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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

    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.
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  • 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.
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