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Thread: Testing Phase rotation with a capacitor

  1. #1
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    Testing Phase rotation with a capacitor

    I keep hearing there's a way you can determine 3 phase rotation with a capacitor and multi meter,
    Some how the capacitor causes a phase shift when its between one leg and the other causing voltages to read differently or something like that,
    Just wondering If anyone else has heard of this

  2. #2
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    Quote Originally Posted by karn View Post
    I keep hearing there's a way you can determine 3 phase rotation with a capacitor and multi meter,
    Some how the capacitor causes a phase shift when its between one leg and the other causing voltages to read differently or something like that,
    Just wondering If anyone else has heard of this
    Your the first t bring it to my attention. I don’t see it happening but I’m a skeptic.

    I want know how charging a cap through a meter would show anything.
    Tom
    TBLO

  3. #3
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    With my previous statement in mind, I don’t know how my FLUKE T+Pro does it. A bit more involved than just a meter and capacitor.
    Tom
    TBLO

  4. #4
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    I was wondering myself how it would work, I've only heard about it but don't know of the details

  5. #5
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    Quote Originally Posted by ptonsparky View Post
    With my previous statement in mind, I don’t know how my FLUKE T+Pro does it. A bit more involved than just a meter and capacitor.
    The T+Pro confused me so much when I first saw it that I didn't believe that feature was real. It obviously does work (although I'm not sure how reliable it is), so I set out to understand how. The instruction manual gives it away: the meter uses your body as a third reference point, and senses capacitive coupling of the two phases to your body through the meter's case. That's why it only works on utility-connected systems, and only if you hold the meter and the probes exactly the way they tell you to. By comparing the phase relationship of the two capacitively coupled waveforms (red probe to user, and black probe to user) it can determine the phase rotation just like any other rotation indicator. It's just sensitive enough to use you as a "virtual" reference point, like a non-contact voltage tester. Clever!

  6. #6
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    181012-2142 EDT

    Try a wattmeter with the capacitor. A wattmeter takes the instantaneous product of voltage and current, averages the product to produce an average reading.

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  7. #7
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    You can do it with a couple of lamps and a capacitor. I don't know how you would do it with just a cap and meter.

    Try a search for "static phase sequence indicators".

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