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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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    544.2 gives rules for sizing the bonding conductor(s) between exposed- and extraneous-conductive-parts.


    To make sense of that I don't think I'd consider the conductor between one item and the EBB in isolation - rather consider the EBB as just part of the bonding conductors that join the various items and consider the overall connections.


    So say we had two items with exposed-conductive-parts (A and B) and one extraneous item (C), all connected together via a single EBB.


    So:

    1. The entire path between A and B (between exposed conductive parts) would have to meet 544.2.1 (minimum = size of the smaller c.p.c.)


    2. The entire path between A and C (between an exposed-conductive-part and an extraneous-conductive-part) would have to meet 544.2.2 (minimum = half of A's c.p.c. size)


    3. The entire path between B and C would likewise need a conductor of at least half B's c.p.c. size.


    So A's supplementary bonding conductor would have to meet both 1. and 2. above, B's would have to meet 1 and 3 and C's 2 and 3.


    All subject to the usual rule of not less than 2.5mm² if protected or 4mm² otherwise.


       - Andy.
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  • 0
    544.2 gives rules for sizing the bonding conductor(s) between exposed- and extraneous-conductive-parts.


    To make sense of that I don't think I'd consider the conductor between one item and the EBB in isolation - rather consider the EBB as just part of the bonding conductors that join the various items and consider the overall connections.


    So say we had two items with exposed-conductive-parts (A and B) and one extraneous item (C), all connected together via a single EBB.


    So:

    1. The entire path between A and B (between exposed conductive parts) would have to meet 544.2.1 (minimum = size of the smaller c.p.c.)


    2. The entire path between A and C (between an exposed-conductive-part and an extraneous-conductive-part) would have to meet 544.2.2 (minimum = half of A's c.p.c. size)


    3. The entire path between B and C would likewise need a conductor of at least half B's c.p.c. size.


    So A's supplementary bonding conductor would have to meet both 1. and 2. above, B's would have to meet 1 and 3 and C's 2 and 3.


    All subject to the usual rule of not less than 2.5mm² if protected or 4mm² otherwise.


       - Andy.
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