26 in Sch80
30 in Sch40


I have to say, this is an extremely odd request. Is it for a test or homework or something?
Anyone really needing to know this would have a copy of the NEC and would know exactly where to look.

May I ask why you are asking this?

We have an under sized generator and have to upgrade it to a 100 kw and the feed from the generator now is 4/0-2/0 AL in 3 in conduit 250 feet from the house

OH!! You asked how large of a 3-wire. Not how many #3 conductors. Sorry.

You would NOT run a "3-wire" cable in conduit. You would run 3 or 4 individual conductors.

I have to say, anyone who does this for you will know what to do.

You really need a 100kW(!? ) genset for a house? For real? Sounds like a real mansion, not even a McMansion.

Believe me it is the 48kw is to small keeps tripping out we are pulling close to 300 A right now

10,000+ sq/ft?

What could you POSSIBLY be running that you are tripping a 48kW genset??
Are you familiar with the idea that you do not have to run everything in your house during emergencies?

I said it is a mansion all the floors are radient heat etc.

That is 300A on each leg we are looking to upgrade to a 800A service

That is for the main house the guest house also runs off the genset it is only a 200A service

I know I need 3 individual conductors what is the largest copper I can put in 3 in PVC I need to know if I have to upgrade the conduit

If the PVC is schedule 40 (thinner stuff) and the wire is THHN which is most common. You can put 3 700 MCM(kCM). You may need a ground too though which will be considered in the pipe fill. This was installed by a licensed electrician right? If so one would hope it was done right. It is overlooked by a lot of home owners though. And good for you for having a gigantic house.

And good for you for having a gigantic house.:rolleyes: