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By estimating the temperature of the cables, the safe long-term current-carrying capacity of the cables can be calculated. 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 ]
However, AWG is dissimilar to IEC 60228, the metric wire-size standard used in most parts of the world, based directly on the wire cross-section area (in square millimetres, mm 2). The AWG tables are for a single, solid and round conductor. The AWG of a stranded wire is determined by the cross-sectional area of the equivalent solid conductor.
The current British Standard for metallic materials including wire is BS 6722:1986, which is a solely metric standard, superseding 3737:1964, which used the SWG system. The IEC 60228 , used in most parts of the world, defines standard wire sizes based on their cross-sectional areas as expressed in mm 2 . [ 3 ]
For systems such as underground power transmission cables, evaluation of the short-term over-load capacity of the cable system requires a detailed analysis of the cable's thermal environment and an evaluation of the commercial value of the lost service life due to excess temperature rise.
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 ...
The current-carrying capacity, or ampacity, of overhead lines starts with the type of conductor used. The conductor choice determines its electrical resistance and other physical parameters for dynamic line rating (DLR).
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For instance, instead of 14 AWG (American wire gauge) copper wire, aluminium wiring would need to be 12 AWG on a typical 15 ampere lighting circuit, though local building codes vary. Solid aluminium conductors were originally made in the 1960s from a utility-grade aluminium alloy that had undesirable properties for a building wire, and were ...