American wire gauge

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"AWG" redirects here. For other uses, see AWG (disambiguation).

American wire gauge (AWG), also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in North America for the diameters of round, solid, nonferrous, electrically conducting wire. Dimensions of the wires are given in ASTM standard B 258.[1] The cross-sectional area of each gauge is an important factor for determining its current-carrying capacity.

Increasing gauge numbers denote decreasing wire diameters, which is similar to many other non-metric gauging systems. This gauge system originated in the number of drawing operations used to produce a given gauge of wire. Very fine wire (for example, 30 gauge) required more passes through the drawing dies than did 0 gauge wire. Manufacturers of wire formerly had proprietary wire gauge systems; the development of standardized wire gauges rationalized selection of wire for a particular purpose.

The AWG tables are for a single, solid, round conductor. The AWG of a stranded wire is determined by the cross-sectional area of the equivalent solid conductor. Because there are also small gaps between the strands, a stranded wire will always have a slightly larger overall diameter than a solid wire with the same AWG.

AWG is also commonly used to specify body piercing jewelry sizes (especially smaller sizes), even when the material is not metallic.[2]

Formula[edit]

By definition, No. 36 AWG is 0.005 inches in diameter, and No. 0000 is 0.46 inches in diameter. The ratio of these diameters is 1:92, and there are 40 gauge sizes from No. 36 to No. 0000, or 39 steps. Because each successive gauge number increases diameter by a constant multiple, diameters vary geometrically. Any two successive gauges (e.g. A & B ) have diameters in the ratio (dia. B ÷ dia. A) of \sqrt [39]{92} (approximately 1.12293), while for gauges two steps apart (e.g. A, B & C), the ratio of the C to A is about 1.12293² = 1.26098. The diameter of a No. n AWG wire is determined, for gauges smaller than 00 (36 to 0), according to the following formula:

d_n = 0.005~\mathrm{inch} \times 92 ^ \frac{36-n}{39} = 0.127~\mathrm{mm} \times 92 ^ \frac{36-n}{39}

(see below for gauges larger than No. 0 (i.e. No. 00, No. 000, No. 0000 ).) or equivalently

d_n = e^ {-1.12436 - 0.11594n}\ \mathrm{inch} = e^ {2.1104 - 0.11594n}\ \mathrm{mm}

The gauge can be calculated from the diameter using

n = -39\log_{92} \left( \frac{d_{n}}{0.005~\mathrm{inch}} \right)+36 = -39\log_{92} \left( \frac{d_{n}}{0.127~\mathrm{mm}} \right)+36 [3]

and the cross-section area is

A_n = \frac{\pi}{4} d_n^2 = 0.000019635~\mathrm{inch}^2 \times 92 ^ \frac{36-n}{19.5} = 0.012668~\mathrm{mm}^2 \times 92 ^ \frac{36-n}{19.5},

The standard ASTM B258 - 02(2008) Standard Specification for Standard Nominal Diameters and Cross-Sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors defines the ratio between successive sizes to be the 39th root of 92, or approximately 1.1229322.[4] ASTM B 258-02 also dictates that wire diameters should be tabulated with no more than 4 significant figures, with a resolution of no more than 0.0001 inches (0.1 mils) for wires larger than No. 44 AWG, and 0.00001 inches (0.01 mils) for wires No. 45 AWG and smaller. Sizes with multiple zeros are successively larger than No. 0 and can be denoted using "number of zeros/0", for example 4/0 for 0000. For an m/0 AWG wire, use n = −(m−1) = 1−m in the above formulas. For instance, for No. 0000 or 4/0, use n = −3.

Rules of thumb[edit]

The sixth power of this ratio is very close to 2,[5] which leads to the following rules of thumb:

A decrease of ten gauge numbers, for example from No. 10 to 1/0, multiplies the area and weight by approximately 10 and reduces the resistance by a factor of approximately 10. Aluminum wire has a conductivity of approximately 61% of copper, so an aluminum wire has nearly the same resistance as a copper wire 2 AWG sizes smaller, which has 62.9% of the area.

Tables of AWG wire sizes[edit]

The table below shows various data including both the resistance of the various wire gauges and the allowable current (ampacity) based on plastic insulation. The diameter information in the table applies to solid wires. Stranded wires are calculated by calculating the equivalent cross sectional copper area. Fusing current (melting wire) is estimated based on 25°C ambient temperature. The table below assumes DC, or AC frequencies equal to or less than 60 Hz, and does not take skin effect into account. Turns of wire is an upper limit for wire with no insulation.

AWGDiameterTurns of wire,
no insulation
AreaCopper
resistance[6]
NEC copper wire
ampacity with
60/75/90 °C
insulation (A)[7]
Approx.
metric
equivalents
Fusing current, copper[8][9]
(in)(mm)(per in)(per cm)(kcmil)(mm2)(Ω/km)
(mΩ/m)
(Ω/kft)
(mΩ/ft)
Preece,
~10 s
Onderdonk,
1 s32 ms
0000 (4/0)0.4600*11.684*2.170.8562121070.16080.04901195 / 230 / 2603.2 kA33 kA182 kA
000 (3/0)0.409610.4052.440.96116885.00.20280.06180165 / 200 / 2252.7 kA26 kA144 kA
00 (2/0)0.36489.2662.741.0813367.40.25570.07793145 / 175 / 1952.3 kA21 kA115 kA
0 (1/0)0.32498.2513.081.2110653.50.32240.09827125 / 150 / 1701.9 kA16 kA91 kA
10.28937.3483.461.3683.742.40.40660.1239110 / 130 / 1451.6 kA13 kA72 kA
20.25766.5443.881.5366.433.60.51270.156395 / 115 / 1301.3 kA10.2 kA57 kA
30.22945.8274.361.7252.626.70.64650.197085 / 100 / 115196/0.41.1 kA8.1 kA45 kA
40.20435.1894.891.9341.721.20.81520.248570 / 85 / 95946 A6.4 kA36 kA
50.18194.6215.502.1633.116.81.0280.3133126/0.4795 A5.1 kA28 kA
60.16204.1156.172.4326.313.31.2960.395155 / 65 / 75668 A4.0 kA23 kA
70.14433.6656.932.7320.810.51.6340.498280/0.4561 A3.2 kA18 kA
80.12853.2647.783.0616.58.372.0610.628240 / 50 / 55472 A2.5 kA14 kA
90.11442.9068.743.4413.16.632.5990.792184/0.3396 A2.0 kA11 kA
100.10192.5889.813.8610.45.263.2770.998930 / 35 / 40333 A1.6 kA8.9 kA
110.09072.30511.04.348.234.174.1321.26056/0.3280 A1.3 kA7.1 kA
120.08082.05312.44.876.533.315.2111.58820 / 25 / 30235 A1.0 kA5.6 kA
130.07201.82813.95.475.182.626.5712.00350/0.25198 A798 A4.5 kA
140.06411.62815.66.144.112.088.2862.52515 / 20 / 2564/0.2166 A633 A3.5 kA
150.05711.45017.56.903.261.6510.453.18430/0.25140 A502 A2.8 kA
160.05081.29119.77.752.581.3113.174.016— / — / 18117 A398 A2.2 kA
170.04531.15022.18.702.051.0416.615.06432/0.299 A316 A1.8 kA
180.04031.02424.89.771.620.82320.956.385— / — / 1424/0.283 A250 A1.4 kA
190.03590.91227.911.01.290.65326.428.05170 A198 A1.1 kA
200.03200.81231.312.31.020.51833.3110.1516/0.258.5 A158 A882 A
210.02850.72335.113.80.8100.41042.0012.8013/0.249 A125 A700 A
220.02530.64439.515.50.6420.32652.9616.147/0.2541 A99 A551 A
230.02260.57344.317.40.5090.25866.7920.3635 A79 A440 A
240.02010.51149.719.60.4040.20584.2225.671/0.5, 7/0.2, 30/0.129 A62 A348 A
250.01790.45555.922.00.3200.162106.232.3724 A49 A276 A
260.01590.40562.724.70.2540.129133.940.811/0.4, 7/0.1520 A39 A218 A
270.01420.36170.427.70.2020.102168.951.4717 A31 A174 A
280.01260.32179.131.10.1600.0810212.964.907/0.1214 A24 A137 A
290.01130.28688.835.00.1270.0642268.581.8412 A20 A110 A
300.01000.25599.739.30.1010.0509338.6103.21/0.25, 7/0.110 A15 A86 A
310.008930.22711244.10.07970.0404426.9130.19 A12 A69 A
320.007950.20212649.50.06320.0320538.3164.11/0.2, 7/0.087 A10 A54 A
330.007080.18014155.60.05010.0254678.8206.96 A7.7 A43 A
340.006300.16015962.40.03980.0201856.0260.95 A6.1 A34 A
350.005610.14317870.10.03150.01601079329.04 A4.8 A27 A
360.00500*0.127*200*78.70.02500.01271361414.84 A3.9 A22 A
370.004450.11322588.40.01980.01001716523.13 A3.1 A17 A
380.003970.10125299.30.01570.007972164659.63 A2.4 A14 A
390.003530.08972831110.01250.006322729831.82 A1.9 A11 A
400.003140.07993181250.009890.00501344110491 A1.5 A8.5 A
AWGDiameterTurns of wire,
no insulation
AreaCopper
resistance
NEC copper wire
ampacity with
60/75/90 °C
insulation (A)
Approx.
metric
equivalents
Fusing current, copper
(in)(mm)(per in)(per cm)(kcmil)(mm2)(Ω/km)
(mΩ/m)
(Ω/kft)
(mΩ/ft)
Preece,
~10 s
Onderdonk,
1 s32 ms

*Exact (by definition)

In the North American electrical industry, conductors larger than 4/0 AWG are generally identified by the area in thousands of circular mils (kcmil), where 1 kcmil = 0.5067 mm². The next wire size larger than 4/0 has a cross section of 250 kcmil. A circular mil is the area of a wire one mil in diameter. One million circular mils is the area of a circle with 1000 mil = 1 inch diameter. An older abbreviation for one thousand circular mils is MCM.

Stranded wire AWG sizes[edit]

AWG gauges are also used to describe stranded wire. In this case, it describes a wire which is equal in cross-sectional area to the total of all the cross-sectional areas of the individual strands; the gaps between strands are not counted. When made with circular strands (see Circle packing), these gaps occupy about 10% of the wire area, thus requiring a wire about 5% thicker than equivalent solid wire.

Stranded wires are specified with three numbers, the overall AWG size, the number of strands, and the AWG size of a strand. The number of strands and the AWG of a strand are separated by a slash. For example, a 22 AWG 7/30 stranded wire is a 22 AWG wire made from seven strands of 30 AWG wire.

Nomenclature and abbreviations in electrical distribution[edit]

Alternate ways are commonly used in the electrical industry to specify wire sizes as AWG.

The industry also bundles common wire for use in electric power distribution in homes and businesses, identifying a bundle's wire size followed by the number of wires in the bundle. The most common type of distribution cable, NM-B, is generally implied:

Pronunciation[edit]

AWG is colloquially referred to as gauge and the zeros in large wire sizes are referred to as aught /ˈɔːt/. Wire sized 1 AWG is referred to as "one gauge" or "No. 1" wire; similarly, smaller diameters are pronounced "x gauge" or "No. X" wire, where x is the positive integer AWG number. Consecutive AWG wire sizes larger than No. 1 wire are designated by the number of zeros:

and so on. [10]

See also[edit]

References[edit]

  1. ^ ASTM Standard B 258-02, Standard specification for standard nominal diameters and cross-sectional areas of AWG sizes of solid round wires used as electrical conductors, ASTM International, 2002
  2. ^ SteelNavel.com Body Piercing Jewelry Size Reference — illustrating the different ways that size is measured on different kinds of jewelry
  3. ^ The logarithm to the base 92 can be computed using any other logarithm, such as common or natural logarithm, using log92x = (log x)/(log 92).
  4. ^ ASTM Standard B 258-02, page 4
  5. ^ The result is roughly 2.0050, or one-quarter of one percent higher than 2
  6. ^ Figure for solid copper wire at 68 °F, computed based on 100% IACS conductivity of 58.0 MS/m, which agrees with multiple sources: High-purity oxygen-free copper can achieve up to 101.5% IACS conductivity; e.g., the Kanthal conductive alloys data sheet lists slightly lower resistances than this table.
  7. ^ NFPA 70 National Electrical Code 2014 Edition. Table 310.15(B)(16) (formerly Table 310.16) page 70-161, Allowable ampacities of insulated conductors rated 0 through 2000 volts, 60°C through 90°C, not more than three current-carrying conductors in raceway, cable, or earth (directly buried) based on ambient temperature of 30°C. Extracts from NFPA 70 do not represent the full position of NFPA and the original complete Code must be consulted. In particular, the maximum permissible overcurrent protection devices may set a lower limit.
  8. ^ Computed using equations from H. Wayne Beaty; Donald G. Fink, eds. (2007), The Standard Handbook for Electrical Engineers (15th ed.), McGraw Hill, pp. 4–25, ISBN 0-07-144146-8 
  9. ^ Douglas Brooks (December 1998), Fusing Current: When Traces Melt Without a Trace, Printed Circuit Design 15 (12): 53 
  10. ^ Glossary of Power Terms | Event Solutions

Further reading[edit]

External links[edit]