrumentation data connections, video and CATV distribution, RF and microwave transmission, and feedlines connecting radio transmitters and receivers with their antenna
Antenna
Antenna may refer to:-Science and engineering:* Antenna , also known as an aerial, a transducer designed to transmit or receive electromagnetic Antenna (pl. antennas in radio/TV, antennae in biology) may refer to:-Science and engineering:* Antenna (radio), also known as an aerial, a transducer...
s.
Most coaxial cables have a characteristic impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
of 50 Ω, 52 Ω, 75 Ω, or 93 Ω. The RF industry uses standard type-names for coaxial cables. Thanks to television, RG-6
RG-6
RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. The term "RG-6" itself is quite generic and refers to a wide variety of cable designs, which differ from one another in shielding characteristics, center conductor composition, and...
is the most commonly used coaxial cable for home use, and the majority of connections outside Europe are by F connectors.
Coaxial cables differ from other shielded cables used for carrying lower frequency signals, such as audio signals, in that the dimensions of the cables are controlled to give a precise, constant conductor spacing, which is needed to function efficiently as a radio frequency transmission line.
Coaxial cables operate at much higher frequencies than UTPs. While 600 MHz might be cutting edge for a twisted pair, a coaxial cable can handle this frequency easily.
While coaxial cables can go longer distances and have better protection from EMI than twisted pairs, coaxial cables are harder to work with and more difficult to run from offices to the wiring closet. For these reasons, it is now generally being replaced with lesser expensive UTP cables for long distances (less than 100 meters or 328 feet) or by fiber optic cables for more capacity.
Limitations in the performance of copper cables are dependent upon size of the cable (e.g., smaller coaxials work better at high frequencies) and size of the wires (e.g., smaller wires have higher losses). Therefore, there are theoretical limitations to both coaxial cables and twisted pairs. Coaxial performance is being approached with new developments in twisted pairs.
Today, many CATV companies still use high performance coaxial cables into homes. These cables, however, are increasingly connected to a fiber optic data communications system outside of the home. Debates ensue regarding copper vs. fiber vs. wireless on premises cabling. This is especially true for Local Area Network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
(LAN) cabling where both fiber and copper may be viable options.
Most building management systems use proprietary copper cabling (e.g., thermostat wiring), as do paging/audio speaker systems. Security monitoring and entry systems, certainly the lower cost ones, still depend on copper, although higher-security facilities, like government and military installations, use fiber, which is more expensive and more secure.
Structured Wiring (for voice, audio, video, data, controls, and security in homes)
Virtually all telephone lines in modern societies now share voice and data simultaneously. Pre-digital quad telephone wiring in homes is unable to handle communications needs for multiple phone lines, Internet service, video communications, data transmission, fax machines, and security services. Crosstalk, static interference, inaudible signals, and interrupted service are common problems with outdated wiring. Computers connected to old-fashioned communications wiring often experience poor Internet performance.“Structured wiring
Structured cabling
Structured cabling is building or campus telecommunications cabling infrastructure that consists of a number of standardized smaller elements called subsystems.Structured cabling falls into six subsystems:...
” is the general term for today's high-capacity telephone, video, data-transmission, security, control, and entertainment wiring systems. Installations usually include a central distribution panel where all connections are made, as well as outlets with dedicated connections for phone, data, TV and audio jacks.
Structured wiring enables computers to communicate with each other error-free and at high speeds while simultaneously resisting interference among various electrical sources, such as household appliances (e.g., microwave oven
Microwave oven
A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
s, vacuum cleaner
Vacuum cleaner
A vacuum cleaner, commonly referred to as a "vacuum," is a device that uses an air pump to create a partial vacuum to suck up dust and dirt, usually from floors, and optionally from other surfaces as well. The dirt is collected by either a dustbag or a cyclone for later disposal...
s, etc.), fluorescent lights, power tools, and external communications signals. Networked computers are able to share high-speed Internet connections simultaneously. Structured wiring can also connect computers with printer
Printer
Printer may refer to:* Printer , a person or a company* Printer , a hardware device* Optical printer for motion picture films* The Moscow subway station Pechatniki, whose name means "Printers"...
s, scanner
Scanner
Scanner may refer to:* WikiScanner, a tool that provides a searchable database of anonymous Wikipedia edits* A personality type described by self-help author Barbara Sher-Technology:* Scanner , for searching for and receiving radio broadcasts...
s, telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
s, fax
Fax
Fax , sometimes called telecopying, is the telephonic transmission of scanned printed material , normally to a telephone number connected to a printer or other output device...
machines, and even home security systems and home entertainment equipment.
Copper Category 5
Category 5
Category 5 may refer to:*Category 5 , an album from rock band, FireHouse*Category 5 cable, used for carrying data*Category 5 computer virus, as classified by Symantec Corporation*Category 5 Records, a record label...
unshielded twisted pair (UTP) wires (i.e., four twisted wire pairs, or eight color coded wires) is the standard for carrying Internet, computer communications, and telephone signals. Category 5 has an approved bandwidth (i.e., information-carrying capacity) of 100 MHz (megahertz), which is many orders of magnitude greater than a modern 56 Kb (kilobits) per second modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
. Category 5 is increasingly being supplanted by a higher-speed version, known as Category 5e ("e" for enhanced). Category 6, which will likely accommodate at least twice the bandwidth of Category 5, will be able to carry at least 1 gigabit
Gigabit
The gigabit is a multiple of the unit bit for digital information or computer storage. The prefix giga is defined in the International System of Units as a multiplier of 109 , and therefore...
(billion bits) per second. This equates to about 50,000 pages of text per second.
Quad-shielded RG-6
RG-6
RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. The term "RG-6" itself is quite generic and refers to a wide variety of cable designs, which differ from one another in shielding characteristics, center conductor composition, and...
can service a large number of TV channels at the same time.
A star wiring pattern, where the wiring to each jack extends to a central distribution device, facilitates flexibility of services, problem identification, and better signal quality. This pattern has advantages to daisy chain loops. Installation tools, tips, and techniques for networked wiring systems using twisted pairs, coaxial cables, and connectors for each are available.
Structured wiring competes with wireless systems (e.g., wireless telephones), single-channel video transmitters, and wireless computer networks in homes. While wireless systems certainly have convenience advantages, they also have drawbacks over copper-wired systems: the higher bandwidth of systems using Category 5e wiring typically support more than ten times the speeds of wireless systems for faster data applications and more channels for video applications. Alternatively, wireless systems are a security risk as they can easily and unintentionally transmit sensitive information to unintended users over similar receiver devices. Also, wireless systems are more susceptible to interference from other devices and systems, which can compromise performance. And certain geographic areas and some buildings may be unsuitable for wireless installations. Incompatibilities exist among wireless systems, thereby making managing these systems more complicated.
Power distribution
Power distribution is the final stage in the delivery of electricity for an end use. A power distribution system carries electricity from the transmission system to consumers.Power cables are used for the transmission and distribution of electric power, either outdoors or inside buildings. Details on the various types of power cables are available.
Copper is the preferred conductor material for underground transmission lines operating at high and ultra-high voltages (64V to 400 kV). The predominance of copper underground systems stems from its higher volumetric electrical and thermal conductivities compared to other conductors. These beneficial properties for copper conductors conserve space, minimize power loss, and maintain lower cable temperatures.
Aluminium may be used for medium-voltage underground transmission cables, but these usually contain as much as 50% copper. Copper continues to dominate low-voltage lines in mines and underwater applications, as well as in electric railroads, hoists, and other outdoor services.
Aluminium is the preferred conductor for overhead transmission lines in many countries due to its lighter weight. Copper is, however, used for overhead transmission lines in some regions. Medium- and low-voltage overhead systems in some countries are being converted to copper underground cables.
Appliance wire
Appliance wire for domestic applications and instruments is manufactured from bunch-stranded soft wire, which may be tinned for soldering or phase identification. Depending upon loads, insulation can be PVC, neoprene, ethylene propylene, polypropylene filler, or cotton.Automotive wire and cable
Automotive wire and cable requires insulation that is resistant to elevated temperatures, petroleum products, humidity, fire, and chemicals. PVC, neoprene, and polyethylene are the most common insulators. Potentials range from 12V for electrical systems to between 300V-15,000V for instruments, lighting, and ignition systems.Magnet wire (Winding wire)
Magnet wireMagnet wire
Magnet wire or enameled copper wire is a copper or aluminum wire covered with thin insulation. It is used in the construction of transformers, inductors, motors, headphones, loudspeakers, hard drive head positioners, potentiometers, and electromagnets, among other applications...
is used in windings of electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
s, transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s, inductor
Inductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
s, generator
Generator
Generator may refer to:* Electrical generator* Engine-generator, an electrical generator, but with its own engine.* Generator , any of several closely related usages in mathematics.Computing:...
s, headphones, loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
coils, hard drive head positioners, potentiometers, electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
s, and other devices.
The most suitable materials for magnet wire applications are unalloyed pure metals, particularly copper and aluminium. When factors such as chemical, physical, and mechanical property requirements are considered, copper is considered the first choice conductor for magnet wire.
Most often, magnetic wire is composed of fully annealed, electrolytically refined copper to allow closer winding when making electromagnetic coils. The wire is coated with a range of polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ic insulations, including varnish
Varnish
Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss...
, rather than the thicker plastic or other types of insulation commonly used on electrical wire.
Aluminium magnet wire is sometimes used as an alternative for large transformers and motors. Because of its lower electrical conductivity, aluminium wire requires a 1.6-times larger cross sectional area than a copper wire to achieve comparable DC resistance.
High-purity oxygen-free copper
Oxygen-free copper
Oxygen-free copper or Oxygen-free high thermal conductivity copper generally refers to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below....
grades are used for high-temperature applications in reducing atmospheres or in motors or generators cooled by hydrogen gas.
Magnet wire in electric motors
Electric motorElectric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
s convert electrical energy into mechanical motion, usually through the interaction of magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s and current-carrying conductors. Electric motors are found in numerous diverse applications, such as fans, blowers, pumps, machines, household appliances, power tools, and disk drives. The very largest electric motors with ratings in the thousands of kilowatts are used in such applications as the propulsion of large ships. The smallest motors move the dials in electric wristwatches.
One of the essential components of electric motors is the coil
Coil
A coil is a series of loops. A coiled coil is a structure in which the coil itself is in turn also looping.-Electromagnetic coils:An electromagnetic coil is formed when a conductor is wound around a core or form to create an inductor or electromagnet...
, which is made from a wound conductor. Electrical conductivity is a key operating parameter in determining which type of material to use in a motor’s coil. Wires made from better electrical conductors result in more efficient transfers of electrical energy into mechanical energy. Poorer conductors generate more waste heat when transferring electrical energy into kinetic energy.
Because of its high electrical conductivity, copper is commonly used in coil windings, bearings, collectors, brushes, and connectors of motors, including the highest quality motors. Copper’s greater conductivity versus other materials enhances the electrical energy efficiency of motors. For example, to reduce load losses in continuous-use induction-type motors above 1 horsepower
Horsepower
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...
, manufacturers invariably use copper as the conducting material in windings. Aluminium is an alternate material in smaller horsepower motors, especially when motors are not used continuously.
One of the design elements of premium motors is the reduction of heat losses due to the electrical resistance of conductors. To improve the electrical energy efficiencies of induction-type motors, load loss can be reduced by increasing the cross section of copper coils. A high efficiency motor will usually have 20% more copper in the stator winding than its standard counterpart.
Early developments in motor efficiency focused on reducing electrical losses by increasing the packing weight of stator
Stator
The stator is the stationary part of a rotor system, found in an electric generator, electric motor and biological rotors.Depending on the configuration of a spinning electromotive device the stator may act as the field magnet, interacting with the armature to create motion, or it may act as the...
windings. This made sense since electrical losses typically account for more than half of all energy losses, and stator losses account for approximately two‐thirds of electrical losses.
There are, however, disadvantages in increasing the electrical efficiency of motors through higher packing densities. This invariably results in an increase in motor size which may not be desirable in certain applications, especially in consumer appliances and in the automotive market.
Magnet wire in transformers
A transformerTransformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
is a device that transfers electrical energy from one circuit to another through its coils (windings). The properties needed for motor windings are similar to those needed for transformers, but with the additional requirement to withstand mechanical vibration and centrifugal forces at operating temperatures.
Transformer windings are normally made from electrolytic-tough pitch (ETP) copper but aluminium is a suitable competitor where weight and first cost are decisive factors.
In North America, aluminium is the predominant choice of winding material for low-voltage, dry-type transformers larger than 15 kilovolt-amperes (kVA). In most other areas of the world, copper is the predominant winding material. Purchasing decisions are generally a function of loss valuations expressed in currency per kilowatt.
Copper used for the manufacture of transformer windings is in the form of wire for small products and strip for larger equipment. For small products, the wire must be strong enough to be wound without breakage, yet flexible enough to provide close-packed windings. Strip products must be of good surface quality so that insulating enamels do not break down under voltage. Good ductility is essential for the strip to be formed and packed while good strength is needed to withstand the high electro-mechanical stresses set up under occasional short-circuit conditions. Copper winding wires in transformers are compatible with all modern insulation materials, such as lacquer
Lacquer
In a general sense, lacquer is a somewhat imprecise term for a clear or coloured varnish that dries by solvent evaporation and often a curing process as well that produces a hard, durable finish, in any sheen level from ultra matte to high gloss and that can be further polished as required...
and enamel
Enamel
Enamel may refer to:* Tooth enamel, the hard mineralized surface of teeth* Vitreous enamel, a smooth, durable coating made of melted and fused glass powder-See also:* Enamel organ, a cellular aggregation that functions in the formation of tooth enamel...
. Lacquers permit the close spacing of windings to give best efficiency in the coils.
A major engineering reason to choose copper windings over aluminium is space considerations. This is because a copper-wound transformer can be made smaller than aluminium transformers. To obtain equal ratings in aluminium transformers, a 66% larger cross-sectional area is required than for copper conductors. However, the use of larger-sized conductors results in aluminium winding strength nearly equivalent to copper windings.
Connectivity is another important benefit of copper-wound transformers. Cleaning and brushing with a quality joint compound to prevent oxidation is not necessary with copper.
Magnet wire in generators
The trend in modern generators is to operate at higher temperatures and higher electrical conductivities with oxygen-free copperOxygen-free copper
Oxygen-free copper or Oxygen-free high thermal conductivity copper generally refers to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below....
for field bars and magnetic wire in place of formerly used deoxidized copper.
Some future trends
Copper will continue to be the predominant material in most electrical wire applications, especially where space considerations are important. The automotive industry for decades has considered the use of smaller-diameter wires in certain applications. This might become more of a reality with copper wire in the future.Due to the need to increase the transmission of high-speed voice and data signals, the surface quality of copper wire is expected to continue to improve. Demands for better drawability and movement towards “zero” defects in copper conductors are expected to continue.
A minimum strength requirement for magnet wire may evolve in order to improve formability and prevent excessive stretching of wire during high speed coiling operations.
It does not seem likely that standards for copper wire will increase beyond the current minimum value of 101% IACS. Although 6-nines copper (99.9999% pure) has been produced in small quantities, it is extremely expensive and probably unnecessary for most commercial applications such as magnet, telecommunications, and building wire. The electrical conductivity of 6-nines copper and 4-nines copper (99.99% pure) is nearly the same at ambient temperature, although the higher-purity copper has a higher conductivity at cryogenic temperatures. Therefore, for non-cryogenic temperatures, 4-nines copper will probably remain the dominant material for most commercial wire applications.
See also
- WireWireA wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...
- CableCableA cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...
- Power cablePower cableA 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...
- High voltage cableHigh voltage cableA high voltage cable - also called HV cable - is used for electric power transmission at high voltage. High voltage cables of differing types have a variety of applications in instruments, ignition systems, AC and DC power transmission...
- Electrical wiringElectrical wiringElectrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. This article describes general aspects of electrical wiring as used to provide power in buildings and structures, commonly referred to as building wiring. This article is intended to...
- Electrical wiring regulations
- Electrical wiring in North AmericaElectrical wiring in North AmericaElectrical wiring in North America follows regulations and standards for installation of building wiring. Electrical wiring in the United States is generally in compliance with the National Electrical Code, a standard sponsored by the National Fire Protection Association which has been periodically...
- Electrical wiring in the United Kingdom
- Electrical wiring in Hong Kong
- Building codes
- Electrical codeElectrical codeAn electrical code is a set of regulations for electrical wiring. The intention of an electrical code is to provide standards to ensure electrical wiring systems that are safe and unlikely to produce either electric shock or fires. Electrical codes are usually devised by national or international...
- National electric code
- Canadian electrical codeCanadian Electrical CodeThe Canadian Electrical Code, CE code, or CSA C22.1 is a standard published by the Canadian Standards Association pertaining to the installation and maintenance of electrical equipment in Canada....
- Copper interconnect
- Ground and neutralGround and neutralSince the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding of equipment and structures...
- Earthing systems
- Oxygen-free copperOxygen-free copperOxygen-free copper or Oxygen-free high thermal conductivity copper generally refers to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below....
- Electrolytic-tough pitch (ETP) copper
- Copper-clad steel
- Copper-clad aluminum
- Mineral-insulated copper-clad cableMineral-insulated copper-clad cableMineral-insulated copper-clad cable is a variety of electrical cable made from copper conductors inside a copper sheath, insulated by inorganic magnesium oxide powder. The name is often abbreviated to MICC or MI cable, and colloquially known as pyro...