May 2016 Archives

Steel Wire Instead

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In electrical applications, it's not unusual to spend a large amount of money acquiring and installing copper wire, or when that is too expensive, changing to a larger gauge or two and using aluminum wire. Sometimes the cost of aluminum wire is still significant, or there are special needs or reasons as to why steel wire may be favored, such as long spans. Long spans of unsupported wire are often seen in antenna applications as well as power distribution. These spans are typically above 125 feet in height, which is roughly the limit for timber which supplies wooden poles used to support such wires from the ground without impacting the antenna pattern.

From a historical text (free on Google Books, so likely well before 1950):

Example: A cable 3/8"-inch in diameter, made of 7 strands of high strength crucible steel, weighs approximately 295 lbs. per 1000 ft. and breaks under a load of 11,500 lbs. Calculate the actual cross sectional area from the fact that steels weights 490 lbs. per cubic foot; then find the resistance per mile, the ohms per circular mil foot being 115. The volume of 1000 ft. = 295/490 = 0.602 cu. ft., hence the cross section = 0.602/1000 = 0.000602 sq. ft. This equals 0.000602 x 144 or 0.0867 sq. in., which equals 86,700 sq. mils and 86,700 / 0.785, or 110,300 C. M. Resistance per mile = 115 x 5,280/110,300 = 5.5 ohms.

(Journal of Electricity, Jan 1, 1921, p. 30.)

3/8" is between 00 and 000 gauge, so one can see that this is still a large wire for any application used, and being larger than #6, satisfies NEC requirements for power distribution wire sizes.

#6: 0.162" or 13.3 mm diameter for solid rod wire.

Probably just cheaper to buy the cable with the insulation on it, unless it's going outdoors and that's a lot of insulation.

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