Standard Wire Gauge
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The British Standard Wire Gauge, often referred to as the Standard Wire Gauge or simply SWG, is a unit used to denote
wire gauge Wire gauge is a measurement of wire diameter. This determines the amount of electric current the wire can safely carry, as well as its electrical resistance and weight. Types of wire gauge Wire gauges may be broadly divided into two groups, t ...
(size) as defined by BS 3737:1964, a standard that has since been withdrawn. It is also known as the Imperial Wire Gauge or British Standard Gauge. Although its use has significantly declined, SWG sizes are still used for measuring the thickness of guitar strings and certain types of electrical wire. In modern applications, wire size is more commonly measured in terms of cross-sectional area, expressed in square millimeters, particularly for electrical installation cables. The current British Standard for metallic materials, including wires and sheets, is BS 6722:1986, which exclusively uses metric measurements.


History

SWG was fixed by
Order of Council An Order of Council is a form of legislation in the United Kingdom. It is made by the Lords of the Privy Council (in practice, ministers of the Crown). Orders of Council differ from Orders in Council in that, while Orders in Council are orders ...
August 23, 1883. It was constructed by improving the Birmingham Wire Gauge. It was made a legal standard on 1 March, 1884, by the British
Board of Trade The Board of Trade is a British government body concerned with commerce and industry, currently within the Department for Business and Trade. Its full title is The Lords of the Committee of the Privy Council appointed for the consideration of ...
. SWG is not to be confused with American wire gauge, which has a similar but not interchangeable numbering scheme.


Standard

A table of the gauge numbers and wire diameters is shown below. The basis of the system is the ''thou'' (or ''mil'' in US English), or . 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. No. 7/0, the largest size, is (500 thou or ) dia., No. 1 is (), and the smallest, No. 50, is ( or ). The system as a whole approximates an
exponential curve Exponential growth occurs when a quantity grows as an exponential function of time. The quantity grows at a rate directly proportional to its present size. For example, when it is 3 times as big as it is now, it will be growing 3 times as fast ...
, plotting diameter against gauge-number (each size is a approximately a constant multiple of the previous size). The weight per unit length diminishes by an average of approximately 20% at each step. Because the weight per unit length is related to the cross sectional area, and therefore to the square of the diameter, the diameter diminishes by approximately 10.6%: :\mbox = 1-\sqrt \approx 10.6\% However, the system is piecewise linear, only approximating the exponential curve loosely. Thus, it runs in constant steps of () through the range No. 49 - No. 39 and of () through No. 39 - No. 30.


See also

* *
IEC 60228 IEC 60228 is the International Electrotechnical Commission (IEC)'s international standard on ''conductors of insulated cables''. the current version is Third Edition 2004-11 Among other things, it defines a set of standard wire cross-sectional ...
, the metric wire-size standard used in most parts of the world. *
Circular mil A circular mil is a unit of area, equal to the area of a circle with a diameter of one mil (one thousandth of an inch or ). It is equal to /4 square mils or approximately . It is a unit intended for referring to the area of a wire with a circul ...
, Electrical industry standard for wires larger than 4/0. * American Wire Gauge (AWG), used primarily in the US and Canada *
Stubs Iron Wire Gauge The Birmingham gauge, officially the Birmingham Wire Gauge and often abbreviated as ''G'' or ''ga'', is unit or wire gauge used to measure the thickness or diameter of wires and tubing, including hypodermic needles and other medical tube products. ...
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Jewelry wire gauge Jewelry wire is wire, usually copper, brass, nickel, aluminium, silver, or gold, used in jewelry making. Wire is defined today as a single, usually cylindrical, elongated strand of drawn metal. However, when wire was first invented over 2,000 ye ...
*
Body jewelry sizes Body jewelry sizes express the thickness of an item of body jewelry, using one of several possible systems. Background Items of body piercing jewelry have an important common factor: the diameter of the part of the item of jewelry where it wil ...
*
Electrical wiring Electrical wiring is an electrical installation of Electrical cable, cabling and associated devices such as switches, distribution boards, sockets, and light fittings in a structure. Wiring is subject to safety standards for design and in ...
*
Number 8 wire Number 8 wire is a gauge of wire on the British Standard Wire Gauge that has entered into the cultural lexicon of New Zealand. Use for farm fencing Early farm fences in New Zealand were generally used to protect crops, gardens, and orchards fr ...
, a term used in the New Zealand vernacular


References

{{reflist Wire gauges 3737