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  1. alan132
    Offline

    alan132 Active EF Member

    Location:
    Essex
    Working on a old property in a slightly remote area installing a new circuit.

    When I looked at the earthing it looked like a tns but I investigated and found a old 2.5mm running towards the rod.

    My problem is I am getting a ze reading of 0.25 ohms.

    Ino we had a really heavy down poor the day before but to be that low?

    I am wait for the dno to confirm the earthing but they ain't rushing.

    Any thoughts
    I know a good reading for tt is 200 ohms or lower. This is the first one I have worked on
     
  2. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Have you got all main protective bonding disconnected to remove parallel paths. How did it look TN-S for it to then become TT.
     
  3. alan132
    Offline

    alan132 Active EF Member

    Location:
    Essex
    Thats is just the main cable nothing else

    When I manage to peak around the wooden board covering the mains it looked like a swa with a earth strap.
    It's under the stairs and I could hardly fit my head in there.
     
  4. Richard Burns
    Offline

    Richard Burns Trusted Advisor

    Location:
    Cambridgeshire
    Business Name:
    Richard Burns
    If you have an earth connection to the sheath of the supply cable and the Ze reading with all other earthing connection disconnected is 0.25Ω then the supply is TNS.
    If it has a rod connected to the MET then there is an earth rod connected to the MET it would not change the earthing of the supply.
     
    • Like Like x 1
  5. alan132
    Offline

    alan132 Active EF Member

    Location:
    Essex
    As I said I assumed it was a swa.
    But looking out side there was only 2 cables going in.
    So I would say that was a tube of some sort

    This place has had works done but no one has left any certificates

    I will have to contact dno again to comfirm the earth.
     
  6. mhar
    Offline

    mhar Electrician's Arms

    Location:
    devon
    You say it is remote, is it on it's own and does it have it's own transformer? If so is the transformer earthed at the pole?
     
  7. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Hi Alan - I've been building up my TT portfolio lately using the larger 5/8" 4ft rods, two at a time. Around here in wet clay this has been good for 10 Ohms or less. I would need to parallel up many many of these to get your numbers, so it's def a DNO means of earthing in my humble opinion. Have you checked Ze against short circuit impedance? Avoid the non trip setting, if you get 0.25 for both then perhaps DNO has PME'd an old TT at some point.
     
  8. alan132
    Offline

    alan132 Active EF Member

    Location:
    Essex
    It's a area they just keep adding to
    There is power pole then when you get to a built up area they stop.

    Can't find a substation near by.

    I don't know if this may affect it but there is a dyke around the place and it on a flood plane
    Ground soft and soak water in
     
  9. mhar
    Offline

    mhar Electrician's Arms

    Location:
    devon
    Properties can be fed from pole mounted transformers not necessarily near a substation.
    There is a method of earthing very occasionally used on single properties in remote locations fed from their own transformer (pnb).
    Have you looked at the pole(s) supplying? If a pme overhead supply there should be a pme label on every third or fourth pole plus you will see an earthing conductor running down the pole.
     
    • Agree Agree x 1
  10. buzzlightyear
    Offline

    buzzlightyear Electrician's Arms

    Location:
    star command
    you are not dowsing for water ,you need to take pic of the set up and show us if poss and speak to dno.
     
    • Funny Funny x 2
  11. Midwest
    Offline

    Midwest Electrician's Arms

    Location:
    Oxfordshire
    Sorry OP for hijacking your thread. Wiko what surveying do you do, if any, when choosing a place to install your earth rods, so as not to hit any other services?

    Just curious as I've not done one yet, and if the 18th has its way, I'd better get some practise in.
     
  12. anthonybragg
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    anthonybragg Electrician's Arms

    Location:
    NORTHAMPTON
    Business Name:
    CHARLTEC ELECTRICAL LTD
    18th compliance already !.
     
    • Like Like x 1
  13. ruston
    Offline

    ruston Trusted Advisor

    Location:
    Northumberland
    I have a three wire overhead supply from a pole transformer, bare and only the line (live lol) insulated from the last pole to the house. Three houses on this one supply.
     
  14. Phil Thompson
    Online

    Phil Thompson Let us light up your life! Electrician's Arms

    Location:
    Newtownards
    Business Name:
    Brite Spark Electrical
    I found those rods give a much better reading myself, going to use them from now on.
     
  15. Midwest
    Offline

    Midwest Electrician's Arms

    Location:
    Oxfordshire
    Same question for you Phil;

    Sorry OP for hijacking your thread. Wiko what surveying do you do, if any, when choosing a place to install your earth rods, so as not to hit any other services?

    Just curious as I've not done one yet, and if the 18th has its way, I'd better get some practise in.
     
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