The heating of copper wires by electric currents

In August 1889, a report was made by one of the present writers¹ to the Edison Electric Light Co., on “The Heating of Conductors by Electric Currents.” The report was published in the minutes of the convention of the Association of Edison Illuminating Companies, at Niagara Falls, August 1889. It contained a large number of measurements of the temperature elevations of active conductors supported in wooden moulding, and in free air, within doors and without. A further report was made in 1893² upon the temperature elevations of electric-light cables. The research reported in the present paper has been undertaken to extend the scope of the above measurements, and also to increase the precision of the results previously obtained. In the measurements of 1889 and 1893, above referred to, the temperature-coefficient of resistivity of copper wires was taken as 0.388 per cent. per degree centigrade of temperature elevation; whereas it is now taken by the American Institute of Electrical Engineers as 0.42 per cent. per degree centigrade from and at 0° cent.³ Again, the law of thermal radiation employed was that of Dulong and Petit;⁴ whereas the law of radiation generally adopted at this time is that of Stefan.⁵