I'm use to using 4/0 for a 200 amp.120/240 single phase service on residential, which I know is approved by Table 310.15(B)(7). I'm running a 200 amp service on a church in 2" conduit. According to Table 310.15(B)(16), I'd have to go to 250mcm to get 200 amps, which I know could not go in 2" EMT. So according to my calculations, I will have to use 3/0 copper conductors to still use the 2" conduit. Am I missing anything?? And yes, the lugs are approved for 75 degree wire. Thanks..
I come up with 2 1/2 inch pipe for (3) 250mcm(2 hots and neutral) and (1) #4 for ground for 200 amp service. I don't want to use 2 1/2" because of conditions getting it down into a stud wall. Going to be hard enough getting 2" down it. (Place of assembly, seating over 100 people requires emt etc., no SER feeder cable)

2 1/2" RMC or EMT is a tad less than 3" O/D so it would fit in a 2x4 stud wall (3.5") but it is a tight fit.

You do have the ampacity right. 3/0 cu or 250kcmil al

Thanks Greg. As far as getting into the wall, the issue is that I'm going to have to cut the hole in the top plate to feed the subpanel. This is a service change is an existing small church. I'm going to have to run 2" conduit from the outside service location, in the attic, and over and down an existing wall. Going to be hot:( and I understand from previous construction, that I'll be having to go through (2) top plates to get down into the wall:( Going to be an exciting job. Suppose to do it Thursday. Suppose to have a high of 86 degrees here. I better get me some wet cloths etc... to cool me down in the attic:(

sparky:
Watch the ambient temp for your run! The 'attic' portion will be the determining factor for your adjustment.

Can you talk them into letting you in there at night? At around 3-4AM that attic will be tamed quite a bit, particularly if you can open the access in the evening and let it vent better. Do you have a big fan or two to get it venting better?
We have lots of hot attic experience down here.
If you are in there in the daytime, just be sure you stay hydrated, take breaks and plan your attack down on the floor before you go up there to cut down the time you are up there. Guys here are using "cool vests" a lot in attics.
Assemble as much as you can down in the environmental air.
The real trick might be snaking that pipe down the wall if this is a low attic.
If you are stuck with 2", I guess this will be a copper run.

You should be able to make pretty short work of the top plate with a big hole saw. Do one layer, clear the arbor and do the second layer. If you have 2 arbors and mandrels it might be worth taking both of them up there just to go faster in the heat. Nothing worse than being hot and nasty trying to get a jammed plug out of the arbor.

I would still try for a 2-3AM start if you can.

3am might be a good idea if it was isolated, but it's right next to a house and that might not be good for the neighbors to get woke up that early. I have pretty much tried to get my plan together before I get up there, but there's always those unexpected things. I see I've got a heat duct to get by, and the pitch of the roof to either get a (2") 90 or 45 by, and (2) top plates to get a 2" hole through for the pipe, a sheet rock wall to cut for a 30/40 200 amp panel, (1) 4 gang switch box to move, run a spare 1 1/2" conduit for future use, and drive 2 grd. rods. and clean up the mess and try not to come out the side of the sheet rock when drilling my holes down the wall. Other than that, everything should go fine:) Oh yes, and swing the existing meter and riser over so I can hook back up temporarily after I'm through. "Piece of cake"