Question
13800 volt cables in conduit,
Two cables (Feeder in Feeder out).
Can they be run in same conduit if correct
sq inch of fill??
Conduit RSC but could be any type raceway.
Yoopersup

Art 215 seems not to address this in the over 600v sections.

Sounds like a design issue with the info you provided. OCP, conductor sizes, what the 'in' & 'out' are, etc., and time to research may all be needed. Derating may be required.

Scott35 what say you??

I am sure you are be derating this to 80% (4-6 conductors) but I can't think of a code reason why it would be prohibited.
If one set was service conductors it is a problem.

310.60 Conductors Rated 2001 to 35,000 Volts.
Derateing HV conductors.
I don't think their done the same as under 600 volts.

Watts is watts and that means heat. I bet if you run that formula you will end up being in the same place.

I suppose you should just demand the calculation because there is not a table for 4-6 conductors.
I am just a "pump and pulley" guy and that sort of math makes my head hurt.

Can you even put more then 3 Phase conductors + ground or Neutral in a single conduit?? I've never seen it Done???
HV ductbanks are derated by the number of conduits in the Ductbank not wires in the conduit.
Figure 310.60 Page 342 NFPA Code handbook.
70-159 NEC 2011

I am not sure why it would be prohibited but I think you pointed out why it is not attractive.

It sounds like you need engineering to determine ampacity.

Purely hypothetical brain teasers are unworthy.

The better question is: At such power levels and cable sizes, when would it ever be economic to do so?

The swift answer is: Never.

Tesla
Sorry not Hypothetical. Read Field problem.
Three 13.8 Switches single feed, Jumpers in between each (line side).
Load off each switch proposed to run thur same nipple as feed to switch! I don't make this stuff up I run into it!
Power calculations, Fill ect no problem.
Yoopersup

Nuff said.

Tesla
Sent you info on the E-mail you listed on here.
Codemanec

Yoop:
I can't find an NEC Article to prohibit this.

As you say, I have never seen more than 3 conductors plus G or N in any conduits or duct banks in >600 volt systems.

Not common practice, but......

I think the only issue might be derating. It sounds like, if you can't use the tables (that only go up to 3), you need engineering.

As for the 3, do harmonic loads throw a fly in the ointment?
(3p wye)

Like I said early on....Scott35 Where are you??

For your Information Problem Solved.
Line Feeder (As it has OCP ahead of it). Comes in thur Nipple in back of cabinet. (Have to see it to understand).
Second Nipple goes out in the fused section. Thus they go same
area different routes. Line feeder not in Fused area.
I still don't think you can put two 13.8 feeders same Conduit.
Yoopersup