Hi All, we have been asked to install tails from a new DNO 400A TPN cut-out to an existing panelboard. This new DNO supply appears to be TN-S (we are trying to source the quotation to confirm the DNO supply arrangement.) The building is of steel frame cons
1No. PME and 1No. TN-S supply into a single steel frame building.
I am reading this post as there has been a second DNO supply run into an existing steel framed building as a upgrade to the supply or to sub divide the installation with the new supply supplying an existing distribution board and that the original supply has a TN-C-S (PME) earthing arrangement, so standard practice would be to TT earth the new supply, so it needs upfront RCD protection.
Even if the new second supply has been installed by the DNO using SNE concentric cable and is deemed to be TNS, it presumably comes from the same transformer as the original TN-C-S (PME) supply, so it needs to be treated as TN-C-S (PME).
I am reading this post as there has been a second DNO supply run into an existing steel framed building as a upgrade to the supply or to sub divide the installation with the new supply supplying an existing distribution board and that the original supply has a TN-C-S (PME) earthing arrangement, so standard practice would be to TT earth the new supply, so it needs upfront RCD protection.
Even if the new second supply has been installed by the DNO using SNE concentric cable and is deemed to be TNS, it presumably comes from the same transformer as the original TN-C-S (PME) supply, so it needs to be treated as TN-C-S (PME).
