Here's the scenario:

I have 6 inverters totaling 112kW, whose 480VAC 3 phase 4 wire outputs are gathered in an AC combiner. The combiner will feed a wye connected stepdown transformer (480Y to 208Y) 205 feet away. What size single copper conductors do I need to run between the combiner and transformer to keep the voltage drop in that segment below 0.5%. Yes, I know that's very low, but I am under some unusual design constraints.

Please show your work (teach a man to fish) and don't just refer me to a calculator; I need to understand how this works.

EDIT: I have gone on line and found three calculators for three phase voltage drop. Interestingly enough, when fed the same input parameters their answers are significantly different.

Aside from that, I am somewhat confused as to what value to use for the current. The three inverters total 112kW at 480V, and their rated output current totals 135A. 112kW divided by 480V is 233.3A, which is 135A times sqrt3. When I am using a calculator, which value for current should I use, 233.3A or 135A?

To confuse me even more, one site I found said that for a delta connection line current equals phase current times sqrt3, but for a wye connection, line current equals phase current. I had thought, possibly erroneously, that a balanced wye connection was basically the same as a delta connection since there would be no current on the neutral.

(Also posted on Holt. Gentlemen, start your engines. )

I have 6 inverters totaling 112kW, whose 480VAC 3 phase 4 wire outputs are gathered in an AC combiner. The combiner will feed a wye connected stepdown transformer (480Y to 208Y) 205 feet away. What size single copper conductors do I need to run between the combiner and transformer to keep the voltage drop in that segment below 0.5%. Yes, I know that's very low, but I am under some unusual design constraints.

Please show your work (teach a man to fish) and don't just refer me to a calculator; I need to understand how this works.

EDIT: I have gone on line and found three calculators for three phase voltage drop. Interestingly enough, when fed the same input parameters their answers are significantly different.

Aside from that, I am somewhat confused as to what value to use for the current. The three inverters total 112kW at 480V, and their rated output current totals 135A. 112kW divided by 480V is 233.3A, which is 135A times sqrt3. When I am using a calculator, which value for current should I use, 233.3A or 135A?

To confuse me even more, one site I found said that for a delta connection line current equals phase current times sqrt3, but for a wye connection, line current equals phase current. I had thought, possibly erroneously, that a balanced wye connection was basically the same as a delta connection since there would be no current on the neutral.

(Also posted on Holt. Gentlemen, start your engines. )

## Comment