American wire gauge

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Short description: North American standard for electrical wire diameters

American Wire Gauge (AWG) is a logarithmic stepped 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 logarithmically decreasing wire diameters, which is similar to many other non-metric gauging systems such as British Standard Wire Gauge (SWG). 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, mm²). The AWG 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 0 gauge wire did. 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 and 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.

While the AWG is essentially identical to the Brown & Sharpe (B&S) sheet metal gauge, the B&S gauge was designed for use with sheet metals as its name suggests. These are functionally interchangeable but the use of B&S in relation to wire gauges, rather than sheet metal gauges, is technically improper.

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

Formulae

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 cross sectional area by a constant multiple, diameters vary geometrically. Any two successive gauges (e.g., A and B ) have diameters whose ratio (dia. B ÷ dia. A) is [math]\displaystyle{ \sqrt [39]{92} }[/math] (approximately 1.12293), while for gauges two steps apart (e.g., A, B, and C), the ratio of the C to A is about 1.122932 ≈ 1.26098.

The diameter of an AWG wire is determined according to the following formula:

[math]\displaystyle{ d_n = 0.005~\mathrm{inch} \times 92^{(36 - n)/39} = 0.127~\mathrm{mm} \times 92^{(36 - n)/39} }[/math]

(where n is the AWG size for gauges from 36 to 0, n = −1 for No. 00, n = −2 for No. 000, and n = −3 for No. 0000. See below for rule)

or equivalently:

[math]\displaystyle{ d_n = e^{-1.12436 - 0.11594n}\ \mathrm{inch} = e^{2.1104 - 0.11594n}\ \mathrm{mm} }[/math]

The gauge can be calculated from the diameter using [3]

[math]\displaystyle{ 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 }[/math]

and the cross-section area is

[math]\displaystyle{ A_n = \frac{\pi}{4} d_n^2 \approx 0.000019635~\mathrm{inch}^2 \times 92^{(36 - n)/19.5} \approx 0.012668~\mathrm{mm}^2 \times 92^{(36 - n)/19.5} }[/math],

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 B258-02 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

The sixth power of 39√92 is very close to 2,[5] which leads to the following rules of thumb:

  • When the cross-sectional area of a wire is doubled, the AWG will decrease by 3. (E.g. two No. 14 AWG wires have about the same cross-sectional area as a single No. 11 AWG wire.) This doubles the conductance.
  • When the diameter of a wire is doubled, the AWG will decrease by 6. (E.g. No. 2 AWG is about twice the diameter of No. 8 AWG.) This quadruples the cross-sectional area and the conductance.
  • A decrease of ten gauge numbers, for example from No. 12 to No. 2, multiplies the area and weight by approximately 10, and reduces the electrical resistance (and increases the conductance) by a factor of approximately 10.
  • For the same cross section, aluminum wire has a conductivity of approximately 61% of copper, so an aluminum wire has nearly the same resistance as a copper wire smaller by 2 AWG sizes, which has 62.9% of the area.
  • A solid round 18 AWG wire is about 1 mm in diameter.
  • An approximation for the resistance of copper wire may be expressed as follows:
Approximate resistance of copper wire[6]:27
AWG mΩ/ft mΩ/m AWG mΩ/ft mΩ/m AWG mΩ/ft mΩ/m AWG mΩ/ft mΩ/m
0 0.1 0.32 10 1 3.2 20 10 32 30 100 320
1 0.125 0.4 11 1.25 4 21 12.5 40 31 125 400
2 0.16 0.5 12 1.6 5 22 16 50 32 160 500
3 0.2 0.64 13 2 6.4 23 20 64 33 200 640
4 0.25 0.8 14 2.5 8 24 25 80 34 250 800
5 0.32 1 15 3.2 10 25 32 100 35 320 1000
6 0.4 1.25 16 4 12.5 26 40 125 36 400 1250
7 0.5 1.6 17 5 16 27 50 160 37 500 1600
8 0.64 2 18 6.4 20 28 64 200 38 640 2000
9 0.8 2.5 19 8 25 29 80 250 39 800 2500

Tables of AWG wire sizes

The table below shows various data including both the resistance of the various wire gauges and the allowable current (ampacity) based on a copper conductor with 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 (77 °F) 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 per unit length" is the reciprocal of the conductor diameter; it is therefore an upper limit for wire wound in the form of a helix (see solenoid), based on uninsulated wire.

AWG Diameter Turns of wire,
without
insulation 		Area Copper wire
Length-specific
resistance[7] 		Ampacity at temperature rating[lower-alpha 1] Fusing current[10][11]
60 °C 75 °C 90 °C Preece[12][13][14][15] Onderdonk[16][15]
(in) (mm) (per in) (per cm) (kcmil) (mm2) (mΩ/m[lower-alpha 2]) (mΩ/ft[lower-alpha 3]) (A) ~10 s 1 s 32 ms
0000 (4/0) 0.4600[lower-alpha 4] 11.684[lower-alpha 4] 2.17 0.856 212 107 0.1608 0.04901 195 230 260 3.2 kA 33 kA 182 kA
000 (3/0) 0.4096 10.405 2.44 0.961 168 85.0 0.2028 0.06180 165 200 225 2.7 kA 26 kA 144 kA
00 (2/0) 0.3648 9.266 2.74 1.08 133 67.4 0.2557 0.07793 145 175 195 2.3 kA 21 kA 115 kA
0 (1/0) 0.3249 8.251 3.08 1.21 106 53.5 0.3224 0.09827 125 150 170 1.9 kA 16 kA 91 kA
1 0.2893 7.348 3.46 1.36 83.7 42.4 0.4066 0.1239 110 130 145 1.6 kA 13 kA 72 kA
2 0.2576 6.544 3.88 1.53 66.4 33.4 0.5127 0.1563 95 115 130 1.3 kA 10.2 kA 57 kA
3 0.2294 5.827 4.36 1.72 52.6 26.7 0.6465 0.1970 85 100 115 1.1 kA 8.1 kA 45 kA
4 0.2043 5.189 4.89 1.93 41.7 21.2 0.8152 0.2485 70 85 95 946 A 6.4 kA 36 kA
5 0.1819 4.621 5.50 2.16 33.1 16.8 1.028 0.3133 795 A 5.1 kA 28 kA
6 0.1620 4.115 6.17 2.43 26.3 13.3 1.296 0.3951 55 65 75 668 A 4.0 kA 23 kA
7 0.1443 3.665 6.93 2.73 20.8 10.5 1.634 0.4982 561 A 3.2 kA 18 kA
8 0.1285 3.264 7.78 3.06 16.5 8.37 2.061 0.6282 40 50 55 472 A 2.5 kA 14 kA
9 0.1144 2.906 8.74 3.44 13.1 6.63 2.599 0.7921 396 A 2.0 kA 11 kA
10 0.1019 2.588 9.81 3.86 10.4 5.26 3.277 0.9989 30 35 40 333 A 1.6 kA 8.9 kA
11 0.0907 2.305 11.0 4.34 8.23 4.17 4.132 1.260 280 A 1.3 kA 7.1 kA
12 0.0808 2.053 12.4 4.87 6.53 3.31 5.211 1.588 20 25 30 235 A 1.0 kA 5.6 kA
13 0.0720 1.828 13.9 5.47 5.18 2.62 6.571 2.003 198 A 798 A 4.5 kA
14 0.0641 1.628 15.6 6.14 4.11 2.08 8.286 2.525 15 20 25 166 A 633 A 3.5 kA
15 0.0571 1.450 17.5 6.90 3.26 1.65 10.45 3.184 140 A 502 A 2.8 kA
16 0.0508 1.291 19.7 7.75 2.58 1.31 13.17 4.016 18 117 A 398 A 2.2 kA
17 0.0453 1.150 22.1 8.70 2.05 1.04 16.61 5.064 99 A 316 A 1.8 kA
18 0.0403 1.024 24.8 9.77 1.62 0.823 20.95 6.385 10 14 16 83 A 250 A 1.4 kA
19 0.0359 0.912 27.9 11.0 1.29 0.653 26.42 8.051 — — — 70 A 198 A 1.1 kA
20 0.0320 0.812 31.3 12.3 1.02 0.518 33.31 10.15 5 11 — 58.5 A 158 A 882 A
21 0.0285 0.723 35.1 13.8 0.810 0.410 42.00 12.80 — — — 49 A 125 A 700 A
22 0.0253 0.644 39.5 15.5 0.642 0.326 52.96 16.14 3 7 — 41 A 99 A 551 A
23 0.0226 0.573 44.3 17.4 0.509 0.258 66.79 20.36 — — — 35 A 79 A 440 A
24 0.0201 0.511 49.7 19.6 0.404 0.205 84.22 25.67 2.1 3.5 — 29 A 62 A 348 A
25 0.0179 0.455 55.9 22.0 0.320 0.162 106.2 32.37 — — — 24 A 49 A 276 A
26 0.0159 0.405 62.7 24.7 0.254 0.129 133.9 40.81 1.3 2.2 — 20 A 39 A 218 A
27 0.0142 0.361 70.4 27.7 0.202 0.102 168.9 51.47 — — — 17 A 31 A 174 A
28 0.0126 0.321 79.1 31.1 0.160 0.0810 212.9 64.90 0.83 1.4 — 14 A 24 A 137 A
29 0.0113 0.286 88.8 35.0 0.127 0.0642 268.5 81.84 — — — 12 A 20 A 110 A
30 0.0100 0.255 99.7 39.3 0.101 0.0509 338.6 103.2 0.52 0.86 — 10 A 15 A 86 A
31 0.00893 0.227 112 44.1 0.0797 0.0404 426.9 130.1 — — — 9 A 12 A 69 A
32 0.00795 0.202 126 49.5 0.0632 0.0320 538.3 164.1 0.32 0.53 — 7 A 10 A 54 A
33 0.00708 0.180 141 55.6 0.0501 0.0254 678.8 206.9 — — — 6 A 7.7 A 43 A
34 0.00630 0.160 159 62.4 0.0398 0.0201 856.0 260.9 0.18 0.3 — 5 A 6.1 A 34 A
35 0.00561 0.143 178 70.1 0.0315 0.0160 1079 329.0 — — — 4 A 4.8 A 27 A
36 0.00500[lower-alpha 4] 0.127[lower-alpha 4] 200 78.7 0.0250 0.0127 1361 414.8 — — — 4 A 3.9 A 22 A
37 0.00445 0.113 225 88.4 0.0198 0.0100 1716 523.1 — — — 3 A 3.1 A 17 A
38 0.00397 0.101 252 99.3 0.0157 0.00797 2164 659.6 — — — 3 A 2.4 A 14 A
39 0.00353 0.0897 283 111 0.0125 0.00632 2729 831.8 — — — 2 A 1.9 A 11 A
40 0.00314 0.0799 318 125 0.00989 0.00501 3441 1049 — — — 1 A 1.5 A 8.5 A
  1. ↑ For enclosed wire at 30 °C ambient,[8] with given insulation material temperature rating, or for single unbundled wires in equipment for 16 AWG and smaller.[9]
  2. ↑ or, equivalently, Ω/km
  3. ↑ or, equivalently, Ω/kft
  4. ↑ 4.0 4.1 4.2 4.3 Exactly, 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 1,000 mil (1 inch) diameter. An older abbreviation for one thousand circular mils is MCM.

Stranded wire AWG sizes

AWG can also used to describe stranded wire. The AWG of a stranded wire represents the sum of the cross-sectional diameter of the individual strands; the gaps between strands are not counted. When made with circular strands, these gaps occupy about 25% of the wire area, thus requiring the overall bundle diameter to be about 13% larger than a solid wire of equal gauge.

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.

As indicated in the Formulas and Rules of Thumb sections above, differences in AWG translate directly into ratios of diameter or area. This property can be employed to easily find the AWG of a stranded bundle by measuring the diameter and count of its strands. (This only applies to bundles with circular strands of identical size.) To find the AWG of 7-strand wire with equal strands, subtract 8.4 from the AWG of a strand. Similarly, for 19-strand subtract 12.7, and for 37 subtract 15.6.

Measuring strand diameter is often easier and more accurate than attempting to measure bundle diameter and packing ratio. Such measurement can be done with a wire gauge go-no-go tool or with a caliper or micrometer.

Nomenclature and abbreviations in electrical distribution

Main page: Engineering:Electric power distribution

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

  • 4 AWG (proper)
    • #4 (the number sign is used as an abbreviation of "number")
    • № 4 (the numero sign is used as an abbreviation for "number")
    • No. 4 (an approximation of the numero is used as an abbreviation for "number")
    • No. 4 AWG
    • 4 ga. (abbreviation for "gauge")
  • 000 AWG (proper for large sizes)
    • 3/0 (common for large sizes) Pronounced "three-aught"
    • 3/0 AWG
    • #000

Pronunciation

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:

  • No. 0, often written 1/0 and referred to as "one aught" wire
  • No. 00, often written 2/0 and referred to as "two aught" wire
  • No. 000, often written 3/0 and referred to as "three aught" wire

and so on.

See also

  • IEC 60228, international standards for wire sizes
  • French gauge
  • Brown & Sharpe
  • Circular mil, North American Electrical industry standard for wires larger than 4/0.
  • Birmingham Wire Gauge
  • Stubs Iron Wire Gauge
  • Jewelry wire gauge
  • Body jewelry sizes
  • Electrical wiring
  • Number 8 wire, a term used in the New Zealand vernacular

References

  1. ↑ "ASTM B258-14 Standard Specification for Standard Nominal Diameters and Cross-sectional Areas of AWG Sizes of Solid Round Wires Used as Electrical Conductors". West Conshohocken: ASTM International. http://www.astm.org/Standards/B258.htm. 
  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 B258-02, page 4
  5. ↑ The result is roughly 2.0050, or one-quarter of one percent higher than 2
  6. ↑ Template:Cite tech report
  7. ↑ Figure for solid copper wire at 68 °F, (Not in accordance to NEC Codebook 2014 Ch. 9, Table 8) 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.
  8. ↑ 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.
  9. ↑ "Table 11: Recommended Current Ratings (Continuous Duty) for electronic equipment and chassis wiring". Reference Data for Engineers: Radio, Electronics, Computer and Communications (7th ed.). pp. 49–16. 
  10. ↑ Computed using equations from Beaty, H. Wayne; Fink, Donald G., eds. (2007), The Standard Handbook for Electrical Engineers (15th ed.), McGraw Hill, pp. 4–25, ISBN 978-0-07-144146-9 
  11. ↑ Brooks, Douglas G. (December 1998), "Fusing Current: When Traces Melt Without a Trace", Printed Circuit Design 15 (12): 53, http://www.ultracad.com/articles/fusingr.pdf, retrieved 2016-08-01 
  12. ↑ Preece, W. H. (1883), "On the Heating Effects of Electric Currents", Proceedings of the Royal Society (36): 464–471, http://rspl.royalsocietypublishing.org/content/36/228-231/464.full.pdf+html 
  13. ↑ Preece, W. H. (1887), "On the Heating Effects of Electric Currents", Proceedings of the Royal Society II (43): 280–295, http://rspl.royalsocietypublishing.org/content/43/258-265/280.full.pdf+html 
  14. ↑ Preece, W. H. (1888), "On the Heating Effects of Electric Currents", Proceedings of the Royal Society III (44): 109–111, http://rspl.royalsocietypublishing.org/content/44/266-272/109.full.pdf+html 
  15. ↑ 15.0 15.1 Brooks, Douglas G.; Adam, Johannes (29 June 2015), "Who Were Preece and Onderdonk?", Printed Circuit Design and Fab, http://pcdandf.com/pcdesign/index.php/magazine/10179-pcb-design-1507 
  16. ↑ Stauffacher, E. R. (June 1928), "Short-time Current Carrying Capacity of Copper Wire", General Electric Review 31 (6), http://ultracad.com/articles/reprints/stauffacher.pdf 



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