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Thread: Service Tap???

  1. #1
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    Service Tap???

    An existing building has a 37.5 KVA, 120/240V, single phase service transformer, and a 200 amp MCB panel. I am reviewing a design that intercepts the service conductors just inside the building wall, installs what they are calling a "pull box," connects a set of #1 wires to the existing service conductors, and runs them to a new 100 amp MCB panel. This seems wrong on many levels. But I will start with, "are we allowed to tap a service"? I know that if they made the connection at the transformer secondary, kept the existing 200 amps worth of wire to the 200 amp MCB panel, and ran 100 amps worth of wire to the new 100 amp MCB panel, they would not be overloading any wires. They might have an issue with two services to the same building, but that's another matter. As shown, they appear to want the existing 200 amps worth of wire to supply both panels, at least up to the location of the pull box.

    What do you think?
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

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    Quote Originally Posted by charlie b View Post
    An existing building has a 37.5 KVA, 120/240V, single phase service transformer, and a 200 amp MCB panel. I am reviewing a design that intercepts the service conductors just inside the building wall, installs what they are calling a "pull box," connects a set of #1 wires to the existing service conductors, and runs them to a new 100 amp MCB panel. This seems wrong on many levels. But I will start with, "are we allowed to tap a service"? I know that if they made the connection at the transformer secondary, kept the existing 200 amps worth of wire to the 200 amp MCB panel, and ran 100 amps worth of wire to the new 100 amp MCB panel, they would not be overloading any wires. They might have an issue with two services to the same building, but that's another matter. As shown, they appear to want the existing 200 amps worth of wire to supply both panels, at least up to the location of the pull box.

    What do you think?
    As long as the service disconnects are grouped and the calculated load for the building does not exceed the conductor ampacity (200 amps?) as you already know the location of the grouped disconnects must be as close as possible entering the building

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    I also don't see any issue. Once service conductors supply more than one disconnect, their overload protection is permitted to be met by multiple ocpd's whose sum exceeds the ampacity.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    I don't know the rating of the service conductors. I think it safe to believe they are good for the existing 200 amp panel's MCB. In the attached image, the new and existing panels are side-by-side, apparently in an indoor corridor. So they meet the "grouped" requirement. It appears that the existing service conductors travel some distance before they connect to the existing panel. By putting a pull point just inside the building's exterior wall, you will now have two sets of service conductors travelling an unknown distance before hitting their respective service disconnecting means (which double as the panel's OCPD).
    Attached Images Attached Images  
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

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    Quote Originally Posted by charlie b View Post
    I don't know the rating of the service conductors. I think it safe to believe they are good for the existing 200 amp panel's MCB. In the attached image, the new and existing panels are side-by-side, apparently in an indoor corridor. So they meet the "grouped" requirement. It appears that the existing service conductors travel some distance before they connect to the existing panel. By putting a pull point just inside the building's exterior wall, you will now have two sets of service conductors travelling an unknown distance before hitting their respective service disconnecting means (which double as the panel's OCPD).
    Charlie,

    As you know, Washington gives you 15' of SEC inside a building. What is a bit of a grey area however is how this is treated when multiple sets are run per 230.40 exception 2.

    Edit to add:

    For the other code references for this installation, see 230.33, and 230.90(A) exception 3.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Quote Originally Posted by charlie b View Post
    I don't know the rating of the service conductors. I think it safe to believe they are good for the existing 200 amp panel's MCB
    The additional panel if adding additional load may exceed the original calculated load the 200 amp service was based on

    Quote Originally Posted by charlie b View Post
    It appears that the existing service conductors travel some distance before they connect to the existing panel. By putting a pull point just inside the building's exterior wall, you will now have two sets of service conductors travelling an unknown distance before hitting their respective service disconnecting means
    If this is an existing violation you may need to add a 200 amp service disconnect with 200 amp feed through lugs that can except an additional 100 amp breaker

    The existing 200 amp feed (service entrance) may need reconfigured to be a feeder to a sub feed 200 amp panel.

    It may become necessary to upgrade the 200 amp service to account for the increase in load

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    Quote Originally Posted by electrofelon View Post
    I also don't see any issue. Once service conductors supply more than one disconnect, their overload protection is permitted to be met by multiple ocpd's whose sum exceeds the ampacity.
    I agree with this statement, but I can't find the code reference to back it up. Little help?

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    The only potential issue I see is the possible overloading of the existing conductors. If a load calculation proves that they're sufficient then there is no issue. Also there should not be a "#6 ground" in the raceway with the new SEC's.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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    Quote Originally Posted by Leespark57 View Post
    I agree with this statement, but I can't find the code reference to back it up. Little help?
    I believe 230.90 Exception 3 covers that,

    I share charlie b's concern but this situation is not much different from having a MLO service panelboard with six overcurrent devices.
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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    From and installation perspective, if there is sufficient room in the existing enclosure, could feed though lugs be installed on the bus? That would keep the existing OC protection in place and remove the need to intercept the service conductors.

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