Thermal and electrical conductivity often go together. For instance, most metals are both electrical and thermal conductors. However, some materials are practical electrical conductors without being good thermal conductors.
==Conductor ampacity==
The [[American wire gauge|ampacity]] of a conductor, that is, the amount of [[Electric current|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 [[fuse (electrical)|fuses]], most conductors in the real world are operated far below this limit, however. For example, household wiring is usually insulated with [[Polyvinyl chloride|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.
