Given that in anywhere that ESCQR  operates, you cannot distribute as TNC after you have connected your first piece of consumers equipment, it is not only right, but essential, that the supplies to outbuildings on submains are carried as the 'S' part of the TNC-S system. Within those buildings you would treat the requirement for bonding and so on, as you would for the main building i,e, plumbing bonds and so on in PME size cables, but apart from that it is all normal.

Mike.

TN-S is only TN-S if the PE is separate from the N all the way back to the source (transformer) - generally it's assumed that any DNO provided earth terminal these days will have "PME conditions" attached, even if it looks like TN-S at the intake.

DNOs even sometimes provide separate earth wires to multiple customers in a multi-occupancy building - connected to a common N-PE link outside - all fed from a conventional TN-C main - all still very much PME.

a separate bond to a dedicated earth bar (i.e. 1No CPC and 1No bond).

That bit looks slightly odd (if I'm reading it right) - BS 7671 requires both c.p.c.s and main bonding conductors to connect to the same MET within each building (to minimise the potential difference between exposed- and extraneous-conductive-parts) - so while two "earth" conductors isn't a problem as such, they really should be connected together at both ends (or go to earth bars which are then connected together).

   - Andy.

The main bonding of the second building, and a protective bonding from the MET of the second building back to the MET of the original building, will still need to be sized in accordance with Table 54.8 using the CSA of the distributor's PEN conductor.