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Miller 320A/BP Line Voltage Question

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  • Miller 320A/BP Line Voltage Question

    I bought my 320 from a gentleman who was using it in a machine shop, where he probably had it wired for 208V, given that he probably had his shop wired for 3-phase power, and I am now running it on 240V single-phase. Unfortunately, I don't have the ability to confirm what voltage my machine is wired for, because the sticker on the inside of the rear panel looks like this:Click image for larger version

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  • #2
    Yep, that is absolutely of very little help!

    You can get manual and a wiring diagram here. First, get the serial number from your machine.

    Go to SUPPORT at the top of this page, then MANUALS AND PARTS. At the bottom of that page, there are two search boxes. You can try putting your serial number in the left box, but generally there are no hits on the older machines. So, put your model name into the right box, and it will give you a list of all available manuals for the machine broken out by serial number range. Find the one appropriate for your welder, and you're in business!

    Treat that baby well and it will probably outlast all of us! A fine classic!

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    • #3
      Unfortunately, the manual itself doesn't have the wiring diagram, and instead directs the reader to the label inside the back panel, shown above. I've searched all over the web for pictures of the wiring diagram, but haven't been able to find any. I was hoping that someone here has one of these old beasts, and can help me out.

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      • #4
        Here you go
        Attached Files

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        • #5
          I picked a random serial number and found the jumper connections in section 3.2 of the manual. Here's the one I looked at. Might want to check for your serial number again.

          https://www.millerwelds.com/files/owners-manuals/O340J_MIL.pdf


          From your pic, yours is wired for 200 volts (208 nominal) as you suspected. That gives me some confidence that the diagram in the book is probably correct for your machine.

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          • #6
            I guess I was wrong. I've been referring to the printed manual I have (from 1985, when my welder was made in 1960), which didn't have the wiring diagram. I grabbed the oldest manual from the Miller website, and it has the diagram, and I confirmed that my machine is indeed wired for 208.

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            • #7
              ...and weld dr. found the label!

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              • #8
                I'm hoping that wiring it for my line voltage will help to solve some problems I've been having. It's been tripping the circuit breaker 1 out of every 5 to 1 out of every 10 times I power it on in stick mode or hit the pedal in TIG mode. Hoping this will resolve that issue.

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                • #9
                  Input
                  Attached Files

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                  • #10
                    I have a 74 model that’s wired for 240v. If you can’t figure it out, I can drag my big ole girl away from the wall and see if it’s the same.

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                    • #11
                      I have an airco heli-welder 300 built in 1963. That's supposed to be the same as a 330A/BP. According to the (original!) paper manual, your jumpers are set for 208. For 230, you want to move the jumper over two places, so that it's between 3 and 4 of that row of 5.

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                      • #12
                        Don't forget to move the two main power jumpers as well.

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                        • #13
                          For sure! Wire for minimum smoke and excitement!

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