Table 496 



421 



Introduction to Wire Tables; 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 Electrical Engineers (Circular No. 31 of the Bureau of Standards). The 

 standard of copper resistance used is " The International Annealed Copper Standard " as 

 adopted Sept. 5, 1913, by the International Electrotechnical Commission and represents 

 the average commercial high-conductivity copper for the purpose of electric conductors. 

 This standard corresponds to a conductivity of 58 X 10" 5 c.g.s. 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 20° C. 

 0.67879 microhm-inch at 20 C. 

 10.371 ohms (mil, foot) at 20° C. 



The temperature coefficient for this particular resistivity is a 2 o = 0.00393, or a = 0.00427. 

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

 conductivity 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 conductivity. A consequence of this relation is that the change of resistivity 

 per degree is constant, independent of the sample of copper and independent of the tem- 

 perature of reference. This resistivity-temperature constant, for volume resistivity and 

 Centigrade degrees, is 0.00681 microhm cm, 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' 5 



Resistivity at 0° C, in microhm-cms 1.5881 



Density at o° C 8.90 



Coefficient of linear expansion per degree C 0.000017 



" Constant mass " temperature coefficient of resistance at o° 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 microhm-cm and a density 

 of 2.70 may be considered to be good average values for commercial hard-drawn aluminum. 

 These values give : 



Conductivity at o° C in c.g.s. electromagnetic units 38.36 X io" 6 



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



" (mile, pound) at 20 C 436. 



Mass per cent conductivity relative to copper 200.7% 



Volume resistivity, in microhm-cm at 20 C 2.828 



in microhm-inch at 20° C 1.1 13 



Volume per cent conductivity relative to copper 61.0% 



Density, in grams per cubic centimeter 2.70 



Density, in pounds per cubic inch 0.0975 



The average chemical content of commercial aluminum wire is 



Aluminum ■ 99-57% 



Silicon 0.29 



Iron 0.14 



Smithsonian Tables 



