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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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  • The reason for the "individually" requirement is that the RCD will be one that provides additional protection (IΔn not exceeding 30 mA), and in that case it is expected that the residual currents expected for an EV charging point may approach the limit for "unwanted tripping" of a 30 mA RCD discussed in Regulation 531.3.2.

    So, whilst it might be OK to have a board with only two 30 mA RCDs, you would need to restrict the RCD supplying the EVSE to just the EV circuit only.

    The designer should also consider the effects of DC residual currents (which may occur in EV charging in N-PE faults, if not other situations, purely due to the pilot functionality).

  • in reply to gkenyon

    I have a question regarding the use of RCBOs and the Hager guide. If a RCBO is installed, am I correct making  sure they are double pole? Furthermore, does following the Hager guide imply that the installer has complied with the manufacturer’s instructions for that particular consumer unit? I personally install an individual unit for the EV when I encounter split boards.

  • in reply to gkenyon

    My interpretation is that the EVCP must have its own RCD somewhere, but as written, I do not think that 722.531.3.101 precludes the installation of one upstream. However I take the point about unwanted tripping.

    I suppose that split boards were introduced: (1) to reduce the risk of tripping due to earth leakage (half as many circuits) and (2) to reduce the consequences of a trip - half the circuits stay alive.

    531.3.2 seems rather ambivalent: on the one hand, RCDs should be selected and erected to "limit the risk of unwanted tripping"; but on the other hand, RCBOs in residential premises, etc. need only be "considered".

    I conclude that whilst RCBOs are the preferred option, split boards remain compliant.

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  • in reply to gkenyon

    My interpretation is that the EVCP must have its own RCD somewhere, but as written, I do not think that 722.531.3.101 precludes the installation of one upstream. However I take the point about unwanted tripping.

    I suppose that split boards were introduced: (1) to reduce the risk of tripping due to earth leakage (half as many circuits) and (2) to reduce the consequences of a trip - half the circuits stay alive.

    531.3.2 seems rather ambivalent: on the one hand, RCDs should be selected and erected to "limit the risk of unwanted tripping"; but on the other hand, RCBOs in residential premises, etc. need only be "considered".

    I conclude that whilst RCBOs are the preferred option, split boards remain compliant.

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