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HVAC tripping breaker mystery

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    #16
    Originally posted by synchro View Post
    A measured 34 amps is somewhat high when the MOCP spec is 60A.
    Agree! That doesn't allow for much starting current.
    Master Electrician
    Electrical Contractor
    Richmond, VA

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      #17
      Originally posted by LarryFine View Post
      Agree! That doesn't allow for much starting current.
      That is pretty typical, in my experience. I don't remember the exact MCA but it is low 50's, which is right around my rule of thumb that actual current is usually pretty close to 2/3rds of MCA. Seems like these days MCA's are not far below the MOCP.
      Ethan Brush - East West Electric. NY, WA. MA

      "You can't generalize"

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        #18
        I think compressor motor currents can vary a lot depending on the temperatures, amount of refrigerant, etc. (which I'm sure StarCat can expound about much better than I can). So I think the expectation would be that the worst case running current is going to be higher than that made on one measurement. Hence the concern for adequate margin. But it's good to hear if things are becoming more tightly controlled with newer equipment.

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          #19
          I dug up the submittal sheet out of the depths of my email. Turns out it's only two compressors - I misheard or someone misspoke. 16.7 each RLA, MCA 49.8, MOCP 60.
          Ethan Brush - East West Electric. NY, WA. MA

          "You can't generalize"

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            #20
            Originally posted by synchro View Post
            A measured 34 amps is somewhat high when the MOCP spec is 60A. Also, was the 34A including all fans? If not then your even closer to running out of breaker, so to speak.
            If soft starting feature is present in the unit, it does not matter.

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              #21
              Starting Current...

              Originally posted by synchro View Post
              I think compressor motor currents can vary a lot depending on the temperatures, amount of refrigerant, etc. (which I'm sure StarCat can expound about much better than I can). So I think the expectation would be that the worst case running current is going to be higher than that made on one measurement. Hence the concern for adequate margin. But it's good to hear if things are becoming more tightly controlled with newer equipment.
              Back in the 90s when Copeland and Carlyle starting putting the first scroll compressors in residential condensing units, there would, without fail be home owners freaking out about dimming lights on start up in the Brutal Texas Heat. It was not uncommon to see instantaneous inrush of 235A on a 5 ton unit on start. Hard Start gear on single phase systems will moderate this a fair degree. I may not have noted all details on the system but someone making a reference to incorrect sequence of operation is correct, and this needs to be verified. The reference to condenser fan motors is correct, and also the capacitors on those motors can cause problems.
              Compressors generally only approach RLA when under what can be considered full to heavy load with condenser entering air temperature at 90F or over.
              I have seen brand new gear with wiring errors or defects. I remember a mentor saying to me when I was quite young, " Don't assume that its right."
              What I have found to be the case on a lot of newer gear is its designed right on the edge, and the quality of components is not what it once was. Much of it is truthfully not worth having.
              Microwave Radiation Dangers should be openly discussed

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