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Thread: 90 Degree wire in existing conduit

  1. #1
    Join Date
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    Omaha, NE, USA
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    90 Degree wire in existing conduit

    I have a 55 Amp Dishwasher that I need to feed through an existing 3/4" conduit. Can I use a 90°C rated #6 THHN that has an allowable ampacity of 75A if I put a 90 degree rated CB in the panel?. I can fit four (4) #6 THHN in a ¾” EMT.

  2. #2
    Join Date
    Feb 2003
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    Not likely. You can only use the 90C column if all components in the circuit have 90C ratings. You are not likely to find terminations rated for 90C. Reference NEC 110.14(C).

    Why do you need four wires? If one is the EGC, that wire need only be #10. You might be able to get three #4 and one #10 in a 3/4" conduit, but you would have to do the math yourself. Also, if one of the four wires is a neutral, it may be possible to downsize it, if you can work out a value for the unbalanced load it will see.

    Welcome to the forum.
    Last edited by charlie b; 08-12-09 at 03:38 PM.
    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  3. #3
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    Welcome to the Forum...
    At 55 amps, the #6 should be sufficient...
    Is the dishwasher a continuous load ?
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  4. #4
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    Quote Originally Posted by augie47 View Post
    At 55 amps, the #6 should be sufficient...

    Sure, give an easy answer. I worked so hard to give a complicated answer. :grin:
    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  5. #5
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    Do you need a 75 ampere circuit? A #6 at 60 degree c is 55 amperes. You might be able to use 240.4(B) and use a 60 amp breaker.
    Steve

  6. #6
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    actually, you answered his question :grin:
    I just asked what may be a pertinent one
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  7. #7
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    #6 THHN in conduit @ 75 degrees C = 65 amps. If no derating is involved and your terminations are rated for 75 degrees C you could load this to 65 amps and protect it on a 70 amp OCPD.
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

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