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480 VAC, 3∅ Distribution Question

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    #61
    Originally posted by LarryFine View Post
    Perfectly normal readings for an ungrounded system.

    You're not seeing 277/277/277 because the meter loads each line slightly as you test it. A low-impedance tester should show much less each time.

    That's my theory.

    Does a delta system produce 277? I thought that was a flavor produced by a Wye system.

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      #62
      Originally posted by Bretzel View Post
      Does a delta system produce 277? I thought that was a flavor produced by a Wye system.
      The floating system will tend to settle around wye voltages due to capacitance with the world.

      That explains why your line-to-ground voltages were what they were, and not zero.
      Master Electrician
      Electrical Contractor
      Richmond, VA

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        #63
        Originally posted by Bretzel View Post
        It has been a long, long battle but we have located two major ground fault and one minor one, all on the same leg of the system. One fault was in an abandoned building. We simply cut power to the building and will deal with it if and when the facility is required in the future. Another fault was in an underground PVC conduit near a metal tower which rises some 60' above average terrain and appears to be ungrounded as it is sitting on concrete piers and has no ground rods. The final one is somewhere in an overhead line heading out to the far end of the property. With these faults cleared or simply off-line we have more normal voltage readings. Phase to phase is 480 volts anywhere on the system. On this 480 volt, ungrounded delta system we should be seeing 480 between each phase and ground. We are seeing 229, 226, and 220 to ground.

        Any thoughts on this situation?

        Thank you in advance.

        Thanks again for coming back.
        Tom
        TBLO

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          #64
          Originally posted by LarryFine View Post
          The floating system will tend to settle around wye voltages due to capacitance with the world.

          That explains why your line-to-ground voltages were what they were, and not zero.
          I agree.

          Originally posted by Bretzel View Post
          Does a delta system produce 277? I thought that was a flavor produced by a Wye system.
          If you have wye configured loads (many common smaller 9 lead motors are wye connected) and happen to have a ground connection to the wye point (intentional or not) you will have reasonably solid ~277 volt to ground readings on said system. But any other wye connected load can do same thing. Most transformer primary circuits will be delta and won't be an issue, but if you happen to have a wye primary or reverse feed a delta-wye transformer, be sure to leave the primary side neutral "floating".
          I live for today, I'm just a day behind.

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            #65
            Originally posted by LarryFine View Post
            Perfectly normal readings for an ungrounded system.

            You're not seeing 277/277/277 because the meter loads each line slightly as you test it. A low-impedance tester should show much less each time.

            That's my theory.

            That sounds reasonable. We did find several Wye connected motors both on our 480 primary voltage and on the 208 side of transformers. We also found a few Wye transformers in the mix. We conducted a complete survey of the entire system nearly down to the last outlet. It was exhaustive and mind boggling how wrong some of the things we found were. Simple things ~ 50 amp double pole breaker feeding a single 14ga conductor AND a white one at that! We hired an additional electrician to start straighten in it out.

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