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TT or PME..best practice?

Evening all,


I’m currently looking into running a submain approx 100m buried from a PME supply to a small outbuilding (timber frame, metal sheet clad) that is being used next to a glamping tent as a place to cook and shower etc. The sub main will be a 16mm SWA..I was initially going to run a 3 core SWA or potentially a 2 core SWA with a seperate 10mm CPC (slight cost reduction) with the later option. I’ve since thought that perhaps a TT install would suffice, and, as possibly in the future I might be asked to extend the power into the tent, which, would require a TT setup. Any thoughts of this from a safety point or preference, also, if deciding on a TT and running a 2 core SWA as a submain which would obviosuly be a cost saver compared to a 3 core, however, would it be best practice to still have a CPC available seeing as a trench is now open...future proofing....? just as a side note, the metal sheets will be bonded to earth and any plumbing in the building is plastic pipes, also, this isn’t a question about cable selection i.e. the sub mains might be 16 or 25mm once I know exactly what the client wants, this question relates to the earthing setup. Thanks in advance!.

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Parents

  • Sparks79:




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    Chris Pearson:




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    UKPN:

    This shed, because of its construction should be protected by an independent earth electrode and rccd. The origin, at the fusebox, PME, protects the cable. The DNO req a min distance of 2 metres from the electrode to PME bonded material. The separate earth lead is a good idea in this case for future use, the cpc of the cable being too small to meet the PME regs.

    Regards, UKPN




    What P.M.E. regs will not be complied with if just the S.W.A. cable armour is used to supply the building, justifying the need for a separate "earth lead". There will be no main bonding to carry out as the incoming water pipe is plastic? 


     

    We are told that this shed has a tin roof, and walls. Should they be bonded or not? If they don't actually reach the ground, and the frame is not conducting, it is difficult to see how they are ECPs, so don't bond.


    PME earths can be "exported" (even after Brexit ? ) but only provided that the CPC is sufficient to provide main bonding.


    If these structures are caravans or tents, then as others have said above, the special locations rules apply.


    Incidentally, I wouldn't worry about the extra cost of 3-core as opposed to 2-core, or even the CSA size of the cable - it is small in comparison with the cost of digging the trench, etc. And BTW, it is difficult to terminate 25 mm2 SWA into a 25 mm2 terminal ('cos the core isn't round) let alone a 16 mm2 one!


     




    I think that the O.P refers to the metal parts of the shed being earthed not bonded. Perhaps with its own earth electrode(s).  I would not bond the metal external shed parts at all, it is not necessary and could introduce a hazard like main bonding a metal walled caravan.


    Are there any extraneous gas pipes in the shed?


    Z


     




    Hi Z, currently no extraneous gas pipes, I believe if any gas is introduced it will be from a gas bottle for a gas hob, no pipes in the ground.


     




    Well, if there are no extraneous-conductive-parts then there is nothing to main bond. Plastic water pipe and no underground gas pipes. 411.3.1.2.


    Z.

Reply

  • Sparks79:




    Zoomup:




    Chris Pearson:




    Zoomup:




    UKPN:

    This shed, because of its construction should be protected by an independent earth electrode and rccd. The origin, at the fusebox, PME, protects the cable. The DNO req a min distance of 2 metres from the electrode to PME bonded material. The separate earth lead is a good idea in this case for future use, the cpc of the cable being too small to meet the PME regs.

    Regards, UKPN




    What P.M.E. regs will not be complied with if just the S.W.A. cable armour is used to supply the building, justifying the need for a separate "earth lead". There will be no main bonding to carry out as the incoming water pipe is plastic? 


     

    We are told that this shed has a tin roof, and walls. Should they be bonded or not? If they don't actually reach the ground, and the frame is not conducting, it is difficult to see how they are ECPs, so don't bond.


    PME earths can be "exported" (even after Brexit ? ) but only provided that the CPC is sufficient to provide main bonding.


    If these structures are caravans or tents, then as others have said above, the special locations rules apply.


    Incidentally, I wouldn't worry about the extra cost of 3-core as opposed to 2-core, or even the CSA size of the cable - it is small in comparison with the cost of digging the trench, etc. And BTW, it is difficult to terminate 25 mm2 SWA into a 25 mm2 terminal ('cos the core isn't round) let alone a 16 mm2 one!


     




    I think that the O.P refers to the metal parts of the shed being earthed not bonded. Perhaps with its own earth electrode(s).  I would not bond the metal external shed parts at all, it is not necessary and could introduce a hazard like main bonding a metal walled caravan.


    Are there any extraneous gas pipes in the shed?


    Z


     




    Hi Z, currently no extraneous gas pipes, I believe if any gas is introduced it will be from a gas bottle for a gas hob, no pipes in the ground.


     




    Well, if there are no extraneous-conductive-parts then there is nothing to main bond. Plastic water pipe and no underground gas pipes. 411.3.1.2.


    Z.

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