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My war against dual rcd boards

Newfutile
As each (RCD) Residual Current Device must not have more than 30% leakage current on it.
It's hard to see how dual (RCD) Residual Current Device boards can be fitted at all these days.
i come across so many dual rcd boards with solar, evse and heat pumps on them, these have all been recently installed.
i wonder if BS7671 should state: Dual (RCD) Residual Current Device boards shall not be fitted, unless it can be shown (and documented) that they are suitable for the combined leakage currents expected .
otherwise developers will keep specifying them and i will have keep educating them on the many reasons a type A rcd should not be shared with other equipment!.
maybe manuafactuers instructions should also state : not suitable for a shared rcd, for certain equipment.
  • in reply to Chris Pearson
    Chris Pearson said:
    What is the economic argument? I doubt that margins are so fine on new-build developments that all-RCBO boards cannot be provided. With after-market solar PV installations costing £thousands, once again a few £tens more on a board change hardly matters

    Try and compare a Hager (other brands are available) split load CU against a Navits CU

    https://www.navitascp.co.uk/product-page/10-way-100a-mainswitch-consumer-units-c-w-t2-spd

    The economic argument goes out of the window (other Apertures are available) 

    I see no reason why a fully RCBO and SPD type2 CU can not be designed and installed in the average UK dwelling

  • in reply to Sergio Fernandez

    Sergio,

    In my exeprience and despite what standards and regulations say, in majority of cases in domestic dwelling house work there is no "Designer". The installer or somebody may be signing paperwork as "Designer". But attitude is still very much "Its only a dwelling" what can go wrong?.

    Cheers GTB

  • in reply to gkenyon
    gkenyon said:
    we don't yet have EV charging and solar PV.

    So no heat pump RCD selection issues then Grinning

  • in reply to GTB

    Or need that little bit extra clarity, particularly about the distinctions between requirements, regulations and specifications (there's a separate thread on that  Requirement Structuring ) Smiley

  • in reply to Philip Oakley

    Not yet ...We won't have a heat-pump for many many years, certainly over 30 years from original CU installation.

    ... and even then (or if I'm wrong on the timescales) there's no reason a second CU can't be fitted for "renewable" technologies. The existing board doesn't have enough ways for EV, PV and HP anyway !

    Don't get me wrong, I'm not saying it's a good idea to provide a dual RCD board for a brand new installation, or on refurb, but simply providing information that supports the fact there's no need to jump at removing these boards because they aren't compatible with new technology. Other options are available.

  • in reply to gkenyon

    Can we assume they are type A RCD and not Type AC RCD

    Can we assume there is also a Type 2 SPD and is fitted pre or post main switch

  • I have a 15 way dual RCD board on my home installation. I have lots of electronic equipment plus a full range of kitchen and laundary appliances, an outside workshop with machinary and a amatuer radio station. I have a standing earth leakage of 11mA acroos the 2 RCDs. Never had a nuisance trip other than the senior management pooring water over her steam iron, this got replaced with an early wedding present (she was lost for words and no dinner for me that night).

    JP

  • in reply to John Peckham

    Are the RCD type AC?  The type AC could mask/blind the nuisance trip

  • in reply to Sergio Fernandez
    Sergio Fernandez said:
    Are the RCD type AC?  The type AC could mask/blind the nuisance trip

    That's an interesting point ... if, with the loads connected, the RCD is still able to operate within parameters from a Type AC RCD test (simulating a supplemental fault over the standing conditions), is that OK?
    (I'm fully aware that what I'm proposing here is very "loose", but certainly a discussion point.)

    However, we also need to consider that, in the "blinding" situations, currents, such as smooth DC, changing/pulsating DC, and/or high frequency AC, need to appear as a residual current ... and not all protective conductor currents, nor all 'leakage' currents are 'residual currents' in the live conductors.

    And ... not all Type AC RCDs are 'blinded' in the same way, to the same thresholds. 

    The actual blinding from some electronic equipment might only occur during a fault downstream of some electronics - as shown in Fig A53.1.

  • in reply to gkenyon
    gkenyon said:
    And ... not all Type AC RCDs are 'blinded' in the same way, to the same thresholds. 

    Agreed

    But we do know they (Type AC RCD) get blinded or may become blinded to a greater or less degree.  Now consider the domestic dwelling for the scenario a light bulb fails (lamp to engineers) Home owner/occupier replaces it.  Firstly the original lamp could of been filament or halogen or florescent/compact florescent the replacement surely by now will be LED thus the resistive load now becomes an electronic load with or without a certain amount of DC leakage.  

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