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Thread: load calcs for addition

  1. #1
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    load calcs for addition

    To size the feeder for a load center, how do I do a load calculation for a residential addition? Do I do the same steps as a regular load calculation minus the (Kitchen SABC, the bathrooms, the appliances...)??

    Thanks for your input.
    Edward
    The only thing I know, is the progressive discovery of my ignorance


  2. #2
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    You do a standard or optional calculation for what the feeder supplies. Note for a feeder less than 100A, you must use the standard method.
    I will have achieved my life's goal if I die with a smile on my face.

  3. #3
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    Where this can be really confusing is when the addition doesn't contain SABC's, laundry, or fixed appliances.

    A bedroom addition you can use 3 VA/ sq ft, and most times only need to add capacity of less then a single branch circuit. Add a garage, porch, etc. the square footage of those are not even included in the 3 VA/ sq ft. for general lighting, and you could possibly add a feeder technically with no load calculated for it. I often default to at least 60 amp feeder for many of those type of situations, presumably you may add something down the road and will be thankful for some extra capacity when that time comes.

  4. #4
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    I did the standard calculation without the following (SABC, Laundry, cooking/kitchen appliances...). but did add furnace, bathroom fans as fastened in appliances.

    Anyway the feeder is sized at 65Amps 4/3 aluminum SER cable.
    Edward
    The only thing I know, is the progressive discovery of my ignorance


  5. #5
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    Quote Originally Posted by edward View Post
    I did the standard calculation without the following (SABC, Laundry, cooking/kitchen appliances...). but did add furnace, bathroom fans as fastened in appliances.

    Anyway the feeder is sized at 65Amps 4/3 aluminum SER cable.
    Don't forget that you have to ascertain the service is capable of handling the added load. So you either have to do a standard load calculation for the service with new loads added in, or use the additional load optional method.
    I will have achieved my life's goal if I die with a smile on my face.

  6. #6
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    Quote Originally Posted by Smart $ View Post
    Don't forget that you have to ascertain the service is capable of handling the added load. So you either have to do a standard load calculation for the service with new loads added in, or use the additional load optional method.
    The panel is being upgraded anyway.
    Edward
    The only thing I know, is the progressive discovery of my ignorance


  7. #7
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    If the feeder runs through any type of insulation (attic for instance) it needs to be figured at at the 60 degree ampacity.

  8. #8
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    Quote Originally Posted by nizak View Post
    If the feeder runs through any type of insulation (attic for instance) it needs to be figured at at the 60 degree ampacity.
    I dont think that applies to SER cable. At least that is the way I read it.
    Edward
    The only thing I know, is the progressive discovery of my ignorance


  9. #9
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    Quote Originally Posted by nizak View Post
    If the feeder runs through any type of insulation (attic for instance) it needs to be figured at at the 60 degree ampacity.
    Quote Originally Posted by edward View Post
    I dont think that applies to SER cable. At least that is the way I read it.
    338.10(B)(4) Installation Methods for Branch Circuits and Feeders.

    (a) Interior Installations. In addition to the provisions of
    this article, Type SE service-entrance cable used for interior
    wiring shall comply with the installation requirements of Part
    II of Article 334, excluding 334.80.

    Where installed in thermal insulation the ampacity shall be
    in accordance with the 60°C (140°F) conductor temperature
    rating. The maximum conductor temperature rating shall be
    permitted to be used for ampacity adjustment and correction
    purposes, if the final derated ampacity does not exceed that for
    a 60°C (140°F) rated conductor
    .
    "Electricity is really just organized lightning." George Carlin


    Derek

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