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Discuss Opinion on Supply System Type Wanted: TN-S or TN-C-S in the New Member Introductions area at ElectrciansForums.co.uk.

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  1. jlrb
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    jlrb EF Member

    Location:
    London
    Hi - My first post to this forum.

    I am having a disagreement with another electrician on the type of the supply characteristics for a domestic installation, i.e. whether it is TN-S or TN-C-S. I have uploaded a photo of the cutout/supply head. To resolve the disagreement I suggested we ask for a 3rd, 4th, 5th .... opinion from the forum.

    The building is in a suburban area and is over 100 years old , not that I am suggesting that the supply head is that old. There are no PME labels/markings. The measured Ze is 0.11 ohms.

    Thanks for your views in advance.

    jlrb

    Supply Type.jpg
     
  2. Lee42
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    Lee42 Lee

    Location:
    England
    I would say TN-S
     
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  3. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    only DNO could tell you for sure . rare to see supply in split concentric.
     
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  4. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    Did you test L-N fault loop?
     
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  5. Lee42
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    Lee42 Lee

    Location:
    England
    Did you have to remove the seals to gain access?
     
  6. jlrb
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    jlrb EF Member

    Location:
    London
    Yes that is what I though - however when I called UKPN they said that they do not have information on supply type. Go figure! So no help there.
     
  7. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    measure both pefc and pscc. if they are the same, i'd opt for TNC-S.
     
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  8. jlrb
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    jlrb EF Member

    Location:
    London
    No, the seal was already broken.
     
  9. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    :eek::eek::eek::eek::eek:
     
  10. jlrb
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    jlrb EF Member

    Location:
    London
    Thanks - that was my thought on next step too if there isn't a barrage of consensus from the forum. Even then it will still be an inferred result which I was hoping to avoid.
     
  11. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    you could always dig up the supply cable and see where the earth is. :(
     
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  12. jlrb
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    jlrb EF Member

    Location:
    London
    Ha ha - I bet the DNO would love that!
     
  13. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
    Business Name:
    F.H. Electrical
    TN-S
     
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  14. jlrb
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    jlrb EF Member

    Location:
    London
    As Murdoch and telectrix suggested:

    Measured PEFC = 2.10 kA (0.11 ohms)
    Measured PSSC = 1.30 kA (0.18 ohms)

    This indicates to me that it is TN-S rather than TN-C-S, but I was expecting the relative values to be the other way around - but on reflection I am not sure why I should expect that.
     
  15. Murdoch
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    Murdoch Electrician's Arms

    Location:
    Woking
    My "guess" would have been TN-S..................
     
  16. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    The earth is separate in the supply cable to the neutral so TN-S
     
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  17. Risteard
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    Risteard Electrician's Arms

    Location:
    Derry, Ireland
    Business Name:
    Walsh Electrical Services
    Surely it must be TN-S as there appears to be a separate neutral and protective conductor. As there is no PEN conductor it can't be TN-C-S.

    It's also in a bloody dangerous condition!
     
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  18. UKMeterman
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    UKMeterman Electrician's Arms

    Hi,
    1. Why did you open the head? You have no right to do so and the older ones can and do go bang. (research arc flash).
    2. When you did the the PEFC test did you isolate the installation, disconnect the earth cable from the terminal shown and test at that terminal?
     
  19. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    It's TNS, no testing necessary, just count the number of incoming conductors!
     
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  20. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    The neutral and cpc are not combined so TN-S.
     
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  21. jlrb
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    jlrb EF Member

    Location:
    London
    Thanks everyone for your input and help on this. Great forum and good advice.
     
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  22. jlrb
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    jlrb EF Member

    Location:
    London
    1. I did not open the head - I was not the photographer.
    2. Yes I did. To avoid any chance of multiple earth paths.
     
  23. Devonchris
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    Devonchris Regular EF Member

    Location:
    Devon
    Business Name:
    O
    I would go for TN-C-S.
    If you look carefully at incoming supply, the concentric cable has only 2 conductors. The centre line conductor and outer stranded neutral. Part of the stranded neutral has been seperated and used to feed the earth terminal. (Effectively creating a link between them) the remaining strands have then been painted black to form the neutral conductor.

    So to my eyesight, which is not what it was, it's combined in the service head, therefore TN-C-S.
     
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  24. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    IMG_2950.GIF
    The neutral and cpc are not combined in the service head and are separate split like the picture
     
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  25. Devonchris
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    Devonchris Regular EF Member

    Location:
    Devon
    Business Name:
    O
    Never seen cable like that Ian.
    Having had another look I think your right.
     
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  26. Lee42
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    Lee42 Lee

    Location:
    England
    I would agree with that.
    My father is a cable jointer for enw and have showed him the picture.
    This was his reply
    It looks like 16 or 26 mm single phase split cable or scne which is separately combined neutral & earth
     
  27. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    I think it looks pretty cool
     
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  28. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
    Business Name:
    F.H. Electrical
    I reckon if that was TN-C-S then the earth would come out of the neutral block.
     
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  29. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    The picture from the OP really couldn't make it any more obvious.
     
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  30. jlrb
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    jlrb EF Member

    Location:
    London
    Thanks for the picture - that looks very much like the configuration in the image I originally posted. Just to clarify is the consensus still that this is TN-S?

    This would align with the observation that the PEFC and PSSC are different.

    Thanks again for very helpful insights from the forum.
     
  31. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Yes TN-S
    As you say your test results of pssc and pefc are what they are.
     
  32. Lee42
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    Lee42 Lee

    Location:
    England
    If it was PME. Both stranded cores would go into the neutral terminal, with the main earth being tapped off from there
     
  33. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Time to go to spec savers I think, there are clearly three separate conductors there!
     
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  34. Lee42
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    Lee42 Lee

    Location:
    England
    I think devonchris might of been on the drink, if he thinks someone would get there paintbrush out, and start painting the copper strands black :tearsofjoy::tearsofjoy:
     
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  35. Devonchris
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    Devonchris Regular EF Member

    Location:
    Devon
    Business Name:
    O
  36. Lee42
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    Lee42 Lee

    Location:
    England
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