How to calculate cable size || Cable calculation formula with example 

How to calculate cable size:
First we must know these three values:
Load - ?
Voltage - ?
% efficiency - ?
Example:
Load (P)=1 kW
Voltage=230 V
% Efficiency=80%
Answer:
Formula-
P = V x I x CosØ x efficiency %
1000 = 230 x I x 0.8 x 0.8
I = 6.79 A
Every Motor have Voltage drop avg.=2%
Voltage drop=6.79 x 2%
=0.1358 A
Total Current=6.79+.135
= 7 A
For Al Cable:
1 sqmm =1.5 A
So
7 A = 1/1.5 x 7
7 A = 4.66 sqmm.
For Cu Cable:
1 sqmm = 2.5 A
So
7 A = 1/2.5 x 7
7 A = 2.8 sqmm.
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