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Wiring Question - "2-phase" Power

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  • Wiring Question - "2-phase" Power

    I've got a Syncrowave 350 LX at my house, setup to run on 240 VAC split-phase. Long story short, I've got a second location I'd like to be able to run my welder but this location only has 208 Y service available. The 350 LX has a max output of 400 amps but I can't see ever running it at more than 150 amps at the second location.

    You reckon I would damage any of the internal electronics if I fed it with 208 two-phase? The long term solution is to get a 3-phase to split phase transformer but I need to do some welding next weekend and don't have time to source a xformer and get it installed by then.

    (I'm make a distinction between "split-phase", 240 VAC service and "dual phase" 208 VAC service where dual phase is meant to mean two phases of the 3 phase service)

  • #2
    According to the manual there are some jumpers you can set for 8 voltages between 200 and 575 volts. You should be OK.

    Dan
    At the end of the project, there is a profound difference between spare parts and left over parts.

    Location: SF East Bay.

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    • #3
      Two phase?

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      • #4
        Originally posted by Illinoyance View Post
        Two phase?
        ...yes. As stated in the OP, "two-phase" refers to two phases of a 3-phase system. This is different than "split phase" because they are 120* out-of-phase instead of 180* out-of-phase so the leg-to-leg voltage is less (i.e. 208 instead of 240, etc.). Back in the old days, 2-phase was common. I've got an old compressor motor that is setup for 4-wire 2-phase power. Although, in that case, I think 2-phase was actually 90* out-of-phase? This would have been early 1900s.
        Last edited by Fasttrack; 03-18-2018, 12:18 PM. Reason: Just checked - it's 4 wire

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        • #5
          It's just single phase 208. The only way you get it is from a 3 phase system, but it's just 2 wires (one phase) of the three phases (not 2 phases).. Extremely common in office buildings and industrial. You will be fine.

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          • #6
            If you use two phases of a three phase system (no neutral) it is single phase, Not 2 phase.
            Max.

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            • #7
              Legs are not phases!
              Legs are not phases!
              Legs are not phases!

              2 legs of a 3 phase system is single phase.
              3 legs of a 3 phase system is 3 phase.

              As an example,
              A rotary phase converter generates 1 leg, and 2 additional phases.

              Terminology maters.
              Learn what you are talking about before you discuss it.

              -Doozer
              DZER

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              • #8
                Yeabut, phase is all about time so a delta connection provides three new phases that are not the same as the input.

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                • #9
                  I love it. Let the games begin.



                  Originally posted by Doozer View Post
                  Legs are not phases!
                  Legs are not phases!
                  Legs are not phases!

                  2 legs of a 3 phase system is single phase.
                  3 legs of a 3 phase system is 3 phase.

                  As an example,
                  A rotary phase converter generates 1 leg, and 2 additional phases.

                  Terminology maters.
                  Learn what you are talking about before you discuss it.

                  -Doozer
                  Paul A.
                  SE Texas

                  And if you look REAL close at an analog signal,
                  You will find that it has discrete steps.

                  Comment


                  • #10
                    Legs ARE phases..... yes indeedy they are, when you have a neutral.

                    Now.... what you are discussing is: What is the "phase of the phases"?

                    To have any "phase" between them other than 180 deg (the difference between the two), you must have a reference, so that you can define each relative to the other, with each measured line to reference (in this case neutral).

                    in a 3 wire 240 system, you have two "phase wires" that have an angle which combines them at full voltage, such that the voltages add directly. "Effectively" it is a single phase. If you use just the two hot wires, you can only have singe phase.

                    The very same PHYSICAL setup can be 3 wire two phase. The ONLY difference between the two is the relative phase of the two wire-to-reference voltages. In one case 90 degrees, in the other case 180 degrees. But that difference causes one to be "single phase", and the other "two phase".

                    So, the 3 wire single phase 240V system in the US is fundamentally the same thing as 208V, taken 2 phase wires at a time. It is just a special case, with the "special" part being the relative phasing of 180 degrees instead of the 120 deg with the 208V (which is also why it is 208 and not 240V)

                    Just to be even more confusing, any two wires alone can only be "single phase", as there is only a single voltage to measure. It makes no difference what the two wires are. Two hot legs of a 3 phase system..... it is single phase. The two hot wires of a two phase system... single phase. One phase wire plus neutral on a three phase system.....single phase. One phase wire plus neutral of a two phase system..... still single phase.
                    Last edited by J Tiers; 03-18-2018, 02:36 AM.
                    CNC machines only go through the motions

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                    • #11
                      OMG not this again. J Tiers is 100% correct. In this country in modern times, its 3 wire 3 phase, 2 wire single phase and in some parts of the East coast they still have some old 4 wire true 2 phase. You folks who are keyboard experts.... keep on typing. The electricians in the group know what is what.
                      Retired - Journeyman Refrigeration Pipefitter - Master Electrician

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                      • #12
                        Just because you don't understand does make it true *

                        * unless you are a Politician

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                        • #13
                          Originally posted by J Tiers View Post
                          in a 3 wire 240 system, you have two "phase wires" that have an angle which combines them at full voltage, such that the voltages add directly. "Effectively" it is a single phase. If you use just the two hot wires, you can only have singe phase.

                          The very same PHYSICAL setup can be 3 wire two phase. The ONLY difference between the two is the relative phase of the two wire-to-reference voltages. In one case 90 degrees, in the other case 180 degrees. But that difference causes one to be "single phase", and the other "two phase"

                          So, the 3 wire single phase 240V system in the US is fundamentally the same thing as 208V, taken 2 phase wires at a time. It is just a special case, with the "special" part being the relative phasing of 180 degrees instead of the 120 deg with the 208V (which is also why it is 208 and not 240V)
                          Thanks, JT. Makes perfect sense; I just wanted to double check that there was no difference (aside from larger current draw) running on 208V instead of 240V. The third wire had me cautious but it's safety ground, not neutral.

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                          • #14
                            I wish I could be more like the folk who don't let this kind of thing phase them, but these kinds of misconceptions just make me want to slap somebody in the phase.

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                            • #15
                              Originally posted by Fasttrack View Post
                              Thanks, JT. Makes perfect sense; I just wanted to double check that there was no difference (aside from larger current draw) running on 208V instead of 240V. The third wire had me cautious but it's safety ground, not neutral.
                              Correct its a green equipment ground not required to run the machine. Some motors and I think you said your welder had a tap for 208 vs 240 volts. Use that connection.
                              Retired - Journeyman Refrigeration Pipefitter - Master Electrician

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