Do you also agree that the G/Y in a kettle lead (to a Class I metal kettle) is probably there for bonding as well as earthing purposes? [before you answer 'no', please consider
I don't think there is anything to consider before answering NO. Are you suggesting your kettle is an extraneous part and should be 'main' bonded?
No, of course not!
considering a L-E fault of sufficient impedance not to operate the OPD with the prevailing Zs].
How is that to happen? There is an inbuilt impedance of sufficient impedance not to operate the opd (13A fuse) of 29Ω (2kW kettle) . Are you considering a fault L to E of, what, 10Ω ? - in the kettle making it 'a bit live'? Wouldn't the kettle and cpc just become a neutral and the fault burn away?
To be honest, I was overlooking the 13A fuse, and thinking of a B32 protecting the circuit
I also should have written "...not to operate the OPD
quickly enough to necessarily save life/limb....".
A better example would be a cooker on a circuit with a B40 MCB and an L-E fault within it of about 1.5Ω. That would represent a fault current of about 150A, which would take a B40 about 20 seconds to disconnect. With a Zs of, say, 0.8Ω, for that 20 seconds the cooker would be at about 80V above (true) earth - and 80V for 20 secs can certainly be damaging or fatal if one is unlucky.
However, this whole discussion is totally academic and semantic, since there would usually be no hazard in the situation I've just postulated.
IF there were a way of 'earthing' the cooker (so as to provide the required disconnection functionality) without also 'bonding' it to the installation's CPCs,
then the above would represent a hazard - but that is obviously just not possible. In reality there obviously is no way of earthing the cooker without also 'bonding' it to (rendering it roughly equipotential with) anything else connected to the CPC network. Hence, in reality, that 80V above true earth for 20 seconds (or for 20 years!) would not usually represent a hazard, since any other exposed-conductive-part (and also any bonded pipework etc.) should also be at roughly the same potential.
However, using the definitions with which you have agreed, the reason why that 80V is not dangerous in the situation I postulated is
not because the cooker is 'earthed' (the earthing is not going to provide rapid enough disconnection to necessarily save life/limb) but, rather, because it is, via CPCs, 'bonded' to (rendered roughly equipotential with) any nearby exposed-conductive-parts (or bonded pipework etc.).
Kind Regards, John.