CALCULATION OF CABLE RESISTANCE

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Consider an example using the reistance formula:-
A copper conductor of length 500 meters is used to supply electrical energy to a lighting load of 1,000W. If the cross sectional area of the conductor is 10mmsq, calculate the resistance of the conductor. If the copper conductor were replaced with an Aluminium conductor of the same length, calculate the resistance of the Aluminium conductor.
Solution:
The resistance per km for copper is given by:


R = 22.5/S(c.s.a)

Here S = 10mmsq


Hence R = 22.5/10 = 2.25 Ohms per km


Length of conductor = 500m =500/1000 = 0.5km


Therefore resistance of copper conductor = 2.25 x 0.5 =1.125 Ohms

Similarly for Aluminium,

The resistance per km for Aluminium is given by:

R = 36/S(c.s.a)


Again S = 10mmsq


Hence R = 36/10 = 3.6 Ohms per km


Length of conductor = 0.5km


Therefore resistance of copper conductor = 3.6 x 0.5 = 1.8 Ohms