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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
    In that photo of the now out of date IET Guidance Note above read the last paragraph warning about not putting a RCD where someone who is elderly or infirmed cannot get to reset it.


    Some years ago I spoke to a member of this forum at an Elex show, he had a contract to install electrical supplies for kidney dialysis machines being installed in peoples homes, not unsurprisingly he installs the RCD on the wall next to the machine so it is accessible to the user of the machine whilst they are connected to it.


    There isn’t always a one size fits all solution to the issues that life throws up when it comes to retrofitting RCD protection in electrical installations.


    It is a requirement that electrical installations are safe, but they also need to serve specific purposes.


    Going back to the original post of this actual discussion, omitting RCD protection from sockets that supply HiFi equipment because of some notion that it improves sound quality is not acceptable. I have actually had to have this conversation with people and have walked away from doing jobs because they argued they didn’t want a RCD installed, as I have when people have refused to have installations made safe before undertaking alterations or extensions.


     Andy Betteridge
  • Former Community Member
    0 Former Community Member
    Just an update on this one:


    I have been able to assess the problem and it is not the RCD which is tripping (as the customer told me) but the MCB due to inrush current (I think someone called it earlier). Replaced with a C16 and all is sorted.

    Going back to the original post of this actual discussion, omitting RCD protection from sockets that supply HiFi equipment because of some notion that it improves sound quality is not acceptable.



    Obviously. That wasn't the customer's complaint though, it was that the "RCD" (actually MCB) was tripping, not that it affected the sound, although he did suggest that it might. Installation of an RCD will of course alter the characteristic of the incoming supply to the hi-fi equipment, nobody is arguing that, but the suggestion that it perceivably alters the sonic quality of a hifi system is very dubious.


    Thanks all for the interesting discussion, even if it did amount to not much in the end!
  • 0

    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.




    A reference to BS 7288 might not have been removed in a textual or editorial sense, but when a requirement that allows you to use any device you like provided it's rated at 30mA and opens within 40ms at 5xIΔn (so included BS 7288 devices) changes to a short list of specific devices (which didn't include BS 7288) it's certainly a logical or meaningful deletion. (Changes to BS 7288 notwithstanding.)

     




    BS 7288:2016 clearly states in the scope that SRCDs to that standard must have fault protection and additional protection upstream of the SRCD.




    I've been wondering about that. The words as reported don't seem to make sense to me (as has already been mentioned, what's the point in an RCD socket or FCU if the supplying circuit already needs its own 30mA RCD protection?) - and I can't see the context in which it's been written - but could it have been intended to say something along the lines of: the circuit upstream of the device will need to have been provided with any additional protection required for that circuit (which might be 30mA RCD protection, or supplementary bonding, or (more usually) nothing at all - depending on the circumstances) - i.e. it's just attempting to emphasis the point that the device only provides downstream protection and you might still need something else if the supply cables are concealed in wall or run within a bathroom or whatever.




    If that were the case, and if isolation is permitted to be manual, (e.g. removing the plug for a SRCD or throwing the DP switch on a FCURCD) then the reasons for omitting BS 7288 from BS 7671's list of permitted devices becomes less clear.


       - Andy.
  • 0
    So, the acid safety test is "does an RCD socket, or a spur to BS 7288 of any revision, provide an equivalent level of safety to a circuit with an upstream RCD, when fitted to an otherwise identical circuit with no RCD protection upstream.? "


    I'd suggest that for an end user holding a portable widget or leaning on the class I appliance, the list of fault conditions it mitigates are similar, nay, identical, but without the extra trudge to reset or test it. Of course it cannot protect cables in the walls, but that is a given, and they could be in earthed conduit or surface wired for the purposes of this thought experiment.
  • 0

    AJJewsbury:

    ... and I can't see the context in which it's been written ...




    Andy, please see my posting of 11 Aug, which gives some context.

  • 0

    Andy, please see my posting of 11 Aug, which gives some context.



    I had thanks - it was the preceding sentence (my emphasis):


    :

    SRCDs are only intended to provide supplementary protection downstream of the SRCD.     SRCDs are intended for use in circuits where the fault protection and additional protection are already assured upstream of the SRCD.

    :





    that hinted to me that the author (or authoring committee) might have had a particular point in mind that perhaps wasn't expressed clearly in the words of the second of those sentences when taken alone. However I'm always a bit uneasy reading bit of text extracted from a larger document  - a sometimes a preceding paragraph or chapter title on the bottom of the previous page can shed quite a different light on things.


      - Andy.
  • 0
    Do Type EV and Type B RCDs provide additional protection?


    Andy Betteridge
  • 0

    Sparkingchip:

    Do Type EV and Type B RCDs provide additional protection?


    Andy Betteridge 




    Can a Type B 30 mA RCD that complies with IEC62423 (EN62423) be used to provide additional protection?



    Andy Betteridge
  • 0

    Can a Type B 30 mA RCD that complies with IEC62423 (EN62423) be used to provide additional protection?



    I don't see why not - BS EN 62423 is listed under 531.3.6 (RCDs for additional protection) as well as 531.3.4.1 (RCDs - selection according to the accessibility of the installation - ordinary persons).


      - Andy.
  • 0

    AJJewsbury:




    Andy, please see my posting of 11 Aug, which gives some context.



    I had thanks - it was the preceding sentence (my emphasis):


    :

    SRCDs are only intended to provide supplementary protection downstream of the SRCD.     SRCDs are intended for use in circuits where the fault protection and additional protection are already assured upstream of the SRCD.

    :





    that hinted to me that the author (or authoring committee) might have had a particular point in mind that perhaps wasn't expressed clearly in the words of the second of those sentences when taken alone. However I'm always a bit uneasy reading bit of text extracted from a larger document  - a sometimes a preceding paragraph or chapter title on the bottom of the previous page can shed quite a different light on things.


    Well, no form of RCD could protect the circuit upstream.


    BS 7288 states that the characteristics of circuit-protective and socket-protective RCDs are different, but doesn't seem to describe the differences or explain them.


    At one time, Hampshire Libraries subscribed to the British Standards, but no more. Happily for me, as an Open University student, I have access through its library.

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