Main earth bonding protective conductors

[cliffed]

he should have put above in the first post so that we are on the first page not the last .

Sorry

If the structure is metal and in contact with the ground than yes it is extraneous. But the next key question that needs to asked is "is it high resistance extraneous or is it low resistance extraneous? The low resistance extraneous is the concerning one. In both situations fault current can be exported and so there is a potential shock risk. However in the low resistance scenario fault current can also be imported (open PEN) and you now have the added danger of having heat damaging currents flowing in the electrical earthing infrastructure

Agree just making the point of plastic entry to building, you can’t put plastic all around the metal structure, it’s all going pear shaped or even earth cable shaped

 

[pc1966]

To throw a random thought into the ring, there are reportedly now more open pen detection devices on the market since the advent of EV chargers.
I have no idea if it is economical to install open pen protection at the origin and whether that would mitigate the scenario discussed above sufficiently.
It might be possible to have more conventional bonding at the outbuildings then if the services are/ can be insulated.

I would doubt that any are up for the sort of current levels on this sort of a system, but it is an idea that would also reduce the risk of damage due to high voltages on phase-neutral arising from unbalanced loads, etc, during such a fault.

But I suspect that some reels of 35mm wire are a simpler, cheaper, and more reliable solution!