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DC on AC supply

nicemark
I have seen a number of videos which demonstrate the problems caused by DC currents on AC supplies with respect to RCD's. An issue which is apparently increasing with increased technology applications.  Please could someone explain how DC gets back into the neutral.


Almost all PSU's in all equipment begin with an isolating transformer. So getting a significant pulsed "dc" signal back that way is not impossible but tricky. (Pulses only occurring on one side of the cycle). 


My thoughts are that the DC is most often "created" by an unbalanced waveform, with a muted positive cycle, giving an overall DC flow.


Please could you direct me to, or give examples of how DC gets into the neutral, and/or just how much of an issue it can be in some homes.
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    perspicacious:

    I was picking up on how you'd written it which said there are EV charging circuits where the pilot function which intentionally puts DC through the protective conductor ! after writing equipment that dumps DC components down the protective conductor.


    When read, this indicates that the dumping is unintentional when we know it is designed to be intentional.


    Regards


    BOD


     


    Indeed - I wasn't trying to say that use of line to protective conductor capacitors wasn't intentional - however, being really pedantic, some of those devices would not be an issue in a split-phase system, it's because we earth the three-phase star point that exacerbates the issue, both the so-called "leakage" and some of the EMC issues that noise filters are trying to handle.


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  • 0
    perspicacious:

    I was picking up on how you'd written it which said there are EV charging circuits where the pilot function which intentionally puts DC through the protective conductor ! after writing equipment that dumps DC components down the protective conductor.


    When read, this indicates that the dumping is unintentional when we know it is designed to be intentional.


    Regards


    BOD


     


    Indeed - I wasn't trying to say that use of line to protective conductor capacitors wasn't intentional - however, being really pedantic, some of those devices would not be an issue in a split-phase system, it's because we earth the three-phase star point that exacerbates the issue, both the so-called "leakage" and some of the EMC issues that noise filters are trying to handle.


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