I need to feed a 200 amp 3ph 120/240 panel from the power co. 450' will be (al) areial and 110' will be (cu)underground over to the panel. How do you size the wire for voltage drop

Compute the two separately, and add up the cumulative voltage drop. You can use the tables in the back of NEC, or one of the calculators online like this one: http://www.csgnetwork.com/voltagedropcalc.html

Do you mean 3-phase 120/208, or 1-phase 120/240?

FYI, the "half-length" the calculations ask for, in your case, would be 450' and 110', as the electricity has to take a return trip down back the same wire, so the actual electrical length required for calculating voltage drop would be twice that.

We need more information to calculate the wire size. Namely what is the expected load on the panel. It would not be practical to size the wire for a 200a. load and try to maintain the 240/120v. status. Once we know the "load" we need to know what voltage drop you can tolerate. Then there are formulae for giving you the wire size.

don't most poco's do the sizing inclusive in their doctrine for us?

~S~

The service is 120/240 3ph hi leg and the connected load is 150 amp. motor load.

Oh wow, there's going to be some SERIOUS kick-down when that motor starts. What's the locked-rotor current for that motor?

This is a textbook case where you're probably better off stepping up to a higher voltage and stepping back down. Any chance of getting your service at 480V and using a 480V motor? This will eliminate the need for two 72kVA transformers. You can throw on a small transformer for the 120V loads, and come out WAY ahead in copper.

I have three 7-1/2 hp one 5 hp thats 108 amps with the 125%, the 42 amps is lighting. I should have listed it earlier in the post it looks like there is 150 amps in motor load but there is not.

I agree with Steve. Consider also getting a separate drop from the utility company. Getting that much power over that distance is extremely expensive. Get an engineer to figure your wire size if you can't get the utility to give you a separate drop. I could figure it out but I think you'd end up with xformers as the best route if the utility can't accommodate you with a drop.

Litebulb:

Is your question in this thread a 'school project'?

Ya know John, I think you are right, I seem to remember that same problem showing up before and it was off some test or school project someplace. I'm sticking with my suggestion and see what happens

I am with those who say let the PoCo do the long run with MV and set a transformer near the load. In the long run it will be cheaper. Bear in mind, even if you get to the magic 3% VD that is still a 3% tax on every watt you use out there.
If this is a school assignment they are probably looking for the computations and the correct wire sizes, even if that is fiscal lunacy.
*** political flag on
Most school teachers went to school at 5 and never left so the real world is an alien planet to them. Sometimes the correct answer on a test is not the right answer.
political flag off ***

Yes, LB is a tech school student, from previous inquiries.

I have no issues with helping him out, and I don't think anyone else does either. Hopefully, my question above didn't chase him away.

One of his situations, he did not want an answer...just a method to arrive at an answer, Steve sent him on the right track above.

Yes George this is a school project they are wanting us to calculate this for wire size. I come up with 4/0 AL. aerial and 250 cu underground.