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Wiring 3 phase motor for inverter use

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  • Wiring 3 phase motor for inverter use

    Hi folks,

    My mill came with a 3 phase motor which the sales guy advised me was dual voltage 440/220. I'm in the UK and have single phase 240v supply. I have been using the mill for about a week now with a VFD which converts my 240v 1ph to 240v 3ph.

    It seems to run fine but I'm not sure if the wiring is right or not. There was no wiring diagram to show how low voltage should be set, and it doesn't mention low voltage on the name plate.

    I've attached a pic below, please could someone advise me if this is right, or should I be altering the links to Delta configuration? The name plate seems to indicate that it's wired for 415v at the moment so it seems odd that it'd be the same for 240v, but it does seem to be working fully, and I don't suspect it's at half power (but maybe I'm wrong!).

    By the way - my wires which are labeled U/V/W are connected to the corresponding U/V/W terminals, just the terminals opposite don't line up, so if it looks like I've connected V to U and W to V then don't worry, I haven't


  • #2
    I suspect the three windings can be hooked Y as shown or DELTA
    (no symbol on the keyboard :-) ) .
    In the case of the delta wiring each winding would have the low voltage
    across it , in the Y config the appropriate voltage would be the
    square root of 3 times the low voltage. Which does check out .
    Sq rt of 3 is 1.732 times 240 = 415 so that looks like its the case.
    The sequence for connecting the 3 for delta I'm not sure but would
    guess it to be diagonal with the end one "wrapped around".

    On the other hand if it doesn't say it's suitable for "low" voltage then
    I'd be a bit reluctant to try it. :-)
    ...lew...
    Last edited by Lew Hartswick; 01-06-2012, 06:15 PM.

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    • #3
      Most motor in UK have the 6 leads for star/delta it looks like you have it connected in Star (HV)
      Delta the links would be 3 vertical ones for low voltage, instead of the top horizontal.
      The incoming power stay the same.
      Max.
      Last edited by MaxHeadRoom; 01-06-2012, 06:21 PM.

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      • #4
        Yeah it's wired in star (Y) at the moment, which the name plate indicates is what it should be for 415v, my question is should I rewire it as Delta (ie with the links running vertically in my photo above) for my 240v supply?

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        • #5
          The vertical connection will give you the delta configuration which should work on 240v, as the salesman told you.
          This is the way I always connected a motor for 240 when working in the UK.
          Max.

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          • #6
            Maybe this helps

            Look at the plate of this standard 3 phase motor just like yours (left side for UK 50Hz)










            .
            "...do you not think you have enough machines?"

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            • #7
              Originally posted by MaxHeadRoom
              The vertical connection will give you the delta configuration which should work on 240v, as the salesman told you.
              This is the way I always connected a motor for 240 when working in the UK.
              Max.
              Yes....

              Right now per picture you have it wired for 400/415V
              CNC machines only go through the motions.

              Ideas expressed may be mine, or from anyone else in the universe.
              Not responsible for clerical errors. Or those made by lay people either.
              Number formats and units may be chosen at random depending on what day it is.
              I reserve the right to use a number system with any integer base without prior notice.
              Generalizations are understood to be "often" true, but not true in every case.

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              • #8
                There was a recent thread, I believe on PM, to the effect that a 440V 3ph
                motor, sans 220V option, could be safely operated with a 220V 1ph VFD
                with a significant HP reduction. It got rather technical, for me, but that
                seemed to be the gist of it. By rewiring your motor, as suggested, you
                would be much closer to the nameplate HP rating, at least around 40-60Hz.
                Steve

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