Conductor Resistance

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The calculation to find the resistance of a specific size and type conductor is basic. If you know the resistance of the conductor for a given length, then you can use a proportion to find the resistance at any length.

Example: If you know that the resistance of a #18 copper conductor is 6.505 ohms per 1000 feet, then the resistance for 400 feet would be what?

Solution: Resistance of the wire for 1000 feet times the length of the wire in the problem then divided by 1000 will yield the resistance for the stipulated length.

So it's 6.505 times 400 divided by 1000 equals 2.602 ohms.

Here are some resistance of small conductors. Find resistance of larger conductors in the NEC Chapter 9.

All are ohms per 1000 feet of annealed copper conductor.

#32    167.2 
#30    105.1
#28    66.11
#24    26.15
#22    16.45
#20    10.34
#18    6.505
#16    4.091
#14    2.573

Find practice problems HERE.

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Find practice problems HERE for building conductors.

Find audio support HERE for building conductors.



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