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    Wire size?

    I am hoping someone could help as I dont have my code book with me. I need to know what size wire AL or CU is needed for a 125A service to a barn. And since it will be in conduit not URD so would THHN AL be okay or is it a better practice to go with copper conductors? The service length is 140'

    #2
    For underground you would need THWN or XHHW. Are you concerned about voltage drop? If not #1 Cu (130 amps) or #2/0 (135 amps) would do.
    Rob

    Moderator

    All responses based on the 2017 NEC unless otherwise noted

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      #3
      Infinity is correcet however you could use 1/0 al instead of 2/0 alu,inum if the calculated load is not over 120 amps. Art. 240.4(B) allows us to use the next size breaker which is 125 amps even though the wire is only good for 120amps.

      Given 140 feet you may want to size to the 2/0 al
      They say I shot a man named Gray and took his wife to Italy
      She inherited a million bucks and when she died it came to me
      I can't help it if I'm lucky

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        #4
        Originally posted by Dennis Alwon View Post
        Infinity is correcet however you could use 1/0 al instead of 2/0 alu,inum if the calculated load is not over 120 amps. Art. 240.4(B) allows us to use the next size breaker which is 125 amps even though the wire is only good for 120amps.

        Given 140 feet you may want to size to the 2/0 al
        If I go with 2/0 AL can I do a #1 AL neutral and than would I need a # 6 or a # 8 EGC?

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          #5
          The neutral needs to be large enough to carry the unbalanced load which #1 should work. For the EGC take a look at table 250.122
          Rob

          Moderator

          All responses based on the 2017 NEC unless otherwise noted

          Comment

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