Open PEN causes?

[pc1966]

The risks related to an open PEN in TN-C-S are often discussed here, say in relation to external supplies to out buildings, etc, but I wondered what is the main reason(s) for an open PEN fault?

I assume it is something to do with bad jointing techniques as with concentric cables it would be virtually impossible to accidentally cut the outer PEN and not short out everything, so I wondered if anyone with DNO links knows the sort of underlying causes and what (if anything) could be done to mitigate them.

TL;DR What causes an open PEN?

 

[Simon47]

Is it an Insane idea (I mentioned this elsewhere) to also calculate what the cost of running a separate earth from the DNO, s trafo to each home.

Are we talking about retrofit ? Or only on new installations ?
Retrofit would be maaaaasively expensive, just think of all the digging up that would be needed. Round our way they've been replacing the old cast gas pipes with plastic. There they only have to dig holes at each service tap and then use a mole that splits the old pipe while dragging the new on in. You can't do that with lecky, so they'd be trenching the whole length of all the roads, and trenching across each property to the mains incomer.
I can tell you that I'd be "a tad unhappy" if the lecky board wanted to do that on our street and into our house. For one thing, the amount of stuff I'd need to move, before I could start lifting the laminate flooring the previous owner was so fond of, before I could get the boards up that would be need to get the cable in - no thank you !
Of course, they'd probably insist on fitting a fuglybox on the front of the house - well they'd be told to go forth and procreate on that point.
It would be more possible where it's 100% overhead, but would still involve disruption in customer premises.

But I'll tos in another thing ...
What is the danger from a lost earth in a TNS setup ? It wouldn't be detected because nothing would stop working, but without adequate local earthing, any L-E fault would simply make multiple properties have live exposed parts. So would we be back to having a local earth rod and incomer RCD - as though it was a TT system ?
EDIT: WTF, you can't use t o s s here, as in "throw someone a ball" kind of t o s s ?