Abstract: An alloy composition used in the manufacture of extension cables, comprises by weight 25.00% to 35.00% of nickel, 0.10% to 1.00% of manganese, 0.10% to 1.75% of cobalt, less than 0.25% of iron, and the balance being of copper. A thermoelement, of a thermocouple extension cable, manufactured from this composition exhibits a resistivity of approximately 240 ohms per circular mil foot. Hence, the loop resistivity of the cable, where the other thermoelement is made from copper, is generally less than 310 ohms per circular mil foot and the calibration accuracy of the cable from 0.degree. to 100.degree. C. is within .+-.2.5.degree. C.