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Group 1 Medical location EBB - connection to the protective system earth - risk in choice of connection location.

Simon Bourke

A similar question was asked a month ago, but there seems to be no answers to this, I suspect it was because the question may have been too wide ranging. 

The question was this:

However to rephrase this question.

Consensus on this forum was that whilst the regulations are silent on the specific location of where the Equipotential Bonding Bar should be connected to, connection to the local DB (distribution board ) rather than the system origin would suffice. 

It would therefore indicate that a direct connection from the EBB to the system source would also be BS7671 compliant. If not can this be clarified?

On the basis that there is a choice of where the EBB is connected to the system earth, then (after my long preamble) - please can you advise with respect to this question:

If the EBB of a medical location is connected to a local DB, is there an increased risk to the integrity of the earthing arrangement?

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    Simon Bourke said:
    It would therefore indicate that a direct connection from the EBB to the system source would also be BS7671 compliant. If not can this be clarified?

    I think that is a big step to take. It certainly depends on the distance to the system source, and what you think 'equipotential' means.

    Other standards are there to help ... for example BS EN 50310 ... which talks about a 'zoned' or 'floor level' hierarchy. Similarly Section 444 of BS 7671.

    In practice, in "large" buildings with many metres of cable, 'equipotential' is anything but ... so it's up to you to decide what you think the intent of the standard is met. I'm sur ethe answer will be different for a very small GP surgery, a local health centre, a small hospital, and a very large hospital. (Only a court of law can interpret a standard - see BS 0.)

    Simon Bourke said:
    If the EBB of a medical location is connected to a local DB, is there an increased risk to the integrity of the earthing arrangement?

    Well ... it might actually increase the integrity of the local bonding arrangement, and if you follow documented practices for earthing in buildings (for example, along the lines of BS EN 50310, BS IEC 61000-5-2, and Section 444 of BS 7671) you won't be far wrong, In reality EMC is usually the worst-case for earthing, because it relies on reactance as well as resistance, but is also affected by conducted interference in the earthing system from other locations and systems ... this is little different to considering what if you conduct fault current from other places through the medical supplementary bonding system (i.e. you don't want to) ... so, see above.

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