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Additional connection to earth 411.4.2

Simon Mitchell

Hi,

Regulation 411.4.2 regarding TN systems now includes a recommendation to install an additional connection to earth using an earth electrode. There is no indication within the regs why you would or wouldn't fit one. The guidance on language on p18 of the regs equates "recommendation" to "should". Therefore we should install an earth electrode to all TN-S and TN-C-S systems.

I can't find any discussion on this when searching but it seems quite a big change to previous regs. Should we be installing earth rods as a standard?

Simon

Parents
  • 0

    There has, for a long time, been advice (via a note) that additional connections between PE and Earth can be made (e.g. from MET) in TN systems.

    However, the thing that has changed in 2022 is the introduction of Chapter 82, which considers operation in island mode where (as Regulation 551.4.3.2.1 says) you can't rely on the distributor's means of earthing.

    The IET Code of Practice for Electrical Energy Storage Systems contains details as to how the switch-over to island mode ought to be effected. It's briefly touched upon in this IET Webinar, which I believe you can register for free and view (even thought he event has passed).

Reply
  • 0

    There has, for a long time, been advice (via a note) that additional connections between PE and Earth can be made (e.g. from MET) in TN systems.

    However, the thing that has changed in 2022 is the introduction of Chapter 82, which considers operation in island mode where (as Regulation 551.4.3.2.1 says) you can't rely on the distributor's means of earthing.

    The IET Code of Practice for Electrical Energy Storage Systems contains details as to how the switch-over to island mode ought to be effected. It's briefly touched upon in this IET Webinar, which I believe you can register for free and view (even thought he event has passed).

Children
  • 0 in reply to gkenyon

    The change in 411.4.2 is from "may" - which indicates that you are permitted to connect an additional earth, without any suggestion of it being advantageous - to "recommended" - which indicates that it would be a good idea but not necessary. If it is to do with PEI then why not reference it as such within 411.4.2?

  • 0 in reply to Simon Mitchell

    I think there is concern that if folk go bashing rods in willy nilly in built up areas then there will be a lot of surprisingly shallow gas mains and drains that are not on the map etc discovered the hard way.

    However, when things are being done anyway for an extension or a new drive or 2hatever and there is a digger on site then the risk balance swings the other way, and adding an electrode does no harm.

    Mike.

  • 0 in reply to mapj1

    Yes, it could cause problems. Also, if every house on a terrace, for example, has an earth rod, the short distances between the spikes could actually introduce problems in the event of a fault, with voltage appearing in adjacent properties. If nothing has changed with regard to TN systems in general, I don't get why this move from a noted "may" to paragraphed "recommended" has happened in 411.4.2 - it should have been in Part 8 regarding PEI and island mode if that's the concern.

  • 0 in reply to Simon Mitchell

    Round here (small market town in Hants) we have streets of 1930s houses with overhead TT, each with an electrode at tripping hazard height by the front door. The usual issue is the rod rotting off or the wire being cut, not induced voltages due to  faults from the neighbours. But of course on a fully TT street, the fault currents injected into the earth are quite low.

    It is more complex when it is a mixture of tt and tnx on the same TX, and I suspect 'what is best' varies case by case,

    Mike

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