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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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    No such design  exists - as far as I know they all need a current transformer, as the L and N do one turn of the core as they have such a large bend radius, while the actuation wiring is thin. Once you have a core, n the secondary you have current reversal, even if on the primary you don't.

    It is Nathaniel, not I who made the point about the permanent magnet version - and they will only release on the part of the ripple waveform that opposes the permanent magnet, so inversion of that will affect the trip time (in the sense of the instant in the cycle when the latch releases), but not the fact that it will at some point in the cycle trip.

    M.
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  • 0
    No such design  exists - as far as I know they all need a current transformer, as the L and N do one turn of the core as they have such a large bend radius, while the actuation wiring is thin. Once you have a core, n the secondary you have current reversal, even if on the primary you don't.

    It is Nathaniel, not I who made the point about the permanent magnet version - and they will only release on the part of the ripple waveform that opposes the permanent magnet, so inversion of that will affect the trip time (in the sense of the instant in the cycle when the latch releases), but not the fact that it will at some point in the cycle trip.

    M.
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