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Thread: Breaker size for apartment load calculations

  1. #1
    Join Date
    Oct 2014
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    Los Angeles
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    Breaker size for apartment load calculations

    Hello All,
    After applying load demand factor Table 220.42 and add 100% of HVAC loads, etc.., the total connected load for one unit at 240V is 58A. So can the feeder breaker 60A or it has to be 80A? (58 x 1.25 = 72.5A round up to the next rating is 80A). I'm not talking about 100% rated breaker. This is the general 80% rated breakers.

    Thanks.

  2. #2
    Join Date
    Feb 2010
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    829
    Quote Originally Posted by fandi View Post
    Hello All,
    After applying load demand factor Table 220.42 and add 100% of HVAC loads, etc.., the total connected load for one unit at 240V is 58A. So can the feeder breaker 60A or it has to be 80A? (58 x 1.25 = 72.5A round up to the next rating is 80A). I'm not talking about 100% rated breaker. This is the general 80% rated breakers.

    Thanks.
    Im not really following you here but it sounds like you are using the "Standard" method to size your apartment services. In order to keep your client happy, you really need to be using the optional method for dwelling unit load calcs. Otherwise, your service size will be much larger then it has to be. Optional method is also easier and quicker.

    Also, unless im mis-understanding you, you shouldnt be multiplying anything by 125% or 80%. If your actual load is 58A, then you need a 58A breaker but you round up to the next standard size breaker which would be 60A.

  3. #3
    Join Date
    Jun 2006
    Location
    Ohio
    Posts
    21,385
    Typically, there are no continuous loads in a dwelling, so 60A will do. The so-called 80% breakers are only 80% for continuous loads. You can connect noncontinuous loads [calculated value] up to 100% of a standard breaker's rating.
    I will have achieved my life's goal if I die with a smile on my face.

  4. #4
    Join Date
    Oct 2014
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    Los Angeles
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    Thanks, everyone.

  5. #5
    Join Date
    Feb 2003
    Location
    San Jose, CA
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    1,436
    Quote Originally Posted by Npstewart View Post
    Im not really following you here but it sounds like you are using the "Standard" method to size your apartment services. In order to keep your client happy, you really need to be using the optional method for dwelling unit load calcs. Otherwise, your service size will be much larger then it has to be. Optional method is also easier and quicker.

    Also, unless im mis-understanding you, you shouldnt be multiplying anything by 125% or 80%. If your actual load is 58A, then you need a 58A breaker but you round up to the next standard size breaker which would be 60A.
    The optional calculation requires the feeder to be 100 amps or greater. I'm not sure how bumping a 60 amp feeder to 100 amps in order to use the optional calculation will save the client money.
    Curt Swartz
    Electrical Contractor

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