Conductor Sizing and Voltage Drop

[eemdude]

I have a 480 V,25 hp motor I am wanting to select the right condutors for. The FLC of the motor is 34 amps and the distance between motor and motor starter is 730 feet. When running a voltage drop calculation to determine the proper size of conductors , should I be using 34 amps as the ampacity of the circuit or should it be 34 amps times 1.25?

 

[buzzp]

Service factor of motor should be used for sizing cable, per the NEC (United States). I am not sure if it needs to be used in voltage drop considerations (sure it does) but I would use it for these calculations as well since you dont want the motor to be operating on a reduced voltage while its in the service factor area since this will cause even more current to be drawn.

 

[davidbeach]

At that distance, I'd look seriously at voltage drop during starting; it will be much worse than any running voltage drop, FLA or FLA*1.25. Without doing any calculations, I'd guess that you are going to be looking at #4 or larger conductors to deal with your nearly 25,000 amp-ft worth of voltage drop inducing current.