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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
    Perhaps the change is due to the more mandatory nature of additional protection, this is a Socket circuit regardless the accessory being an SRCD one or not....so with an SRCD you could have part of the upstream circuit not having additional protection but the appliance plugged into SRCD will have AP

    Possibly the wording, perhaps imperfectly, is covering a potential issue of an SRCD socket being replaced with an ordinary one ?


    ​​​​​​

  • 0
    411.3.3.(i) just states that socket outlets need protecting with a 30mA RCD; it says nothing about the circuit supplying that socket. So long as other conditions aren't violated (cable buried in wall, passing through bathroom etc), there's no reason the RCD has to be at the origin of the circuit.
  • 0

    wallywombat:

    411.3.3.(i) just states that socket outlets need protecting with a 30mA RCD; it says nothing about the circuit supplying that socket. So long as other conditions aren't violated (cable buried in wall, passing through bathroom etc), there's no reason the RCD has to be at the origin of the circuit.




    Well, playing devil's advocate, you could conceivably plug table lamp into the socket-outlet, so 411.3.4 would then apply (that requires the whole circuit to be protected). Being more sensible ... fused spur taken off for the odd lamp would also change the requirement for RCD for the circuit ...


     

  • 0
    Or one of those fancy illuminated mirrors that the client has bought through Amazon or the like to have fitted in their bathroom, though there tends to be a bigger problem than providing them with RCD protection in that the shaver socket doesn’t have an isolation transformer to British Standard requirements.


    Andy Betteridge
  • 0
    7ca20437ae3256654a7d7fbb076ad163-huge-20190828_231133.jpg

    Advert for the new Timeguard SRCD devices in their brochure that arrived in the post. 

    32158151753fd9804aee5f015d556fe1-huge-20190828_231116.jpg

  • 0
    “And meets the latest IET Wiring Regulations”


    That is a simple statement that doesn’t sound particularly controversial.  


    Andy Betteridge
  • 0

    Sparkingchip:

    32158151753fd9804aee5f015d556fe1-huge-20190828_231116.jpg

     




    Oh no, I couldn't live with that on the wall. What were the designers thinking of?


    So we have a long miserable face with eyes closed, a little red nose, a little grey mouth and a bit of chin stubble. Yuk! ?

  • 0

    “And meets the latest IET Wiring Regulations”


    That is a simple statement that doesn’t sound particularly controversial.  



    Ah, but to be pedantic, it doesn't say in what way it meets the wiring regs - i.e. for what purpose it can be used and so which particular BS 7671 requirement it meets. It may be good as just a general purpose socket outlet (with additional protection provided upstream) and meet all BS 7671 requirements for that purpose, it's almost certainly not good as it is as an outdoor socket (insufficient IP rating). Whether it's good for providing additional (30mA RCD) protection, isn't stated.


       - Andy.
  • 0
    When the 17th Edition (BS 7671: 2008) was published, only BS EN 61008-1 and BS EN 61009-1 were still listed (Regulation 411.4.9 refers). However, this does not preclude the use of RCDs to BS 4293, BS 7288 and BS 7071, where appropriate, for fault protection and/or additional protection, provided they meet the relevant operating time requirements.

    Pocket guide 25 ELECSA, ECA, NICEIC and Certsure LLP.



  • 0
    Yesterday I was faced with extending a circuit protected by a BS4293 RCD and a BS3871 MCB, the RCD tested out  all okay, so I saw no reason to put either down as a departure on the minor works certificate I issued.


    Would any of you have entered the RCD as a departure on the MWC?


    Andy Betteridge 


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