*>'^A Tables 407-413. 



WIRE TABLES. 



TABLE 407. —Introduction. Mass and Volume Resistivity of Copper and Aluminum. 



The following wire tables are abridged from those prepared by the Bureau of Standards at the 

 request and with the cooperation of the Standards Committee of the American Institute of Elec- 

 trical Engineers (Circular No. 31 of the Bureau of Standards). The standard of copper resist- 

 ance used is "The International Annealed Copper Standard " as adopted Sept. 5, 1913, by the 

 International Electrotechnical Commission and represents the average commercial high-conduc- 

 tivity copper for the purpose of electric conductors. This standard corresponds to a conductivity 

 of 58. Xio-^ cgs. units, and a density of 8.89, at 20° C. 



In the various units of mass resistivity and volume resistivity this may be stated as 



0.15328 ohm (meter, gram) at 20° C. 

 875.20 ohms (mile, pound) at 20° C. 

 1.724 1 microhm-cm. at 2C° C. 

 0.67879 microhm inch at 20° C. 

 10.371 ohms (mil, foot) at 20° C. 



The temperature coefficient for this particular resistivity is 020 = 0.00393 or 00 = 0.00427. 

 The temperature coefficient of copper is proportional to the conductivity, so that where the con- 

 ductivity is known the temperature coefficient may be calculated, and vice-versa. Thus the next 

 table shows the temperature coefficients of copper having various percentages of the standard con- 

 ductivity. A consequence of this relation is that the change of resistivity per degree is constant, 

 independent of the sam.ple of copper and independent of the temperature of reference. This re- 

 sistivity-temperature constant, for volume resistivity and Centigrade degrees, is 0.00681 michrom- 

 tm., and for mass resistivity is 0.000597 ohm (meter, gram). 



The density of 8.89 grams per cubic centimeter at 20° C., is equivalent to 0.321 17 pounds per 

 cubic inch. 



The values in the following tables are for annealed copper of standard resistivity. The user of 

 the tables must apply the proper correction for copper of other resistivity. Hard-drawn copper 

 may be taken as about 2.7 per cent higher resistivity than annealed copper. 



The following is a fair average of the chemical content of commercial high conductivity copper: 



Copper 99.91% Sulphur 0.002% 



Silver 03 Iron 002 



Oxygen 052 Nickel Trace 



Arsenic 002 Lead " 



Antimony 002 Zinc " 



The following values are consistent with the data above : 



Conductivity at 0° C, in c.g.s. electromagnetic units 62.969 X io~^ 



Resistivity at 0° C, in michroms-cms 1.5881 



Density at 0° C 8.90 



Coefficient of linear expansion per degree C 0.000017 



" Constant mass " temperature coefficient of resistance at 0° C 0.00427 



The aluminum tables are based on a figure for the conductivity published by the U.S. Bureau 

 of Standards, which is the result of many thousands of determinations by the Aluminum Company 

 of America. A volume resistivity of 2.828 michrom-cm., and a density of 2.70 may be considered 

 to be good average values for commercial hard-drawn aluminum. These values give: 



Mass resistivity, in ohms (meter, gram) at 20° C 0.0764 



" " " " (mile, pound) at 20° C 436. 



Mass per cent conductivity 200.7% 



Volume resistivity, in michrom-cm. at 20° C 2.828 



" " in microhm-inch at 20^ C i-ii3 



Volume per cent conductivity 61.0% 



Density, in grams per cubic centimeter 2.70 



Density, in pounds per cubic inch 0-097S 



The average chemical content of commercial aluminum wire is 



Aluminum 99.57% 



Silicon 0.29 



Iron 0.14 



Smithsonian Tables. 



