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Thread: Backfed Main Breaker

  1. #1
    Join Date
    Mar 2005
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    Wyoming
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    Backfed Main Breaker

    Hi everyone, would it be permissible to take a small main lug panel and back feed it with a 100 amp breaker (using an approved hold down per 408.16f) and then use the existing main lugs to feed a 100 amp subpanel inside the home? Personally, I don't see a problem with it, but curious what you think.

  2. #2
    Join Date
    Dec 2004
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    North Carolina
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    Re: Backfed Main Breaker

    Go for it.
    Mike Whitt
    God answers Knee-Mail.

  3. #3
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    New Jersey
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    Re: Backfed Main Breaker

    but curious what you think.
    I'm curious as to why you would need an arrangement like this?
    Rob

    Chief Moderator

    All responses based on the 2011 NEC unless otherwise noted

  4. #4
    Join Date
    Jun 2005
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    NJ
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    Re: Backfed Main Breaker

    I don't know that there's anything that prohibits you from doing it this way, but I just don't like the idea of using the main lugs to feed another load. They're for your supply power. It could lead to some confusion in the future to do it your way. But like I said, I don't think you can't do it, I just don't think I would.

    John
    John

  5. #5
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    May 2005
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    Richmond, Virginia
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    Re: Backfed Main Breaker

    Wouldn't the outgoing sub-panel feeder require a breaker?
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  6. #6
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    Mar 2005
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    North Texas, DFW area
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    Re: Backfed Main Breaker

    408.16(F)= 2002 NEC
    408.36(F)= 2005 NEC

    I don't see any code violation with it as long as your subpanel and its feeder are both rated 100A.

    The feeder and the subpanel would both be protected by the 100A backfed main. That should comply with 408.36(A)(Exception No. 1).

    Edited to add: You're just using the panels MLO lugs as a form of "feed-through" lugs. The use of feed-through lugs is fairly common with panelboards to add a second MLO panelboard section (used to get 84 circuits), protected by the MCB in the first section.

    [ August 26, 2005, 12:09 PM: Message edited by: tx2step ]

  7. #7
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    Feb 2003
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    Minnesota
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    Re: Backfed Main Breaker

    I just put together a 150 A 120/240 V single phase residential service using a Sq D QO1816M150FTRB rainproof feed through panel. I don't see any difference between what I did and what is described by torcho above.

    In my case, the 150 A service disco protects the 150 A feeder to the subpanel. There's no need for a second 150 A feeder breaker in series with the service disco.
    Another Al in Minnesota

  8. #8
    Join Date
    Mar 2005
    Location
    Wyoming
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    Re: Backfed Main Breaker

    Thanks for the replies guys. We use a lot of SquareD 200 amp meter/main combos with feed through lugs and they work very well when we locate the main lighting/appliance board inside the house, then we can feed the a/c from the outside panel. We were asked to bid a house that is served by a pedestal meter/main and the AHJ requires a disconnect on the house as well, the main panel will be inside (for esthetics, the customer does not want a "big ugly panel" on the outside of the house) I was just trying to find a smaller/convenient disconnecting means. The calculated load in only 91 amps, and everything will be fed from the panel inside the house. In the past we have used a SquareD QO breaker enclosure (I'll try to find the number) but they are huge. Thanks for the help. :cool:

  9. #9
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    Mar 2004
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    Arizona
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    Re: Backfed Main Breaker

    torcho,

    To be on the safe side I would check the manafacture's instructions to be sure this is allowed.If the AHJ don't like it he could use 110.3 to violate the installation.
    Frank Arizona,USA

  10. #10
    Join Date
    Apr 2003
    Location
    Westchester County, New York
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    Re: Backfed Main Breaker

    "240.21 Location in Circuit. Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their
    supply except as specified in 240.21(A) through (G). No conductor supplied under the provisions of 240.21(A) through (G) shall supply another conductor under those provisions, except through an overcurrent protective device meeting the requirements of 240.4."

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