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Chiller Feeder Calculation

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    #31
    UL 1995 36.14 seems to be the US standard for determining equipment MCA:

    Minimum Circuit Ampacity
    36.14 The minimum circuit ampacity (MCA) required by Clause 36.3(h) shall be determined as follows. All
    concurrent load conditions are to be considered in the determinations, see Figure 36.1. Whichever load
    condition provides the highest value shall be used.
    a) For a motor group only, a load consisting of two or more motors, the rated current of the largest
    motor or branch circuit selection current, if marked, (see Clauses 36.11 and 36.12), multiplied by 125
    per cent, added to the rated currents of all of the other motors.
    b) For a combination load, a load consisting of one or more motors, electric heaters, and any other
    loads, that incorporates one or more compressor motors, the rated current of the largest motor
    compressor or branch circuit selection current, if marked, (see Clauses 36.11 and 36.12), multiplied by
    125 per cent, added to which shall be the value obtained by multiplying the rated current of the electric
    heaters by 125 per cent, and adding to that total the sum of the ratings of all other loads.
    c) For a combination load, a load consisting of one or more motors, electric heaters, and any other
    loads, not involving a hermetic refrigerant motor compressor, the sum of the rated currents multiplied by
    125 per cent.
    Exception: The rated current of the heater load may be multiplied by 100 percent, rather than 125 per cent,
    provided that
    1) the rated heater load at a field wiring terminal is 50 kW or more;
    2) the minimum conductor size that may be field-connected to such terminal is still to be marked;
    and
    3) the heater element circuits connected to the field wiring terminals are subdivided as specified in
    Clause 30.8 and are arranged to be controlled by one or more temperature-actuated devices to
    reduce the likelihood of continuous simultaneous operation of all of the element circuits.


    Also, it looks like nameplate motor currents aren't always used to calculate MCA;

    https://www.titus-hvac.com/softwares...ecalculate.pdf

    Comment


      #32
      Originally posted by david luchini View Post
      It distinguishes between motor operated equipment with a heretic refrigerant motor-compressor and equipment without.
      Those heretic types are the worst. [emoji3]

      They’re always in trouble with the Pope!

      Comment


        #33
        Originally posted by david luchini View Post
        It doesn't mention "chillers" anywhere in the article. Where would you find a chilled water chiller?
        NEC requirements for air conditioners (other than room air conditioners) and chillers are same. So the article about air conditioners is also about chillers.

        Originally posted by david luchini View Post

        They would test a product to UL standards, not to what this article says.
        The calculations in the article are based on UL standard. ( Post#31).

        Comment


          #34
          Originally posted by Sahib View Post
          NEC requirements for air conditioners (other than room air conditioners) and chillers are same. So the article about air conditioners is also about chillers.
          Mostly yes, if there is hermetic compressors involved art 440 usually applies.
          I live for today, I'm just a day behind.

          Comment


            #35
            Ok I was finally able to track down the datasheets for these chillers. Chiller rated capacity is 348 (assuming tons) with 205kW at rated 100% load.

            The datasheet gives the following: Compressor RLA = 124/158A, MCA=321A, MOP=450A. (3) identical chillers with these values.

            I'm not quite sure what the RLA would be provided with (2) different values? These would lead to two very different feeder calcs.

            New Feeder Calc using 124A RLA will be: 321A + 124A + 124A = 569A

            New Feeder Calc using 158A RLA will be: 321A + 158A + 158A = 637A

            Am I looking at these feeder calcs right based off of this new information? Which RLA value to use will have a pretty significant impact in that it will determine weather we are over/under the 600A threshold which will have impact on breaker rating, ATS rating, etc......

            Thanks for the help!

            Comment


              #36
              Originally posted by mull982 View Post
              Ok I was finally able to track down the datasheets for these chillers. Chiller rated capacity is 348 (assuming tons) with 205kW at rated 100% load.

              The datasheet gives the following: Compressor RLA = 124/158A, MCA=321A, MOP=450A. (3) identical chillers with these values.

              I'm not quite sure what the RLA would be provided with (2) different values? These would lead to two very different feeder calcs.
              The chiller has two compressors. One with 124A RLA, one with 158A RLA.

              Originally posted by mull982 View Post
              New Feeder Calc using 124A RLA will be: 321A + 124A + 124A = 569A

              New Feeder Calc using 158A RLA will be: 321A + 158A + 158A = 637A

              Am I looking at these feeder calcs right based off of this new information? Which RLA value to use will have a pretty significant impact in that it will determine weather we are over/under the 600A threshold which will have impact on breaker rating, ATS rating, etc......

              Thanks for the help!
              321A+282A+282A=885A

              Comment

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