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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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  • Former Community Member
    0 Former Community Member

    Legh Richardson:


    What sort of HiFi system requires 10 power supplies one wonders? 




    Pre-amp, power-amp, record player, cd player, tuner, both electrostatic speakers... I've guessed as far as 7 but yeah, no idea beyond that. Hi-fi is an industry full of magic and snake oil and you'll be surprised what audiophiles spend their cash on! EDIT: Some of it could be quite old too - 'vintage mojo' I believe it's called!




    "The customer has now decided he doesn't want RCD anyway for 'reasons' " must be a qualified electrical engineer!


    Legh




    The customer did at one point say that an RCD could 'colour the sound' of the hi-fi. That is clearly subjective but who am I to argue?

     



    AJJewsbury:





    I don't see how you can omit the 30mA RCD protection and claim either BS 7671 compliance or 'no less degree of safety' - without the RCD it lacks additional protection even if ADS is fine. A 100mA RCD isn't likely to be much better on that score either (no point in an 100mA RCD if 50mA can kill).






    I agree. It would be deviation from the regulations once a 30ma RCD is omitted. I suppose it's shades of compliance...

     




    If the inrush current is well beyond the RCD's current-carrying rating (e.g. 40A or 80A, not 30mA) then the L & N coils can saturate the torroid and combined with manufacturing tolerances can mean the L and N coils don't quite balance as they should and the sense coil sees an imbalance larger than it really is.





    That's really interesting, I'll look into that for future reference. However, this circuit has a 63A 61008 and the overload protective device is a B16 60898. It's difficult to imagine this scenario. There will also be a 13A BS1362 in the multi strip he has plugged all the equipment into (hopefully!).

    (or just let the user switch things on one at a time).


      - Andy.



     





    This is my preferred option.
     



    Maybe the RCD is serving its intended purpose.


    A debatable solution is to remove the upfront RCD and replace it with as many BS8277 30mA RCD protected socket outlets as are required to spread the leakage or identify the actual problem.


    The customer won’t like that, so the other solution is to walk away if you cannot identify a specific problem with the connected equipment.


     Andy Betteridge 




    The customer definitely won't like that. We had many discussions on aesthetics during installation and a single, un-switched socket outlet was the only agreeable option.


    I think I need to look at this hi-fi system for myself and work out why >15ma of current is leaking to earth.


    I wonder if 411.3.3 is unnecessarily strict with regards to dwellings. I liked the 'specially labelled socket for a specific piece of equipment' in the 17th AM3 because it makes sense in scenarios like this, particularly for those who work from home with a home workshop or multiple pieces of IT equipment. Oh well, I don't make the rules! 


    Thanks everyone.
Reply
  • Former Community Member
    0 Former Community Member

    Legh Richardson:


    What sort of HiFi system requires 10 power supplies one wonders? 




    Pre-amp, power-amp, record player, cd player, tuner, both electrostatic speakers... I've guessed as far as 7 but yeah, no idea beyond that. Hi-fi is an industry full of magic and snake oil and you'll be surprised what audiophiles spend their cash on! EDIT: Some of it could be quite old too - 'vintage mojo' I believe it's called!




    "The customer has now decided he doesn't want RCD anyway for 'reasons' " must be a qualified electrical engineer!


    Legh




    The customer did at one point say that an RCD could 'colour the sound' of the hi-fi. That is clearly subjective but who am I to argue?

     



    AJJewsbury:





    I don't see how you can omit the 30mA RCD protection and claim either BS 7671 compliance or 'no less degree of safety' - without the RCD it lacks additional protection even if ADS is fine. A 100mA RCD isn't likely to be much better on that score either (no point in an 100mA RCD if 50mA can kill).






    I agree. It would be deviation from the regulations once a 30ma RCD is omitted. I suppose it's shades of compliance...

     




    If the inrush current is well beyond the RCD's current-carrying rating (e.g. 40A or 80A, not 30mA) then the L & N coils can saturate the torroid and combined with manufacturing tolerances can mean the L and N coils don't quite balance as they should and the sense coil sees an imbalance larger than it really is.





    That's really interesting, I'll look into that for future reference. However, this circuit has a 63A 61008 and the overload protective device is a B16 60898. It's difficult to imagine this scenario. There will also be a 13A BS1362 in the multi strip he has plugged all the equipment into (hopefully!).

    (or just let the user switch things on one at a time).


      - Andy.



     





    This is my preferred option.
     



    Maybe the RCD is serving its intended purpose.


    A debatable solution is to remove the upfront RCD and replace it with as many BS8277 30mA RCD protected socket outlets as are required to spread the leakage or identify the actual problem.


    The customer won’t like that, so the other solution is to walk away if you cannot identify a specific problem with the connected equipment.


     Andy Betteridge 




    The customer definitely won't like that. We had many discussions on aesthetics during installation and a single, un-switched socket outlet was the only agreeable option.


    I think I need to look at this hi-fi system for myself and work out why >15ma of current is leaking to earth.


    I wonder if 411.3.3 is unnecessarily strict with regards to dwellings. I liked the 'specially labelled socket for a specific piece of equipment' in the 17th AM3 because it makes sense in scenarios like this, particularly for those who work from home with a home workshop or multiple pieces of IT equipment. Oh well, I don't make the rules! 


    Thanks everyone.
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