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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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  • Former Community Member
    0 Former Community Member
    Nathaniel:
    Weirdbeard:

    What I have wondered with regards this situation is if an installation has equipment that can apparently disable commonly found RCDs, would this disablement also apply to other installations that share a supply, for example with looped supplies? 


    This is a question I got elsewhere a year ago, mainly about worries with solar PV installations and EV chargers affecting other customers on the network by their possible dc, and so a need to have type-B RCDs as default regardless of whether the installation included such devices. The answer: practically, no. 

     




    Thanks for the reply, are you aware of any common consumer appliances that are likely to defeat a typical 30mA RCD and render the RCD useless as additional protection against electric shock?

     


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  • Former Community Member
    0 Former Community Member
    Nathaniel:
    Weirdbeard:

    What I have wondered with regards this situation is if an installation has equipment that can apparently disable commonly found RCDs, would this disablement also apply to other installations that share a supply, for example with looped supplies? 


    This is a question I got elsewhere a year ago, mainly about worries with solar PV installations and EV chargers affecting other customers on the network by their possible dc, and so a need to have type-B RCDs as default regardless of whether the installation included such devices. The answer: practically, no. 

     




    Thanks for the reply, are you aware of any common consumer appliances that are likely to defeat a typical 30mA RCD and render the RCD useless as additional protection against electric shock?

     


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