American wire gauge

From Academic Kids

American wire gauge (AWG) is used in the United States and other countries as a standard method of denoting wire diameter, especially for non-ferrous, electrically conducting wire. Increasing gauge numbers give decreasing wire diameters, which is similar to many other non-metric gauging systems. This seemingly-counterintuitive numbering is derived from the fact that the gauge number is related to the number of drawing operations that must be used to produce a given gauge of wire; very fine wire (for example, 30 gauge) requires far more passes through the drawing dies than 0 gauge wire.

Note that for gauges 5 through about 14, you can think of the wire gauge as the number of bare solid wires that, when placed side by side, span 1 inch. That is, 8 gauge is about 1/8" in diameter.

AWG is also commonly used to specify body piercing jewelry sizes.

Media:Gauge_Chart.pdf Chart comparing all known wire gauges to each other

Contents

Formulas

By definition, No. 36 AWG is 0.005 inches diameter, and No. 0000 is 0.46 inches diameter. The diameter increases by 0.46/0.005=92 times, evenly divided into 39 sizes. Intermediate diameters can be calculated as follows:

<math>D = 0.005 \left ( 92 ^ \frac{{36-AWG}}{39} \right ) <math>

where diameter D is in inches. When calculating the diameter of a conductor of n/0 AWG, an AWG value of −(n−1) should be put into the formula.

The ratio between sucessive sizes is the 39th root of 92, or approximately 1.122932. The sixth power of this ratio is nearly 2.0, which means for an increase in 6 gauge numbers, the wire diameter is changed by a ratio of two (No. 10 is about one-half the diameter of No. 4 AWG). An increase of three gauge numbers doubles the area of a wire. An increase of 10 gauge numbers, for example from No. 10 to 1/0, multiplies the area and weight by approximately 10 and reduces the resistance by approximately 10.

Current-carrying capacity of wires

The current-carrying capacity (ampacity) of practical wires is limited by two factors:

  • The amount of voltage lost to electrical resistance in the form of <math>V=IR<math> voltage drop and
  • The amount of heating of the wire caused by the <math>P=I^2R<math> power dissipated in the wire as a result of that voltage drop.

While copper (or aluminium) can carry substantial current before melting, practical plastic wire insulation will melt (allowing short circuits) or even catch fire at much lower temperatures, limiting the current-carrying capacity of any insulated wire to a much lower value than that point at which the wire itself will melt.

For relatively high-voltage circuits, the temperature of the insulation thus provides a limit to the current-carrying capacity of the wire and the wire gauge to be used must be selected to provide reliable, safe operation of the insulation. (And various kinds of insulation can withstand varying degrees of heat.) For low voltage circuits, it is instead the voltage drop as a result of <math>IR<math> losses that usually dominates the choice of wire gauge.

Table of AWGs and approximate corresponding sizes

The table below shows various data including both the resistance of the various wire gauges and the allowable current 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. The table below assumes DC or low frequency operation of the wires and does not take skin effect into account.


<tr><td>0000000(6/0)<td>0.5800<td>14.732<td><td><td> <tr><td>000000(5/0)<td>0.5165<td>13.119<td><td><td> <tr><td>00000(4/0)<td>0.4600<td>11.684<td>104.091<td><td> <tr><td>000(3/0)<td>0.4096<td>10.404<td>84.004<td><td> <tr><td>00(2/0)<td>0.3648<td>9.266<td>67.399<td><td> <tr><td>0(1/0)<td>0.3249<td>8.252<td>53.454<td><td> <tr><td>1<td>0.2893<td>7.348<td>42.384<td><td>110 <tr><td>2<td>0.2576<td>6.543<td>33.606<td><td>95 <tr><td>3<td>0.2294<td>5.827<td>26.653<td><td>85 <tr><td>4<td>0.2043<td>5.189<td>21.137<td><td>70 <tr><td>5<td>0.1819<td>4.621<td>16.755<td><td> <tr><td>6<td>0.1620<td>4.115<td>13.292<td><td>55 <tr><td>7<td>0.1443<td>3.665<td>10.544<td><td> <tr><td>8<td>0.1285<td>3.264<td>8.350<td><td>40 <tr><td>9<td>0.1144<td>2.906<td>6.626<td><td> <tr><td>10<td>0.1019<td>2.588<td>6.271<td>1.0<td>30 <tr><td>11<td>0.0907<td>2.304<td>4.156<td><td> <tr><td>12<td>0.0808<td>2.052<td>3.302<td><td>20 <tr><td>13<td>0.0720<td>1.829<td>2.629<td><td> <tr><td>14<td>0.0641<td>1.628<td>2.088<td><td>15 <tr><td>15<td>0.0571<td>1.450<td>1.652<td><td> <tr><td>16<td>0.0508<td>1.291<td>1.308<td><td> <tr><td>17<td>0.0453<td>1.150<td>1.039<td><td> <tr><td>18<td>0.0403<td>1.024<td>0.823<td><td> <tr><td>19<td>0.0359<td>0.9119<td>0.653<td><td> <tr><td>20<td>0.0320<td>0.8128<td>0.516<td>10.0<td> <tr><td>21<td>0.0285<td>0.7239<td>0.411<td><td> <tr><td>22<td>0.0253<td>0.6426<td>0.322<td><td> <tr><td>23<td>0.0226<td>0.5740<td>0.255<td><td> <tr><td>24<td>0.0201<td>0.5106<td>0.205<td><td> <tr><td>25<td>0.0179<td>0.4547<td>0.162<td><td> <tr><td>26<td>0.0159<td>0.4038<td>0.12826<td><td> <tr><td>27<td>0.0142<td>0.3606<td><td><td> <tr><td>28<td>0.0126<td>0.3200<td><td><td> <tr><td>29<td>0.0113<td>0.2870<td><td><td> <tr><td>30<td>0.0100<td>0.2540<td><td>100<td> <tr><td>31<td>0.0089<td>0.2261<td><td><td> <tr><td>32<td>0.0080<td>0.2032<td><td><td> <tr><td>33<td>0.0071<td>0.1803<td><td><td> <tr><td>34<td>0.0063<td>0.1601<td><td><td> <tr><td>35<td>0.0056<td>0.1422<td><td><td> <tr><td>36<td>0.0050<td>0.1270<td><td><td> <tr><td>37<td>0.0045<td>0.1143<td><td><td> <tr><td>38<td>0.0040<td>0.1016<td><td><td> <tr><td>39<td>0.0035<td>0.0889<td><td><td> <tr><td>40<td>0.0031<td>0.0787<td><td>1000<td> </table> In the North American electrical industry, conductors larger than 4/0 AWG are generally identifed by the area in thousands of circular mils (kcmil). (A circular mil is the area of a wire one mil in diameter.) One million circular mils (1000 kcmil) is the area of a rod 1000 mils (one inch) in diameter. An older abbreviation for one thousand circular mils is mcm. Outside Canada and the U.S., wire is typically specified in terms of its area in mm2.

Reference

  • Donald G. Fink and H. Wayne Beaty, Standard Handbook for Electrical Engineers, Eleventh Edition,McGraw-Hill, New York, 1978, ISBN 007020974X, page 4-18 and table 4-11.
AWG Diameter
(in)
Diameter
(mm)
Area
(mm²)
Copperwire
(Ω/1000 ft)
Current rating
with 60 C insulation
(A)
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