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Thread: Help with article 230 Part III Service calcs.

  1. #1
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    Question Help with article 230 Part III Service calcs.

    Greetings, I am 3 class nights away from finals for Part 1 of the NEC.

    We are doing service feeder calcs for a single family dwelling and for the life of me, I cannot find a demand factor listed in the code.

    What I am trying to locate and verify is the 25% demand factor used in calculating the "Largest appliance motor".

    For example, the diswasher, we were given a 1kW D/W and told to get the largest motor calc for that D/W simply multiply the 1kW by 25% (1000va*0.25=250va).

    The 250VA would then be added to the loads.

    Where is this calculation supported in the NEC 2008 code?
    Last edited by donf; 07-18-10 at 11:35 AM. Reason: Typos

  2. #2
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    I think you may be talking about the 75% demand factor in 220.53
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

  3. #3
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    Look at 220.18(A). That I believe is what you want.

    220.18 Maximum Loads.
    The total load shall not exceed the rating of the branch circuit, and it shall not exceed the maximum loads specified in 220.18(A) through (C) under the conditions specified therein.
    (A) Motor-Operated and Combination Loads. Where a circuit supplies only motor-operated loads, Article 430 shall apply. Where a circuit supplies only air-conditioning equipment, refrigerating equipment, or both, Article 440 shall apply. For circuits supplying loads consisting of motor-operated utilization equipment that is fastened in place and has a motor larger than hp in combination with other loads, the total calculated load shall be based on 125 percent of the largest motor load plus the sum of the other loads.

  4. #4
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    How about this?

    220.50 Motors. Motor loads shall be calculated in accordance
    with 430.24, 430.25, and 430.26 and with 440.6 for
    hermetic refrigerant motor compressors

    430.24 Several Motors or a Motor(s) and Other
    Load(s). Conductors supplying several motors, or a motor(
    s) and other load(s), shall have an ampacity not less
    than 125 percent of the full-load current rating of the highest
    rated motor plus the sum of the full-load current ratings
    of all the other motors in the group, as determined by
    430.6(A), plus the ampacity required for the other loads.
    "Electricity is really just organized lightning." George Carlin


    Derék

  5. #5
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    I would not consider the motor of a dishwasher as the main item to base the load from, Maybe its just me, but most dishwashers motors are very small, and are only a fraction of the dishwashers load, to me its the heating element that grabs my attention, some of these can be many times the current of the motor?

    Am I wrong of thinking this way?
    Wayne A. From: N.W.Indiana
    Be Fair, Be Safe
    Just don't be fairly safe

  6. #6
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    Quote Originally Posted by hurk27 View Post
    I would not consider the motor of a dishwasher as the main item to base the load from, Maybe its just me, but most dishwashers motors are very small, and are only a fraction of the dishwashers load, to me its the heating element that grabs my attention, some of these can be many times the current of the motor?

    Am I wrong of thinking this way?
    I agree. I missed the DW part.
    "Electricity is really just organized lightning." George Carlin


    Derék

  7. #7
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    Quote Originally Posted by jumper View Post
    I agree. I missed the DW part.
    I could be wrong, as code doesn't really define what kind of load a dishwasher is, but basing it on the motor to me is wrong?:confused:
    Wayne A. From: N.W.Indiana
    Be Fair, Be Safe
    Just don't be fairly safe

  8. #8
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    Quote Originally Posted by hurk27 View Post
    I could be wrong, as code doesn't really define what kind of load a dishwasher is, but basing it on the motor to me is wrong?:confused:
    A dishwasher is a mixed load, as you stated, IIRC it has a pump motor and a heating element. I doubt that it is ever going to be the largest motor load.

    MCA would be based on both.

    The teacher probably made a mistake or the OP read the question wrong, IMHO.
    "Electricity is really just organized lightning." George Carlin


    Derék

  9. #9
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    IMO - a (Household) DW is an "Appliance" first then it is a mixed load - Rememebering this off the top of the head since I do calc's on spreadsheets that I just plug the load into on... But more than 4 appliances "fastened in place" is 75%....

    OK - I'll look it up....


    220.14 A) Specific Appliances or Loads.
    An outlet for a specific
    appliance or other load not covered in 220.l4(B) through
    (L) shall be calculated based on the ampere rating of the

    appliance or load served.

    220.53 Appliance Load - Dwelling Unites).
    It shall be
    permissible to apply a demand factor of 75 percent to the
    nameplate rating load of four or more appliances fastened
    in place, other than electric ranges, clothes dryers, spaceheating
    equipment, or air-conditioning equipment, that are
    served by the same feeder or service in a one-family, twofamily,

    or multifamily dwelling.
    Uh - from the 05 code - so go check whatever you are being tested on.....
    Electric heretic
    It's always gonna be in the last place you look....

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