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HVAC Unit loads and demand factors

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    HVAC Unit loads and demand factors

    So normally if we have equipment such as a natural gas rooftop unit, or other packaged equipment, I take the MCA of the nameplate, turn it into VA based on the voltage/phase and divide that by how many poles are feeding it. I put that value into each leg of the panelboard schedule. I take a 100% demand factor to size feeders, service, etc. The maximum overcurrent protection device is selected based on the value given on the nameplate.

    Is this the correct way to do this?

    #2
    I am wondering if my question did not make sense. 94 views an no comments.

    Comment


      #3
      Originally posted by jjs View Post
      So normally if we have equipment such as a natural gas rooftop unit, or other packaged equipment, I take the MCA of the nameplate, turn it into VA based on the voltage/phase and divide that by how many poles are feeding it. I put that value into each leg of the panelboard schedule. I take a 100% demand factor to size feeders, service, etc. The maximum overcurrent protection device is selected based on the value given on the nameplate.

      Is this the correct way to do this?
      I would use the fla of the units and turn it into VA.

      And then add 25% of the single largest motor.

      Comment


        #4
        Originally posted by david luchini View Post
        I would use the fla of the units and turn it into VA.

        And then add 25% of the single largest motor.
        It is my understanding that the MCA given on the nameplate is exactly that.

        Comment


          #5
          Originally posted by david luchini View Post
          I would use the fla of the units and turn it into VA.

          And then add 25% of the single largest motor.
          Originally posted by jjs View Post
          It is my understanding that the MCA given on the nameplate is exactly that.
          But the issue is of you use the mca for multiple units, you are counting that extra 25% for every unit, vs if you use David's method, you don't "over count" and end up with a higher than needed feeder or service load.
          Ethan Brush - East West Electric. NY, WA. MA

          "You can't generalize"

          Comment


            #6
            Sounds like you're filling in the loads on a panel schedule. Using published MCA as the actual connected load is conservative, as it will include the extra 25% of the largest motor.

            If you want to use the actual connected load, you have to dig deeper into the electrical data for the mechanical equipment. Be sure you account for all the motors. MCA is always the right way to size the wire and MOCP for the breaker, but neither of these can be solved for connected load.
            Alternate current
            Line to ground and ground to line
            Current alternates

            Comment


              #7
              220.14(C) refers to 440.6 for service/feeder sizing
              440.6(A) exception 1 seems to say use the MCA for sizing if there is a equipment nameplate
              440.6(B) Seems to say to use the nameplate rating also.
              I don't see the 125% in 440.6
              In Mike Holt's book Understanding the NEC Volume 1 (2014) in the introduction it says "Thus, Article 440 requires you to use the nameplate circuit protection rather than what you develop from applying Article 430"

              Then it says :
              "Three key points to remember so you apply Article 440 correctly are:
              1. Hermetic motors are different. ...
              2. Use the NAMEPLATE information.
              3. ..."

              Lots of times I am only given MCA/MOCP and I don't have the individual motor values. But it sure seems to me like the MCA is the value to be used based on the wording in the code.
              Can someone explain to me what I am missing?

              Comment


                #8
                Originally posted by jjs View Post
                220.14(C) refers to 440.6 for service/feeder sizing
                440.6(A) exception 1 seems to say use the MCA for sizing if there is a equipment nameplate
                440.6(B) Seems to say to use the nameplate rating also.
                I don't see the 125% in 440.6
                In Mike Holt's book Understanding the NEC Volume 1 (2014) in the introduction it says "Thus, Article 440 requires you to use the nameplate circuit protection rather than what you develop from applying Article 430"

                Then it says :
                "Three key points to remember so you apply Article 440 correctly are:
                1. Hermetic motors are different. ...
                2. Use the NAMEPLATE information.
                3. ..."

                Lots of times I am only given MCA/MOCP and I don't have the individual motor values. But it sure seems to me like the MCA is the value to be used based on the wording in the code.
                Can someone explain to me what I am missing?
                There's nothing in Article 440 about feeders, only branch circuits.

                430.24 talks about Several motors or a Motor(s) and Other Load(s)

                Comment


                  #9
                  220 is service and FEEDERS, 220.14(C) refers to 440.6 for sizing the feeders and services.

                  Comment


                    #10
                    Originally posted by jjs View Post
                    220 is service and FEEDERS, 220.14(C) refers to 440.6 for sizing the feeders and services.
                    220.14(C) is for BRANCH CIRCUITS

                    Comment


                      #11
                      Sorry should have been 220.50 which says the same thing.

                      Comment


                        #12
                        Originally posted by jjs View Post
                        Sorry should have been 220.50 which says the same thing.
                        And 220.50 directs you to 430.24, which is for Several Motors or a Motor(s) and Other Load(s), which is what you have.

                        In addition, 440.1 Scope says
                        The provisions of this article apply to electric motor-driven air-conditioning and refrigerating equipment and to the BRANCH CIRCUITS and controller for such equipment.
                        In addition, 440.3(A) Article 430 says
                        These provisions are in addition to, or amendatory of, the provisions of Article 430 and other articles in the Code, which apply except as modified in this article.

                        Comment


                          #13
                          Not saying you are wrong David. But that interpretation brings up lots of questions in my mind. I appreciate all the time you have already given this.

                          Originally posted by david luchini View Post
                          And 220.50 directs you to 430.24, which is for Several Motors or a Motor(s) and Other Load(s), which is what you have.
                          I don't believe that is true. I have a piece of refrigeration equipment. The multiple motors 430 is talking about are standalone motors that are being connected to the same circuit by the electrician. Not a packaged unit that is assembled by the manufacturer that then puts a nameplate on the entire unit.
                          In 430.1 there is a FPN#1 says ... A/C and refrigerating equipment are covered in Article 440.

                          Originally posted by david luchini View Post
                          In addition, 440.1 Scope says
                          The provisions of this article apply to electric motor-driven air-conditioning and refrigerating equipment and to the BRANCH CIRCUITS and controller for such equipment.
                          Yes it does. And 220.50 says to use those rules to size your feeders and services for A/C equipment
                          430.1 scope does not refer to services. But in 220.50 it directs us to 430 for our service sizing requirements when we have motors.
                          Why would the same not apply to 440.6 when 220.50 directs us there for feeders and services?

                          Originally posted by david luchini View Post
                          In addition, 440.3(A) Article 430 says
                          These provisions are in addition to, or amendatory of, the provisions of Article 430 and other articles in the Code, which apply except as modified in this article.
                          Yes, and 440.6 specifically amends what 430 says, so they take precedence over article 430

                          If I have a dishwashing machine. I don't try and figure out the FLA of the motor for water pump, the Amps of the heating element, the fla of the possible garbage disposal motor, the control circuits, etc. It is an appliance and they give me a completed nameplate value for it. 440 seems to do the same for packaged hvac eqiupment.

                          Comment


                            #14
                            Originally posted by jjs View Post

                            Yes, and 440.6 specifically amends what 430 says, so they take precedence over article 430
                            There is nothing in 440.6 about feeders. There is nothing in Art 440 at all about feeders, so there is nothing to "take precedence" over the feeder requirements in Art 430.

                            Art 440 tells you in plain language that it is about equipment with hermetic refrigerant compressors and about their Branch Circuits. It also tells you that Art 430 also applies to that equipment. I don't know how it could be more clear that you would have to look to Art 430 when sizing feeders for that equipment.

                            Comment


                              #15
                              jjs, now you know why you went so long with no answer
                              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.

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