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Supplementary bonding conductor in a medical location

Julien Leblanc
Hello,


After reading from many sources about the medical locations' supplementary equipotential bonding, everything is mixed in my head...


Suppose we have a current using device inside a group 1 medical location (TN-S supplied).

Then the protective conductor of that device must be connected to the EBB installed in this location by means of a supplementary equipotential bonding conductor.

Could someone clarify this:  that bonding conductor, should it comply with art. 544.2.1 or with art. 544.2.2 from BS7671, that is, the EBB should be considered an extraneous-conductive-part or an exposed-conductive-part ?


Thank you.
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    The EBB is neither an extraneous-conductive-part nor an exposed-conductive-part. It is a protective bonding terminal.


    In the UK, the conductor connecting it to the protective earthing system is sized in accordance with Regulation 710.415.2.3:
    The equipotential bonding busbar shall be connected to the system earthing using a protective conductor having a cross-sectional area greater than or equal to the largest cross-sectional area of any conductor connected to the equipotential bonding busbar.



    Andy is quite right, that the sizing of individual bonding conductors for supplementary local equipotential bonding is based on Regulation Group 544.2, but in the case of a medical location, a higher level of performance is required:
    • maximum simultaneous touch voltage not to exceed 25 V AC (Regulation 710.411.3.2.5), whereas in the general case for supplementary local equipotential bonding (Regulation 419.3) the touch voltage is limited to 50 V AC; and

    • Regulation 710.415.2.2 requires that the maximum resistance between earth terminals of socket-outlets or fixed equipment, and exposed-conductive-parts [within the location] and/or extraneous-conductive-parts [of the location] should not exceed 0.2 Ω.



    Whilst BS 7671 is based on HD 60364-series, which is aligned with IEC 60364-series, national variations exist.
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  • 0
    The EBB is neither an extraneous-conductive-part nor an exposed-conductive-part. It is a protective bonding terminal.


    In the UK, the conductor connecting it to the protective earthing system is sized in accordance with Regulation 710.415.2.3:
    The equipotential bonding busbar shall be connected to the system earthing using a protective conductor having a cross-sectional area greater than or equal to the largest cross-sectional area of any conductor connected to the equipotential bonding busbar.



    Andy is quite right, that the sizing of individual bonding conductors for supplementary local equipotential bonding is based on Regulation Group 544.2, but in the case of a medical location, a higher level of performance is required:
    • maximum simultaneous touch voltage not to exceed 25 V AC (Regulation 710.411.3.2.5), whereas in the general case for supplementary local equipotential bonding (Regulation 419.3) the touch voltage is limited to 50 V AC; and

    • Regulation 710.415.2.2 requires that the maximum resistance between earth terminals of socket-outlets or fixed equipment, and exposed-conductive-parts [within the location] and/or extraneous-conductive-parts [of the location] should not exceed 0.2 Ω.



    Whilst BS 7671 is based on HD 60364-series, which is aligned with IEC 60364-series, national variations exist.
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