411.3.2.2 is the main regulation in the original BS7671:2008 not exceeding 32A "NOTE 2: Where compliance with this regulation is provided by an RCD" clearly states an RCD can be used as one has to with a TT supply.
That is true, but as we've often discussed, 415.1.2 says
"The use of RCDs is not recognised as a sole means of protection and does not obviate the need to apply one of the protective measures specified in Sections 411 to 414". I think that (despite the note to Table 41.1 which you quote) most people interpret this as meaning that, unless it is unavoidable (i.e. in TT systems), one should not rely on an RCD to achieve the required disconnection times but should achieve that per 411 (i.e. with an OPD).
So in the main using a RCD means one does not have to have a Zs under 1.44Ω for a B32 MCB. ...
As above, I don't think that's how most people interpret the above regs, particularly 415.1.2 - but maybe I'm wrong.
....The question is do you need a line - neutral loop impedance of under 1.44Ω?
If (as I presume is the case) one wants disconnection by the magnetic trip of an MCB (i.e. in less than about 10 seconds), then one clearly has no choice but to impose that requirement for L-N loop impedance, even in a TT installation.
Clearly 1.44Ω with a ring final line - neutral reading would mean an unacceptable volt drop but as to if that presents a danger is another question.
As above, an L-N loop impedance >1.44Ω (at 230V) would/could result in disconnection in response to a 'dead short' taking longer than 10 secs - I would think that could be said to 'present a danger'.
How can you tell a home owner his house was safe in 2014 but without any change to his house in 2015 it's no longer safe because the IET made a mistake with their recommendation.
'Safe' obviously comes in shades of grey, and opinions (both official and general) about what degree of 'safeness' is required vary,both between individuals/organisations and with time. I could easily rephrase your question by asking "How can you tell a driver in Scotland that a level of alcohol in his blood which would have been regarded as 'acceptable' just 5 weeks ago is regarded as unacceptable ('unsafe' and illegal) today?".
So I will rephrase the question if you are going to issue a C3 because the Zs limit has been reduced what would you tell the home owner in layman's terms is the reason for failing it?
I think I would read to him my previous paragraph - adding that although his/her installation is obviously no less safe than it used to be, views about what level of safeness is required have changed. So many of the things which went on, and were accepted, when you and I were at school would today be condemned (and in many cases outlawed) as being 'unacceptably unsafe'!
So in real terms unless well over the permitted value one can't really give it a coding. So I would say for a ring final over 1.5Ω yes report under that then I would not enter as a code.
If you're saying that simply because you don't trust the accuracy of your measurements, then it may be fair enough. However, if you were confident that the true Zs was >1.44Ω, even if only slighly so, you really ought to 'report' it, shouldn't you?
Kind Regards, John