Neutral Reduction?

[PaTerminator]

I?m putting in an underground service for a customer?s farm outbuilding. (120/240 single phase) The total run from the pole to the meter base on the building is 400?, I?m kind of amazed that the POCO is even allowing this long of a run to begin with, but the primary line is on the other side of the highway and the terrain is not very friendly for them to run distribution closer to the outbuilding, so maybe it?s a hardship thing.
The POCO engineer told the customer to use USE 350 mcm Al. because of voltage drop ( we supply and install the lateral). The building currently has no electric and is probably going to be used for storage and light maintenance (Lights, air compressor, small welder, etc?) so I can?t really do a very good load calculation. I agree on running 350 mcm for the ungrounded conductors, and I haven?t spoken to the engineer yet, but I?m curious why the neutral can?t be downsized to say? 250 mcm.
I?m more familiar with typical residential applications where I?m using 4/0-4/0-2/0 Al either in SE cable or in a riser. I have never seen where that combo wouldn?t work in reference to a neutral load calculation.
Is there a table or chart I?m not seeing that refers to this? I have been looking at 220.61, but I?m not seeing an answer if I can reduce the neutral?
FWIW we?re using the 2005 code and the POCO is First Energy.

 

[nakulak]

230.31 C ? ->250.24 C -> 250.66

 

[charlie]

The air compressor and welder are probably both 240 volts and the rest of the loads should be balanced. Why not reduce the neutral would be a better question. The only way to know for sure is to use 220.61.

 

[ohm]

The air compressor and welder are probably both 240 volts and the rest of the loads should be balanced. Why not reduce the neutral would be a better question. The only way to know for sure is to use 220.61.

With only a welder (50A) and an air compressor (20A and a few lights you could probably get by w/ 4/0 4/0 2/0 AL