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Thread: Breakers of the same size in series

  1. #1
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    Breakers of the same size in series

    I have a client that insist on installing one breaker in series with a second breaker of the same size; i.e., 150 A feeder breaker in one panel feeding a 150 A main breaker in a second panel. Is there any code issues to prevent them from doing this?

  2. #2
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    No. The first one would be overcurrent protection, and the downstream could be a local disconnect.
    The more they overthink the plumbing, the easier it is to stop up the drain

  3. #3
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    They have both as functioning breakers. I tell them that either or both may trip in a fault condition, but they insist on doing it this way. Is there any code issue that I can site which will prevent this?

  4. #4
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    Quote Originally Posted by RCHaySr View Post
    They have both as functioning breakers. I tell them that either or both may trip in a fault condition, but they insist on doing it this way. Is there any code issue that I can site which will prevent this?
    No. It is not a code issue. Yes, either one may trip.
    The more they overthink the plumbing, the easier it is to stop up the drain

  5. #5
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    Some folks feel the need to have a main on every panel, it's a personal preference. It adds nothing to the safety, or reliability of the installation as long as the wire is properly protected at the source.

    Another similar install that gets people worried sometimes is a smaller breaker, say 100A, feeding a larger, 200A main breaker panel.
    Once in a while you get shown the light
    In the strangest of places if you look at it right. Robert Hunter

  6. #6
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    Quote Originally Posted by RCHaySr View Post
    I tell them that either or both may trip in a fault condition, but they insist on doing it this way.
    True, and that is perfectly acceptable.
    Quote Originally Posted by RCHaySr View Post
    Is there any code issue that I can site which will prevent this?
    No, as others have already said. My question: why would you want to prevent this?

    Charles E. Beck, P.E., Seattle
    Comments based on 2014 NEC unless otherwise noted.

  7. #7
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    Technically, the downstream breaker COULD just be a main switch, i.e. no trips. But what you will find is that the only "switch" available in a panelboard is a Molded Case Switch, which is a breaker with no trip elements. However, if you try ordering it that way, you find out that it's a special so you actually pay more, even though technically the MCD could be cheaper because it has fewer parts. It's really all about volume.

    But an MCS is available as an option in many cases, specifically BECAUSE you can't predict which one will trip first, and in a situation where down time is thousands per minute, taking 1 minute longer to figure out which breaker tripped is going to cost you more than the difference in the cost of the Main device.
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  8. #8
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    Why don't you want twice the protection?

    Also, that is not considered "in series".

  9. #9
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    Quote Originally Posted by jaylectricity View Post
    Why don't you want twice the protection?

    Also, that is not considered "in series".
    Why do you think it is not in series?

    It definitely is not in parallel.

  10. #10
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    I once had a fault in a 30 amp circuit, my helper at the time thought tightening the clamp on the romex connector meant turn the screws until they don't turn anymore I guess. Not only did my helper need clean underpants, it tripped the 30 amp breaker as well as the 200 amp main breaker in the panel.

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