Answer Posted / imran khan
Cable size of motor is decided on the following factors:
1. Full load current of motor(Since P=VICoso/Sqrt3VICoso)
2. Length of Cable.
3. Method of cable laying.(Air(Tray)/Underground(duct)).
4. Voltage drop of cable.
Calculation will be as:
1. If cable is laid on Tray/underground take its
corrosponding derating factors.
2. Multiply all derating factors & this derating factor is
multiplied by current carrying capacity of the cable which
you are going to sellect(from catalogue).
3. Above current should not be less than full load current
of motor.
4. Then check voltage drop (Vd=(IxLxmV/A/m)/(Rx1000))
where Vd=Voltage drop, I=Current(full load),L=length of
Cable(site requirement),mV/A/m=millivolt/Ampere/meter(from
catalogue),R=No. of Runs of cable.
5. Above voltage drop should not be more than 4%/2.5%(As
per requirement).
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