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Omitting 30ma RCD Protection for single S/O in a domestic property

Former Community Member
Former Community Member
I installed a dedicated circuit for a hifi system for a customer last year. The customer requested a 6mm2 radial from a 16A MCB housed in its own independent consumer unit into a single, un-switched socket outlet. No problem, bit unusual but no worries.I wired it using a 3c 6mm2 armoured cable as I half anticipated the forthcoming...


The hifi equipment is causing the rcd to trip when started up. I haven't been over to have a look but I am assuming that the startup current for the many power supplies (he has told me there are ten!) coupled with electronic earth leakage is causing a CPC current that is sufficient to trip the RCD (perhaps only 16ma but enough). The earthing is high integrity having a 6mm2 cpc + armour and the Zs is sufficiently low enough that the 16A MCB can be used for fault protection. So, if this wasn't domestic I'd ditch the RCD (or replace with a 100ma) assuming that my assumptions to this point are correct.


The customer has now decided he doesn't want RCD anyway for 'reasons' but I'm still wary of removing it in a domestic situation, not because I believe the installation would become less-safe but just because it contravenes regulations.


Assuming there's no fault on the equipment and it is just a case of startup/inrush current and earth leakage, what approach would you take? Remove the RCD and write it up as a deviation from 7671 with a signed disclaimer/waiver from the customer? Install a 100ma RCD? Do nothing and walk away? Something else?


  • 0
    Much the answer I expected.


    During the week there was a discussion on the Jeremy Vine Radio 2 show about the health risks from 5G mobile networks. 


    There was a woman being interviewed who said thst she had to ask her neighbours to turn their Wi-Fi boxes off at night as they gave her headaches and made her physically ill.  Another guy being interviewed said she sounded like the neighbour from he'll. After a bit more discussion Jeremy Vine said to the woman that apparently Wi-Fi had given her genital sores, yes said the woman it has.


    I must admit I laughed at this, I can go so far with theories about electrical interference resulting in possible health risks issues and so on, but not as far as Wi-Fi causing genital sores. 


    Bit on the other hand,  just be careful of which pocket you keep your phone in.


    Andy B. 


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    Hang on Andy,


    The change was advertised quite clearly, on Page 5 of BS 7671, which says that Chapter 53 has been completely revised.

    Regulations 531.3.4.1 and 531.3.6 are definitely included in that.



    But no-one went around saying "Big change in the 18th - RCD sockets/FCUs no longer permitted" - so I still reckon it was easy to overlook that particular implication (unlike SPDs or AFDDs).

     

    the installer must ensure that such devices can provide isolation in accordance with Regulation 531.1.1



    I've been wondering about what exactly was meant by "Devices for protection against electric shock by automatic disconnection of supply shall be suitable for isolation..."


    Do they mean that if ADS is activated that the circuit must be automatically and immediately isolated (so 3mm+ contact gaps, also disconnecting N in TT systems etc) or just that the same device used for ADS can also be used for manual isolation.


    For instance, with fuses I can easily ensure a 3mm gap by pulling the fuse out, but I'm not sure I can if the fuse blows of its own accord (thinking of rewireable fuses, while the fusewire often vapourises entirely, sometimes you just end up with a small break).


    And (depending on what we decide 'low resistance' of 461.2 means) is this the end of SP switching RCBOs (and possibly single pole MCBs too).


    If it's just manual isolation is needed, then things get a lot simpler.


      - Andy.

  • 0

    AJJewsbury:




    Hang on Andy,


    The change was advertised quite clearly, on Page 5 of BS 7671, which says that Chapter 53 has been completely revised.

    Regulations 531.3.4.1 and 531.3.6 are definitely included in that.



    But no-one went around saying "Big change in the 18th - RCD sockets/FCUs no longer permitted" - so I still reckon it was easy to overlook that particular implication (unlike SPDs or AFDDs).




    Why would a change be advertised? BS 7671 never made reference to BS 7288 at all, in the 17th Edition Amendment 3 (2015) or earlier, so it's not been removed.


    Further, the change has (apprently) been made to the product standard in 2016 (between 17th AMD3 and 18th), removing the requirement for the RCD in the product to provide 3 mm isolation, and a resulting number of changes to the Scope - i.e. a MAJOR change to the use-case. Where was that advertised to the industry?

     


    the installer must ensure that such devices can provide isolation in accordance with Regulation 531.1.1






    I've been wondering about what exactly was meant by "Devices for protection against electric shock by automatic disconnection of supply shall be suitable for isolation..."


    Do they mean that if ADS is activated that the circuit must be automatically and immediately isolated (so 3mm+ contact gaps, also disconnecting N in TT systems etc) or just that the same device used for ADS can also be used for manual isolation.


    For instance, with fuses I can easily ensure a 3mm gap by pulling the fuse out, but I'm not sure I can if the fuse blows of its own accord (thinking of rewireable fuses, while the fusewire often vapourises entirely, sometimes you just end up with a small break).


    And (depending on what we decide 'low resistance' of 461.2 means) is this the end of SP switching RCBOs (and possibly single pole MCBs too).


    If it's just manual isolation is needed, then things get a lot simpler.


      - Andy.



    Well, I absolutely agree these are good discussion points and could do with some further clarification.

  • 0

    Further, the change has (apprently) been made to the product standard in 2016 (between 17th AMD3 and 18th), removing the requirement for the RCD in the product to provide 3 mm isolation, and a resulting number of changes to the Scope - i.e. a MAJOR change to the use-case. Where was that advertised to the industry?





    By this, I mean in a "special" way - there was a DPC.
  • 0
    If you go back and refer to the earlier editions of the IET Guidance Notes to the regulations you will find references to SRCD devices. 


    Is there an assumption that most domestic electrical installations have been regularly updated inline with changes to the electrical regulations and a lack of RCDs is an exception rather than what is found. 


    I can assure the committee's that there still is a general lack of RCD protection, often in the homes of older and vulnerable people who don't have the means or the wherewithal to have what was considered a perfectly safe electrical installation when it was installed updated inline with changes to the regulations. 


    It all comes to a head when they need electrical equipment installed to help them with their mobility and to allow them to continue living in their own homes 


    Having put their homes in hock to raise cash by taking "equity release" on their home to pay for adaptions to allow them to remain living in it to be told that they need to pay several hundred pounds more for an electrician to replace the existing fuse board to connect the battery charger to the new bath hoist may just be a step too far for them. 


    Andy B.
  • 0
    When does a double pole RCD become an isolator rather than a switch disconnector, which is what they are advertised as?
    https://www.toolstation.com/mk-incomers/p86327


  • 0
    British Standard?????
  • 0
    Indeed, and even if they do not meet the letter of the current standard as written, an RCD socket or spur is a good way of performing a cost-effective addition of a stair lift or whatever, such that the new bit is protected to a  level equivalent to current standards, while the rest is no more dangerous than it was the day before.

    One of the unintended consequences of regulation changes and restriction as to what is permitted, pushes up costs and in turn that does mean that the old stuff we were trying to get rid of tends to stay in service longer .

    I fear that those informing the committees, live in million pound houses in the South East, all have TNC-s  or TNS supplies, and think nothing of a few hundred quid here or there. Reality  is that further from the centre, there is TT, there are fused neutrals, and 50 year old wiring is very much still in service on BS3036 fuses, and a CU change is an expensive luxury that may have to wait it's turn.

  • 0

    mapj1:

    Indeed, and even if they do not meet the letter of the current standard as written, an RCD socket or spur is a good way of performing a cost-effective addition of a stair lift or whatever, such that the new bit is protected to a  level equivalent to current standards, while the rest is no more dangerous than it was the day before.

     




    But BS 7288:2016 itself says it's not an RCD equivalent to a BS EN 61008 or BS EN 61009 RCD ... so without further clarification on the specific points we've been discussing re BS 7671,  I'm not sure "the new but is protected to a level equivalent to current standards" - however, the former BS 7288:1990 could perhaps demonstrate it was?

     



    One of the unintended consequences of regulation changes and restriction as to what is permitted, pushes up costs and in turn that does mean that the old stuff we were trying to get rid of tends to stay in service longer .

    I fear that those informing the committees, live in million pound houses in the South East, all have TNC-s  or TNS supplies, and think nothing of a few hundred quid here or there. Reality  is that further from the centre, there is TT, there are fused neutrals, and 50 year old wiring is very much still in service on BS3036 fuses, and a CU change is an expensive luxury that may have to wait it's turn.



    Installations to previous versions of BS 7671 and the Wiring Regulations are not necessarily deemed unsafe, at least according to BS 7671 itself.


    However, it's also true industry, and standards, shouldn't stand still.


    Certainly in the case of BS 7288, there must be a reason why it says what it does ... and I'm not going to argue one way or the other on that without being in possession of the facts.

     

  • 0
    If the amendment to BS7288 in 2016 had not happened would we even be having these conversations?


    Go back to Guidance Note 1 of BS7671:2001 including amendment 1:2002 and 2:2004.


    This gives us a choice of nine types of RCD devices:
    • RCD

    • RCCB

    • RCBO

    • CBR

    • SRCD

    • PRCD

    • RCM

    • MRCD

    • SRCBOs


    It then goes on to discuss "A WIDE CHOICE" of operating currents, discrimination  and types. 


    In those days of old additional protection was called supplementary protection and was not a general requirement in domestic installations.

    7b893f2fa04f4994226085813202c456-huge-20190818_110346.jpg


    BS7288:1990 RCD devices were considered fit for purpose and as far as I know still are.


    To me the issue is that the British Standard for these devices has been rewritten in 2016 and it is the NEW VERSIONS of these devices thst are not fit for purpose  to the point I cannot understand why they are being manufactured as they do not appear to be of any use.


    BS7288:1990 devices are readily available, so why would anyone buy the new 2016 versions?


    Whilst we are at it do not forget that there are many BS4293 RCD devices still in use that are presumably still considered fit for purpose, otherwise we should be coding them on a EICR.


    I know things change and we need to keep up to current requirements, but the electrical installations unfortunately in people's homes are not frequently updated and at times there is a need to get a safe job done to the minimum standards then advise the client that actually it is time they updated the whole installation. 


    Obviously if there is a significant danger then you cannot proceed without dealing with it.


    Andy Betteridge 


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