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High Ampacity Conductors for Large Motors

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    High Ampacity Conductors for Large Motors

    Is there any NEC approved high capacity cabling for wiring 600hp, 720AMP (nameplate) motors? Is diesel locomotive cable ( RHH, RHW-2) the highest capacity that can be used? Even with this type cable is would still take 720 x 1.25 = 900AMPs of cable at 75 degrees C because the 90 degree C is only for de-rating.

    #2
    What is the system voltage?



    Originally posted by Leo1 View Post
    Is there any NEC approved high capacity cabling for wiring 600hp, 720AMP (nameplate) motors? Is diesel locomotive cable ( RHH, RHW-2) the highest capacity that can be used? Even with this type cable is would still take 720 x 1.25 = 900AMPs of cable at 75 degrees C because the 90 degree C is only for de-rating.
    PJHolguin 8-)

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      #3
      [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

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        #4
        Originally posted by pjholguin View Post
        What is the system voltage?
        The 720A suggests 460V.
        Si hoc legere scis nimium eruditionis habes.

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          #5
          [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

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            #6
            Originally posted by Leo1 View Post
            Is there any NEC approved high capacity cabling for wiring 600hp, 720AMP (nameplate) motors? Is diesel locomotive cable ( RHH, RHW-2) the highest capacity that can be used? Even with this type cable is would still take 720 x 1.25 = 900AMPs of cable at 75 degrees C because the 90 degree C is only for de-rating.
            It does not matter what kind of conductor you use. You still need 900A of ampacity. In most cases you cannot exceed the 75 deg C column in the chart.

            1000 kcm is the largest wire I have even heard of. I doubt that even it is sufficient for 900A.

            I think you will need to run smaller conductors in parallel. maybe two sets of 2X 250 kcm in 2 conduits.
            Bob

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              #7
              Don, Illinois
              (All code citations are 2017 unless otherwise noted)

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                #8
                Can you use 3-350mcm THHN per phase?

                We've done 500HP 480v motors and it took 2-500mcm THHN per phase. How many and what size conduit entries into the motors j-box? That'll usually dictate what your options are.

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                  #9
                  Originally posted by Cow View Post
                  ... How many and what size conduit entries into the motors j-box? That'll usually dictate what your options are.
                  Not always. Many are removable, and I've seen termination boxes replaced with larger ones.
                  [COLOR=RoyalBlue]I will have achieved my life's goal if I die with a smile on my face.[/COLOR]

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                    #10
                    Originally posted by pjholguin View Post
                    What is the system voltage?
                    480VAC, 3 phase

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                      #11
                      Originally posted by Leo1 View Post
                      480VAC, 3 phase
                      Bummer. I got it wrong. Silly me. I was thinking of the motor voltage. We daft Brits don't distinguish between supply voltage and motor voltage.
                      Si hoc legere scis nimium eruditionis habes.

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                        #12
                        If you find higher ampacity conductors you are still limited by termination temperature ratings. And for 600 volt and less that is almost always going to be limited to 75C.
                        I live for today, I'm just a day behind.

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