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TT earthing at kiosk and Barn Stable with large distance between both

Duncan G

I have an install on a field to do where the supply comes in from a power networks overhead pole transformer to a kiosk roughly 8 meters away, in the kiosk there will be the DNO cut out / supplier meter / 100A switch fuse.

From here there will then be a 70mm 4 core swa running underground 250 meters to the barn where it will terminate using 2 cores for phase and 2 cores for neutral to comply with voltage drop allowance.

My question is do I earth stake the Kiosk end for earthing at that end so as to protect the armouring of the swa and housings of the switch fuse then earth stake at the barn with earth separation of the SWA to prevent 2 earth paths and what precautions do i need to consider as there will be horses at the barn. Your comments will be greatly appreciated. 

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    Probably need a few more details .. like does the DNO provide a PE terminal - that'll dictate whether the 250m cable is TT or can be TN, and whether the 100A switchfuse will do for ADS (but double check Zs as the armour will be "small" compared with doubled cores, especially for that length) or whether you'll need an RCD at the supply end as well.

    Unless the DNO are willing to guarantee a non-PME supply or there's a buried grid you can bond to, the stable end is likely to to have to be TT - but whether the 250m cable is part of the same earthing system will be a design choice. The TT system the TN system (if any) will have to be kept strictly and reliably separated - and nothing exposed and connected to differing earthing systems within reach of each other.

    Horses mean section 705 of BS 7671 will apply (Agricultural and horticultural premises) - there's more in there than I can reasonably type here, but there are lots of additional requirements to deal with everything from the brute force and the "conductive liquids" that horses can bring, to the fire hazard from the straw. "Long wheel base" 4-legged animals are also particularly prone to differences in potential across the ground surface - so take care with the positioning/depth of electrodes.

       - Andy.

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  • 0

    Probably need a few more details .. like does the DNO provide a PE terminal - that'll dictate whether the 250m cable is TT or can be TN, and whether the 100A switchfuse will do for ADS (but double check Zs as the armour will be "small" compared with doubled cores, especially for that length) or whether you'll need an RCD at the supply end as well.

    Unless the DNO are willing to guarantee a non-PME supply or there's a buried grid you can bond to, the stable end is likely to to have to be TT - but whether the 250m cable is part of the same earthing system will be a design choice. The TT system the TN system (if any) will have to be kept strictly and reliably separated - and nothing exposed and connected to differing earthing systems within reach of each other.

    Horses mean section 705 of BS 7671 will apply (Agricultural and horticultural premises) - there's more in there than I can reasonably type here, but there are lots of additional requirements to deal with everything from the brute force and the "conductive liquids" that horses can bring, to the fire hazard from the straw. "Long wheel base" 4-legged animals are also particularly prone to differences in potential across the ground surface - so take care with the positioning/depth of electrodes.

       - Andy.

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