208 vs 220 three phase power
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  1. #1
    jimm51 is offline Plastic
    Join Date
    Mar 2010
    arizona, usa

    Question 208 vs 220 three phase power

    I have a CNC mill that is wired for 208 volts three phase. I have 220 three phase available, will this 220 volt three phase harm the 208 three phase machine? thanks for any insite. jim

  2. #2
    metlmunchr is offline Diamond
    Join Date
    Jul 2004
    Asheville NC USA


    Have you checked the actual voltage on your system? 240V is much more common, and the phase to phase voltage on those can often run 250-255V. If the machine is Japanese, it would likely be rated for 200V unless its fairly new. Some people get away with operating 200V machines on 240V systems, but some do have problems.

    On a 208V system, any phase measures 120V to neutral. Other systems typically have one high leg which will read about 200V to neutral. If your system has a high leg, and the machine is picking up 120V for the control from the 3 phase power, then you need to make sure one of the 120V legs is attached to the point where the control power is picked up.

  3. #3
    misterT's Avatar
    misterT is offline Cast Iron
    Join Date
    Mar 2009
    Indiana USA


    You might also take a look at the transformer in the machine to see if it has taps for 220? ( 3 phase is generally 230V). It is generally recommended to run within 10% of the rated voltage which would be 187-229 V for 208. Running under voltage is usually immediately apparant because the machine will trip out or just not start. Unfortunately running overvoltage just tends to burn things up after a while. Like metlmunchr said how much overvoltage you can run is a guess. Definately check what your voltage actually measures and the actual rating of the machine. If worse comes to worse you may have to buy a buck boost transformer.


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