Equipotential bonding required for new boiler?

[Harry Bloomfield]

Nobody wants or needs a situation where everything is bonded including the picture hooks.

I agree, and there are no bonded picture hooks, door handles, or towel rails bonded - bonding those would just be unnecessary, and extreme, but the main items which are touchable, and might potentially become live, are bonded.

 

[trojanhawrs]

and assuming, as is the case here, that all metalwork which could possible, reasonably become live, is bonded - then where is the risk?

Anything connected to the supply earth can potentially become live so if it doesn't need to be earthed, it shouldn't be. Bonding is designed to mitigate in that scenario, whereas being isolated from earth eliminates that risk.

 

[JohnW2]

Are you saying that each and every radiator in your house is connected by G/Y cables back to the CU (I presume MET)?

Yes, has you have found, you cannot necessarily rely upon continuity being provided by the pipework.

My goodness

Is each radiator also connected by G/Y cables) to all exposed-c-ps and other extraneous-c-ps in the location? If not, then it is presumably 'earthing', not supplementary bonding.

 

[EFLImpudence]

My goodness

 

[JohnW2]

Theoretically possible, but bonding everything and increasing the risks for everyone in all locations is not the answer to that extremely improbable situation.

Exactly.

Nobody wants or needs a situation where everything is bonded including the picture hooks.

Quite so. A picture hook is so small, and quite probably not very easily touchable, that even those who are obsessed with such things might not feel that they "want or need" to earth or bond it. However, it's just as likely that a screw could penetrate a buried cable when it is attaching something much larger and touchable, like a wall-hung metal cabinet, shelving or whatever.

 

[ebee]

Yes you need to balance the credible to the incredible and . as I eluded to, that balance might change to one or the other in a very small number of very limited cases. If you are aware of such peculiarities then you might decide on this one rare occasion you could "flip the choice" but usually you would categorise one way or the another accordingly.
Lets say you test resistance (impedance) of something to determine whether extraneous or not and you get a reading very near the boundary of one reading or another and you know that their is a realistic chance that it will go one way or the other and you are pretty sure the outcome is more likely than not then you might flip choice if you have carefully considered all scenarios with best of intent, the good. but the prime endevour must always to be to class it one way or the other and justify a choice once made. I am not suggesting there are many borderline cases because the are quite rare, however just sometimes it can be a choice that requires good thought, but only rarely, it is usually quite clear cut.