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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
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  • 0
    Sorry but I'm completely confused now this all seems overly complicated am I right in thinking that if the neutral between the intake and the transformer breaks then the whole lot will go off but if the earth come off of its rod at the house then things will continue to work and be protected because of the link at the head also the barn supply will be ok because it's still connected properly. Most of the houses in my area are earthed via the metal cable sheath but at 2 property's rewired a few years back there is a neutral earth bond which is connected to the MET and also to a metallic water pipe is this what the farms got?

    Think of the electrode connected at the cut-out as the supplier's source earth (the one at the transformer in the textbook diagrams), if that goes AWOL then the LV system isn't (reliably) referenced to Earth any more and (via capacitive coupling from the HV side of the transformer) may drift up to some nasty voltage above true earth, but there will still be 230V between L and N so things will still function (if more likely to go bang as the insulation to true Earth is over-stressed).


    Yes if the supply N breaks then things will stop working. Depending on whether the system is PME or PNB (and which version of PNB) that might also mean the consumer's earth terminal being pulled up to something approaching line voltage.


       - Andy.
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  • 0
    Sorry but I'm completely confused now this all seems overly complicated am I right in thinking that if the neutral between the intake and the transformer breaks then the whole lot will go off but if the earth come off of its rod at the house then things will continue to work and be protected because of the link at the head also the barn supply will be ok because it's still connected properly. Most of the houses in my area are earthed via the metal cable sheath but at 2 property's rewired a few years back there is a neutral earth bond which is connected to the MET and also to a metallic water pipe is this what the farms got?

    Think of the electrode connected at the cut-out as the supplier's source earth (the one at the transformer in the textbook diagrams), if that goes AWOL then the LV system isn't (reliably) referenced to Earth any more and (via capacitive coupling from the HV side of the transformer) may drift up to some nasty voltage above true earth, but there will still be 230V between L and N so things will still function (if more likely to go bang as the insulation to true Earth is over-stressed).


    Yes if the supply N breaks then things will stop working. Depending on whether the system is PME or PNB (and which version of PNB) that might also mean the consumer's earth terminal being pulled up to something approaching line voltage.


       - Andy.
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