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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
    gkenyon:
    The product standard BS 7288 has changed in 2016, so the product we used to fit for the job is no longer suitable for that job. The product standard itself says so.



    If you have some new old stock product manufactured under BS 7288:1990, it still would be?


    Have manufacturers actually degraded their product to reflect the reduced functionality under the new standard?


  • 0
    Strictly not, the standard is not listed as acceptable for RCDs in the 18th Edition.
  • 0
    "Begs the question, what the actual purpose of a BS 7288 SCRD is now."


    Because if you are 100 yards down the bottom of your garden in your man cave in the middle of winter the last thing you want to do is walk back up the garden to reset a duplicated trip.Snowflake


    Does it mention that in on your site guide, guidance notes 1, 3, 6? 


    Regards, UKPNZap
  • 0
    Owain:

    If you have some new old stock product manufactured under BS 7288:1990


     






    Have the all manufacturers actually stopped making the older version?


     


  • 0
    UKPN:


     the last thing you want to do is walk back up the garden to reset a duplicated trip.


    Regards, UKPNZap




    How do you achieve discrimination to ensure the RCD in the shed trips, but not the upstream RCD?


  • 0
    UKPN:

    "Begs the question, what the actual purpose of a BS 7288 SCRD is now."


    To provide additional protection for a particular socket in an installation that pre-dates routine RCD fitment in the CU and which is otherwise sound and a change of CU is not desired.


  • 0
    Chris Pearson:
    UKPN:

    "Begs the question, what the actual purpose of a BS 7288 SCRD is now."


    To provide additional protection for a particular socket in an installation that pre-dates routine RCD fitment in the CU and which is otherwise sound and a change of CU is not desired.




    Except that BS 7288 is not recognised by the 18th Edition in Regulation 531.3.4.1. So, in either an addition or alteration, or a new circuit, a BS 7288 socket-outlet can provide neither additional protection nor fault protection without a departure. And with the current Edition of BS 7288 saying what it does in the introduction, effectively additional protection and fault protection should be provided upstream in accordance with BS 7671, it's arguably difficult to justify that departure.


  • 0
    And with the current Edition of BS 7288 saying what it does in the introduction, effectively additional protection and fault protection should be provided upstream in accordance with BS 7671, it's arguably difficult to justify that departure.

    I'm surprised that RCD socket manufacturers haven't lynched the BS 7288 committee...

       - Andy.
  • 0
    gkenyon:
    Chris Pearson:
    UKPN:

    "Begs the question, what the actual purpose of a BS 7288 SCRD is now."


    To provide additional protection for a particular socket in an installation that pre-dates routine RCD fitment in the CU and which is otherwise sound and a change of CU is not desired.




    Except that BS 7288 is not recognised by the 18th Edition in Regulation 531.3.4.1. So, in either an addition or alteration, or a new circuit, a BS 7288 socket-outlet can provide neither additional protection nor fault protection without a departure. And with the current Edition of BS 7288 saying what it does in the introduction, effectively additional protection and fault protection should be provided upstream in accordance with BS 7671, it's arguably difficult to justify that departure.




    Ouch! I can feel my knuckles being rapped for putting one in so that I might use an electric hedge trimmer more safely. In fact, I know that one should put the flex over the shoulder i.o.t. reduce the risk of slicing through the cable, and even if I did slice through it, I wouldn't be daft enough to pick up the live end. Sadly it's all a bit academic 'cos box blight seems to be killing the wee hedges. ?


    Let's not forget that short of Part P, there is no obligation to install to BS 7671. Thanks largely to this forum, I think that I am in a good position to decide when to depart.


  • 0
    Racked with guilt, faced with the shame and humiliation of being judged by my peers if a case came to court, I will be up at the crack of dawn to remove my two "BS 7288" RCD sw skt outlets. It was all going so well. In case I was unwell and my wife was needing to use the heavy Flymo on the lawn I enquired at the local B and Q store if there was such a thing as a safety device which would save your life if a cable was severed and a person inadvertently touched the live wire. "Oh yes", the sales lady said, these sw/skt RCDs are one our most popular lines, we sell thousands each year. Easy to fit she said. I bought two, one for the rear of the house, one for the rear. Dont forget to switch off your fusebox! she said. No mention of BS 7288, Regulation 531.3.4.1, departures, additional protection, fault protection, upstream, downstream, RCD in the fuseboard, (in fact new fuseboard), in fact re wirewing the ring circuit because it is less than 50mm deep.

    But to my horror, word had got around the neighbourhood where the safety devices were as common as double glazing, two special "wiring regulation" officers, PCs Jewsbury and Kenyon were tasked to call on every home in search of the "illegal" devices. A skip appeared in the street, and residents were seen with suspicious bags being emptied into the skip. B and Q put a notice up, "normal sw/skts out of stock" Safe from prosecution, life went on. The Flymos appeared on front gardens, with a note "free, please help yourself" Sales of petrol mowers soared. 


    Regards, UKPN

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