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    14 3Hp

    Will 14 3 hp fans be any more difficult to start than a single 50 hp? Fans are axial flow.

    Basically, I’m plannining on starting all 14 at one time.
    Tom
    TBLO

    #2
    limitations in the supply will act like a soft starter either way, especially for low starting torque that is required here.
    I live for today, I'm just a day behind.

    Comment


      #3
      For standard stuff, Code G, Design B, FLA from T430.250, T430.251.B
      3hp, 3ph, 480V, 4.8 FLA, LRA = 32A, total running A = 67A, total starting A = 448A
      50 HP, 3ph, 480, 65 FLA, LRA = 363A

      First approximation, the 50HP is ~20% less locked rotor current than 14 each, 3hp.
      Low starting torque doesn't change the LRA.

      On a 150KVA xfm, 200A, either will blink the snot out of the lights
      On a 1000KVA xfm, 1200A both will be barely noticeable

      Not sure where this is headed. Give us some context.
      Without data you’re just another person with an opinion – Edwards Deming

      Comment


        #4
        Originally posted by iceworm View Post
        For standard stuff, Code G, Design B, FLA from T430.250, T430.251.B
        3hp, 3ph, 480V, 4.8 FLA, LRA = 32A, total running A = 67A, total starting A = 448A
        50 HP, 3ph, 480, 65 FLA, LRA = 363A

        First approximation, the 50HP is ~20% less locked rotor current than 14 each, 3hp.
        Low starting torque doesn't change the LRA.

        On a 150KVA xfm, 200A, either will blink the snot out of the lights
        On a 1000KVA xfm, 1200A both will be barely noticeable

        Not sure where this is headed. Give us some context.
        No but impedance in the supply circuit does, and effect on lights like you mentioned is an indicator that you don't have same thing in each case.

        Starting of one motor may be able to reach LRA, but with the overall higher current level when starting 14 of them, you may not be able to reach that high of current - sort of like using soft starter. You will get slower acceleration than if only starting one also.
        I live for today, I'm just a day behind.

        Comment


          #5
          Three phase 480v fans each with manual motor starter will tap from a feeder controlled by a typical PP. I figured a 50 hp was adequate. Taps less than 10 feet, FWIW.
          Tom
          TBLO

          Comment


            #6
            Originally posted by ptonsparky View Post
            Three phase 480v fans each with manual motor starter will tap from a feeder controlled by a typical PP. I figured a 50 hp was adequate. Taps less than 10 feet, FWIW.
            What is a "typical PP"? I don't know what that is.

            Disclaimer: I have never been involved with design or installation of any similar multi-motor system. This is just a code review exercise. Makes me think I wouldn't be listening to me very hard.

            So, the manual motor starters supply the overloads for each fan motor. The manual Motor Starters are on all the time. And the PP provides the ON-OFF control. Okay.
            What provides the short circuit protection for each motor? If you are using a TM CB, that limits each branch circuit (or group of branch circuits) to 15A. You can't use a single 150A CB. And I'm thinking you already know this. I don't yet understand the control/feeder scheme.

            Code answer:
            If the "PP" is part of 430.110.C.1, then an unqualified "maybe".
            The 50 HP rating is okay, your connected HP is 42hp.

            The T430.251 currents, not so much. The 14 ea, 3hp FLA, LRA currents exceed that listed for a 50hp.

            Practical answer:
            Depending on exactly what a "PP" is, I'd guess the application is fine.
            Without data you’re just another person with an opinion – Edwards Deming

            Comment


              #7
              kw -
              You lost me.

              Originally posted by kwired View Post
              ...Starting of one motor may be able to reach LRA, but with the overall higher current level when starting 14 of them, you may not be able to reach that high of current - sort of like using soft starter. ....
              I'm assuming no one is going to purposefully design a feeder to under-power the loads. If the feeder/service is undersize, the system will under-perform. No one is going to feel bad about that. I'm not too fussed about the combined LRA causing starting Vd. Whether the load is 14 ea, 3hp, or 1 ea, 50hp, the effects are about the same - Still not too fussed.


              Originally posted by kwired View Post
              .... You will get slower acceleration than if only starting one also.
              edit to delete previous, and add:
              Okay - got this one. Starting 14 motors will sag the voltage more than starting one. Yep - that's true.
              Last edited by iceworm; 08-21-19, 05:34 PM. Reason: figured out the second part of kw post. edited response
              Without data you’re just another person with an opinion – Edwards Deming

              Comment


                #8
                PP = Pump Panel.

                The MMS are suitable for use with tap conductors or words to that affect according to their instructions.
                Tom
                TBLO

                Comment


                  #9
                  PP probably = Pump Panel, a low cost way of buying a Combo Starter in the Ag world.

                  14x 3HP = 52HP, technically over the limit for a 50HP (Size 3) Pump Panel. Probably fine, but technically not.

                  If you could use a Siemens /Furnas Size 3-1/2 though, that would meet all criteria. Don’t know if anyone else does the half size NEMA starters any more though. But a 60HP IEC rated PP would work too.

                  But to be legal, you would need to use the IEC style MMS units that have both the SC and OL protection built in. Otherwise your SCPD in the PP will be way way too big for the 3HP motors, so you would have to add fuse blocks or something like that for each one. This is the kind of thing I like those all-in-one IEC Manual Starters for.

                  Brain fart... 42HP... never mind.
                  Last edited by Jraef; 08-21-19, 07:05 PM.
                  __________________________________________________ ____________________________
                  Many people are shocked when they discover I am not a good electrician...

                  I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

                  Comment


                    #10
                    Originally posted by Jraef View Post
                    PP probably = Pump Panel, a low cost way of buying a Combo Starter in the Ag world.

                    14x 3HP = 52HP, technically over the limit for a 50HP (Size 3) Pump Panel. Probably fine, but technically not.

                    If you could use a Siemens /Furnas Size 3-1/2 though, that would meet all criteria. Don’t know if anyone else does the half size NEMA starters any more though. But a 60HP IEC rated PP would work too.

                    But to be legal, you would need to use the IEC style MMS units that have both the SC and OL protection built in. Otherwise your SCPD in the PP will be way way too big for the 3HP motors, so you would have to add fuse blocks or something like that for each one. This is the kind of thing I like those all-in-one IEC Manual Starters for.
                    My calculator must be broken. It repeatedly come up with 42.
                    Tom
                    TBLO

                    Comment


                      #11
                      Originally posted by Jraef View Post
                      PP probably = Pump Panel, a low cost way of buying a Combo Starter in the Ag world.

                      14x 3HP = 52HP, technically over the limit for a 50HP (Size 3) Pump Panel. Probably fine, but technically not.

                      If you could use a Siemens /Furnas Size 3-1/2 though, that would meet all criteria. Don’t know if anyone else does the half size NEMA starters any more though. But a 60HP IEC rated PP would work too.

                      But to be legal, you would need to use the IEC style MMS units that have both the SC and OL protection built in. Otherwise your SCPD in the PP will be way way too big for the 3HP motors, so you would have to add fuse blocks or something like that for each one. This is the kind of thing I like those all-in-one IEC Manual Starters for.

                      Brain fart... 42HP... never mind.
                      Your suggestions earlier this year pointed me to the IEC style MMS. Only one of the area suppliers was able to come up with what I wanted, which included Non-metallic enclosure suitable for the dairy environment they were in. Not washdown, just damp. The project appears to be headed in the right direction. We've started anyway.

                      Tom
                      TBLO

                      Comment


                        #12
                        Originally posted by Jraef View Post
                        PP probably = Pump Panel, a low cost way of buying a Combo Starter in the Ag world.
                        Yes. Can buy Pump panel that has fused switch contactor, overload and hand off auto control all in N3,4,12 enclosure for less than I can buy the mangetic starter alone. Starter needs replaced? cheaper to buy pump panel and take parts out of it.

                        I live for today, I'm just a day behind.

                        Comment

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