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Earthing advice

Discussion in 'Electrics UK' started by dan77714, 13 Oct 2021.

  1. dan77714

    dan77714

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    Hi all

    Just wondered if someone would be able to give me some advice regarding earthing.

    I've had the DNO out recently to have a survey done to replace my service head from the old cast iron one we have. My current earthing is TNS however the current earth cable is just strapped on the incomming pipe. DNO said this does not provide sufficient earthing. They also warned that on replacing the head they would possibly have to leave my installation unearthed if there was not enough slack on the cable in the pipe to get to the lead sheath within and that I'd have to get an electrician to install an earth electrode and make it a TT system.

    When I asked about changing it to a TN-C-S PME arrangement, they said this would require pulling in a new cable?

    My understanding of TN-C-S is that the earth and Neutral are combined in the DNO supply cable out in the street so the neutral can be separated and used as an earth from the service head? Is my understanding correct? And if so is it just a case the neutral and earth being connected together in the new service head? I do know a few of my other neighbours have a TN-C-S arrangement so i'm fairly sure this is available in my area.

    Many Thanks!
     
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  3. EFLImpudence

    EFLImpudence

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    I would say your understanding is correct with the proviso that TNCS does not necessarily mean PME if they have not fitted the ME - Multiple Earths.

    The DNO is, I believe, obligated to maintain your earth if they already provide it - but they are not renowned for honouring their obligations.

    So - if it does, for whatever reason, require a new cable, I would say that that is their responsibility and explains why they are saying YOU must TT it.
     
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  4. EFLImpudence

    EFLImpudence

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    Just noticed you are in London; are you in a fully built-up urban part?
     
  5. dan77714

    dan77714

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    Hey, thanks for your response, Yeah im not entirely convinced by some of the advice given by the guys who came to survey. There were some other things they said which were a bit questionable.

    And yepp i'm in a fully built up urban part of London
     
  6. bernardgreen

    bernardgreen

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    Some good information here

     
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  7. JohnW2

    JohnW2

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    Literally and physically, that's obviously correct but my understanding is that, at least in the UK (and probably most/all places), it is not permissible to provide a TN-C-S supply if the "ME" is not present.

    What makes no sense is the suggestion that providing a TN-C-S supply (to replace the currently unsatisfactory, TN--S one) would require "pulling in a new cable". If the current supply is not PMEd (i.e. no "ME"s), then that would need to be addressed (obviously outside of the property in question), but there's no reason why the supply cable to the property would need to be replaced.

    Kind Regards, John
     
  8. EFLImpudence

    EFLImpudence

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    Fair enough.

    It would be odd if the OP's is the first TNS to break down in the locality, so...
     
  9. dan77714

    dan77714

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    thanks for the response,

    yes this is what didn't make sense to me either (granted, though my knowledge and experience is somewhat limited here)

    The engineer just kept saying earthing was not their responsibility and if they cant gain access to the lead sheath to provide an earth, I would have to get an electrician to make it a TT arrangement or alternatively have a new cable put in to make it TN-C-S.

    To add a bit more context here the reason the work is being done is to replace the current cast iron service head and also unloop our supply from next door which should allow the service to be upgraded to 80a from the current 30a.

    The work is supposed to be free of charge so I wonder if they aren't too keen on doing the job/would rather I paid to have a new supply put in?
     
    Last edited: 13 Oct 2021
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  11. JohnW2

    JohnW2

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    I'm glad that it's not just me.
    I don't know how true it is, but it always seems to be said thatv if a DNO ever supply an earth (TN-S or TN-C-S) then it remains their responsibility to continue providing an earth 'for evermore'. Anyway ...
    That's the bit which makes no sense to me. To have a TN-C-S supply merely requires incoming L and N conductors, which you already have. Everything else to do with providing a TN-C-S supply relates to things they have to do external to your property, to make sure that the "ME" of "PME" are present.
    Well, that may well require a new cable to your new service head, but that's nothing to do with the earthing, and seems to make even more nonsense of what they have said about "a new cable to make it TN-C-S"!
    It sounds as if they are going to 'do the work', anyway - and nothing additional would be required to make it TN-C-S (provided the external distribution network is PMEd).

    Kind Regards, John
     
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  12. JohnW2

    JohnW2

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    Quite so. What they are saying seems to be total nonsense, particularly given what the OIP has told us about what other work they are doing.

    Kind Regards, John
     
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  13. dan77714

    dan77714

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    Yeah, they did say if I wanted a 100a supply i'd need to pay for a new supply cable (understandably), however they said the existing one should support 80a once unlooped but would have the earthing problem...
     
  14. JohnW2

    JohnW2

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    I'm surprised, but it sounds as if the person who said this probably "didn't know what he was talking about". I think you probably need to find someone different, maybe 'more senior', to talk to.

    Kind Regards, John
     
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  15. dan77714

    dan77714

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    Yeah, I think I do. I'll contact the manager assigned to my case, see what the verdict is following the survey and hopefully I can get more clarification on this earthing thing. I just wanted to check here if I understood correctly the way earthing is supposed to work first so I can question it:unsure:.

    They're also trying to charge me for lifting floorboards in my neighbour's house to put their new supply in which i'm not too happy about either.

    but thanks for all the advice! much appreciated :)
     
  16. JohnW2

    JohnW2

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    I think you understand perfectly - it's the people you're talking to in whom that is more questionable :)
    That also sounds 'a bit rich'. Looped supplies only came into existence so that they could save effort/money, so I would have thought it would be down to them to bear the costs of 'undoing' that. I would certainly think that you should have a good moan about that, too!

    Kind Regards, John
     
  17. dan77714

    dan77714

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    Don't get me started on this.:LOL:
    I did mention this to the engineer however he said
    "but this is what EVERYONE has [the looped supply] we're only required to provide a 60A service and that's what we've supplied"- (obviously also forgetting he had just told me that my supply was 30A :rolleyes:)
     
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