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Thread: Conduit Sizing

  1. #1
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    Default Conduit Sizing

    Buddy just got a new Tesla all electric car. You can charge the car at home with a 50 amp circuit. He has a 50 amp receptacle he currently uses for his table saw. He wants to run a new set of wires from the 50 amp breaker in the panel across the ceiling of the garage via conduit and mount a receptacle convienent to charge the vehicle.

    He is planning on using a 6-3 with a 10 ground. He wants to use the proper size conduit. Can someone help point me in the correct direction in the NEC to help size the conduit?

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  2. #2
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    Default Re: Conduit Sizing

    The tables in Chapter 9 will be used to size the conduit.

    Note that the major diameter of the cable needs to be used in the calculation if elliptical.

    All answers based on unamended National Electrical codes.

  3. #3
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    Default Re: Conduit Sizing

    Dang, table saw with a 50amp breaker. Must be a Tim The Tool Man saw. 50HP motor?


  4. #4
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    Default Re: Conduit Sizing

    A single NM cable in a pipe is considered a single conductor. As result conduit fill is allowed @ 53%. Southwire 6-3 w/g is listed with a diameter of 650 mils(.65") which is .332 square inches. I believe a 1" pipe would be compliant. Hope it's a straight pull.

    Last edited by Brad Richter; 12-05-2013 at 09:59 AM.

  5. #5
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    Default Re: Conduit Sizing

    Can you please show me in the NEC where you size conduit by the OD of an NMB cable?


  6. #6
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    Default Re: Conduit Sizing

    Don, this is Note 9 from the Notes for Chapter 9.

    (9) A multiconductor cable or flexible cord of two or more
    conductors shall be treated as a single conductor for
    calculating percentage conduit fill area. For cables that
    have elliptical cross sections, the cross-sectional area
    calculation shall be based on using the major diameter
    of the ellipse as a circle diameter.

    All answers based on unamended National Electrical codes.

  7. #7
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    Default Re: Conduit Sizing

    Quote Originally Posted by Garry Sorrells View Post
    Dang, table saw with a 50amp breaker. Must be a Tim The Tool Man saw. 50HP motor?

    Motor rules are different & W/ a 5* HP motor & meeting the conditions specs in art 430 means that 50A is prob. fine.

    * OP did not spec HP, so just a guess on my part.


  8. #8
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    Default Re: Conduit Sizing

    Is the entire length of the cable going to be in conduit or just a short section? (like for protection down a wall)

    If the cable is using the conduit for protection for only part of its' length the fill tables don't apply - - Notes To Tables for Chapter 9 (2)

    Occam's eraser: The philosophical principle that even the simplest solution is bound to have something wrong with it.

  9. #9
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    Default Re: Conduit Sizing

    Hi,

    I was just re-reading the OP and I noticed that the "Buddy", says he has a 50 Amp Recep., not a 50 Amp circuit. I've played with some woodworking equipment in my time, but a 50 amp tool would be awesome! Not to mention the rest of the tools in that playroom!

    I guess I'm curious as to the relevance of the receptacle at all since as indicated in the OP, it needs to be moved and a new cable installed
    why not do a whole new circuit an be done with it. Unless he is panning on tapping off of the 50 amp recep which means that now the amperage o the existing circuit needs to be verified to make sure it is sufficient to charge the vehicle.



  10. #10
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    Default Re: Conduit Sizing

    Quote Originally Posted by Donald Farrell View Post
    Hi,


    I guess I'm curious as to the relevance of the receptacle at all since as indicated in the OP, it needs to be moved and a new cable installed
    why not do a whole new circuit an be done with it. Unless he is panning on tapping off of the 50 amp recep which means that now the amperage o the existing circuit needs to be verified to make sure it is sufficient to charge the vehicle.
    The OP stated the "buddy" was going to run a new set of wires from the 50 ampere breaker in the garage panel. The 6-3 in a 1" emt will work. Personally I would just use 3 #6 thhn and a #10 thhn instead of fooling around with trying to pull a nm cable in the conduit. As a side note: stripping the jacket off the NM and using the conductors by them selves is a code violation as the individual conductors in NM do not have the code required markings on them.


  11. #11
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    Default Re: Conduit Sizing

    If conduit was being used 8 AWG THHN is good for 50A.


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