DC on AC supply

Broadgage, none of those things are "DC mains current", they are distorted mains AC waveforms. Above I gave a definition of DC, and none of these meet it. A half-wave rectified waveform will pass through a transformer and the only thing which does not is a waveform where dV/dt (the rate of change of voltage/current) is zero. An RCD differences two dI/dt waveforms and the resultant is the leakage current. The DC we are talking about here is a real DC current (dI/dt = 0) which is present on only one of the windings, usually the N-E bond and DC-fault in an appliance between some version of the supply and Earth.


The overall problem with all this is that the "what if" brigade has tried to find a reason to fit more complex and expensive protection for less and less likely faults. A proper analysis says that many of these faults are not dangerous to persons, need at least two faults to occur simultaneously (such as an undetected DC fault and an accidental touch of a phase conductor), and the likelihood is probably similar to being hit by a falling piece of an aeroplane flying overhead. It is much more likely that such faults disconnect for other reasons, and result in appliance failure, which is a nuisance but not dangerous.  If we apply a similar criterion to roads, nothing except slow-walking would be allowed, and certainly no 2 wheeled devices, or use at all if the road was frosty or covered in snow. Just like so many other things, and Covid is one of them, "Authority" has gone too far, with extremely dire consequences for everyone. I for one have not enjoyed my 1-year largely solitary confinement prison sentence, without any visits, and I have to do all my own catering as well! You will notice that the only way to make any of these things "serious" is to exaggerate the risk and use false statistics to make a case. Just how many people are killed on RCD protected circuits by contact with a live conductor and no other co-morbidities? I suggest that the number is probably zero, or possibly 1 from bad luck in the circumstances.

Broadgage, none of those things are "DC mains current", they are distorted mains AC waveforms. Above I gave a definition of DC, and none of these meet it. A half-wave rectified waveform will pass through a transformer and the only thing which does not is a waveform where dV/dt (the rate of change of voltage/current) is zero. An RCD differences two dI/dt waveforms and the resultant is the leakage current. The DC we are talking about here is a real DC current (dI/dt = 0) which is present on only one of the windings, usually the N-E bond and DC-fault in an appliance between some version of the supply and Earth.


The overall problem with all this is that the "what if" brigade has tried to find a reason to fit more complex and expensive protection for less and less likely faults. A proper analysis says that many of these faults are not dangerous to persons, need at least two faults to occur simultaneously (such as an undetected DC fault and an accidental touch of a phase conductor), and the likelihood is probably similar to being hit by a falling piece of an aeroplane flying overhead. It is much more likely that such faults disconnect for other reasons, and result in appliance failure, which is a nuisance but not dangerous.  If we apply a similar criterion to roads, nothing except slow-walking would be allowed, and certainly no 2 wheeled devices, or use at all if the road was frosty or covered in snow. Just like so many other things, and Covid is one of them, "Authority" has gone too far, with extremely dire consequences for everyone. I for one have not enjoyed my 1-year largely solitary confinement prison sentence, without any visits, and I have to do all my own catering as well! You will notice that the only way to make any of these things "serious" is to exaggerate the risk and use false statistics to make a case. Just how many people are killed on RCD protected circuits by contact with a live conductor and no other co-morbidities? I suggest that the number is probably zero, or possibly 1 from bad luck in the circumstances.