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Thread: 3 Phase Puzzle

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    3 Phase Puzzle

    Hi there,
    I was wondering whether someone may be able to help me with an issue I have come across.
    I am testing an installation for compliance for a sale of property. It is a farm and is supplied by an Eskom 3 phase transformer.
    It is a 40A 3 phase supply.
    When I test from neutral to red I get 230V, neutral to yellow 230V and neutral to blue 230V.
    When I test from earth to red I get 230V, earth to yellow 230V and earth to blue 230V.
    When I test from red to yellow I get 412V, red to blue 411V. Now when I test from yellow to blue I get 0V!!
    How is this possible??
    I have tested right back at the Eskom box and I get this same result even at the meters in the Eskom box.
    I cannot test the top of the Eskom breakers as they are locked with tags.
    Someone please help shed some light on this.
    Luckily, at present, there is no 3 phase equipment installed on the premises, however the new owners may well install a 3 phase pump or something and then I would be sure that they would start having problems!
    Many thanks
    Simon
    We are not human beings undergoing a spiritual phase.....we are spiritual beings undergoing a human phase....

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    Site Caretaker Dave A's Avatar
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    Yellow and blue are supplied by the same phase.
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    Full Member MullerR's Avatar
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    I agree with Dave. Try to get hold of Eskom to open their box (good luck with that). It could be that in the past the transformer gave problems with the one phase so they connected the two phases together. I had to do it once in an emergency situation,but changed the transformer a week after that.

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    Quote Originally Posted by MullerR View Post
    I agree with Dave. Try to get hold of Eskom to open their box (good luck with that). It could be that in the past the transformer gave problems with the one phase so they connected the two phases together. I had to do it once in an emergency situation,but changed the transformer a week after that.
    Thanx guys.
    This was the only logical conclusion that I could come to as well. I stood on the ground under the transformer and looked up at it and it certainly looked like all 3 phases were separate at the transformer.
    They all had their own tappings off of the windings and nowhere were they even bridged across each other.
    This puzzled me, as if it is, and it must be, like you suggested, then either the transformer has shorted its windings inside the transformer, or it is bridged further down the line somewhere?!
    I will see if I can get onto Eskom today.
    I'll update once I resolve this one...
    Peace
    We are not human beings undergoing a spiritual phase.....we are spiritual beings undergoing a human phase....

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