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Miller XMT 300 Input Wiring Help

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  • Miller XMT 300 Input Wiring Help

    I just acquired a Miller XMT 300 CC/CV (serial # KF93...) and am having trouble getting the unit to work. The unit did not come with a pig tail.

    I am trying to use a pig tail from another XMT 300 -I took it off of a non-working machine -this pigtail has 4 wires, but the white was cut off and not used. The black and red were wired (with ring terminals) to a part with a copper coil at the bottom. From there the black wire goes to a terminal block and the Red wire goes first to the the main switch and then back to the terminal block. As I mentioned, the white wire was cut off and not used.

    I wired the "new" XMT exactly the same way. I am using at my home with 230 volt power. I have plugged in the unit and nothing happens. Could fact that the white wire is not hooked up to the main switch (as the diagram shows) be my problem?

    The guy I got the welder from assured me it works -he made sure of it when he picked him up and I trust him.

    I printed out the wiring diagram from Miller's technical manual, and as best I can tell the white wire should be used....goes directly to the main switch (S1).

    This machine came from a technical school which could have used 3 phase power -but I'm not sure. Can anyone help me figure out how this machine's input power should be properly connected?


  • #2
    forgot to mention ground wire

    I forgot to mention but the 4th wire is the green ground wire and it is directly attached to the machine's chassis.


    • #3
      My welder was wired for 3 phase also. What I did was leave the red wire on L2 - but when I wired up my 4 way plug in the wall I left that prong on the plugin disconnected. White & Black wires can be inter changed between L1 and L3 in my case. So you could cut off the red wire if it isnt the wire you need.

      What you should do is use a continuity tester to test and see which prongs have power & only use those wires with the wall plug.

      In my case the L shaped prong was linked to the red wire, and the two straight prongs were white & black, green is ground.


      • #4
        In single phase operation, the red wire is the wire not used. This is assuming you have it wired per the original diagram. No telling who could have been in there messing things up before.



        • #5
          I spent a lot of time with the Miller wiring diagram, owners manual and technical manual. I rewired following the correct procedure and the machine cranked right up. Miller does an excellent job of providing all the information you need to figure these things out, it just takes a little research. And never assume the previous owner had his wiring "right" -That's what I did and it cost me a lot of time...but I did learn a lot so overall not a waste of time!

          Thanks for your comments!