Direct Burial Wire In Conduit - Do I Need To Detrate It?

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Old 11-13-09, 07:36 AM
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Direct Burial Wire In Conduit - Do I Need To Detrate It?

I am going to pull the power out to the shop in the next couple weeks. The shop has a 100A sub. I am a one-man operation so don't need nearly that much. However, I plan to size the cable for 100A because the price difference on the cable is not much between 60 and 100A. I will probably install a 90A breaker to feed it since the 90A is a fair bit cheaper here and I won't miss the 10A. I will use 2-2-4-6 Al rated for burial but plan to run it in 1.5" conduit. I can run it in 1.25" but I think it will be easier to pull in the larger. Question is, because it is rated for burial and has different insulation do I need to derate the cable inside the conduit? Also, does the ground count towards the fill measurement? I didn't think so. I haven't measured the run yet but it will be 90'<>100'
 
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Old 11-13-09, 09:17 AM
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Originally Posted by crokett View Post
I will probably install a 90A breaker to feed it since the 90A is a fair bit cheaper here and I won't miss the 10A.
90A is the max for #2 aluminum now anyway.

I will use 2-2-4-6 Al rated for burial but plan to run it in 1.5" conduit. I can run it in 1.25" but I think it will be easier to pull in the larger.
Either size is okay for those conductors, but you're right that bigger is easier to pull through.

Question is, because it is rated for burial and has different insulation do I need to derate the cable inside the conduit?
Yes you would need to derate it, but you only have two current carrying conductors and no derating is required until you exceed three.

Also, does the ground count towards the fill measurement?
Yes. All conductors count toward fill, only current carrying conductors count towards derating.
 
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Old 11-13-09, 06:39 PM
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Thanks for the reply. I was getting ready tomake this post again. I had problems with the site earlier and didn't think it had gotten through.
 
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