I agree that my interpretation relies on understanding that a PEN performs the function of a PEC.
As for the definition; ESR 4(2)applies; and basically requires us to use definitions from Act or ESRs (if they exist) in preference to those in a Standard.
The term "PEN conductor" is not defined in Act, ESRs, or the currently-cited edition of "3000".
As you've noted, it is defined in 2018 edition; which is useful for understanding but not legally binding.
It comes from IEC, and is defined in "60050" as
IEV ref 195-02-12
PEN conductor
conductor combining the functions of both a protective earthing conductor and a neutral conductor
While similarly not binding via ESR 4(2) for a term used in a Standard; both would legally apply for a term used in ESRs ,via ESR 4(3).
Either of these definitions makes it clear that a PEN does perform the function of a PEC.
And on that basis, I believe a PEN must be treated as a PEC, for purposes of 5.5.2.1.
Add to that the fact that the only purpose for which PENs are permitted, beyond installation MEN (at MSB), is for outbuilding(s);
The restrictions that apply to adopting this option only allow for sourcing the PEN at MSB;
either directly or via intermediate DBs in other outbuildings.
And if there is any intermediate swbd, the submain has to be continuous all the way back to MSB regardless of any connection(s) made at the intermediate swbd(s).
Taken as a whole, I can't see how connecting a PEN to the N-bar of a PEC-fed DB can possibly be seen as compliant.
That configuration simply doesn't met requirements (iv) & (v) of 5.5.3.2 for PEN supply to outbuildings;
and it doesn't comply with 5.5.2.1.
Others may reach a different interpretation; but I believe mine is soundly based,
and I've yet to see any good argument as to how it does comply.
all I've seen so far is about maybe it isn't specifically non-compliant; and in my opinion those arguments are weak (at best)
Looking at the practical side
1 I wouldn't do it
2 as an inspector, I wouldn't accept it
Technically ,as you noticed, only the earthing system and not the submain is HRPEW.
But I still wouldn't issue a "compliant & safe to connect" RoI;
and if they wouldn't correct it I would report it to EWRB as non-compliant work,
and also to Worksafe as an immediate hazard found while carrying out PEW.
Of course, as DougP pointed out, many practitioners don't ask for an inspection for these "outbuilding" earthing systems.
So we have no idea how often people get this wrong.
I know that ES has admitted - though not publicly, and not in writing - that currently ESRs do make outbuilding earthing system high risk
I am aware of one case, where the contractor did want an inspection, but their employee simply didn't bother having it done.
The employer had no system in place to ensure certification and inspection actually happened
Employee also didn't bother getting the earthing system right (left the link off);
and - some months later -a plumber under that classroom wore the effects of a fault in a fluo light (live ground, water pipe bonded at main building). Very nearly lethal.
So the risks are clearly there,exactly the same as for a main earthing system at MSB.
And arguably worse, because with outbuildings there's more chance of other conductive parts being bonded to the MSB's earthing system instead of the outbuildng's.
I am not aware of any cases relating to the specific question of connecting a PEN submain to a PEC-fed DN.
But I am firmly of the opinion that the usual reason for adopting PEN is all about saving money;
with little if any consideration of safety aspects.
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Side issue; for anyone who may find it useful
there's an on-line resource called "Electropedia" :
https://www.electropedia.org
which gives easy access to a huge range of definitions .
There are often several for the same term; for various contexts. But all you have to do is choose the one for "electrical installations".
This can be easier than downloading a copy of IEC 60050.
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