Type A rcd . EICR coding ? etc

What I find most worrying with type AC is that there is no guarantee that it will even trip for half-wave rectified current, i.e. a fault via a single diode. That's not a strange type of fault.  I have tested some RCDs that are marked AC yet behave largely as A. But I've also met AC ones that will not trip even for many times the rated residual operating current when it's half-wave rectified in one direction: the other direction will typically work (I've a feeling I already explained the reason for this sometime in the spring). Type AC is not required (by IEC6100[89]) to trip for any half-wave waveform.


Given that many loads contain diodes connected to their inputs, I think it's very desirable to protect against accidental contact with such parts or against earth faults from such parts in TT systems.  A plausible range of earthing resistance in a TT system could result in such a fault continuing without tripping an RCD or breaking the diode.


If it cost a lot more to be sensitive to half-wave rectified AC, there'd be a justification for considering more of the cost/benefit of what harms are caused by earth-fault-through-diode situations.  However, the cost difference is negligible between AC and A ... this claim will probably raise some eyebrows, so let me explain more: when regulations are sloppy, as previously in the UK, almost everyone does the cheapest thing, so ready-made CUs come with AC, retailers stock mainly or only AC, and A becomes a more specialised device with a higher price-tag (because they can, or because the admin is divided between a few sales, or whatever). If none of type AC are sold, type A becomes practically the same price as AC was.  The difference is basically in the magnetic material used. I made a study of the prices a year ago, comparing prices in the UK and France (which widely use AC) with Germany and Sweden (which don't use AC).  There's some difficulty in comparison due to the fact that one bloc would commonly use 2pole RCDs of higher current rating, and the other would commonly switch to 4pole for loads above 16A or so.  But basically, you can get an AC or A RCD for around the £25 mark.  More recently I see many RCDs in the UK becoming type A, such as some BG(manufacturer) ones I bought recently, without increased price from the older AC models that have quietly been replaced. 


So, I maintain that among all the safety choices in recent regulations, getting protection from through-diode earth faults for negligible extra cost is pretty much top of the list, compared to more sophisticated RCD types, EV worries (UK specific), and let alone AFDDs!  However, I take the point that there might not even be a demonstrable case of harm that would have been avoided by type A instead of AC. I'd be surprised, but I can't point out a case (anyone?).


As indicated above, it is not the case that all of Europe is happy with type AC.  On the contrary, Germany doesn't recognise them for

 RCD protection of anything. Sweden doesn't have them to find on sale. (It's a puzzling distribution, where countries more known for using TT systems, e.g. France, appear less averse to type AC.)


Moving from type AC was the main thing I thought good in the recent proposal.

What I find most worrying with type AC is that there is no guarantee that it will even trip for half-wave rectified current, i.e. a fault via a single diode. That's not a strange type of fault.  I have tested some RCDs that are marked AC yet behave largely as A. But I've also met AC ones that will not trip even for many times the rated residual operating current when it's half-wave rectified in one direction: the other direction will typically work (I've a feeling I already explained the reason for this sometime in the spring). Type AC is not required (by IEC6100[89]) to trip for any half-wave waveform.


Given that many loads contain diodes connected to their inputs, I think it's very desirable to protect against accidental contact with such parts or against earth faults from such parts in TT systems.  A plausible range of earthing resistance in a TT system could result in such a fault continuing without tripping an RCD or breaking the diode.


If it cost a lot more to be sensitive to half-wave rectified AC, there'd be a justification for considering more of the cost/benefit of what harms are caused by earth-fault-through-diode situations.  However, the cost difference is negligible between AC and A ... this claim will probably raise some eyebrows, so let me explain more: when regulations are sloppy, as previously in the UK, almost everyone does the cheapest thing, so ready-made CUs come with AC, retailers stock mainly or only AC, and A becomes a more specialised device with a higher price-tag (because they can, or because the admin is divided between a few sales, or whatever). If none of type AC are sold, type A becomes practically the same price as AC was.  The difference is basically in the magnetic material used. I made a study of the prices a year ago, comparing prices in the UK and France (which widely use AC) with Germany and Sweden (which don't use AC).  There's some difficulty in comparison due to the fact that one bloc would commonly use 2pole RCDs of higher current rating, and the other would commonly switch to 4pole for loads above 16A or so.  But basically, you can get an AC or A RCD for around the £25 mark.  More recently I see many RCDs in the UK becoming type A, such as some BG(manufacturer) ones I bought recently, without increased price from the older AC models that have quietly been replaced. 


So, I maintain that among all the safety choices in recent regulations, getting protection from through-diode earth faults for negligible extra cost is pretty much top of the list, compared to more sophisticated RCD types, EV worries (UK specific), and let alone AFDDs!  However, I take the point that there might not even be a demonstrable case of harm that would have been avoided by type A instead of AC. I'd be surprised, but I can't point out a case (anyone?).


As indicated above, it is not the case that all of Europe is happy with type AC.  On the contrary, Germany doesn't recognise them for

 RCD protection of anything. Sweden doesn't have them to find on sale. (It's a puzzling distribution, where countries more known for using TT systems, e.g. France, appear less averse to type AC.)


Moving from type AC was the main thing I thought good in the recent proposal.