RPC Voltage question.
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  1. #1
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    Default RPC Voltage question.

    Hi, trying to wire up a 10 hp RPC. Starts and runs fine, but buzzes pretty loudly. L1-ground is 115v. L2-ground is 120v. L3-ground is 260v. L1-L2 is 240v. L2-L3 is 280v. L1-L3 is 260v. Is this ok?

    Paul

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    Provide a drawing of the circuit.

    Identify what part is buzzing.

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    I am guessing the voltages that are at 260 and 280 are to the generated leg.

    I am also guessing that you have "balance capacitors" in place.

    The 280V is so high that it is way out of the normal highest voltage for 240VAC. That may be the source of the buzzing. Assuming you DO have balance capacitors on it, take them off (disconnect) and see if it still buzzes as well as has high voltage..

    Circuit diagram would help.

    And do not bother to measure to ground, that is always misleading.
    .

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    I was trying not to guess but,

    If there is no load motor connected then 280Vac might not be too bad.

    What is buzzing is probably the contactor. A circuit diagram drawn by hand would probably clear up the problem.
    Last edited by rons; 02-05-2020 at 09:04 AM.

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    Thankyou! Will get a diagram tomorrow. Don't have a load hooked up, will hook up a motor and retest.
    Yes there are balancing caps.
    Paul

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    With no load the wild legs to natural should not be too much higher than 260 V at idle. Under full load, the wild legs to natural should not be too much under 210 V. During a machine start, they can drop below 210 V for maybe six seconds. But… I don’t like to see it drop too much below 160 V for more than two seconds.

    If you want to test the wild leg to ground, it should be close to 208 V while the machines are online.

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    Buzzing is almost always the contactor.

    Take it apart and clean it. lightly file the contacts. Or some can be turned over for a brand new surface.

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    Quote Originally Posted by Matt Matt View Post
    With no load the wild legs to natural should not be too much higher than 260 V at idle. Under full load, the wild legs to natural should not be too much under 210 V. During a machine start, they can drop below 210 V for maybe six seconds. But… I don’t like to see it drop too much below 160 V for more than two seconds.

    If you want to test the wild leg to ground, it should be close to 208 V while the machines are online.

    Yes. The maximum high voltage for a nominal 240V power line is 264V (corresponding to a 120V max of 132V). That is the UL/CE max voltage at which the 240V equipment needs to be safe as far as overheating, etc. And it is a "maximum", the "tolerance" is between 240V and 264V.

    Not a good idea to go over that limit, especially for things like contactor coils, transformers , etc, that may still be powered at the no load condition..

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    quick diagram.

    img_8314.jpg

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    Check that your timer/relay is performing a one-shot operation correctly. If the chattering noise is coming from the small relay then
    it is not working correctly.

    You have a run capacitor array consisting of six capacitors between L2 and what I am calling T3 (going out to the motor). But no run capacitor between L1 and T3.
    You won't get a good set of balance voltages that way.

    A schematic drawing does not reflect the orientation of parts in a box. It is drawn with clarity in mind and should have component part numbers and values.
    Last edited by rons; 02-06-2020 at 09:36 AM.

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    Thanks to all who have replied! I will digest the info and do some testing.
    Paul


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