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Farm Outbuilding Office & TT Earthing etc.

Zoomup

The wild geese are migrating now. We can see them overhead flying south as they appear out of the morning mists, calling to each other as they fly in large numbers in a large V formation. Then they disappear back into the high level mists. Some say that they will fly to S. Africa.

Wild Geese Flying - Bing video

Meanwhile, a local smallholder who keeps four footed animals, has built a new wooden building to be used as an office and farm storage unit. The new proposed office is only about 25 metres square.

He asked me about installing a few sockets and lighting in the new building.

Presently the nearest supply is a plastic cased TT earthed consumer unit.

Near to the new build there are two earth electrodes used solely by the electric fencer unit. These are run in parallel. How far away from any TT L.V. installation earth electrode should they be?

Will the electric fencer interfere in any way with I.T. equipment?

Shall I supply the office with P.M.E. earthing, or shall I TT it?

I have my own thoughts on these matters, but wish not to have missed any safety issues.

There is a miniature Shetland pony that can't eat regular grass. It is allergic to it. Its hay has to be “sterilised” in a hay steamer rated at just under 3kW.

Thanks,

 

Z.

 

 

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    davezawadi (David Stone): 
     

    Graham, whilst it might be possible to find a farm with a TN-S supply, such would be considerably unusual. A private transformer might do this (I have seen a few of these for grain installations) but most distribution outside of towns is from pole-mounted transformers without a distributed Earth. TN-C is not permitted, and this I understand from 705.411.4, not that it may be not used for final circuits which are not permitted anyway elsewhere, but the supply. 705.411.1 then specifies that RCD protection must be provided everywhere on all final circuits. 

    705.411.4 does not mean TN-C-S (PME) is not permitted.

    You could have an installation with its own generator and no public supply, in which case ESQCR wouldn't apply and it may be possible to use TN-C … the purpose of 705.411.4 is to prohibit Tn-C from agricultural and horticultural premises. It has nothing to do with PME.

    Zoomup asks if he can export a PME supply, which is not permitted on a farm anyway for obvious reasons. 

    ???

     

    The conclusion is that his new building should be TT, as it has no particular disadvantage. This could be an ambiguity with the exact wording of a regulation, but I would not want an area with animals with a PME supply, even if they seem isolated from possible fault voltages, which may even be external to the farm.

    I don't disagree with the conclusion, just not sure about the “not permitted” bit (unless the DNO has particular conditions) - overall, I think it is permitted, but not recommended … two different things.

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  • 0

    davezawadi (David Stone): 
     

    Graham, whilst it might be possible to find a farm with a TN-S supply, such would be considerably unusual. A private transformer might do this (I have seen a few of these for grain installations) but most distribution outside of towns is from pole-mounted transformers without a distributed Earth. TN-C is not permitted, and this I understand from 705.411.4, not that it may be not used for final circuits which are not permitted anyway elsewhere, but the supply. 705.411.1 then specifies that RCD protection must be provided everywhere on all final circuits. 

    705.411.4 does not mean TN-C-S (PME) is not permitted.

    You could have an installation with its own generator and no public supply, in which case ESQCR wouldn't apply and it may be possible to use TN-C … the purpose of 705.411.4 is to prohibit Tn-C from agricultural and horticultural premises. It has nothing to do with PME.

    Zoomup asks if he can export a PME supply, which is not permitted on a farm anyway for obvious reasons. 

    ???

     

    The conclusion is that his new building should be TT, as it has no particular disadvantage. This could be an ambiguity with the exact wording of a regulation, but I would not want an area with animals with a PME supply, even if they seem isolated from possible fault voltages, which may even be external to the farm.

    I don't disagree with the conclusion, just not sure about the “not permitted” bit (unless the DNO has particular conditions) - overall, I think it is permitted, but not recommended … two different things.

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