3 phase service conductors

[Constantin]

Hi all
Here is my situation (2023 NEC):
Upgrading from a 200 amp 3 phase service to a 400 amp 3 phase service for a comercial building.
Planning to install a 400 amp meter socket on the side of the building and a 400 amp fused disconnect on the other side of the wall in the basement.
The conduit from the meter socket to the disconnect will be longet than 24".
Do I need to derate the ampacity of the conductors because I have 4 current carying conductors?
According to Table 310.16, 600KCmil copper is rated for 420 Amps at 75 degrees, but if apply the 80% deration rule for 4 conuctors I will need 900 KCmil conductors (520 Amps x0.8=416 Amps).
Is this correct?
And if I install a pull point, like a 24"x24" can and have less than 24" of conduit from the meter socket to the can and from the can to the disconnect, will I avoid complying to the deration rule?
Thanks

 

[augie47]

It is very rare for a structure to meet the "Major portion of the load to be non-linear". What type of loads are you feeding.
(It is also uncommon for a "400 amp service" actual calculated load to exceed 380 amps thus requiring a 600 vs a 500 kcil)

 

[electrofelon]

You might also consider 2 parallel runs of 250AL or 3/0 CU.

Also make sure Poco is okay with class 320 sockets for 3 ph commercial, many are not.

And I agree with augie: no one counts the neutral of a wye system as a CCC.

 

[infinity]

And I agree with augie: no one counts the neutral of a wye system as a CCC.

I agree as well except for a MWBC with only three conductors.

 

[electrofelon]

I agree as well except for a MWBC with only three conductors.

I agree. I Should have been clearer on that.