Electrical Dwelling design

Discussion in 'General Electronics Chat' started by h.immo, Sep 1, 2013.

  1. h.immo

    Thread Starter New Member

    Apr 17, 2012
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    0
    Hi there :)
    I hope this is the right place to post it ( if not I'm very sorry)

    I'm facing a problem with the calculations of an multifamily dwelling building.
    In the article 220 of the NEC it is written that I have to use a demand factor of 23% (if I have more then 62 dwelling).
    But on the other hand I have to use a demand factor of 100% for mechanical loads like A/C, and 40% for lighting.

    What do I have to do? calculate the power for each dwelling->multiply it by 100% for mechanical load+ 40% for the rest, then add them all together and then multiply by 23%.
    Or just calculate the individual loads and add them all together?

    I hope I made my problem clear.
    Thank you for your time and help
    Regards
    H.immo
     
    Last edited: Sep 1, 2013
  2. Wendy

    Moderator

    Mar 24, 2008
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    This forum is good. I suspect another moderator has been here before I. If you have problems with a thread that needs moved just use the alert system ("[​IMG]")
     
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  3. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    The way I read it, yes... Your demand is cumulative, and your supply must be able to keep ahead of demand...

    Any attempt to shortcut it will not enamour your project to electrical inspectors...:(

    Tear-out and re-do gets enormously expensive...
     
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  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    I'm not the one to help you as I abide by the CEC, but here's some things to look for;

    Your basic demand load may require a first group of units at 100%, a second group at something less, and the balance at something even less. Electric ranges are added in similar fashion. A/C and heat are added at 100%, unless interlocked, then the higher load. Other loads are added at some percent. Common areas and parking are then added at some declining contribution.
     
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  5. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    Phone the inspectors for advice. If that fails, pay a real electrician to do the math. A couple of hundred dollars is cheap for the insurance it is going to buy you.
     
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  6. h.immo

    Thread Starter New Member

    Apr 17, 2012
    10
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    sry didnt quit get what u meant ^^" ( what do you mean with "yes" )

    The problem is that I was taught different than the NEC standarts ( or I dont get them right :/ )

    thank you all for your help
     
  7. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    Your demand is cumulative, and your supply must be able to keep ahead of demand...

    So yes, you must add all your demand together, and inlcude a small percentage for a " fudge factor "
     
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  8. h.immo

    Thread Starter New Member

    Apr 17, 2012
    10
    0
    ok that was very helpful, thank you very much for your help
     
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