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IndustryArena Forum > MetalWorking Machines > Okuma > Changing MC-4VA from 480 to 220V
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  1. #1
    Join Date
    Nov 2013

    Changing MC-4VA from 480 to 220V

    I need to change my new to me machine to 220 3ph from 480V.
    It looks like power comes into the main on/off switch, then goes to a multi tap transformer assembly next to the ATC.
    I think I just need to reposition the three bus bars to the 220v position to change the machine to 220v. Is this correct?
    The machine came with a 277/480 surge protector, but I guess i'll have to get a 220v delta unit instead.

    I ordered a phase rotation tester. I'm assuming if I connect the input wires in the "clockwise" rotation everything should be OK?
    Also, the rotary phase converter instructions don't recommend using the manufactured leg to power the controls and so on. Instead, to use L1 and L2 to power the controls. Is this possible or does this machine use 3ph for the controls? If not, which leg should I attach the manufactured lead to?

    Is there any way to verify I have the power leads connected in the proper rotation?


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  2. #2
    Join Date
    Apr 2009

    Re: Changing MC-4VA from 480 to 220V

    You are correct that moving the taps to the required voltage indicated will work.

    Phase can be confirmed by checking for hydraulic pressure. If that builds then phases are correct.

    I believe that the middle leg should go to the manufactured leg if I remember correctly.

    The control should be running off of the 24v power supply. 110 is only used for the fans and lights on your machine.

    Best regards,
    Experience is what you get just after you needed it.

  3. #3
    Join Date
    Nov 2013

    Re: Changing MC-4VA from 480 to 220V

    After poring over the schematics, it looks like the 3rd leg is the one to use.
    L1 and L2 are used for the single phase loads.
    Quite a bit of stuff is 3 phase, including the spindle control, axis motors control, hydraulic pump, coolant pump, spindle lube pump, way lube pump & oil temp controller.
    A bunch of stuff goes through a triple coil transformer in the equipment cabinet. It has output windings for a 120v & 100v outputs and three 24v outputs. Don't really know if the 3rd phase passes through or not. I don't really understand how this transformer works. Certainly 3ph input, but five separate output coils? Do input phases correspond to any of the specific outputs?


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