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Farm earthing arrangements.

Sparkingchip
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Some years ago I started doing electrical work at a farm, originally the farm buildings and house were both connected to the DNO earth terminal.


I altered it so that the farm buildings are TT , but left the house connected to the DNO earth terminal. The possible issues are that there is a steel clad switch fuse enclosure for the house inside a wooden cupboard in the farm workshop and the SWA cable for the house passes through the ground immediately adjacent to the farm building. But there was no physical connection between the house and farm earthing arrangements.


It had been like that for a few years as the house has not had any alterations at all, just a few repairs. So the house installation is effectively exactly the same as it was when the house and the farm buildings were thirty years ago and connected up as a new installation by the DNO.


However (you knew there was going to be a however!) a couple of years ago PV panels were installed on the farm building roof and the installers used the DNO and house earth terminal rather than the farm buildings earth terminal, despite the PV system being in and on the farm buildings and it having storage batteries that feed back into the both installations as they share a meter; and the storage batteries act as a supply to emergency lighting in the farm buildings when the installation is off-grid.


I am now reviewing the earth arrangements, the house is empty and needs tidying up, thirty two lights need replacing and odd repairs, there won't be any alterations it is just replacing fittings and replacing MCBs in the split load consumer unit with RCBOs to give additional RCD protection in the house. 


I will leave it at that and not express my thoughts, as it will be more interesting to see what your thoughts are rather than trying to get you to consider mine.


Comments please. 


Andy B
Parents
  • 0
    And that is the nub of the problem I think - when is TN-S not TN-S ?

    In terms of the broken PEN risk, and all the attendant  'not suitable for livestock, caravans, building sites, cars, or anything else that worries regulation writers  of a nervous disposition '  , the answer is very simple, when there is a multiplicity of NE links, instead of just one.

    Sadly in terms of sensible definition, this is not always the one used, so we find we can have.

    PNB -TNC-s or

    PNB TN-S


    To me in terms of the true risk, this sounds more like TNS and until another property is added to the transformer with an NE link at the cut out, it will remain immune to the rise of earth potential risk associated with PEN failures.


    You can have add many and various buried electrodes to TN-S of course, so long as you do so to the CPC, and not to the neutral.

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  • 0
    And that is the nub of the problem I think - when is TN-S not TN-S ?

    In terms of the broken PEN risk, and all the attendant  'not suitable for livestock, caravans, building sites, cars, or anything else that worries regulation writers  of a nervous disposition '  , the answer is very simple, when there is a multiplicity of NE links, instead of just one.

    Sadly in terms of sensible definition, this is not always the one used, so we find we can have.

    PNB -TNC-s or

    PNB TN-S


    To me in terms of the true risk, this sounds more like TNS and until another property is added to the transformer with an NE link at the cut out, it will remain immune to the rise of earth potential risk associated with PEN failures.


    You can have add many and various buried electrodes to TN-S of course, so long as you do so to the CPC, and not to the neutral.

Children
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