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551.4.3.2.1 Flats how to provide earth rod in island mode

DA

So reading the latest regs I take it we are to provide an earth rod in a prosumer setup for island mode supplies.

Any ideas how this works practically in a top floor flat?

Parents
  • 0

    Interesting question. As it is probably impossible to isolate the Earth from incoming services and thus the Mains Earth, why should I fit an Earth rod? If the island supply is from a battery, thus effectively IT, do I need an Earth connection anyway? In such an installation is there a significant shock risk, or is the risk of a battery fire greater? Please discuss.

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  • 0

    Interesting question. As it is probably impossible to isolate the Earth from incoming services and thus the Mains Earth, why should I fit an Earth rod? If the island supply is from a battery, thus effectively IT, do I need an Earth connection anyway? In such an installation is there a significant shock risk, or is the risk of a battery fire greater? Please discuss.

Children
  • 0 in reply to David Stone

    Thanks for the input David. Yes I need an earth to provide ADS. I think the shock risk is sufficient given the multiple circuits that the island CU supplies.

    The MET earth stays connected (but cannot be solely relied on) as indicated in 826.1.1.2.1 which also states the need for an earth electrode - which gave rise to my original question:

    How to provide an earth electrode in installations where this is tricky. Eg flats.

  • 0 in reply to David Stone
    David Stone said:
    As it is probably impossible to isolate the Earth from incoming services and thus the Mains Earth, why should I fit an Earth rod

    There is no requirement to isolate from a DNO provided earthing arrangement, and as David said that might be a fool's errand, but:

    • we know we can't always rely on extraneous-conductive-parts as the fault current path for fault protection
    • the normal fault current path, in the case of a distributor's earthing terminal, could well be interrupted by repairs to network cables.

    This is what Regulation 551.4.3.2.1 is all about. 551.4.3.2.1 is not a new Regulation, it's been in BS 7671 in some form or another for a very, very long time.

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