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Thread: Tiny house feeder sizing 'question'

  1. #1
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    Tiny house feeder sizing 'question'

    What do you all think of this question, (it will be used in a class I am going to teach):

    A feeder for a new detached building is requested, the design of which is not entirely known. It is known that it will have provisions for independent living, including provisions for cooking, sleeping and sanitation. The building will be a 'tiny house' that is 500 SQFT or less. The feeder disconnect will be a two pole breaker located in a main house loadcenter. The loadcenter manufacturer identifies and lists all its breakers 60 Amps and up for 75C wire. No other load information is known.
    What is the minimum size feeder disconnect?
    And what are the minimum size aluminum XHHW-2 feeder conductors; ungrounded, grounded and equipment ground?
    Show code references with your answers.
    [Question is based on 2017 NEC but other recent versions will likely come up with same answer]

  2. #2
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    So, in short-it’s a dwelling unit.....
    "Electricity is really just organized lightning." George Carlin


    Derek

  3. #3
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    ... and thus needs a load calc.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  4. #4
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    'of unknown design...' ... If the tiny house is permanently mounted to a trailer, it is not a dwelling, rather it is an RV.

    It may have changed, however I believe in Virginia any structure less than 150 square feet is also not considered a dwelling.
    Electricians do it until it Hertz!

  5. #5
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    It would either be a 60A or 100A depending on how the unit is classified, ie; dwelling, outbuilding, etc.
    That would be the minimum size allowed.
    If you aim at nothing, you will hit it every time!

  6. #6
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    Thanks for the replies, yeah I was going after dwelling, perhaps ill add that's its on a foundation and at change it to between 400 and 500 SQ ft.

  7. #7
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    I would use the 100 amp unless it is a trailer..and even as a trailer or mobile home would probably use that for my panel boxes and such... just for future stuff... because I have seen some real idiots in trailer parks..
    Student of electrical codes. Please Take others advice first.

  8. #8
    Join Date
    Aug 2006
    Location
    Atlanta
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    34
    good question,it almost got me. See NEC 230.79(C) for minimum rating of service disconnecting means for a One-family dwelling.

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