RCD socket outlet.

Thanks for replying GK, but if The product BS was not listed 10 years ago in BS7671, I am not entirely sure how it is more relevant that is still not included in the latest edition! 

Previous editions of BS 7671 didn't specify acceptable RCD by product standard - they just said words to the effect of '30mA RCD that trips within 40ms at 5x I_Δn' so you were free to pick any type you liked as long as it would do that. The latest edition however takes a different approach - it no longer specifies the required perormance at 150mA but instead specifies certain product standards the RCD must comply with - and BS EN 61008, 61009, etc. are on the list, but BS 7288 isn't.


There might have been several reasons for the change in approach - not least the reports that some BS EN 61008/9 devices haven't been tripping within 40ms at 150mA - and the realization that their product standard permits that (as long as they trip within 40ms at 250mA) - which had apparently lead to some aggro between manufacturers (working to BS EN 61008 etc) and electricians (working to BS 7671).


Then there's the question of why BS 7288 wasn't put on the list. One theory was that the list was copied from EN/CENELEC standards which naturally lacked references to UK specific devices - and nobody thought to add them in. Another report is that BS 7288 itself rules itself out at a useful product. Certainly the quoted wording from BS 7288 is magnificently lacking in clarity - it hardly seems credible that a product standard for 30mA RCDs would demand the presence of an 30mA RCD upstream - making their entire product range about as much use as a chocolate teapot - but the wording is certainly open to that interpretation (even though it doesn't actually say upstream 30mA RCD is required - there are other methods of additional protection). Personally I still think it far more likely that they were just trying to emphasise the point from earlier in the same paragraph that the device (naturally) provides no protection upstream and where additional protection is also required upstream it needs to be provided elsewhere (or the need for it avoided). But the words certainly don't clearly say that, and it's a pretty fundamental rule of the BSI that things must be based on what standards actually say, rather than what someone thinks the committee originally had in mind (or should have had in mind), so I can see that JPEL/64 might have their hands tied on that one (at least until someone can jolt the committee behind BS 7288 to issue a corrigendum).


BS 7671 doesn't do itself any favours either - e.g. the requirements for devices selected for ADS etc to provide isolation - which feeds into the argument about contact gaps on BS 7288 device - BS 7671 isn't at all clear whether the isolation function needs to operate when the device opens automatically or whether manual only facility on the same device would be acceptable. So for fuses does the melting of the fuse element necessarily have to provide the necessary gaps for isolation, or is just pulling the fuse carrier acceptable? Or, for this discussion, is a small contact gap on a SRCD acceptable if isolation can be achieved by means of the switch or removing the fuse in the same unit? The apparent lack of official explanation from the IET etc and apparently contradictory information from manufacturers hasn't helped either.


Interesting times, as they say, when they want to be polite about an avoidable mess that can't be solved by those most affected by it.


   - Andy.

Thanks for replying GK, but if The product BS was not listed 10 years ago in BS7671, I am not entirely sure how it is more relevant that is still not included in the latest edition! 

Previous editions of BS 7671 didn't specify acceptable RCD by product standard - they just said words to the effect of '30mA RCD that trips within 40ms at 5x I_Δn' so you were free to pick any type you liked as long as it would do that. The latest edition however takes a different approach - it no longer specifies the required perormance at 150mA but instead specifies certain product standards the RCD must comply with - and BS EN 61008, 61009, etc. are on the list, but BS 7288 isn't.


There might have been several reasons for the change in approach - not least the reports that some BS EN 61008/9 devices haven't been tripping within 40ms at 150mA - and the realization that their product standard permits that (as long as they trip within 40ms at 250mA) - which had apparently lead to some aggro between manufacturers (working to BS EN 61008 etc) and electricians (working to BS 7671).


Then there's the question of why BS 7288 wasn't put on the list. One theory was that the list was copied from EN/CENELEC standards which naturally lacked references to UK specific devices - and nobody thought to add them in. Another report is that BS 7288 itself rules itself out at a useful product. Certainly the quoted wording from BS 7288 is magnificently lacking in clarity - it hardly seems credible that a product standard for 30mA RCDs would demand the presence of an 30mA RCD upstream - making their entire product range about as much use as a chocolate teapot - but the wording is certainly open to that interpretation (even though it doesn't actually say upstream 30mA RCD is required - there are other methods of additional protection). Personally I still think it far more likely that they were just trying to emphasise the point from earlier in the same paragraph that the device (naturally) provides no protection upstream and where additional protection is also required upstream it needs to be provided elsewhere (or the need for it avoided). But the words certainly don't clearly say that, and it's a pretty fundamental rule of the BSI that things must be based on what standards actually say, rather than what someone thinks the committee originally had in mind (or should have had in mind), so I can see that JPEL/64 might have their hands tied on that one (at least until someone can jolt the committee behind BS 7288 to issue a corrigendum).


BS 7671 doesn't do itself any favours either - e.g. the requirements for devices selected for ADS etc to provide isolation - which feeds into the argument about contact gaps on BS 7288 device - BS 7671 isn't at all clear whether the isolation function needs to operate when the device opens automatically or whether manual only facility on the same device would be acceptable. So for fuses does the melting of the fuse element necessarily have to provide the necessary gaps for isolation, or is just pulling the fuse carrier acceptable? Or, for this discussion, is a small contact gap on a SRCD acceptable if isolation can be achieved by means of the switch or removing the fuse in the same unit? The apparent lack of official explanation from the IET etc and apparently contradictory information from manufacturers hasn't helped either.


Interesting times, as they say, when they want to be polite about an avoidable mess that can't be solved by those most affected by it.


   - Andy.