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  1. #1
    Join Date
    Mar 2012
    Location
    Lansdale, PA
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    876

    Default Code citation regarding split bus panel

    I have tried to find the code reference that prohibited the use of split bus panels. I have read that this occurred in the 1981 NEC. All the references I find regarding 6 disconnects for services and no more than 2 for panelboards seem to exist in earlier and later codes. IIR, sections 230-71(a) and 384-16 are two areas that I looked at. I would appreciate it if someone can explain this and confirm whether 1981 was the year.

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  2. #2
    Join Date
    Aug 2012
    Location
    Columbus, Ohio
    Posts
    89

    Default Re: Code citation regarding split bus panel

    Quote Originally Posted by Mark Reinmiller View Post
    I have tried to find the code reference that prohibited the use of split bus panels. I have read that this occurred in the 1981 NEC. All the references I find regarding 6 disconnects for services and no more than 2 for panelboards seem to exist in earlier and later codes. IIR, sections 230-71(a) and 384-16 are two areas that I looked at. I would appreciate it if someone can explain this and confirm whether 1981 was the year.
    As far as I know, the code still allows up to 6 actions, i.e. six breakers to be turned off, to remove power from the house. So, as long as a split bus has 6 or less "mains" which are usually 5 double pole breaker slots plus a double pole breaker that cuts power to the second bus, you are OK.


  3. #3

    Default Re: Code citation regarding split bus panel

    I too don't know the code, but understand that even in large apartment buildings, there can be no more than 6 throws to turn off the entire building. This gets interesting when there are more than 6 apartments each with separate meters.... It means there needs to be a Franken-switch before the meters. Lots of places get into trouble when they include power, which means no meters, and they start tapping off the trough and loose track of how many disconnects there really are...


  4. #4
    Join Date
    Mar 2010
    Location
    California
    Posts
    26

    Default Re: Code citation regarding split bus panel

    Split-bus panels became possible after the 1965 NEC included the following statement: “Individual protection for lighting and appliance branch circuit panelboards is not required where such panelboards are used as service equipment in supplying an individual residential occupancy and where any bus supplying 15 or 20 ampere circuits is protected on the supply side of the service.” That language was part of an exception to the basic rule that required a lighting and appliance panelboard to be protected by not more than two main circuit breakers or fuses having a combined rating not greater than that of the panelboard. In the 1978 NEC the restriction on 15 and 20 amp circuits was removed, and there could theoretically be 15-amp circuits in the main or upper section of the split bus panel. The 1981 NEC restricted this section in 384-16(a) exc #2 to “existing installations” and thereafter no new split bus panels were made. The present language of NEC [408.36 Exception 1] states that panelboards protected by three or more main circuit breakers cannot supply a second bus structure within the same assembly.

    Split bus panels were always a form of "value engineering" and I would expect you seldom find ones that you are comfortable with.

    Douglas Hansen
    www.codecheck.com


  5. #5
    Join Date
    Mar 2012
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    Lansdale, PA
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    876

    Default Re: Code citation regarding split bus panel

    Douglas,
    Thank you. I read many editions of the NEC and could never figure that out.


  6. #6
    Join Date
    Oct 2014
    Location
    Maryland, DC, and Northern Virginia, electrical only
    Posts
    116

    Default Re: Code citation regarding split bus panel

    Quote Originally Posted by Douglas Hansen View Post

    Split bus panels were always a form of "value engineering" and I would expect you seldom find ones that you are comfortable with.

    Douglas Hansen
    www.codecheck.com
    Great answer.

    I will say that without having looked at the time-current curves, I always felt a little better about backing up a 15 amp branch circuit breaker with a 60 amp main than with a 150.

    Without having done the research, my ideal was a tiny service panel with a single main, backing up a few feeder breakers: maybe a 100 to protect the panel serving the stove and dryer or electric heating, and a 60 or two feeding panels serving normal branch circuits.


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