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I realise this is a much-discussed topic, I have certainly read a lot on the forums already! However I wish to ask about the subtitles of earthling the outbuilding and the cost/practicality consequences.
The outbuilding (a DIY’s workshop) will have one socket ring and two lighting radials. I wish to install a garage CU, this one probably: British General 5-Module 3-Way Populated Garage Consumer Unit - https://www.NoLinkingToThis/p/british-general-5-module-3-way-populated-garage-consumer-unit/1926g
The shed has some metal parts (sheets of powder-coated steel cladding) but 1) I cannot foresee any situation where I could be touching exposed metal and 2) they are not at earth, being on a timber frame. So, I think it qualifies as “no extraneous-conductive-parts”.
This being the case, and because I am TNC-S, I would rather run power out on SWA from my house, using a spare way on the house’s CU. I think I am on TN-S. (I can clearly see the earth bonded to the sheath/armour of the incoming supply).
The outbuilding is 25m away, so to comply with voltage drop regs for the lighting ring I was going to use 3-core, 6mm^2. I.E bring the protective conductor to the outbuilding on 6mm^2.
6mm^2 is certainly adequate current wise.
But what about the earthling? If in the future I decide to bond the cladding I need to be at 10mm^2 to comply. To help the cost I have the option of bring the SWA into the house at a different point (via a rated junction box) and go 10 meters inside, under the floorboards. But I cannot use 10mm^2 ‘twin and earth’ because the earth is always smaller than the earth. At the point I have to use 10mm T&E and run 10mm green/yellow cable too. I can do it but it’s become a little bit complicated and very expensive.
So I think I have these choices.
1) Treat the install as no extraneous-conductive-parts, run my 3-core 6mm SWA all the way from house CU to outbuilding.
2) Treat it as having extraneous-conductive-parts and run 10mm^2 SWA (with some extra 10mm plus T&E in the house)
3) Use and earthling rod and make a TT system at the outbuilding. Almost all the forums I have read seem pretty negative about this, citing changeable ground conditions and high impedance.
I think there my choice all hangs on the no extraneous-conductive-parts definition, and if yes there is a substantial increase in cost and complexity.
I have read a lot of the forum debate on this, and I don’t want to open a can of worms. I read the guide by John Ware (2005) and enjoyed sinewave’s “The Ultimate PME/TNS Exportation! by Sinewave“. (A good guide For 'exported PME' and outbuildings! - https://www.electriciansforums.co.uk/threads/a-good-guide-for-exported-pme-and-outbuildings.28159/page-2) . I also watched most of John Ward’s stuff but am still not 100% clear.
Please, any/all advice appreciated. I think I ‘know the answer – I have to 10mm everything to be safe.
Dan
The outbuilding (a DIY’s workshop) will have one socket ring and two lighting radials. I wish to install a garage CU, this one probably: British General 5-Module 3-Way Populated Garage Consumer Unit - https://www.NoLinkingToThis/p/british-general-5-module-3-way-populated-garage-consumer-unit/1926g
The shed has some metal parts (sheets of powder-coated steel cladding) but 1) I cannot foresee any situation where I could be touching exposed metal and 2) they are not at earth, being on a timber frame. So, I think it qualifies as “no extraneous-conductive-parts”.
This being the case, and because I am TNC-S, I would rather run power out on SWA from my house, using a spare way on the house’s CU. I think I am on TN-S. (I can clearly see the earth bonded to the sheath/armour of the incoming supply).
The outbuilding is 25m away, so to comply with voltage drop regs for the lighting ring I was going to use 3-core, 6mm^2. I.E bring the protective conductor to the outbuilding on 6mm^2.
6mm^2 is certainly adequate current wise.
But what about the earthling? If in the future I decide to bond the cladding I need to be at 10mm^2 to comply. To help the cost I have the option of bring the SWA into the house at a different point (via a rated junction box) and go 10 meters inside, under the floorboards. But I cannot use 10mm^2 ‘twin and earth’ because the earth is always smaller than the earth. At the point I have to use 10mm T&E and run 10mm green/yellow cable too. I can do it but it’s become a little bit complicated and very expensive.
So I think I have these choices.
1) Treat the install as no extraneous-conductive-parts, run my 3-core 6mm SWA all the way from house CU to outbuilding.
2) Treat it as having extraneous-conductive-parts and run 10mm^2 SWA (with some extra 10mm plus T&E in the house)
3) Use and earthling rod and make a TT system at the outbuilding. Almost all the forums I have read seem pretty negative about this, citing changeable ground conditions and high impedance.
I think there my choice all hangs on the no extraneous-conductive-parts definition, and if yes there is a substantial increase in cost and complexity.
I have read a lot of the forum debate on this, and I don’t want to open a can of worms. I read the guide by John Ware (2005) and enjoyed sinewave’s “The Ultimate PME/TNS Exportation! by Sinewave“. (A good guide For 'exported PME' and outbuildings! - https://www.electriciansforums.co.uk/threads/a-good-guide-for-exported-pme-and-outbuildings.28159/page-2) . I also watched most of John Ward’s stuff but am still not 100% clear.
Please, any/all advice appreciated. I think I ‘know the answer – I have to 10mm everything to be safe.
Dan
