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How big does a 3 phase in-balance need to be to mask an open pen fault

Alan B

This is looking at the previous project I was  discussing with two EVCP's on two phases of a 3 phase supply.
Just realised that I may have issues relying on single phase voltage based open pen detection when connecting to a 3 phase supply.


AI says Regulation 722.411.4.1(iv) of BS 7671:2018+A1:2020 prohibits the use of a protection device for open-PEN (Protective Earth and Neutral) detection in single-phase EV charging points supplied by a three-phase installation. This is because this specific type of open-PEN protection is designed for single-phase installations only, and a three-phase supply has different electrical characteristics that are not compatible with this protective measure. 

Looking at amendment 2 I can't see this wording, am I just missing it, or has it been removed?


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    White check mark Regulation 722.411.4.1 Breakdown (Amendment 2, 2022)

    BS 7671 doesn’t ban open-PEN protection on 3-phase supplies. It provides multiple compliant methods under 722.411.4.1:

    1. Clause (i) – The EV point is part of a balanced 3-phase installation; fault voltage remains ≤70 V rms.
    2. Clause (ii) – An earth electrode limits voltage to ≤70 V rms during PEN loss.
    3. Clause (iii) – A detection/protection device monitors CPC vs. earth (or derived reference) and disconnects if >70 V rms.
    4. Clause (iv) – A device for single-phase circuits with similar functionality.
    5. Clause (v) – Alternative equivalent methods meeting requirements (iii) or (iv). 

    Pushpin Key Point

    724.411.4.1 does not ban open-PEN detection in three-phase systems—it merely requires the correct detection/protection device. There's no blanket prohibition, and the wording has not been removed—it's clear in Amendment 2.

    Wrench Best Practice

    • Use a proper open-PEN detection device (e.g., O-PEN) for 3-phase PME systems.
    • Ensure any detection monitors CPC-to-earth or derived references and triggers isolation when >70 V for >5 s. 
    • Avoid relying solely on single-phase voltage monitoring without device compliance under (i) to (v).
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  • 0

    White check mark Regulation 722.411.4.1 Breakdown (Amendment 2, 2022)

    BS 7671 doesn’t ban open-PEN protection on 3-phase supplies. It provides multiple compliant methods under 722.411.4.1:

    1. Clause (i) – The EV point is part of a balanced 3-phase installation; fault voltage remains ≤70 V rms.
    2. Clause (ii) – An earth electrode limits voltage to ≤70 V rms during PEN loss.
    3. Clause (iii) – A detection/protection device monitors CPC vs. earth (or derived reference) and disconnects if >70 V rms.
    4. Clause (iv) – A device for single-phase circuits with similar functionality.
    5. Clause (v) – Alternative equivalent methods meeting requirements (iii) or (iv). 

    Pushpin Key Point

    724.411.4.1 does not ban open-PEN detection in three-phase systems—it merely requires the correct detection/protection device. There's no blanket prohibition, and the wording has not been removed—it's clear in Amendment 2.

    Wrench Best Practice

    • Use a proper open-PEN detection device (e.g., O-PEN) for 3-phase PME systems.
    • Ensure any detection monitors CPC-to-earth or derived references and triggers isolation when >70 V for >5 s. 
    • Avoid relying solely on single-phase voltage monitoring without device compliance under (i) to (v).
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