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Thread: Outdoor main lug sub-panel tapped from load side of 150A service/meter disconnect

  1. #1
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    Outdoor main lug sub-panel tapped from load side of 150A service/meter disconnect

    I want to add outdoor sub panel next to the meter service disconnect (150A) combo. Thinking of tapping the 2/0 aluminum conductors on the load side of the service disconnect.
    I'll follow 240.21B1 and tap with #2 aluminum conductors that will supply an outdoor main lug sub panel that will be about 12" from the meter/service disconnect equipment.
    The calculated load of the house is around 80A.
    Are there any codes that will prevent me from doing that?

  2. #2
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    If it's a main lug panel then (oddly enough, to me) your panel rating can't be more than the conductor ampacity. So with #2 aluminum you would be somewhat hard pressed to find a subpanel that is not rated more than 90A. You might have to put in #1 for a 100A subpanel, or 2/0 for a 125A panel. (That is, if you want to stick with aluminum.)

    Most 125A or less MLO panels these days have provisions to install a main breaker.

    If there's a solar system or other interactive inverter anywhere there are some additional rules that come into play. See 705.12(B)(2) (2017 NEC reference).

  3. #3
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    Quote Originally Posted by jaggedben View Post
    If it's a main lug panel then (oddly enough, to me) your panel rating can't be more than the conductor ampacity.
    Yeah, thats that odd "...not less than the rating of the equipment containing an overcurrent device(s)...." phrase. But then there is 408.36 to contend with which makes it a no go either way. OP, why not just put a 100A main breaker panel in? Its probably the same price or even cheaper than a MLO.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  4. #4
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    I can put 100A main breaker with 2/0 tap conductors
    if that is better solution.
    Do I have to run 4 conductors there as if the main breaker was sub-panel? (no connection between neutral and ground)
    He has solar panels being installed on 4/19/17 and the electrician who is doing this installation is coming Thursday.
    Best option would to be also to install 1 of these if I could find one for 150A
    http://m.homedepot.com/p/GE-200-Amp-...g&gclsrc=aw.ds

  5. #5
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    Quote Originally Posted by pkelectrical View Post
    I can put 100A main breaker with 2/0 tap conductors
    if that is better solution.
    Do I have to run 4 conductors there as if the main breaker was sub-panel? (no connection between neutral and ground)
    He has solar panels being installed on 4/19/17 and the electrician who is doing this installation is coming Thursday.
    Best option would to be also to install 1 of these if I could find one for 150A
    http://m.homedepot.com/p/GE-200-Amp-...g&gclsrc=aw.ds
    If you run 2/0 aluminum you have no tap conductors, as 2/0 is properly protected by 150 amps overcurrent ahead of it. Main breaker would not be required in your subpanel. A main lug panel bus would need to be rated for minimum of 150 amp though.

    Everything beyond the service disconnect needs separated grounded and equipment grounding conductors, existing feeders to separate buildings and existing three wire circuits to ranges/clothes dryers is only place there may be exceptions.

  6. #6
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    Quote Originally Posted by pkelectrical View Post
    I can put 100A main breaker with 2/0 tap conductors
    if that is better solution.
    Do I have to run 4 conductors there as if the main breaker was sub-panel? (no connection between neutral and ground)
    He has solar panels being installed on 4/19/17 and the electrician who is doing this installation is coming Thursday.
    Best option would to be also to install 1 of these if I could find one for 150A
    http://m.homedepot.com/p/GE-200-Amp-...g&gclsrc=aw.ds
    If the solar is going into the new sub then you need additional downstream protection for the original feeder. Maybe you can add a main breaker to the original subpanel inside the house or else maybe a new serive panel makes more sense.

  7. #7
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    Quote Originally Posted by kwired View Post
    If you run 2/0 aluminum you have no tap conductors, as 2/0 is properly protected by 150 amps overcurrent ahead of it. Main breaker would not be required in your subpanel. A main lug panel bus would need to be rated for minimum of 150 amp though.

    Everything beyond the service disconnect needs separated grounded and equipment grounding conductors, existing feeders to separate buildings and existing three wire circuits to ranges/clothes dryers is only place there may be exceptions.
    There is already sub-panel in the basement that is being fed from the 150A disconnect, now I want to add sub-panel outside and tap into those conductors again with 2/0. If the service disconnect had double lugs it would be no problem but it doesn't so I need to make a tap.

  8. #8
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    Quote Originally Posted by jaggedben View Post
    If the solar is going into the new sub then you need additional downstream protection for the original feeder. Maybe you can add a main breaker to the original subpanel inside the house or else maybe a new serive panel makes more sense.
    I am adding sub-panel for hot tub, I have no idea what the solar people will do and how they will make their connections, I want to do this before they show up to do their installation.

  9. #9
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    Quote Originally Posted by pkelectrical View Post
    There is already sub-panel in the basement that is being fed from the 150A disconnect, now I want to add sub-panel outside and tap into those conductors again with 2/0. If the service disconnect had double lugs it would be no problem but it doesn't so I need to make a tap.
    Understand it is not a "feeder tap" as 240.21(B) covers though, if the overcurrent device is properly sized to protect the conductor at it's ampacity, it is just another extension to the feeder.

    If you wanted to connect say a 100 amp conductor here, that would be a "feeder tap", and it would have to end in an overcurrent device and not just in a main lugs only panelboard.

  10. #10
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    Quote Originally Posted by kwired View Post
    ...

    If you wanted to connect say a 100 amp conductor here, that would be a "feeder tap", and it would have to end in an overcurrent device and not just in a main lugs only panelboard.
    Except 408 still requires a main breaker for the panelboard.

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