Max conduit fill for short runs

[don_resqcapt19]

In mikes dvd he said dlo was not in 310 104 A so it cant be used. Is that right?

That is correct. Wire types not listed in that table are not permitted for NEC applications. (Note that Table 310.104 became Table 310.4(A) in the 2020 code)
That being said, there is dual rated DLO on the market. It rated DLO/RHW and with that rating it can be used for NEC applications. The ampacity would be based on Table 310.16 for that use, however, the 2020 code with new language in 310.15(A) permits the interpolation of ampacities for non-standard conductor sizes under engineering supervision.

310.15(A) ... Under engineering supervision, ampacities of sizes not shown in ampacity tables for conductors meeting the general wiring requirements shall be permitted to be determined by interpolation of the adjacent conductors based on
the conductor’s area.

 

[oldsparky52]

If you can get by with 418 amps instead of 420 amps, could you parallel 4/0 in the same 2.5" conduit? Looks to me that you could. Now, do you have terminations that accept (2) 4/0?

 

[electrofelon]

Side question on this topic: When a _cable_ is inserted into a conduit, you take the largest diameter of the cable and use that to calculate the cross section as if it were round, then you treat it as a single wire. This can be a big benefit because if you only have a _single_ wire in a conduit (or a single cable assembly) then you can use 53% as your maximum fill.

For purpose of this section, what is an acceptable 'cable assembly'? If the OP were to take the requisite wires, bundle them together neatly, and then use 'lacing' to form them into an assembly, would that count?

(To the OP, I think you are stuck anyway. If you assemble 10 #3/0 and 1#1/0 you exceed the 53% fill number...I think you could do it with custom 'sector' conductors', but now you are talking big $$)

There has been some discussion in the past as to whether "plexed stuff" like URD, mobile home feeder, etc are or can be considered a "cable assembly". Yes You get the 53%, but then you also have to count all the voids in the plexed assembly so I doubt you would come in ahead (just assuming, I didnt run any numbers). One big advantage of plexed assemblies like URD is they are not prone to jamming, so although not a code requirement, in practice you can often use a smaller conduit than you should with individual conductors. I recently pulled 700' of 250 URD through 2" PVC and I dont think it would have worked with individuals.

 

[Julius Right]

I agree with Carultch.
According to NEC it is not permissible. However, it is possible to run these cables [theoretically- anyway you have to check the actual cable diameter]
and to use a suitable grease. It has to be at the end of routing in order to reduce the initial friction force.
(Based on Chapter 9: Table 1, Table 4, and Table 5)
600 mcm XHHW 1.051" diameter,3/0 0.584,1/0 0.486
Then maximum bunch diameter is 2.1642" and RMC conduit of 21/2" inner diameter=2.489.

 

[winnie]

I think oldsparky has the most likely to succeed approach in post 22.

If you split the phase conductors then you have to derate in the conduit, but can derate from the 90C ampacity without having to then transition to 75C conductors.

Unfortunately even using compact stranded 2/0 Cu conductors (3 per phase) I don't think you can get below about 45% fill.

-Jon