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  • Electrical connection requirements

    Hello all! I'm not a welder, but an electrician. I have a customer with a MillerMatic 350. We are to connect it to 3 phase 240V. The specs clearly state 30A draw and minimum conductor is #10. The personal at technical support just told me that I should install a 50A breaker and that a 30A safety switch would not be adequate. Am I crazy or does it just seem like he is not understanding or doesn't know. At minimum wire size of #10, a 50A breaker is illegal.

  • #2
    It is allowable due to the machine' duty cycle.

    Normal operating FUSE you would use a 50amp fuse and 10g wire IS MINIMUM
    Wiring following NEC art 630 wiring and that is what they use for the manual.



    Time delay fuse = 30amp rated and 10g wire.

    http://www.millerwelds.com/om/o1327ah_mil.pdf
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    • #3
      Sorry. Disregard. I am not as familiar with Art. 630 than I should be. So I guess the actual question I have is will this welder operate properly connected via 30A non-fuse disconnect, #10 wire
      Last edited by unionsparky; 10-17-2014, 02:30 PM.

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      • #4
        Originally posted by unionsparky View Post
        Sorry. Disregard. I am not as familiar with Art. 630 than I should be. So I guess the actual question I have is will this welder operate properly connected via 30A non-fuse disconnect, #10 wire
        Are you talking about a normal Circuit Breaker?



        3-phase 240v 30amp CB and 10g wire
        Ed Conley
        http://www.screamingbroccoli.net/
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        • #5
          I believe you can use a overcurrent device up to 200% of the nameplate I1eff, or 200% of nameplate current x multiplier from 630.11(A) What is the duty cycle of the welder?

          It is my opinion that a disconnect switches load only in extreme emergency. Its requirements are the same as the conductors supplying.
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          • #6
            As long as I have the control board set for 230V, will welder care which leg is high leg?

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            • #7
              I had a similar experience with a Lincoln Power Wave 455... previous owner had it connected to a 120/240 three phase with a high leg. The machine would randomly shut down and the owner just thought it was unreliable. I ran it on a 208 three phase and never had any issue. I think in the previous owner's situation, the wild leg would get outside of the voltage tolerance when other loads in the shop changed, and that's what I figured was going on when I picked up this pulse-spraying beast for a song.

              In this case, I spoke with engineers at Lincoln and they confirmed that the supply voltage was sensed from the L1 and L3 input terminals.

              You might want to give Miller a call and ask them about powering this with unbalanced three phase and see what their engineers say.

              80% of failures are from 20% of causes
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              • #8
                Originally posted by Bodybagger View Post
                You might want to give Miller a call and ask them about powering this with unbalanced three phase and see what their engineers say.
                Yeah, working now. They're closed, unless someone has a special number. To be more specific, their service is running ' hot ' at 125V/248V, and 211V high leg. I'm hoping the controls, if derived from 120V are being pulled from A phase. If they are 230V, I hope the welder handles the higher voltage ok.

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                • #9
                  Originally posted by unionsparky View Post
                  Yeah, working now. They're closed, unless someone has a special number. To be more specific, their service is running ' hot ' at 125V/248V, and 211V high leg. I'm hoping the controls, if derived from 120V are being pulled from A phase. If they are 230V, I hope the welder handles the higher voltage ok.
                  120v Control voltages are supplied from inside the machine via a transformer since there is NO NEUTRAL in the supply circuit.
                  Ed Conley
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                  • #10
                    Well, I decided to put high leg on B phase, white in cord. I saw elsewhere that red is unused for single phase. Meaning that if it has any sensitivity to high leg on A, white must be acceptable. I can't see Miller making equipment that can't be connected to center tapped deltas via single phase.

                    Thanks for all the replies.

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                    • #11
                      Delta 120/208/240 Three phase is 240 balanced on three phase. 240 single phase is available from any phase 120 single phase is available from 2 legs to neutral. 208 single phase is available from the high leg to neutral.
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                      • #12
                        If it works on three phase, why not use three phase?
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                        • #13
                          Originally posted by WillieB View Post
                          Delta 120/208/240 Three phase is 240 balanced on three phase. 240 single phase is available from any phase 120 single phase is available from 2 legs to neutral. 208 single phase is available from the high leg to neutral.
                          I'm completely aware of how their service functions. My lack of familiarity is with Miller welders. My question was, if the 208V high leg could damage any control circuits that were expecting to see 120V.

                          Originally posted by WillieB View Post
                          If it works on three phase, why not use three phase?
                          It is connected to 3 phase. I only brought up the 240V single phase scenario as a matter of trying to determine if the equipment would be unhappy with the 208V on a certain leg of the supply. Since the unit is capable of 120V operation, is it entirely possible that the single hot configuration may want only 120V. This would mean that the second conductor used, when connected as single phase 240V would most certainly have to accept 208V on that leg, since I'm sure Miller would not sell equipment that wouldn't have the option to connect single phase 240V to a high leg delta, which could be necessary if the customer has space constraints.

                          It is hooked up and working at 230V 3 phase connection settings.

                          Thanks again everyone!

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                          • #14
                            Does the welder connect to neutral? If it does it is the first I've seen connected to neutral. Without neutral there is no high leg. Delta is three transformer windings connected in a triangle diagram. The wild leg or 208 is neutral to the opposite corner of said triangle. Your welder doesn't know about 208.
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                            • #15
                              A Miller Matic 350 connects to 120Volt?
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