400 amp services

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p051981

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Houston, Texas
I am trying to practice sizing the wires for a 400 amp service for a single dwelling home. From my meter can going underground I would run parallel 2/0 thhn for my hot and a # 3 thhn for my neutral. The size conduit I would use is an 1 1/4 schedule 40 pvc. Is this correct? If not, what would be the correct way to do it. I've never done one on my own before and would like to learn how. Please explain how you did it, I would appreciated.
 
Although the wording is not clear in 310.15(B)(6), I think the intent is that once you split to multiple sets of conductors (whether Service Conductors or Feeders), the sizing in 310.15(B)(6) no longer applies. So you'd need 3/0 copper for each 200A run.

I think you may be a little small on the neutrals too. Did you do a service load calculation for neutral loads? You get to apply a .7 factor to electric range and clothes dryers neutrals (if 120/240V circuits). But otherwise, you're going to need some purely 240V loads in order to reduce the neutral much more. Typical neutral reduction would be 2 or 3 wire sizes. Also note the neutral can not be smaller than the size in 250.66 (#4 for a 2/0 or 3/0 ungrounded conductor) regardless of how small the calculated load is.

I think a 1.25" conduit sounds a bit tight for this. Check the fill tables, but I think you'll want a 1.5" minimum.
 
For a parallel neutral you would need at least #1/0 since that's the smallest conductor permitted to be run in parallel.
 
We are all over the place here. I think the OP needs to explain whether he is running to sets of conductors in 2 1 1/4" conduits, or if he/she is running one parallel set in one conduit. Either way help is needed and running 2 sets may be a violation of 225.30. More info is needed
 
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