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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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  • 0
    Thank you.

    Your explanation makes lots of sense to me.


    I've found an ABB guide on the internet:
    https://library.e.abb.com/public/8641f847b0d4483f9d959245c8dd05a0/Hospital Line practical guide_web.pdf


    At page 23, it says:

    "The conductors that connect the extraneous conductive parts to the equipotential bonding bus bar are defined as equipotential conductors and must have a cross-section of no less than 6 mm2".

    It looks like they are sizing these conductors as the main protective bonding conductors? But the EBB is not the main earthing terminal...


    Also "The conductors that connect the conductive parts to the equipotential node are protection conductors (PE) and their cross-section must be established using the criteria specified by the general standard; in other words, it must be at least equal to that of the phase conductors."

    There is also an image on the same page with a sizing example.


    I don't understand their approach. In this book, https://shop.theiet.org/guide-to-electrical-installations-in-medical-locations, figure 14.7 clearly shows that we are talking about supplementary bonding conductors, not main bonding conductors or PE.

    Am I misunderstanding something? The IEC standards are very similar to BS standards, so I don't know where does the different approach come from.


    Thank you.

Reply
  • 0
    Thank you.

    Your explanation makes lots of sense to me.


    I've found an ABB guide on the internet:
    https://library.e.abb.com/public/8641f847b0d4483f9d959245c8dd05a0/Hospital Line practical guide_web.pdf


    At page 23, it says:

    "The conductors that connect the extraneous conductive parts to the equipotential bonding bus bar are defined as equipotential conductors and must have a cross-section of no less than 6 mm2".

    It looks like they are sizing these conductors as the main protective bonding conductors? But the EBB is not the main earthing terminal...


    Also "The conductors that connect the conductive parts to the equipotential node are protection conductors (PE) and their cross-section must be established using the criteria specified by the general standard; in other words, it must be at least equal to that of the phase conductors."

    There is also an image on the same page with a sizing example.


    I don't understand their approach. In this book, https://shop.theiet.org/guide-to-electrical-installations-in-medical-locations, figure 14.7 clearly shows that we are talking about supplementary bonding conductors, not main bonding conductors or PE.

    Am I misunderstanding something? The IEC standards are very similar to BS standards, so I don't know where does the different approach come from.


    Thank you.

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