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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?


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  • 0
    An interesting debate.


    I suggest that BS 7671:2018 has made BS 7288 obsolete for new circuits.


    BS 7288:2016 Scope:

    This British Standard applies to residual current-operated devices (RCD) incorporated in, or specifically intended for use with, single pole and neutral and single pole and switched neutral and double pole socket-outlets, with provision of earthing of the socket-outlet for household and similar uses (SRCD: socket-outlet residual current devices). SRCDs, according to this standard, are intended to be used in single phase systems such as phase to neutral. 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. (My emphasis)


    Wires in walls,sockets, and now lights all need RCD protection at the origin of the circuit, so why provide it at a socket?


    As for isolation, BS 7288:2016 introduction:

    The isolation function is not necessary since pulling out the plug from the socket-outlet is recognized as providing effective isolation. The absence of permanently connected long conductors downstream of the RCD, together with a limited number of powered appliances, justifies reduced EMC levels. Residual current devices covered by this standard are intended for additional protection in case of direct contact only. These particular features having been considered, it was recognized that a dedicated standard for socket-outlet residual current devices (SRCDs) was necessary.


    Then we have the reason for SRCDs (back to scope):

    SRCDs are only intended to provide supplementary protection downstream of the SRCD.


    Supplementary protection is not defined in either BS 7288 or BS7671, but may have been in previous editions.


    What is clear to me is that there is no requirement for a chain of RCDs.


    So why make them?


    It seems that MK no longer make RCD FCUs (Sentryspur).


    I suggest that the answer is (1) like for like replacement in older installations; (2) when a customer (or DIYer) wants RCD protection without going to the bother and expense of fitting RCD protection at the origin of the circuit; and more obviously, where the fitting of RCD protection in the CU is impossible.


    Oh, and by the way, there is no statutory requirement to work to the current regulations.


    Back to the OP: if this was a new circuit, it cannot be compliant without a 61008/9 device at the origin of the circuit.
Reply
  • 0
    An interesting debate.


    I suggest that BS 7671:2018 has made BS 7288 obsolete for new circuits.


    BS 7288:2016 Scope:

    This British Standard applies to residual current-operated devices (RCD) incorporated in, or specifically intended for use with, single pole and neutral and single pole and switched neutral and double pole socket-outlets, with provision of earthing of the socket-outlet for household and similar uses (SRCD: socket-outlet residual current devices). SRCDs, according to this standard, are intended to be used in single phase systems such as phase to neutral. 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. (My emphasis)


    Wires in walls,sockets, and now lights all need RCD protection at the origin of the circuit, so why provide it at a socket?


    As for isolation, BS 7288:2016 introduction:

    The isolation function is not necessary since pulling out the plug from the socket-outlet is recognized as providing effective isolation. The absence of permanently connected long conductors downstream of the RCD, together with a limited number of powered appliances, justifies reduced EMC levels. Residual current devices covered by this standard are intended for additional protection in case of direct contact only. These particular features having been considered, it was recognized that a dedicated standard for socket-outlet residual current devices (SRCDs) was necessary.


    Then we have the reason for SRCDs (back to scope):

    SRCDs are only intended to provide supplementary protection downstream of the SRCD.


    Supplementary protection is not defined in either BS 7288 or BS7671, but may have been in previous editions.


    What is clear to me is that there is no requirement for a chain of RCDs.


    So why make them?


    It seems that MK no longer make RCD FCUs (Sentryspur).


    I suggest that the answer is (1) like for like replacement in older installations; (2) when a customer (or DIYer) wants RCD protection without going to the bother and expense of fitting RCD protection at the origin of the circuit; and more obviously, where the fitting of RCD protection in the CU is impossible.


    Oh, and by the way, there is no statutory requirement to work to the current regulations.


    Back to the OP: if this was a new circuit, it cannot be compliant without a 61008/9 device at the origin of the circuit.
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