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Thread: 320v single phase

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    320v single phase

    How does one go about dealing with Eskom if a single phase voltage supply is 320v its unacceptable and the cause of major losses in house holds and industries. 12 sewing machines and other appliances where damaged due to this
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    Site Caretaker Dave A's Avatar
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    Silly question, perhaps. But did you disconnect the installation from the Eskom point of supply before taking the point of supply readings?

    On the installation side the 0V reading between blue and white looks pretty suspect.
    The trouble with opportunity is it normally comes dressed up as work.

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    Yes I did switch off the 3 phase isolator. My suspect is there is a fault on the supply neutral

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    Quote Originally Posted by david2677 View Post
    My suspect is there is a fault on the supply neutral
    That doesn't explain the phase to phase results on the installation though.

    Your phase to phase on the supply side is only marginally distorted. Your installation phase to phase readings are way off...

    Which indicates the possibility of a cable fault or incorrect connection (which might be what is distorting the supply neutral readings).
    The trouble with opportunity is it normally comes dressed up as work.

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    Diamond Member AndyD's Avatar
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    Your tests are incomplete, you didn't give a Ze or state N-E voltage or L-E voltages. Also what is 'red alone', 'white alone' and 'blue alone'? What exactly were you testing there?

    It does look like there's a high impedence neutral on the supply side but there's also something hinkey going on with the phase to phase results in the first tests that wouldn't be caused by the supply neutral problem. The results are inconsistant to the point where I'd retest from scratch if I were you and include the earth tests as well. Also prove your test equipment first on a 'known good' supply.
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    The alone readings I normally conduct on the phase to see if there is power which in this case was not necessary to include. Phase to earth was basically the same as phase to neutral. and the neutral to earth was zero

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by david2677 View Post
    The alone readings I normally conduct on the phase to see if there is power which in this case was not necessary to include.
    I don't understand what you're testing, this 'alone' result is very confusing. Every voltage test you make is from one point in the supply with respect to another point. So if you test between phases you're seeing the voltage difference between them, likewise if you test between live and neutral you're seeing the voltage difference between them. There's no such thing as an 'alone' test. You can't test the voltage of a phase compared to or with respect to nothing else.


    Quote Originally Posted by david2677 View Post
    Phase to earth was basically the same as phase to neutral. and the neutral to earth was zero
    These were your test results;

    1. Red to Neutral 320v
    2. White to Neutral 105v
    3. Blue to Neutral 105v
    4. Red to White 400v
    5. Red to Blue 400v
    6. White to Blue 0 v

    1. Red to yellow 405 v
    2. Red to blue 403 v
    3. Yellow to Blue 400 v
    4. Red to Neutral 330 v
    5. Yellow to neutral 330 v
    6. Blue to neutral 70 v

    These results are physically impossible to have simultaneously on a 3-phase supply. Try resolving the voltages into vectors on a graph and you'll see what I mean.

    I think you're either using the wrong test equipment for the job or your tester is faulty (or flat battery maybe) or you misinterpreted/misread the results or the supply developed a fault in between the tests...which is pretty unlikely.

    I'd strongly suggest you start the testing again from scratch and double check each and every one of your results using an analogue tester which will have a lower input resistance and won't give you confusing readings if capacitively coupled 'ghost' voltages are present.
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    Bronze Member mikilianis's Avatar
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    Hi david2677 when we speak of voltage we mean potential differance, the potential differance between two phases is 400 Volts, the potential differance between a phase and neutral is 230Volts, that is in a healthy circuit. Have you checked any potential differance to earth in a healthy circuit the p.d. between a phase and earth should give you a reading of 230V and there should be no p.d. between neutral and phase

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    Bronze Member mikilianis's Avatar
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    Quote Originally Posted by mikilianis View Post
    Hi david2677 when we speak of voltage we mean potential differance, the potential differance between two phases is 400 Volts, the potential differance between a phase and neutral is 230Volts, that is in a healthy circuit. Have you checked any potential differance to earth in a healthy circuit the p.d. between a phase and earth should give you a reading of 230V and there should be no p.d. between neutral and phase
    Sorry for mistake I wrote there should be no p.d. between neutral and phase I correct this should read no p.d. between neutral and earth. so a phase conducter on its own cannot give you a voltage ( p.d. ) reading,

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