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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.
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 ...
Some tables give conversions to circular millimetres (cmm). [3] [4] The area in cmm is defined as the square of the wire diameter in mm. However, this unit is rarely used in practice. One of the few examples is in a patent for a bariatric weight loss device. [5]
No. 7/0, the largest size, is 0.50 inches (500 mils or 12.7 mm) in diameter (250 000 circular mils in cross-sectional area), and the smallest, No. 50, is 0.001 inches (1 mil or 25.4 μm) in diameter (1 circular mil [cross-sectional area] or 0.7854 millionths of a square inch).
A square mil is a unit of area, equal to the area of a square with sides of length one mil. A mil is one thousandth of an international inch . This unit of area is usually used in specifying the area of the cross section of a wire or cable.
For example, the United States National Electrical Code, Table 310.15(B)(16), specifies that up to three 8 AWG copper wires having a common insulating material (THWN) in a raceway, cable, or direct burial has an ampacity of 50 A when the ambient air is 30 °C, the conductor surface temperature allowed to be 75 °C. A single insulated conductor ...
For wire sizes smaller than AWG No. 2 (33.6 mm 2, 0.0521 sq in), this term is also generally regarded as insignificant. R c , a {\textstyle R_{c,a}} is the effective thermal resistance between the conductor and the ambient conditions, which can require significant empirical or theoretical effort to estimate.
A table of the gauge numbers and wire diameters is shown below. [1] [2] The basis of the system is the thou (or mil in US English), or 0.001 in. Sizes are specified as wire diameters, stated in thou and tenths of a thou (mils and tenths). The wire diameter diminishes with increasing size number.