"17 edition"consumer units still being sold.

Andy are you suggesting that a short to case after a rectifier makes a DC fault? First the fault current available is on average half the PSSC, and secondly if there is a large capacitor there as well the fault current will be the whole PSSC. This will not trip the CPD I suppose! Also it is not a DC fault, hence my comment above about smooth and continuous DC, because a single rectifier will give an AC fault current which WILL operate the RCD. Getting a DC fault on a mains powered piece of equipment is much more difficult than you are imagining, and is very unlikely without multiple faults being present, most of which would stop the equipment operating at all. Imagine the PSSC at a socket is only 100A, how long do you think even a 10A rectifier diode will last, across the mains? It might last 1 or 2 cycles and by then the CPD will have tripped. Take an induction hob. Is there any smooth DC there at all? Probably not in a form you would recognise, as the induction circuit probably works off straight rectified DC, with the usual full wave rectified waveform in order to provide unity power factor! The idea that electronics can provide sources of the DC current as used in the video, or my RCD experiments, by accident due to faults is living in a fantasy where broken electronics still work perfectly (which is never!). This rectified waveform will trip an RCD just fine, but just how many faults do you need to get it to a person who gets a shock from the earthed case?


I am not particularly suggesting that type AC RCDs are ideal or adequate in all cases, but as they are almost exactly the same as a type A, perhaps with a better current transformer costing very little extra, perhaps the manufacturers would like to sell them at the same price? There is no reason why they should cost more here than across Europe, we are supposed to have a level playing field (Barnier!).


Hertzal123, there is a lot more to this than the words DC might indicate, and the complexities need sorting by JPEL/64 if anywhere. Just stick to BS7671 and there will not be any problems for you. Anyone with any doubts should probably study the problems themselves by experiment, you will find the learning to be fun, and very worthwhile. Transformers of all sizes respond to changing currents through the windings. DC does not stop them completely even if saturated, a larger AC current in the opposite direction still gives secondary current some of the time, and so this is only a potential difficulty where the RCD is used for additional (personal) protection. Those used for ADS on TT will not stop working with Earth faults even with some DC. In the video you will notice that the DC curents used are fairly small, nothing like that which Andy is considering above with direct short faults. With amperes of DC no type will work at 30mA and will need amperes of fault to trip at all. It is a subtle matter of degree.

Andy are you suggesting that a short to case after a rectifier makes a DC fault? First the fault current available is on average half the PSSC, and secondly if there is a large capacitor there as well the fault current will be the whole PSSC. This will not trip the CPD I suppose! Also it is not a DC fault, hence my comment above about smooth and continuous DC, because a single rectifier will give an AC fault current which WILL operate the RCD. Getting a DC fault on a mains powered piece of equipment is much more difficult than you are imagining, and is very unlikely without multiple faults being present, most of which would stop the equipment operating at all. Imagine the PSSC at a socket is only 100A, how long do you think even a 10A rectifier diode will last, across the mains? It might last 1 or 2 cycles and by then the CPD will have tripped. Take an induction hob. Is there any smooth DC there at all? Probably not in a form you would recognise, as the induction circuit probably works off straight rectified DC, with the usual full wave rectified waveform in order to provide unity power factor! The idea that electronics can provide sources of the DC current as used in the video, or my RCD experiments, by accident due to faults is living in a fantasy where broken electronics still work perfectly (which is never!). This rectified waveform will trip an RCD just fine, but just how many faults do you need to get it to a person who gets a shock from the earthed case?


I am not particularly suggesting that type AC RCDs are ideal or adequate in all cases, but as they are almost exactly the same as a type A, perhaps with a better current transformer costing very little extra, perhaps the manufacturers would like to sell them at the same price? There is no reason why they should cost more here than across Europe, we are supposed to have a level playing field (Barnier!).


Hertzal123, there is a lot more to this than the words DC might indicate, and the complexities need sorting by JPEL/64 if anywhere. Just stick to BS7671 and there will not be any problems for you. Anyone with any doubts should probably study the problems themselves by experiment, you will find the learning to be fun, and very worthwhile. Transformers of all sizes respond to changing currents through the windings. DC does not stop them completely even if saturated, a larger AC current in the opposite direction still gives secondary current some of the time, and so this is only a potential difficulty where the RCD is used for additional (personal) protection. Those used for ADS on TT will not stop working with Earth faults even with some DC. In the video you will notice that the DC curents used are fairly small, nothing like that which Andy is considering above with direct short faults. With amperes of DC no type will work at 30mA and will need amperes of fault to trip at all. It is a subtle matter of degree.