4/0 conduit sizing??

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My chart shows an outside diameter of .635 inches for 4/0 USE

The area, then of each conductor (pi*r^2) is .3167 square inches.
6*.3167 = 1.9 square inches.

Table 4, for sched 80 pvc, shows 2.577 square inches are available in a 3 inch conduit (40% fill). The next size down, 2.5, will only allow 1.65 square inches of conductors.

3 inch conduit.

Eric
 
OK,
That was the easy answer. Why 6? Are you running 2 per phase?
You'll have to derate the cables to 80% of their ampacity. 310.15(B)(2)(a)

If this is 2 per phase, can you run two conduits?


Eric
 
Running 400 amp service to a 400amp trans "S" cabinet. Running 2 sets of 4/0 triplex instead of 1 set of a larger cable.
 
pjwinstalls said:
Running 400 amp service to a 400amp trans "S" cabinet. Running 2 sets of 4/0 triplex instead of 1 set of a larger cable.
Click to expand...

Does this triplex have factory twisting? If so, I don't think you can count two runs of triplex as being the same as 6 runs of USE.
 
hardworkingstiff said:
Does this triplex have factory twisting? If so, I don't think you can count two runs of triplex as being the same as 6 runs of USE.
Click to expand...

Good point, in that case I think you must treat it as two cables and base the raceway size on the cables OD.
 
pjwinstalls said:
Running 400 amp service to a 400amp trans "S" cabinet. Running 2 sets of 4/0 triplex instead of 1 set of a larger cable.
Click to expand...


How do you get 400 amps out of 2 sets of #4/0 AL triplex in the same raceway?
 
its two seperate sets....each set is factory individually twisted. I am direct burying the cable, just need to run it up to the trans "s" cabinet. So I can't use 3" for that??

Thanks

Philip
 
10-4,
If it were a cable, it would be based on the cable OD and then 53% fill would be used.

The original problem statement appeared to me to be single conductors.

Eric
 
infinity said:
How do you get 400 amps out of 2 sets of #4/0 AL triplex in the same raceway?
Click to expand...

I guessing Table 310.15(B)(6) x 2 which if that is the situation is a violation before we even get around to derating.
 
pjwinstalls said:
There are individual conductors, they are just twisted around each other. There is no jacket going around all 3.
Click to expand...

Jacket or not it is a multi conductor cable and if you try to size the raceway based on 6 individual conductors you will have trouble.
 
i would use seperate conduits but i then need two conduits for the load leaving the cabinet. I only have three knockouts on the bottom of the cabinet up to 4" each. I am running the load to 2 200amp panels.
 
Running both in the same conduit would be rough at best. The way you are supposed to approach this is to consider the overall outside diameter of each bundle. Calculate the are of each bundle. (my guess is that this is real close to 2 square inches, but that is a guess). Now, since you have two bundles, you can't use any more than 31%.

4 inch sched 80 shows about 3.5 available square inches for the 31% column. It doesn't look good.

But Bob and Trevor bring up a larger issue. It looks like there's an ampacity issue here.

Eric
 
This is the cable i am using....why would ampacity be an issue?






Triplex Conductor 600 V Secondary Type URD Cable - Aluminum Conductor
Directly buried or installed in ducts for 600 volt secondary distribution.



Specifications

Phase Conductor Size AWG 4/0


Phase Conductor Stranding 19/w


Phase Conductor Insulation Thickness 80 mls


Neutral Size AWG 4/0


Neutral Stranding 19/w


Neutral Insulation Thickness 80 mls


Single Phase Conductor .672 Inches


Outside Diameter 1.457 Inches


Weight Per 1000ft 828 Lbs


Ampacity Direct Burial 315 Amps


Ampacity In Duct 240 Amps


Standard Package Length (Feet) 1000 ft.


Standard Package Weight (Lbs.) 740 Lbs


Real Size NRC 42.26
 
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