AWG, American Wire Gauge, Brown & Sharpe
Copper vs Aluminum
Temperature Coefficients of Resistance

Wire Resistance megaConverter #29

Introduction and Overview
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This megaConverter is intended to provide a number of measurements for various types and sizes of conductive wire. It provides pounds weight per 1000 feet, which is a standard size roll of wire, kilograms per kilometer, diameter in millimeters and inches, cross-sectional area in square millimeters and square inches, and the area in circular mils, which is the area of a circle one mil (.001 inch) in diameter. It also gives the resistance in Ohms per mile and Ohms per kilometer for both Aluminum wire and Copper wire (see below). The Ohm field is per mile because when wire is strung up on high lines, that is a handier way to consider distance than 1000s of feet. The wire density also changes between Aluminum and Copper. Metric measure of wire is not given as a gauge but simply as the square millimeters of the wire. This converter will allow users of metric specified wire to interpolate between the AWG numbers to get approximate resistance and weight of that wire.

To learn more about conductive wire and its properties see "Mark’s Standard Handbook for Mechanical Engineers," available in most libraries.

* Much of our written history still refers to things in common units. The Bible does not refer to meters or kilograms, but to cubits and stadia, or shekels and drachma. Wouldn't it be nice to know what they were talking about way back then? Now you can use megaConverter! This megaConverter is specifically for kitchen volume measurements commonly used today in the US, Britain, and by the SI system. See megaConverters Ancient Volume #36 and Foreign Volume #37 for volume conversions common in ancient times and foreign countries. For a more complete listing of ancient, foreign, and obsolete measures, download our 'megaSpreadsheet' of conversions in MS Excel format.

For the most comprehensive treatment of measurements, find "NTC's Encyclopedia of International Weights & Measures" by William D. Johnstone at your local library.

Glossary of Conversions:

American Wire Gauge, Brown & Sharpe
Used for non-ferrous sheets, rod, or wire. Primarily for aluminum or copper, but can be used for all materials. Used extensively in the electronics industry. Gauges above 0000 are not given here because those gauges are not used except in cables which are twisted weavings of smaller wires. It is necessary to consider each individual wire in a cable as a separate wire and parallel the resistances as needed.

Copper vs Aluminum
Copper is used much more extensively than aluminum because of its lower resistivity, solderability, mechanical properties, and resistance to oxidation. However, aluminum is used a great deal in high voltage applications and where weight is a factor because of its much lower density. Per weight, aluminum has lower resistivity than copper. This can be easily seen in the converter. Aluminum expands more with temperature and thus can sag more on overhead lines. This can be a problem in windy areas where wires might come in contact with one another. Since aluminum melts at a lower temperature, arc-overs are more likely to cause failures. In many instances, aluminum cables have a steel core for better tensile strength. Aluminum is much cheaper than copper and this is a factor in its use as well.

Resistivity is the resistance to the flow of electrons in a material. It is given in Ohms*cross-sectional area/linear dimension. The resistivity of copper at 20oC is 10.371 Ohms*circular mils/ft, and the resistivity of aluminum at the same temperature is 17.01 Ohms*circular mils/ft. To get resistance, multiply resistivity by the length of the wire and divide by the cross-sectional area.

Temperature Coefficients of Resistance
As the temperature changes, the resistivity of most materials also changes, usually increasing with increasing temperature. The resistivity of copper at 20oC is 10.371 Ohms*circular mils/ft, whereas the resistivity at 40oC is 11.186 Ohms*circular mils/ft. In the range or temperatures 0oC to 100oC, use the formula R2/R1=(234.5+t2)/(234.5+t1). As you can see, the resistance of a strand of wire can be very dependent on the temperature range it is used in. For aluminum, use the formula R2/R1=(228+t2)/(228+t1)

Note: Because of round-off errors, converting from very large units to very small units or vice-versa may not be accurate (or practical). Conversion factors can be found by converting a quantity of 1 unit to another unit several steps above or below the first. You may need to string several conversion factors together to find the factor from a very large unit to a very small unit, and then you can use a calculator with sufficient digits to find your answer.