If one takes that view, it's surely even more clear that the bath can't be an extraneous-c-p - since it is entirely contained within the bathroom?
So, how would you determine that?
By observation and common sense, with further investigation in the (rare) cases in which observation leaves some uncertainty? If the bath is entirely within the room, it clearly cannot, itself, normally "introduce a potential" (any potential) into that room. If potentials are being introduced into the room, it must be something else introducing them (even if that something else is a soaking wet ground floor).
As I said before, 701.415.2(v) only applies IF the bath is a extraneous-c-p.
How do you determine that it is not? .... So, you just decide that it is not an extraneous-c-p and then ignore?
Sort-of, I suppose - just as you would probably decide that an incoming metal service pipe, coming from a 'well above ground' outside meter which was fed by a plastic, was not an extraneous-c-p that required bonding.
Do your tests if you like, but we both know what the results would virtually always be - the resistance between bath and MET (or exposed-C-Ps) would either be extremely low (if pipework etc. were providing a path to the bath) or else extremely high (if the bath really was 'floating') - in neither of which cases would bonding be required. The 'observation' part of the decision process would/should identify those cases in which there was uncertainty - e.g. a possible metal waste that entered the ground or a bath standing on a soaking wet ground floor solid floor.
Do you believe that it would suddenly turn into an extraneous-c-p if I connected it via a 15kΩ resistor to something in continuity with the PEB/MET - and, if so, why?
Would it not because it would have the same effect?
You seem to be overlooking what all this is about. The concern is about a degree of 'connection' between an exposed metal part and something (e.g. true earth) which might possibly be at a
different potential from that of the equipotential zone (i.e. MET/PEB potential). Conductive paths (whether 1Ω, 1,665Ω or whatever) between exposed metal and something which is
AT that MET/PEB potential are of no real consequence, which is why they don't qualify as extraneous-c-ps. I suppose things would be clearer if extraneous-c-ps were defined as parts which were "liable to introduce a potential
different from the potential of the equipotential zone", or something like that.
What is the difference between that and a bath on the ground (floor) with the same resistance?
A big difference. Whilst, as above, a path from the bath to the MET/PEB is of no concern (and does not make it an extraneous-c-p), a path from the bath through a waterlogged solid floor to
truth earth (which possibly
could be at a potential different from that of the equipotential zone) IS a concern, and could render the bath an extraneous-c-p. As I said, observation would identify those cases in which this was a possibility, such that some tests (or, better, treating it as if it definitely
were an extraneous-c-p) would then be appropriate.
Please tell me - for a part that you would agree IS an extraneous-c-p what is meant by "effectively connected to PEB" and how you would determine this?
In the obvious way, I suppose, by measuring the resistance from it to the PEB - and I wouldn't regard a resistance anything like as high as 1,666Ω as representing an 'effective connection' - I would be looking for a very small number of ohms, at most. However, this is the opposite way around from what we are talking about. The finding of a (any, of your choice) particular resistance between a bit of metal and the PEB never means that the bit of metal is
necessarily an extraneous-c-p.
Kind Regards, John