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    RLeasure's Avatar
    RLeasure Posts: 1, Reputation: 1
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    #1

    Dec 6, 2008, 05:44 PM
    Can my Circuit breakers add up to more than my main breaker?
    I have a 100 amp main and all of the circuit breakers in my main service panel and my sub-panel add up to about 180 amps. Is this all right or do I need to upgrade to a 200 amp main? Any help would be appreciated thanks!
    tkrussell's Avatar
    tkrussell Posts: 9,657, Reputation: 724
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    #2

    Dec 6, 2008, 06:34 PM
    Yes,

    Can my Circuit breakers add up to more than my main breaker?

    Adding the branch breaker ratings is totally irrelevant.

    The Main is sized according to the calculated load, and each breaker is sized by other means, and often do end up much more than the main.


    Why do you ask?

    Is there a problem your having, or just curious?

    The detailed answer is much more than I have given, but too detailed to give now without knowing why you ask.

    If your inquisitive and like to read, review Article 220 of the NFPA 70: National Electrical CodeŽ.

    You will see why electricians are usually so grumpy.
    guimo's Avatar
    guimo Posts: 2, Reputation: 1
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    #3

    Mar 25, 2010, 08:24 PM

    Hello there TKR,would you please explain a bit more about this subject,see, I'm just an apprentice and had asked the same question where I work but they just tell me "it doesn't work that way".Thanks in advance.
    tkrussell's Avatar
    tkrussell Posts: 9,657, Reputation: 724
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    #4

    Mar 26, 2010, 02:47 AM
    Usually when you get an answer like that, means they don't know.

    To be fair, he,he he, they probably know but don't know how to explain it.

    Keep asking questions, read as much as you can, get your on the job training, take your appreticship classes, and believe it or not, some day this trade will all make sense.

    Services are sized according to Article 220, and are rated to handle the total CALCULATED load. You will notice, you add up certain loads per Art 220, use the examples in the back of the NEC book, and the first 3000 watts are at 100%, and only 35% of the remaining are added to the first 100%, the other certain loads are added at 100%.

    The 35% rating helps reduce the total load, as it has been determined that not all load will be on at the same time.

    This does not prevent each circuit from being rated individually. So, for example, there will be a 20 amp breaker for the laundry, however, a clothes washer does not draw 20 amps. The circuit is rated to handle a motor that runs at, say, 10 amps, but motors need larger breakers than the running load to allow overcoming the locked rotor amperage, sometimes, but, erroneously called in rush amps.

    Certain loads, that will be considered as running more than three hours, will be considered as continuous, and that circuit the breaker must be rated 25% higher than the running load, or no more than 80% of the rating of the breaker.

    So, hopefully, you can see, by adding the rating of each breaker, and each breaker is a bit higher than what each circuit really draws, the total will add up to more than the Main.

    The 35% is called a demand factor, after learning Article 220 completely you will find other demand factors.
    Stratmando's Avatar
    Stratmando Posts: 11,188, Reputation: 508
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    #5

    Mar 26, 2010, 06:38 AM

    Probably 99% of Panels I see, the breakers total more than the Service size.
    guimo's Avatar
    guimo Posts: 2, Reputation: 1
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    #6

    Mar 27, 2010, 06:43 AM

    tkrussell,thank you very much for your explanation and advise,certainly I do need read more and learn about this subject,I hope you don't mind if I come up with some more questions.
    tkrussell's Avatar
    tkrussell Posts: 9,657, Reputation: 724
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    #7

    Mar 28, 2010, 04:43 AM
    guimo, your welcome, and ask away, that is what we are here for.

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