How to Calculate Cable size l Cable selection calculation l Step by Step

How to calculate cable size?
3 phase 15HP motor located at a distance of 750 metre from power supply.
Full load current - 20A
Applied Voltage - 415v
Motor effiency - 80%
How to select ?
If consider a 3 core 16 sq.mm cable ?
If consider a 3 core 25 sq.mm cable ?
If consider a 3 core 35 sq.mm cable ?
Step : 1
Let us consider a 3 core 16 sq.mm cable
Resistance of cable = 2.5 ohms / KM
Voltage drop in 3 phase circuit = √3 x I x R = 1.732x 20 x 2.5 x 0.750 = 65v
Percentage of Voltage drop = (65 /415 ) x 100 = 15%
Step : 2
Let us consider a 3 core 25 sq.mm cable
Resistance of cable = 1.5 ohms / KM
Voltage drop in 3 phase circuit = √3 x I x R = 1.732x 20 x 1.5 x 0.750 = 39v
Percentage of Voltage drop = (39 /415 ) x 100 = 10%
Step : 2
Let us consider a 3 core 35 sq.mm cable
Resistance of cable = 0.90 ohms / KM
Voltage drop in 3 phase circuit = √3 x I x R = 1.732x 20 x 0.90 x 0.750 = 23v
Percentage of Voltage drop = (23 /415 ) x 100 = 5%
Voltage drop
3 core 16 sq.mm cable - 15 %
3 core 25 sq.mm cable - 10 %
3 core 35 sq.mm cable - 5 %
It is advisable to select 35 sq.mm cable in this case

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Vd=IL[1.732√(Rccosθ+Xcsinθ)