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Dual RCD boards are unlikely to be suitable for EV charging installations even with type A or B RCDs, discuss

IronFreely

I’ll paraphrase Regulation 722.531.3.101, “each charging point shall be protected individually by an RCD”. With that in mind a dual RCD board where both RCDs protect multiple circuits will not be suitable as the requirement is for the charge point to be individually protected. The reason I open this up to discussion is because so many installers seem completely unaware of the wording of 722.531.3.101 as about 50% of the installations I see the charger is protected by an RCD protecting multiple circuits, in particular new builds were the provision for electric vehicle charging has been made during development. I also often give quotations to prospective clients where they’ve already had at least one quotation where the previous installer has said “great you’ve got a spare way in your dual RCD board, so we can use that” and I’m thinking “erm no you can’t”

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  • I think in the average dwelling the day of installing Dual or split load RCD board has passed.  Lots still sold with type AC rather than type A minimum.

    Personally I think the CU/DB in a dwelling should be full RCBO with SPD as a minimum.  There are so many reasons for this.  A Few below

    Overload or potential overload of the RCD in split way

    Nuisance tripping

    More and more requirement for circuits to have their own individual RCBO (RCD)

    Earth leakage currents soon adds up to the 30mA for that half of the board

    Segmenting circuits to remove single or multiple points fo failure.  (EG downstairs lights on same circuit as outdoor PIR flood light, fast forward 6 months or a year and the PIR flood fails probably with moisture ingress and hey presto downstairs light fault)

    If there is an RCD fault it takes out half a board so maybe 6 MCBs

    The cost of an average RCBO for a dwelling is a few pounds so why not fully populate a CU with them rather than a daul split load board.  I went to a Taylor Wimpey home 6 months ago after handover and it had a split load RCD CU.  In that situation the installer has to follow the design which means that the installation designer need to be educated/convinced/forced by BS7671.  House builders are more concerned about the buy in price of the CU and install cost rather than the ongoing cost.  Imagine the electrician who goes in next week to find a fault and there is 1 RCD module covering 6 MCBs

Reply

  • I think in the average dwelling the day of installing Dual or split load RCD board has passed.  Lots still sold with type AC rather than type A minimum.

    Personally I think the CU/DB in a dwelling should be full RCBO with SPD as a minimum.  There are so many reasons for this.  A Few below

    Overload or potential overload of the RCD in split way

    Nuisance tripping

    More and more requirement for circuits to have their own individual RCBO (RCD)

    Earth leakage currents soon adds up to the 30mA for that half of the board

    Segmenting circuits to remove single or multiple points fo failure.  (EG downstairs lights on same circuit as outdoor PIR flood light, fast forward 6 months or a year and the PIR flood fails probably with moisture ingress and hey presto downstairs light fault)

    If there is an RCD fault it takes out half a board so maybe 6 MCBs

    The cost of an average RCBO for a dwelling is a few pounds so why not fully populate a CU with them rather than a daul split load board.  I went to a Taylor Wimpey home 6 months ago after handover and it had a split load RCD CU.  In that situation the installer has to follow the design which means that the installation designer need to be educated/convinced/forced by BS7671.  House builders are more concerned about the buy in price of the CU and install cost rather than the ongoing cost.  Imagine the electrician who goes in next week to find a fault and there is 1 RCD module covering 6 MCBs

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