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Thread: 230.79(C) - one-family dwellings

  1. #1
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    230.79(C) - one-family dwellings

    So I read this as all single family dwellings require a minimum 100A service disconnecting means.

    What about individual units within a two or multi family dwelling? Typically I provide minimum 100A regardless of the diversified load but I have another engineer who is trying to make the OCPDs for apartment units 80A.

  2. #2
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    I think you are in the wrong section. What you are describing is not the service but a feeder and is based on the calculated load. You should be looking in 220

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    Quote Originally Posted by luckylerado View Post
    I think you are in the wrong section. What you are describing is not the service but a feeder and is based on the calculated load. You should be looking in 220

    So you answered my follow up question... I agree with your response that it is not a service, I just typically provide 100A because my loads tend to be close to that anyway with the type of units I design around.'

    Another question is in regards to section 225.39(C), which states, "For a one family dwelling, the feeder disconnecting means shall have a rating not less than 100A, 3-wire"

    I know that 225 is for "outside branch circuits and feeders" but then why would you include such a broad statement?

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    Quote Originally Posted by lielec11 View Post
    So you answered my follow up question... I agree with your response that it is not a service, I just typically provide 100A because my loads tend to be close to that anyway with the type of units I design around.'

    Another question is in regards to section 225.39(C), which states, "For a one family dwelling, the feeder disconnecting means shall have a rating not less than 100A, 3-wire"

    I know that 225 is for "outside branch circuits and feeders" but then why would you include such a broad statement?
    Got me.. IS this a single family dwelling? Each of the separate units are not considered single family dwellings unless they stand alone.

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    Quote Originally Posted by luckylerado View Post
    Got me.. IS this a single family dwelling? Each of the separate units are not considered single family dwellings unless they stand alone.
    It is just a general question that came up from a friendly discussion. For the sake of your question let's just say it is part of a multifamily building. If fed from a common meter center then the unit load centers can be whatever size the calculations in 220 dictate, correct?

    Edit: I just looked up the code definition of "dwellin unit" and "dwelling, single family" .... I think I was mistakenly lumping these into the same category.

  6. #6
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    Agreed...you were lumping the two together. The application as expressed lead to the following:

    225.39(D) All Others. For all other installations, the feeder or branch-circuit disconnecting means shall have a rating of not less than 60 amperes.

    Assuming the engineer provides the calculated load calculation in accordance with Art.220 the disconnection means aspect of your question is answered again in 225.39 (D).

    Comments based on the 2017 National Electrical Code.
    *All code responses are based on the 2017 National Electrical Code[NEC]

  7. #7
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    Let's be clear, if this is a multifamily building then, IMO, the feeder does not have to be 100 amps to each apartment. 225.39 is for single family dwelling.
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  8. #8
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    225 is also for outside feeders. If you are supplying a stand alone single family dwelling that 100 amp disconnect capacity applies.

    If you are feeding a dwelling unit within a building you only need to supply it with whatever art 220 load calculation applies to the dwelling. A very basic dwelling will have at least 2 - 1500 VA small appliance branch circuits plus 3 VA per square foot. If you get all that into 400 square feet you may only have a load calculation of only 4200 VA, and could supply it with a 35 amp 120 volt feeder or a 20 amp 120/240 feeder.

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    The op was mentioning perhaps multi-family dwelling. I don't see the nec states what size must be run to the units.
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  10. #10
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    Quote Originally Posted by kwired View Post
    225 is also for outside feeders. If you are supplying a stand alone single family dwelling that 100 amp disconnect capacity applies.
    If you get all that into 400 square feet you may only have a load calculation of only 4200 VA, and could supply it with a 35 amp 120 volt feeder or a 20 amp 120/240 feeder.
    You just described every new apartment unit in NYC, Brooklyn, etc., etc...

    Quote Originally Posted by Dennis Alwon View Post
    The op was mentioning perhaps multi-family dwelling. I don't see the nec states what size must be run to the units.
    I don't think it does, this was the basis for my original post to see if any of you code guru's on here knew of a certain section I haven't come across yet...

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