Type A rcd . EICR coding ? etc

That is a very good synopsys of RCD design Nathaniel. In reading it I hope that many of you find it rather primitive and that the specification seems to have been written after the device is made to work, rather than before as might be expected. What alternatives do we have to a differential current transformer based design? If we really want DC sensitivity, a transformer is difficult, so we need to consider other DC connected measuring methods. One would be a Hall sensor in the magnetic circuit of the differential core, which would measure both AC and DC differential current. Obviously this would need some amplification and level detection, but at the expense of a very small current would be easy enough. It would be important that the core could not become permanantly magnetised by a large differential fault current, something which does seem to happen to standard RCDs sometimes. A big enough core of hard magnetic material should be able to sort that problem. There is little reason for this to cost any more than a complex mechanical arrangement, and we could control the tripping characteristic fairly easily. It could be faster or slower, have adjustable trip current, and have a big a solenoid driven by a semiconductor  to ensure that "sticking" was very unlikely. This must be more reliable than a mechanical version, a million hour MTBF would not be unlikely (about 100 years).

That is a very good synopsys of RCD design Nathaniel. In reading it I hope that many of you find it rather primitive and that the specification seems to have been written after the device is made to work, rather than before as might be expected. What alternatives do we have to a differential current transformer based design? If we really want DC sensitivity, a transformer is difficult, so we need to consider other DC connected measuring methods. One would be a Hall sensor in the magnetic circuit of the differential core, which would measure both AC and DC differential current. Obviously this would need some amplification and level detection, but at the expense of a very small current would be easy enough. It would be important that the core could not become permanantly magnetised by a large differential fault current, something which does seem to happen to standard RCDs sometimes. A big enough core of hard magnetic material should be able to sort that problem. There is little reason for this to cost any more than a complex mechanical arrangement, and we could control the tripping characteristic fairly easily. It could be faster or slower, have adjustable trip current, and have a big a solenoid driven by a semiconductor  to ensure that "sticking" was very unlikely. This must be more reliable than a mechanical version, a million hour MTBF would not be unlikely (about 100 years).