# Service feeders



## SamJones20 (Mar 14, 2021)

I'm a 1st year student in the EC&M program, was wondering if someone can confirm my homework. 

I have a transformer feeding my CT cabinet with 3inch pvc, CT cabinet is feeding my main panel with 800amps also 3inch pvc. I have it figured it will take 400 MCM XHHW (AL)


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## SWDweller (Dec 9, 2020)

Back to the drawing board. 
I have never used 400 in my career.
AL 400 mcm is good for 225 to 270 amps depending on what temp column your using
Do not know the distance so even 400 is a guess by golly.


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## SamJones20 (Mar 14, 2021)

SWDweller said:


> Back to the drawing board.
> I have never used 400 in my career.
> AL 400 mcm is good for 225 to 270 amps depending on what temp column your using
> Do not know the distance so even 400 is a guess by golly.


Alright thanks for your input


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## SamJones20 (Mar 14, 2021)

SWDweller said:


> Back to the drawing board.
> I have never used 400 in my career.
> AL 400 mcm is good for 225 to 270 amps depending on what temp column your using
> Do not know the distance so even 400 is a guess by golly.


I should've mentioned I have 3 3inch pipes going to the main


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## HertzHound (Jan 22, 2019)

400 kcmil aluminum at 75c = 270A
270 x 3 = 810A
(4) 400 kcmil in a 3” PVC conduit is 31.8% full
40% fill is max

So you have (3) 3” conduits?


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## SamJones20 (Mar 14, 2021)

HertzHound said:


> 400 kcmil aluminum at 75c = 270A
> 270 x 3 = 810A
> So you have (3) 3” conduits?


Correct (3) 3" pvc conduits


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## HertzHound (Jan 22, 2019)

350 kcmil Aluminum at 75c = 250A
250 x 3 = 750A

You could use 350 kcmil and fuse it at 800A as long as the calculated load is under 750A. See 240.4 (b) and (c) for going next size higher. The cutoff is 800A, then you have to go lower.


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