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2%-not milk

Morning All&Mike T. My volts were 214-208-202.The 2% rule is what I was taught,although the ICM#450 control has a range from 2-20% unbalance voltage .I'm willing to learn,I'm willing to bend some rules.Enjoy your day!


  • Techman
    Techman Member Posts: 2,144
    2% -not milk

    Hidy-ho neighbors!In a 3 phase system for AC,I have had several shutdowns by a newly installed add-on safety control.The control is an ICM# 450, one of its functions is to sense the voltage imbalance between phases(the reason for safety shutdown). Copeland CompCo says that the largest imbalance is to be limited to 2%.The AC units (10) have been operating for 11 years and not a single compressor change out, I checked the comp name tags.Now ,the building super looks at me funny.There is a voltage problem in the bldg that is being adressed,as of yesterday.SO, my knowledge of unbalanced systems is limited to the readings I get on my meter. 2% is what is called for and I will endever to persurvier.What happens with short or long running times, as compared to continous running .Enjoy your day!
  • Empire_2
    Empire_2 Member Posts: 2,343
    Hi Techman.....

    Generally the the accepted voltage imbalance is 10% and Current imbalance is 2 %. I think that is what they were telling you. Both problems can be caused by a number of things including loose connections, bad contacts, improper wire size, actual load problems, and also voltage problems off the pole. An actual phase imbalance can only be measured by a oscilloscope instrument. I do not think this would be your problem though. What are your voltages at the disconnect unloaded (unit off)and loaded? How about the amps on the compressor when running? Each leg to groung would help.....

    Mike T.
  • Empire_2
    Empire_2 Member Posts: 2,343
    Looking at those readings,

    The incoming voltage is definitely a problem or potential problem. One leg is over and 1 is under. That's if it should be 208vac3Phz. If the normal voltage is 230 vac, then you have bigger problems.;-)

    Mike T.
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