Paralleled Conductors

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Duuuuug

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400amp/480VAC Feed to a MCC from a Panelboard.
Conduit Run is approx. 200FT.
I would like to run 2-4/0's per phase and 1-#3 gnd in a 4"Conduit. This is because we have a lot of it in stock.
Since there would be six 4/0's in the same conduit (Six current carrying conductors)then Table 310-15(b)(2)(a) applies with 80% derate.
So in order to stay with 2-4/0's per phase, the wire would have to be 90degC rated according to Table 310-16.
1-4/0 = 260amps
2-4/0's = 520amps
520x0.8=416amps
okay to use on 400amp breaker.
Just want to make sure I am thinking correct??
 
Re: Paralleled Conductors

I'm kind of gun shy on sticking my neck out around here but,I'm going to say this anyway.You could use 3/0's rated at 90 degree and still be legal,at 80% deration 360 amps falls under being able to be protect at the next standard size breaker or 400 amps.(not taking into consideration any voltage drop).
 
Re: Paralleled Conductors

At 75 degC, 2 sets of 4/0 would give 460 amps, which derates to 368 amps. That can be protected by the next standard size breaker, which is 400A. So if your load is actually less than 368 amps, you could use 75 deg wire.

Since 2 4/0's are good for 460 amps, there is that rule about upsizing the ground for larger feeder conductors. So you may want to think about using a #2 or even a #1 ground. (I can't remember exactly how the rule is phrased, so I just wanted to mention you may want to check that).

Also, I think 8 4/0's and a ground fit in a 3" per NEC fill, but I'm not sure how easy the pull would be.
 
Re: Paralleled Conductors

Is there any code that says I can't run parallel feed wires with one ground wire in one conduit??
I can't find anything so far.
 
Re: Paralleled Conductors

Originally posted by jap2525:You could use 3/0's rated at 90 degree and still be legal . . . .
Click to expand...
I agree with your statement, but we need to add the statement made by Steve66:
Originally posted by steve66: So if your load is actually less than 368 amps, you could use 75 deg wire.
Click to expand...
You can indeed upsize to the next higher breaker rating. But you have to start by selecting a conductor that is rated for every bit of the load. Then you select the breaker.
 
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