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Help!! Delta... 3 phase 240v!!

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    Help!! Delta... 3 phase 240v!!

    Hello to all first off. I am a commercial electrician and recently landed a job doing more industrial than commercial. Anyway, I do not understand three phase 240v... I get the wild leg B phase is high leg but I don't get how A to ground reads 120v, B - G reads 240volts, and C to ground is 120v. Its almost like single phase 240??...????????. How does a a 2 pole breaker get 240v when B phase is 240v?? Or a motor say wye example, 3 phase in peckerhead would be L1-a, L2-b, L3-c, 4-7, 5-8, 6-9.. How do I run 240v 3phase to motor??? Hope that isn't to confusing. I just can't wrap my head around this Delta. Thanks

    #2
    Here's an illustration that should help.



    Roger
    Moderator

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      #3
      For the motor hook-up you look at the motor nameplate and make the hook-up based on the supply voltage.
      Don, Illinois
      (All code citations are 2017 unless otherwise noted)

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        #4
        Originally posted by TNGuy81 View Post
        ?? Or a motor say wye example, 3 phase in peckerhead would be L1-a, L2-b, L3-c, 4-7, 5-8, 6-9.. How do I run 240v 3phase to motor??? Hope that isn't to confusing. I just can't wrap my head around this Delta. Thanks
        When it's 240V you use your low voltage L1 is 1,7, L2 2,8, L3, 3,9 and 4,5,6 tie together.
        If Billy Idol is on your playlist go reevaluate your life.

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          #5
          thanks

          But wouldn't that be single phase?? @roger, lets say I am landing a standard 2 pole breaker. Would AB = 240v on a delta 3 phase, or BC? Is it possible to run 240v just from B. (theoretically speaking). If B to ground is 240, why do I need A or C?? Or if I landed a single pole on B, would it get 240 or 120v? I'm use to 120/208, 277/480.. Thanks to all
          Last edited by TNGuy81; 03-31-15, 07:33 PM. Reason: cuz

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            #6
            Originally posted by ActionDave View Post
            When it's 240V you use your low voltage L1 is 1,7, L2 2,8, L3, 3,9 and 4,5,6 tie together.
            That assumes that that motor is a wye connected motor. We don't know that.
            Don, Illinois
            (All code citations are 2017 unless otherwise noted)

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              #7
              Originally posted by don_resqcapt19 View Post
              That assumes that that motor is a wye connected motor. We don't know that.
              He said wye in the OP.
              If Billy Idol is on your playlist go reevaluate your life.

              Comment


                #8
                Originally posted by TNGuy81 View Post
                Hello to all first off. I am a commercial electrician and recently landed a job doing more industrial than commercial. Anyway, I do not understand three phase 240v... I get the wild leg B phase is high leg but I don't get how A to ground reads 120v, B - G reads 240volts, and C to ground is 120v. Its almost like single phase 240??...????????. How does a a 2 pole breaker get 240v when B phase is 240v?? Or a motor say wye example, 3 phase in peckerhead would be L1-a, L2-b, L3-c, 4-7, 5-8, 6-9.. How do I run 240v 3phase to motor??? Hope that isn't to confusing. I just can't wrap my head around this Delta. Thanks
                B to ground should be 208V. Many places just use the A and C phases with ground as 240V split (single) phase for most of the loads.

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                  #9
                  Originally posted by TNGuy81 View Post
                  But wouldn't that be single phase??
                  No. It's three phase...... L1, L2, L3..... A, B, C. A to B 240V, B to C 240V, C to A 240V.
                  If Billy Idol is on your playlist go reevaluate your life.

                  Comment


                    #10
                    Adave

                    Not 208. A-g= 120, B-g= 240, c-g=120
                    @aDave, thank u sir, that registered. So, regardless of B @ 240v any order of the phases still gets me at 240v, correct? Obviously not considering rotation, I know to switch out a phase/rotate..
                    Last edited by TNGuy81; 03-31-15, 07:59 PM. Reason: adave

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                      #11
                      Originally posted by TNGuy81 View Post
                      Not 208. A-g= 120, B-g= 240, c-g=120v
                      Are you testing with a digital meter or a wiggy?
                      If Billy Idol is on your playlist go reevaluate your life.

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                        #12
                        Originally posted by ActionDave View Post
                        He said wye in the OP.
                        That is not clear to me, because the word "example" was used along with wye.
                        Don, Illinois
                        (All code citations are 2017 unless otherwise noted)

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                          #13
                          wiggy!!

                          No! Digi multimeter..
                          @Don , as In not center tapped delta. Like 277/480 ABC-G= 277, AB=480, BC=480V
                          Last edited by TNGuy81; 03-31-15, 08:04 PM. Reason: Don

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                            #14
                            Originally posted by TNGuy81 View Post
                            Not 208. A-g= 120, B-g= 240, c-g=120
                            @aDave, thank u sir, that registered. So, regardless of B @ 240v any order of the phases still gets me at 240v, correct? Obviously not considering rotation, I know to switch out a phase/rotate..
                            Yes. Phase to phase is 240V every time.

                            Got to run for now. The fact this is driving you crazy means you can get this. Hang in there.
                            If Billy Idol is on your playlist go reevaluate your life.

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                              #15
                              dave

                              Really?? Billy idol hater?? Lol, rock the cradle, white wedding.. Classic!

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