I'll ignore the sarcasm Pete (seen far worse on here! ). I was thinking about the similarity to metal capping, which I think is now supposed to be earthed ( certainly in 522.6.6 outside of a 'zone' ). Earthing of concealed metallic cable covering is only common sense in a house - regs or not. Everything has to be hidden - even sockets.
I've had experience of this in my existing house AND the previous one! I got a good belt when I touched the end of a wall capping under the floorboards - good job I didn't have the other hand on the CH pipes! Turned out the Dado Rail in the room below was nailed exactly over the capped ring main cables, vertically above a socket! - I was wondering why that circuit had a lowish IR! - 5Mohm.
In the previous house the wall in the hall had a faint 'rough ' feeling in the area above a socket - that circuit also had a 'lowish' IR , guess what? - nail through the capping, fixing the Dado Rail!
In both cases the capping can remain live for years - and it wouldn't trip an RCD either. If the capping is earthed, a penetrating nail/screw/drill would trip an MCB if it touched a live, or at least an RCD (hopefully).
So, hence my comment about the protection plate - which wouldn't be required if the joist were to be drilled! - and no, I wouldn't earth radiators (which are connected to earthed pipework), nails, screws,
or metallic windows ( unless they are motorised).
Better keep my head down now!
John.