Question

Calculate the resistance of 1 km long cable composed of 19 stands of similar copper conductors. each strand being 1.32mm in diameter. Allow 5% increase in length for the 'lay' (twist) of each strand in completea cable. Resistivity of copper may be taken as 1.72 x 10^-8Ω-m.

Answer 1

Allowing for twist, the length of the stands. 

= 1000 m + 5% of 1000m =1050 m 

Area of cross.section of 19 strands of copper conductors is

19 x π x d²/4 = 19π x (1.32 x 10^-3)²/4 m²

Now, R = ρ(l/A) = (1.72 x 10^-8 x 1050 x 4)/(19π x 1.322 x 10^-6) = 0.694Ω