subject: Electrical Conductor - China Playground Veggie House Series - Playground Zoo Series [print this page] Power engineering Power engineering
In power engineering, an electrical wire is a length of metal, usually surrounded by an insulating sheath, that is used to conduct electricity.
Conductor size
In many countries, conductors are measured by their cross section in square millimeters. However, in the United States, conductors are measured by American wire gauge for smaller ones, and circular mils for larger ones.
Conductor materials
Of the metals commonly used for conductors, copper has a high conductivity. Silver is more conductive, but due to cost it is not practical in most cases. However, it is used in specialized equipment, such as satellites, and as a thin plating to mitigate skin effect losses at high frequencies. Because of its ease of connection by soldering or clamping, copper is still the most common choice for most light-gauge wires.
Main article: Aluminum wire
Aluminium has been used as a conductor in housing applications for cost reasons. It is actually more conductive than copper when compared by unit weight, but it has technical problems that have lead to problems when used for household and similar wiring, sometimes having lead to structural fires:
a tendency to form an electrically resistive surface oxide within connections, leading to heat cycling of the connection (unless protected by a well-maintained protective paste).
A tendency to "creep" under thermal cycling, causing connections to get looser due to a low mechanical yield point of the aluminum.
A coefficient of thermal expansion sufficiently different from the materials used for connections to accelerate the creep problem, addressed by using only plugs, switches, and splices rated specifically for aluminum.
These problems do not affect other uses, and are commonly used for the low voltage "drop" between a power pole and the household meter. It is also the most common metal used in high-voltage transmission lines, in combination with steel as structural reinforcement.
The surface of anodized aluminium does not conduct electricity and sometimes this must be considered when aluminum enclosures are to be electrically bonded for safety or to enclose or exclude electromagnetic radiation.
Conductor ampacity
The ampacity of a conductor, that is, the amount of current it can carry, is related to its electrical resistance: a lower-resistance conductor can carry more current. The resistance, in turn, is determined by the material the conductor is made from (as described above) and the conductor's size. For a given material, conductors with a larger cross-sectional area have less resistance than conductors with a smaller cross-sectional area.
For bare conductors, the ultimate limit is the point at which power lost to resistance causes the conductor to melt. Aside from fuses, most conductors in the real world are operated far below this limit, however. For example, household wiring is usually insulated with PVC insulation that is only rated to operate to about 60 C, therefore, the current flowing in such wires must be limited so that it never heats the copper conductor above 60 C, causing a risk of fire. Other, more expensive insulations such as Teflon or fiberglass may allow operation at much higher temperatures.
The American wire gauge article contains a table showing allowable ampacities for a variety of copper wire sizes.
Isotropy
If an electric field is applied to a material, and the resulting induced electric current is in the same direction, the material is said to be an isotropic electrical conductor. If the resulting electric current is in a different direction from the applied electric field, the material is said to be an anisotropic electrical conductor.
See also
Resistivity
Charge transfer complex
Bundle conductor
Superconductivity
Semiconductor
Wikimedia Commons has media related to: Electrical conductors
Categories: Electricity | Hardware (mechanical) | Power engineering | Fundamental physics conceptsHidden categories: Articles lacking sources from January 2009 | All articles lacking sources
