Ok, The DNO WILL NOT supply TNCS to a steel framed multi occupancy structure, end of.
They will supply ONE unit, but all the rest have to have TT
Reason is this;
Say there are 10 customers each with their own TNCS supply. All customers have quite correctly bonded their MET to the frame of the building in their own unit.
Now, at the service head the neutral is connected to the earth, which in turn is connected to the earthing conductor, which is connected to the MET, which is bonded to the shed frame..
Now, electricity will try to take the path of least resistance. So, what happens in practice, is, say the LV main feeding these units is near one end, the service cable to the first supply intake will be comparatively short. So what happens, is that EVERYONES neutral current, will try to flow through bonding conductors and the shed frame, and all try to disappear back down the supply neutral with the least resistance. This is grossly overloaded, and so could burn out and apart from the fire risk, we all know what happens with TNCS when you have a neutral fault...
You can also have problems with all these "stray currents" flowing through the frame of the building causing other effects such as interferance with the proper working of computers and other kit that is liable to be affected by weird magnatic effects caused by the shed now being a live conductor..
john...