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  1. #1
    Join Date
    Apr 2012
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    203

    Question Correct Backfeed Breaker?

    I'm in the process of buying a new generator (http://www.generac.com/Portables/LP5500/). I have a Square D load center (HOM20M100C). I will be using a back-feed kit (square d # HOMCRBGK1). The problem I'm having is I can't locate which is the correct back feed breaker to use. I called Square D and they told me to use a 40 amp breaker, but that doesn't make sense. The generator has 5500 watts running watts, and 6875 starting watts. He said that would be around 28 amps. So wouldn't I use a 30 amp breaker? Square D said it was 'too close' for a 30 amp breaker and it would trip all the time, but if it's pulling 28 amps and I use a 40 amp breaker, wouldn't that be too high (and effectively like not having a breaker at all)? I'm confused
    Last edited by MyMilan; 03-19-2013 at 05:39 PM.

  2. #2
    Join Date
    Jul 2010
    Location
    SoCal
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    5,436

    Default Re: Correct Backfeed Breaker?

    It's not confusing at all. Think of it as driving a small car. A small car can theoretically go 140 mph, but would you go that fast in a small car? the answer is no. You will go 65 or 70. OK, 80. But why not 130? because at 130 you'll have a breakdown and also might get a ticket.

    Use a 40 amp breaker. With a smaller breaker you'll be generating excessive heat and will trigger the breaker.

  3. #3
    Join Date
    Apr 2012
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    203

    Smile Re: Correct Backfeed Breaker?

    That doesn't make sense. The circuit breaker on the generator would trip first. It just seems like a 40 amp breaker would offer very little, if any protection. The wiring and breaker should be sized as 125% of the continuous load. 5500W is 23A, and 125% of that is 28.6A. So a 30A breaker should be fine I would think.

  4. #4
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,621

    Default Re: Correct Backfeed Breaker?

    Quote Originally Posted by MyMilan View Post
    That doesn't make sense. The circuit breaker on the generator would trip first. It just seems like a 40 amp breaker would offer very little, if any protection. The wiring and breaker should be sized as 125% of the continuous load. 5500W is 23A, and 125% of that is 28.6A. So a 30A breaker should be fine I would think.
    Wrong, the breaker's purpose is to protect the wiring not the generator, plus the rated surge voltage the generator can handle is 6875 watts which is 28.6 amps 125% of that is 35.8 amps. Install a 40 amp breaker.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  5. #5
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,621

    Default Re: Correct Backfeed Breaker?

    Oh and by the way I prefer the Reliant transfer switch. You can install a larger than needed like this http://www.reliancecontrols.com/Prod...il.aspx?30310A and switch circuits on and off and leave the main breaker on so you know when power is restored.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  6. #6
    Join Date
    Aug 2008
    Posts
    69

    Default Re: Correct Backfeed Breaker?

    I second the motion on a transfer switch-------they're easy to install on any electric main panel for a low price, the smaller ones (4 circuits) need only switch to a few critically needed circuits during an outage; very easy to use.

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