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Thread: service wire calculations

  1. #1
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    Jun 2018
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    edinburg texas
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    service wire calculations

    If I have 5 different disconnects connected to one gutter box adding to 1200 Amps. How would the service wire be sized if its from the gutter box to a step down transformer 208/120v 3-PHASE mounted on concrete pad? The conductors will run underground in a conduit. Looking at table 310.15(B)16 under the 75 degree C column it only goes to 665 Amps. WHAT TABLE AND COLUMN SHOULD BE USED HERE?
    WHERE CAN THIS BE FOUND IN THE NEC BOOK.

    Can it be sized like this? :
    3 RUNS OF 4#600 KCMILS, 1#3/0 , 4"C

    WHERE EACH PHASE WILL HAVE 3 CONDUCTOR OF 600 KCMIL AND NEUTRAL WILL ASLO HAVE 3 600 KCMIL WIRE. GROUND WILL HAVE 1 #3/0 WIRE.


  2. #2
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    Sure you can parallel the runs but make sure you know the rules to parallel -- 310.10(H).

    What you have setup should work although I didn't calculate the pipe size.

    Normally one runs a full boat in each conduit but there are circumstances where you can run all of one phase in each conduit.
    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



  3. #3
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    Jun 2018
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    edinburg texas
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    If I have 5 different disconnects connected to one gutter box adding to
    1200 Amps
    . How would the service wire be sized if its from the gutter box to a step down transformer 208/120v 3-PHASE mounted on concrete pad? The conductors will run underground in a conduit. Looking at table 310.15(B)16 under the 75 degree C column it only goes to 665 Amps. WHAT TABLE AND COLUMN SHOULD BE USED HERE?
    WHERE CAN THIS BE FOUND IN THE NEC BOOK.

    CORRECTION -->
    Can it be sized like this? :
    1
    RUN OF 4#600 KCMILS, 1#1, 4"C
    WHERE EACH PHASE WILL GET 400A TO TOTAL THE 1200A

  4. #4
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    New Jersey USA
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    I think you are correct check article 250.122F , 310.15B16 , Table C.9 but increase size of conduit if you can so would be easier to pull cables.

  5. #5
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    How did you come up with the 1200 amps?
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  6. #6
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    SERVICE WIRE CALCULATION

    400A+200A+200A+200A+200A= 1200A IS THE ADDITION OF 5 PANEL SIZES.

  7. #7
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    Cherry Valley NY, Seattle, WA
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    If these 5 disconnects are service disconnects, the common conductors can be sized to the load, they need not be sized to the sum of the disconnects. Unless these are feeder taps, it's not really clear, then you have to look at the tap rules and the ocpd protecting the feeder.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  8. #8
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    SERVICE WIRE CALCULATION

    they are feeder disconnects

  9. #9
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    Quote Originally Posted by robert1234 View Post
    they are feeder disconnects
    Are they service disconnects? I assume so as I just realized the title of the thread Is "service wire....."
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  10. #10
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    Quote Originally Posted by robert1234 View Post
    400A+200A+200A+200A+200A= 1200A IS THE ADDITION OF 5 PANEL SIZES.
    Quote Originally Posted by robert1234 View Post
    they are feeder disconnects
    So there is a main ahead of the 5 disconnects?
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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