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J. H. Neher and M. H. McGrath were two electrical engineers who wrote a paper in 1957 about how to calculate the capacity of current (ampacity) of cables. [1] The paper described two-dimensional highly symmetric simplified calculations which have formed the basis for many cable application guidelines and regulations.
Comparison of SWG (red), AWG (blue) and IEC 60228 (black) wire gauge sizes from 0.03 to 200 mm² to scale on a 1 mm grid – in the SVG file, hover over a size to highlight it. In engineering applications, it is often most convenient to describe a wire in terms of its cross-section area, rather than its diameter, because the cross section is directly proportional to its strength and weight ...
Conductors installed so that air can freely move over them can be rated to carry more current than conductors run inside a conduit or buried underground. High ambient temperature may reduce the current rating of a conductor. Cables run in wet or oily locations may carry a lower temperature rating than in a dry installation. A lower rating will ...
One important property of the insulation which affects the current-carrying capacity of the wire is the maximum conductor temperature. This, in combination with the ambient temperature and ability of the environment to absorb heat, determines the amount of tolerable copper loss in the wire, and therefore its size in relation to the load current ...
Similarly, if two conductors are near each other carrying AC current, their resistances increase due to the proximity effect. At commercial power frequency , these effects are significant for large conductors carrying large currents, such as busbars in an electrical substation , [ 2 ] or large power cables carrying more than a few hundred amperes.
Accordingly, one pound of aluminum has the same current carrying capacity as two pounds of copper. [3] Since copper costs about four times as much as aluminum by weight (roughly US$4 /lb [5] vs. US$1 /lb [6] as of 2024), aluminum wires are one-eighth the cost of copper wire of the same conductivity.
All electrical cables are somewhat flexible, allowing them to be shipped to installation sites wound on reels, drums or hand coils. Flexibility is an important factor in determining the appropriate stranding class of the cable as it directly affects the minimum bending radius. Power cables are generally stranding class A, B, or C.
Conductor sizes range from 12 mm 2 (#6 American wire gauge) to 750 mm 2 (1,590,000 circular mils area), with varying resistance and current-carrying capacity. For large conductors (more than a few centimetres in diameter), much of the current flow is concentrated near the surface due to the skin effect. The center of the conductor carries ...