RCD socket outlet.

"Aren’t the SRCD trip times faster?


Andy B. I`m not sure that this is the case.


Our old BS for RCDs was within 200ms at x1 wheras the EN we now all use is within 300ms at x1, which in itself makes our old standard appear superior.

However I find that in practice all of the functioning RCDs I`ve tested trip well within those times of both standards. In fact if I found one that approached say 90ms area I would be very alarmed as I once was when a pal of mine tested two RCDs on a connected circuit. We soon established the number of fridges/freezers running to be skewing the results.


Anyone else concour or disagree (mine is only a limited sample)?

I think it more embarrassment and a need to regroup and replan.


There has been a huge amount of time and money invested in the new SRCD and FCURCD devices manufactured to the new version of the British Standard that you are being advised not to install.


There was a comment above that we may see these devices being tested and sold as approved to three British Standards including BS 61008, I wonder how far off complying they already are?


Andy Betteridge

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.

'you will find the things related to the discussion have disappeared'


I love a good conspiracy...

I love my rcd double socket, it's been in around 2 years but so many stores sell them I can't remember where I bought it. B andQ? Wickes? Screw fix? Homebase? Tool shop? Hundreds of thousands of hardware shops all over the country. And so easy to fit, about 15 mins. Testing? The circuit feeding it, loop test 0.3, time? about 10 ms. Backed up by an MCB. Great for when I am using the mower, working on the car in the garage, the list is endless. They devices are everywhere, so many people have got them. Save you or your families life. And you dont have to walk through the house to reset yet another trip.

Regards, UKPN

So why should I not rely on an SRCD?


I agree with your sentiment completely Chris but if the standard says I shouldn't do it then I cannot go against their express instruction. Here is a recent publication you may have already read that is a gamut of information on all RCDs but curiously when it comes to list all the BS numbers at the end BS7288 isn't there.
http://www.beama.org.uk/resourceLibrary/the-rcd-handbook---guide-to-the-selection-and-application-of-residual-current-devices.html

Aren’t the SRCD trip times faster?


Andy B.

It seems to me that the reason this subject is so topical now is because the old BS7288 has only just ceased to be current.

BS7288 2016 says, 'SRCDs are intended for use in circuits where the fault protection and additional protection are already assured upstream of the SRCD.' 

BS7288 1990 has only just ceased to be current (30 Nov 2019)

BS7671 has never listed BS7288 as being suitable additional protection.

BS7288 products have improved their testing standards but still do not match the standard applied to BSEN 61008.

Quite why it has taken 30 years to have the blinkers removed on this subject, despite questions through the ages, is beyond me.

A big shout out to John Peckham for his valuable insights.


Having said that, I wouldn't want to see a decline in use of SRCD's.