Wire gauge

Wire gauge is a measurement of how large a wire is, either in diameter or cross sectional area. This determines the amount of electric current a wire can safely carry, as well as its electrical resistance and weight per unit of length. Wire gauge is applicable to both electrical and non-electrical wires, being important to electrical wiring and to structural cable.

Wire gauges may be broadly divided into two groups, the empirical and the geometric. The first includes all the older gauge measurements, notably the Birmingham (B.W.G. or Stubs) and the Lancashire. The origin of the B.W.G. is obscure. The numbers of wire were in common use earlier than 1735. It is believed that they originally were based on the series of drawn wires, No. 1 being the original rod, and succeeding numbers corresponding with each draw, so that No. 10, for example, would have passed ten times through the draw plate. But the Birmingham and the Lancashire gauge, the latter being based on an averaging of the dimensions collated from a large number of the former in the possession of Peter Stubs of Warrington, have long held the leading position, and are still retained and used probably to a greater extent than the more recent geometrical gauges.

The first attempt to adopt a geometrical system was made by Messrs Brown & Sharpe in 1855. They established a regular progression of thirty-nine steps between the English sizes, No. 0000 (460 mils or about 12 mm) and No. 36 (5 mils or about 0.13 mm). Each diameter was multiplied by 0.890526 to give the next lower size. This is now the American wire gauge (AWG), and is used to a considerable extent in the United States.

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