Diameter, 293.9 mils. Pounds per mile, 419.4. Resistance per mil foot, 17.6 ohms at 25° C. Resistance per mile at 25° C., 1.00773 ohms. Conductivity as to copper of same size, 59.9 per cent. Number of twists in six inches for fracture, 17.9. Tensile strength per square inch, 32,898 pounds.
This wire also stood the test of wrapping six times about its own diameter and then unwrapping and wrapping again. It was found in tests for tensile strength that the wire in question took a permanent set at very small loads, but that at points between 14,000 and 17,000 pounds per square inch the permanent set began to increase very rapidly. From this it appears that aluminum wires and cables should be given enough sag between poles so that in the coldest weather the strains on them shall not exceed about 15,000 pounds per square inch. This rather low safe working load is a disadvantage that aluminum shares with copper. From the figures just given it is evident that the strains on aluminum conductors during their erection should not exceed one-half of the ultimate strength in any case, lest their sectional areas be reduced.
+----------------------------+-------+-----+--------+-------+----------+ | | | | | | Size of | | | Number|Miles|Circular|Strands| Strands. | | Locations. | of | of |Mils of | per |B. & S. G.| | |Cables.|Each.| Each. |Cable. | Approx- | | | | | | | imate. | +----------------------------+-------+-----+--------+-------+----------+ |Niagara Falls to Buffalo | 3 | 20 | 500,000| .. | .. | |Shawinigan Falls to Montreal| 3 | 85 | 183,708| 7 | 6 | |Electra to Mission San José | 3 |100 | 471,034| 37 | 9 | |Colgate to Oakland | 3 |144 | 211,000| 7 | 5-6 | |Farmington River to Hartford| 3 | 11 | 336,420| 7 | 3 | |Lewiston, Me. | 3 | 3.5| 144,688| 7 | 8 | |Ludlow, Mass. | 6 | 4.5| 135,247| 7 | 7 | +----------------------------+-------+-----+--------+-------+----------+
This table of transmission systems using aluminum conductors is far from exhaustive. Aluminum is also being used to distribute energy to the sub-stations of long electric railways, as on the Aurora and Chicago which connects cities about forty miles apart. The lower cost of aluminum conductors is also leading to their adoption instead of copper in city distribution of light and power. Thus at Manchester, N. H., the local electric lines include about four miles each of 500,000 and 750,000 circular mil aluminum cable with weather-proof insulation. The larger of these cables contains thirty-seven strands of about No. 7 wire.