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Thread: 80% rule for branch circuits

  1. #1
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    80% rule for branch circuits

    can you exceed the 80% rule on over current protection for branch circuits when you include 125% for continuous duty

  2. #2
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    There isn't an 80% rule, but I understand your question. The answer is yes.

    a 20A rated breaker is rated for 20A, as long as that load does not operate for more than 3 hours. Therefore, a 16A load run continuously can be protected by a 20A breaker forever.
    Bryan P. Holland, MCP

  3. #3
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    I'm always curious about phantom codes, and this one is a biggie.
    "Electricity is actually made up of extremely tiny particles called electrons, that you cannot see with the naked eye unless you have been drinking."

  4. #4
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    I think it's just a design issue and not a bad practice to only load up a circuit to about 80%.
    Tom

    " And all the science I don't understand, it's just my job five days a week "

  5. #5
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    Quote Originally Posted by A/A Fuel GTX View Post
    I think it's just a design issue and not a bad practice to only load up a circuit to about 80%.
    Why though?
    "Electricity is actually made up of extremely tiny particles called electrons, that you cannot see with the naked eye unless you have been drinking."

  6. #6
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    Just so the OCPD and wire are not too close to the edge. Just a personal choice and not knocking anyone that chooses to take her up to the max.
    Tom

    " And all the science I don't understand, it's just my job five days a week "

  7. #7
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    Quote Originally Posted by stickboy1375 View Post
    Why though?
    Because the breakers we use are not designed to be run at 100% for 3 hours or more.

    From the UL General Directory (The White Book) to you


    CIRCUIT BREAKERS, MOLDED-CASE AND
    CIRCUIT BREAKER ENCLOSURES (DIVQ)


    Unless otherwise marked, circuit breakers should not be loaded to exceed 80 percent of their current rating, where in normal operation the load will continue for three hours or more.

  8. #8
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    Quote Originally Posted by iwire View Post
    Because the breakers we use are not designed to be run at 100% for 3 hours or more.

    From the UL General Directory (The White Book) to you


    CIRCUIT BREAKERS, MOLDED-CASE AND
    CIRCUIT BREAKER ENCLOSURES (DIVQ)
    I realize that... but in the residential world continuous loads are far and few.
    "Electricity is actually made up of extremely tiny particles called electrons, that you cannot see with the naked eye unless you have been drinking."

  9. #9
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    Quote Originally Posted by stickboy1375 View Post
    I realize that... but in the residential world continuous loads are far and few.
    I agree.:smile:

  10. #10
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    Although Captain Obvious is not exactly sure what's being discussed here, he feels compelled to be of service.

    The load is 80% of the breaker.... the breaker is 125% of the load....

    1 /.80 = 1.25.... It's the same thing.:smile:
    Last edited by realolman; 11-26-08 at 05:00 PM.
    Everything I say is fully substantiated by my own opinion

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