minimum size service

Discussion in 'Homework Help' started by albn, Jul 6, 2012.

  1. albn

    Thread Starter New Member

    Jul 6, 2012
    12
    0
    An apartment building has 12 dwelling units with 1640 square feet of space plus the FF: equipment, 12kw water heater,5 kw dyer, 10.5 kw baseboard heater. what is the minimum service permitted for this building @ 120/240 volts ?

    A. 859 amperes
    B. 1074 amperes
    C. 1110 amperes
    D. 2096 amperes

    Please help I've tried already so many times still could not arrived to any numbers mentioned above, your kind assistance is highly appreciated.:confused:<SNIP> Thanks
     
    Last edited by a moderator: Jul 6, 2012
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    The correct answer is E;

    A. 859 amperes
    B. 1074 amperes
    C. 1110 amperes
    D. 2096 amperes
    E. Do your own homework
     
    albn likes this.
  3. albn

    Thread Starter New Member

    Jul 6, 2012
    12
    0
    thanks anyway I think you don't know the answer
     
  4. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    27*12 I don't know the answer I need to press the button on my keyboard for Windows calculator. Sometimes using Microsoft hardware can be of advantage.
     
    albn likes this.
  5. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,345
    albn likes this.
  6. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,128
    266
    Perhaps the answer comes from electrical code, not electrical engineering.
     
    albn likes this.
  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    x2, but because the OP failed to identify his location, it would be a waste of time to even begin. But I'll ask anyway, no range?
     
    Last edited: Jul 6, 2012
    albn likes this.
  8. albn

    Thread Starter New Member

    Jul 6, 2012
    12
    0
    thanks for you reply but like what you mentioned, I did tried and still confused about the calculation that's why I posted in here! to find somebody who can show how to solve it right. Thank you
     
  9. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    you still haven't told us what code your applying. Generally, you find your base area wattage, add your other loads as per demand allowance, compensate for range/no range, strip out your heat, calculate the unit contribution to the overall, add back in your heat as per demand allowance, add common area, parking, lighting, etc.
     
    albn likes this.
  10. mlog

    Member

    Feb 11, 2012
    276
    36
    You really need to do your own work, but we'll help you get started.

    Pardon my ignorance of the subject, but I'll start by asking some questions.

    1. What is FF?

    2. Does the 1640 sq ft of living space affect the lighting and other electric usage? I think so. What is the equation for this? Is it linear? Is it of the form y=mx+b?

    3. Is there a water heater, dryer, and baseboard heater in each of the 12 units?

    4. Is there any additional power requirement for the building that is not contained within the 12 units? What about hall lights, outside lights, heating for the hallways (are there hallways?), etc.?

    Only baseboard heating...I guess there's no air conditioning....

    Making my own assumptions, I get something like this.

    Total power per unit = Water heater + Dryer + Baseboard heater + General lighting and other usage

    Total building power = 12 units x Total power per unit

    Total building current = Total building power / Voltage

    After you get the current, is there a margin applied to it, say 50% above the calculated load?

    Just a quick check on the back of a napkin suggests to me that only one of the answers can possible be correct.
     
    albn likes this.
  11. albn

    Thread Starter New Member

    Jul 6, 2012
    12
    0
    Sorry what Imean to type is following abbreviated by FF:
     
  12. albn

    Thread Starter New Member

    Jul 6, 2012
    12
    0
    Sorry again each unit is 1640 sq.feet and equipt with range,water heater, baseboard heater,and dryer. There's no formula like the one you mentioned like: y=mx+b, it's just what the NEC Code book calculation which is subject to different adjustment per location, and application. What I typed in my latest post are the same what the code given samples. Thanks again
     
  13. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    obviously I can't help you much, as I work by the CEC. They are not greatly different, and becoming closer with each revision.

    I noticed that you did add a range.

    why dont' you show us some of your work;
    what's your basic (area) calculated load per/unit,
    what's your calculated range per/unit (I assume there all the same rating?)
    What's your other load calculations per/unit
    Are you stripping out your heat?
    How does each unit contribute to the overall?
    Are you adding back in your heat?
    Are there undisclosed loads in common areas?

    Help us help you , or not.
     
  14. BSomer

    Member

    Dec 28, 2011
    433
    106
    Do you have an up to date code book available? In the back (Annex D) are examples of how to calculate your loads, feeder conductor sizes, etc... The main article of concern for these calculations is 220.

    Specific tables that would be used:
    Table 220.42 - Lighting Load Demand Factors
    Table 220.54 - Electric Dryer Demand Factors
    Table 220.55 - Electric Range/Cooking Appliance Demand Factors

    There are others but if you read through Article 220 and pay attention to the "multifamily dwelling" sections I think that you can work your way through it.
     
    albn likes this.
  15. #12

    Expert

    Nov 30, 2010
    16,262
    6,768
    (27.5KW x 12) /240V = 1375Amps
    This is greater than A, B, or C
    So, the answer must be ?
     
    albn likes this.
  16. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    In multi family, units are derated by a unit number/factor.

    I doubt it matters though, as the OP has not given us any indication as to his ability, and his assignment date has likely gone by.
     
    albn likes this.
  17. albn

    Thread Starter New Member

    Jul 6, 2012
    12
    0
    we'll your calculation is the same as mine but still not matched the answer, it must be the the right answer otherwise it's wrong. thanks anyway.
     
  18. albn

    Thread Starter New Member

    Jul 6, 2012
    12
    0
    we'll I've checked that out already still I could not arrive to the right answer, thanks anyway for your input I really appreciated.
     
  19. albn

    Thread Starter New Member

    Jul 6, 2012
    12
    0
    I responded with complete computation according to the sample on annex D of NEC cod book but I don't know to whom I responded cuz' it's not showing here. thanks anyway for your input I really appreciated.
     
Loading...