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Is a Junction Box a Raceway?

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    Is a Junction Box a Raceway?

    For reasons I'm not going to describe, we ended up with a generator supplied circuit that comprises of 150' of (3) 600 XHHW kcmil/phase in conduit, transitions to (3) 4/0 RHW-2 cables inside a junction box for a length of about 6ft then transitions back to another 200' of (3) 600 kcmil/phase in conduit. It's protected by a 1200A breaker.

    One interpretation is that the junction box is not considered a raceway and the free air rating of 405A is applicable for each of the 90C RHW-2 with its 90C rated terminations.
    Others do consider the junction box a raceway, with each RHW-2 only good for 260A.

    A third opinion is that the raceway vs not a raceway question is irrelevant based on the 310.A.2 exception for the 6ft of RHW-2.

    I'm curious where the experience here falls with this question.

    Thank you!


    #2
    Originally posted by mjr5097 View Post
    One interpretation is that the junction box is not considered a raceway and the free air rating of 405A is applicable for each of the 90C RHW-2 with its 90C rated terminations.
    The conductors are not in free air if they are in an enclosure, unless there is sufficient ventilation. I know of no way to calculate the air flow requirements, so I would just use the 'in raceway" rating.
    Just because you can, doesn't mean you should.

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      #3
      Originally posted by jim dungar View Post

      The conductors are not in free air if they are in an enclosure, unless there is sufficient ventilation. I know of no way to calculate the air flow requirements, so I would just use the 'in raceway" rating.


      Roger
      Moderator

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        #4
        How is this run allowed to be protected by a 1200 amp breaker with the 4/0 RHW-2 in place?

        JAP>

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          #5
          Originally posted by jap View Post
          How is this run allowed to be protected by a 1200 amp breaker with the 4/0 RHW-2 in place?
          One interpretation cited by the OP used the 90C rating of 405 amps. Three of those would have an ampacity over1200. But I agree with Jim that the free air rating would not apply.


          Charles E. Beck, P.E., Seattle
          Comments based on 2017 NEC unless otherwise noted.

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            #6
            Thanks.

            I overlooked that, and, I also agree with you and Jim.

            JAP>

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              #7
              I would add that a junction box is not a raceway.
              Rob

              Moderator

              All responses based on the 2017 NEC unless otherwise noted

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                #8
                Thank you all for the responses. I thought I was losing my mind....


                Originally posted by infinity View Post
                I would add that a junction box is not a raceway.
                Trying to think why this matters now based on the info provided by all above.

                Is this why we don’t necessarily derate for a parallel run with 2 conductors per phase that could have 6 conductors in a junction box but only 3 in each raceway?


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                  #9
                  Originally posted by mjr5097 View Post
                  Thank you all for the responses. I thought I was losing my mind....




                  Trying to think why this matters now based on the info provided by all above.

                  Is this why we don’t necessarily derate for a parallel run with 2 conductors per phase that could have 6 conductors in a junction box but only 3 in each raceway?

                  Yes, that would be one example of why it's not a raceway. Another would be 24" nipple>junction box>24" nipple >junction box, etc, no derating required.
                  Rob

                  Moderator

                  All responses based on the 2017 NEC unless otherwise noted

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