Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 54 replies
  • Subscribers 33 subscribers
  • Views 15334 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Farm earthing arrangements.

Sparkingchip
009a7dbbf62372ab469269cf2662d114-huge-20200425_145756.jpg


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
  • 0
    Drawing not to scale, but is the farmstead the only customer from the transformer?


    Is the DNO's earth rod connected to the service head; and if so, is the N-E bond made there? If that is the case, with the DNO's agreement, why not sever the N-E bond, retain the rod, and make the whole lot TT?
  • 0
    Jump forward.


    I will say that the earthing arrangement is considered to be TN-C-S, but is PNB not PME. So is considered by people on a far higher pay grade than me as effectively TN-S.


    So as an electrician I have to consider the DNO system as TN-C-S, which is not banned on farms, but actually this version of TN-C-S may not have the risks that are normally associated with it because it is effectively TN-S, but I cannot declare it as that.


    Until the PV system was installed there was no interconnection between the house and buildings by protective conductors or extraneous conductive parts, but now there is.


    So where to from here?


     Andy Betteridge
  • 0

    Sparkingchip:
    88906f5ca0892a9854b2587a041b6b36-huge-20200425_173713.jpg


    Read the note to 421.4.3


    That makes the reference to a ban  in agriculture installations of using a TN-C earthing system a red herring,  because we cannot use it anywhere in the UK anyway. 


    Andy Betteridge 




    Indeed Andy, but I think that you mean Reg. 411.4.3 NOTE.


    Z.

  • 0
    So is it 411.3.1.1 that concerns us? 


    Z.
  • 0
    88906f5ca0892a9854b2587a041b6b36-huge-20200425_173713.jpg


    Read the note to 421.4.3


    That makes the reference to a ban  in agriculture installations of using a TN-C earthing system a red herring,  because we cannot use it anywhere in the UK anyway. 


    Andy Betteridge
  • 0
    If TN-C  (earthed concentric wiring) is normally forbidden for use in the U.K. then why make a special mention of it in reg. 705.411.4? Many respected writers have pointed out that P.M.E. supply requests  will often be refused to agricultural installations by the D.N.O. So is your farm supply provided with TT earthing? Enquiries need to be made.


    Edit. Page 38 and the definition of the expression TN-C system clarifies the matter.


    Z.


  • 0
    2a23fac2d9596779e8d3239c89d7c285-huge-20200425_171329.jpg

    BS7671 Part 2 Definitions. System. 


    Red herring? 


    Andy Betteridge
  • 0
    There’s a question to answer, also precisely what is the DNO earthing arrangement?


    I deliberately did not label the earthing arrangements apart from the TT that I installed for the farm buildings.


     Andy Betteridge.
  • 0

    Sparkingchip:

    Possible red herring alert.


    We cannot use  TN-C anywhere in the UK can we?


    Andy Betteridge 




    Does the TN-C reference not apply to TN-C-S and include it as well?


    Z.

  • 0
    Possible red herring alert.


    We cannot use  TN-C anywhere in the UK can we?


    Andy Betteridge

Community Rules & Guidelines