Feeder Question / Advice

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JFletcher said:
If they are changing to two parallel runs of copper 250 MCM (instead of the initial 4 / 0) between the 90-degree terminations, that gives 580 amps, derated to 80% for 6 CCC in 1 conduit, 464 amps, Which is higher than the required 452.

So yes, if they upsize from 4 / 0 to 250 MCM, use 90-degree terminations on each end, then appropriately-sized jumpers to the 75 degree terminations, I believe it would be code compliant.
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I think you are looking at it backwards. I believe they want to replace short sections of the #4/0 at the beginning and end of the circuit so that they can leave the existing #4/0 between the 90 degree terminations.
 
david luchini said:
I think you are looking at it backwards. I believe they want to replace short sections of the #4/0 at the beginning and end of the circuit so that they can leave the existing #4/0 between the 90 degree terminations.
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Yeah, you are correct. I miss read what the original poster was trying to do versus what that graphic showed.

That said, I believe if they yanked out the 4/0 and ran 250 MCM between the 90* terminations, they would have sufficient ampacity in the entire circuit as you mentioned as required.
 
Using 90C terminations permits the use of the wire at its 90C ampacity.

This does not help in this situation, because the wire is already being used at its 90C ampacity.

By running the parallel sets in the same conduit, they need to derate the ampacity to 80% of the normal value. But this derating is taking from the 90C ampacity.

-Jon
 
winnie said:
Using 90C terminations permits the use of the wire at its 90C ampacity.

This does not help in this situation, because the wire is already being used at its 90C ampacity.

By running the parallel sets in the same conduit, they need to derate the ampacity to 80% of the normal value. But this derating is taking from the 90C ampacity.

-Jon
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I agree.

Changing terminal rating only is an advantage if there is still some ampacity to give in the raceway portion of the run.

80% adjustment you get from going from 3 CCC's to six is likely too much of a change in most cases to not need a larger conductor though.

You might be able to pull such a thing off if you have a smaller adjustment factor for ambient temp such as the .96 or .91 factors for 87 thru 104 deg F ambient temps.
 
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