Aside from the way out reading of r1 +r2 on 10mm,
can someone confirm that if you have correct mcb and also protection by an rcd the max zs allowed is 1667 taken from table 41.5 page 50 17th edition.
Don't forget that section 411.5 is referring to TT systems.
In essence what you are saying is correct in as much that a Zs not exceeding 1667ohms will ensure touch voltage cannot exceed 50v with a 30ma RCD / RCBO. BUT... as Batty points out, Applaud Smiley a correctly wired TN-S or TN-C-S would NEVER have a Zs reaching 1667ohm.
It would imply you have dropped a big smelly brown one somewhere on your installation methods & workmanship! Blushing:O
you should be verifying your R1+R2'S match up with your expected cable types & lengths.. so the only high bit would be coming from the External earth loop path, Ze which on a TN-S or TN-C-S it just ain't going to get that high!
TT yes with poor ground conditions... but again Ra's over 200ohm are considered to potentially be unstable.
I don't think I would every be happy with a Zs of 1667ohm in a domestic situation even if TT.
Possibly on a large rambling agricultural installation may be more likely?
but you would need more input off those who do more Agricultural to verify my supposition..
or to see if I need to put the pants on me head again!