How you calculating the current for a 2.5 Sqmm cable.
A 30 Hp 3 phase AC motor of power what size of cable is
used for this motor.


Answer Posted / shashank

deciding a cable has to consider following parameters also,
1. Safety factor of the cable (margin for starting current
say 1.25 in numerator side)
2. Deterioration / Degradation factor (say 0.8 in
denominator)
calculate the current of the motor by considering running
pf (power factor) say 0.8
as motor gives real power
e.g.
W = V * I Cos (phi)
30*746 = 415 * I * 0.8
I = 30 * 746 / (415*0.8)
I = 67.41 Amp,
Thus Current considered for cable (Icb) = 67.41*1.25/0.8
Icb = 105.3 Amps.
Select from the catalogue suitable copper cable for this
motor. Dont forget to consider the voltage drop per meter,
the total voltage drop shall not be more that + - 5%.

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