After a conversation about if its compliant to have a sub db board (no MEN with own PE) supplying a sub MEN board, a reason given from master electrician was that
IEC 60364-1 standards does not let you recombine earth and neutral into a PEN once separated.
Questions
-I couldn't find anything that outright says this (It may be there I couldn't find it) but the diagrams do seem to indicate this. Is this the case?
- are we obligated to comply with this international standard or can we use this "or" our own standards
- what is your interpretation of 5. 5.3.1 (3000)and our own standards is this is allowed?
Feedback appreciated
Once a PEN is separated can it be combined again in one installation
Re: Once a PEN is separated can it be combined again in one installation
Short answer: I believe it's not compliant
For long answer; lets start with some history - sometimes boring but often useful.
Prior to 1993; we had the 1976 Regs.
The system those Regs set up gave "Electrical Supply Authorities" enormous power;
and any matter of interpretation, or any details that weren't clearly set out in the Regs, came down to the beliefs / prejudices of the local ESA's Inspectors.
Rules for earthing systems being a case in point.
Many ESAs insisted on installation earths meeting some locally-set measure of effectiveness.
Some , particularly in poor ground conditions like alluvial gravel, insisted that every outbuilding submain had to be PEN.
In both cases; what they were really doing was pulling their distribution neutrals down to approx earth potential bit passing the cost of this onto the individual consumers.
Remember that for the MEN system, safety depends on keeping the N potential low; and for this what matters is not the efficacy of each individual installation earth, but rather the effect of all those multiple installation earths in parallel.
Under 1993 Act, ESAs were abolished; and the 1993 Regs were quite prescriptive about switchboards & earthing.
There were 3 types of swbd: MEN (as we still know them), linked-busbar (like an MEN except no MEC or electrode; and not fed PEN), and distribution ( same as now: no link & no electrode, and fed with PEC).
You could have any number of the various types, but there were restrictions on how they could be fed.
MEN could only be fed from another MEN (or a distribution system, or a generator).
Linked-busbar could only be fed from either an MEN or another linked-busbar, not from a DB.
A DB could be fed from an MEN or from another DB, but not from from an L-B.
(refer 1993 Rs 71 - 730
So these rules followed the principle that once you've moved from TN-C to TN-S, ie separating the functions of N & PEC, you couldn't go back.
(Not that that principle was set out anywhere; this was prescriptive rules. No need to understand, as long as you obey).
1997 Regs continued this system [Rs 81 - 83].
Notably the use of a PEN submain to feed an MEN sub- swbd was not limited to only outbuildings.
Over time, first ECPs and then Standards came into play; being introduced by Amendments to Regs
And yes our AS/NZS "3000" and companions are based on IEC 60364 series.
But until 2010 ESRs; only some specific clauses of these were mandated; the rest was guidance.
As in; you must be safe, and if you comply with <cited Standard> you will be deemed safe.
Under "3000" (starting with NZS 3000: 1997); the L-B form of swbd was no longer permitted - though of course existing ones continued in service and some still do.
The big problem with L-B swbds is that you end up with load current flowing on the submain PEC; which is not desirable.
Back to the present.
2010 ESRs do not specify any of this stuff; instead they require compliance with '3000".
One thing ESRs do NOT do is allow us to use any other Standard. ESR 59 is very specific on this: Part 1 or part 2, with restrictions on the Part 2 option.
So no; we not only are not obliged to follow "60364", we are not allowed to follow it (except maybe as guidance towards a Part 1 design).
Part 2 gives us only 2 types of swbd; we have MEN swbds, and we have DBs.
The MEN swbd closest to supply is the MSB.
An MEN swbd is always fed PEN, and a DB is always fed PEC.
5.5.3.1 specifically permits using a PEN submain to supply an outbuilding.
However it notes that there can be problems; and it regards them as MSBs of "separate installations".
Which has the effect that when this option is adopted, a dull "main earthing system" must be installed at the outbuilding.
And as work on such a combination of fittings is defined in ESRs as 'mains work";
installation of this additional main earthing system is classified as high risk PEW, and requires inspection.
Which is entirely logical; as the risks that can arise from getting it wrong are exactly the same as for a "main earthing system" at MSB.
"3000" doesn't specifically say PEN submain must be fed from an MEN swbd; but if you think about it that's the only way.
If you commence a PEN from a DB ( ie downstream of the change from distribution / mains TNC to installation TN-S, which happens at the MEN); you won't have an earthing system that meets requirements.
(not all of which are clearly stated in Section 5; for example prohibition on load current flowing in PECs isn't specified until Section 8)
Fault currents will flow via the PEN of 2nd submain, then onwards via a N of 1st submain instead of via a PEC.
This is contrary to 5.5.2.1; which specifies that PECs - and, by extension, PENs - must be connected to either the MEC or another point of the earthing system that's connected to the MEC. There are 4 acceptable options; as illustrated by Fig 5.3.
The PEN of the 2nd submain performs a protective earthing function (that's why it's called a PEN and not just an N).
As such, it has to comply with all the rules for a PEC; in this case option (c) requires that it be connected to an earthing terminal / bar.
But if we do that, we end up with load current flowing in the E-bar & submain PEC of DB1 - which is non-compliant.
True there's a parallel fault current path via DB2's MEC & electrode.
But it's minor and unlikely to be capable of meeting EFLI disconnection times on its own.
Same for the MEN / MEC / electrode at MSB.
The primary fault current path is via the supply PEN conductor.
So the answer you were given was correct: once we've made a change from TNC to TN-S, we can't change back.
Indirectly this is from IEC 60364 series (though not from the stated part 1 ).
But the direct path is via ESRs & "3000".
Doesn't matter that the principle isn't set out plainly, . Standards are not text-books, they're not primarily about education.
Primary purpose is setting minimum requirements. So they don't always explain the 'why".
What matters is that the requirements, if followed, have the desired effect.
As for 5.5.3.1 ; the reason PEN submains are only permitted for outbuildings is because of the risks of simultaneously accessible conductive parts being at significantly different potentials, due to being connected to different earthing system.
Without the physical separation between the structures, the risk would be unacceptably high.
As it is if there are any other conductive paths between the two, eg a water pipe.
If you look at 2018 edition; there are a number of changes relating to earthing and bonding for outbuildings, all about avoiding different potentials between simultaneously-accessible parts.
And likely more change in next edition; after a case where the separation of a small outbuilding from a large main building was small enough that, when power was needed at far end of main building; it was closer to take the supply from the outbuilding than from MSB at other end of main building.
For long answer; lets start with some history - sometimes boring but often useful.
Prior to 1993; we had the 1976 Regs.
The system those Regs set up gave "Electrical Supply Authorities" enormous power;
and any matter of interpretation, or any details that weren't clearly set out in the Regs, came down to the beliefs / prejudices of the local ESA's Inspectors.
Rules for earthing systems being a case in point.
Many ESAs insisted on installation earths meeting some locally-set measure of effectiveness.
Some , particularly in poor ground conditions like alluvial gravel, insisted that every outbuilding submain had to be PEN.
In both cases; what they were really doing was pulling their distribution neutrals down to approx earth potential bit passing the cost of this onto the individual consumers.
Remember that for the MEN system, safety depends on keeping the N potential low; and for this what matters is not the efficacy of each individual installation earth, but rather the effect of all those multiple installation earths in parallel.
Under 1993 Act, ESAs were abolished; and the 1993 Regs were quite prescriptive about switchboards & earthing.
There were 3 types of swbd: MEN (as we still know them), linked-busbar (like an MEN except no MEC or electrode; and not fed PEN), and distribution ( same as now: no link & no electrode, and fed with PEC).
You could have any number of the various types, but there were restrictions on how they could be fed.
MEN could only be fed from another MEN (or a distribution system, or a generator).
Linked-busbar could only be fed from either an MEN or another linked-busbar, not from a DB.
A DB could be fed from an MEN or from another DB, but not from from an L-B.
(refer 1993 Rs 71 - 730
So these rules followed the principle that once you've moved from TN-C to TN-S, ie separating the functions of N & PEC, you couldn't go back.
(Not that that principle was set out anywhere; this was prescriptive rules. No need to understand, as long as you obey).
1997 Regs continued this system [Rs 81 - 83].
Notably the use of a PEN submain to feed an MEN sub- swbd was not limited to only outbuildings.
Over time, first ECPs and then Standards came into play; being introduced by Amendments to Regs
And yes our AS/NZS "3000" and companions are based on IEC 60364 series.
But until 2010 ESRs; only some specific clauses of these were mandated; the rest was guidance.
As in; you must be safe, and if you comply with <cited Standard> you will be deemed safe.
Under "3000" (starting with NZS 3000: 1997); the L-B form of swbd was no longer permitted - though of course existing ones continued in service and some still do.
The big problem with L-B swbds is that you end up with load current flowing on the submain PEC; which is not desirable.
Back to the present.
2010 ESRs do not specify any of this stuff; instead they require compliance with '3000".
One thing ESRs do NOT do is allow us to use any other Standard. ESR 59 is very specific on this: Part 1 or part 2, with restrictions on the Part 2 option.
So no; we not only are not obliged to follow "60364", we are not allowed to follow it (except maybe as guidance towards a Part 1 design).
Part 2 gives us only 2 types of swbd; we have MEN swbds, and we have DBs.
The MEN swbd closest to supply is the MSB.
An MEN swbd is always fed PEN, and a DB is always fed PEC.
5.5.3.1 specifically permits using a PEN submain to supply an outbuilding.
However it notes that there can be problems; and it regards them as MSBs of "separate installations".
Which has the effect that when this option is adopted, a dull "main earthing system" must be installed at the outbuilding.
And as work on such a combination of fittings is defined in ESRs as 'mains work";
installation of this additional main earthing system is classified as high risk PEW, and requires inspection.
Which is entirely logical; as the risks that can arise from getting it wrong are exactly the same as for a "main earthing system" at MSB.
"3000" doesn't specifically say PEN submain must be fed from an MEN swbd; but if you think about it that's the only way.
If you commence a PEN from a DB ( ie downstream of the change from distribution / mains TNC to installation TN-S, which happens at the MEN); you won't have an earthing system that meets requirements.
(not all of which are clearly stated in Section 5; for example prohibition on load current flowing in PECs isn't specified until Section 8)
Fault currents will flow via the PEN of 2nd submain, then onwards via a N of 1st submain instead of via a PEC.
This is contrary to 5.5.2.1; which specifies that PECs - and, by extension, PENs - must be connected to either the MEC or another point of the earthing system that's connected to the MEC. There are 4 acceptable options; as illustrated by Fig 5.3.
The PEN of the 2nd submain performs a protective earthing function (that's why it's called a PEN and not just an N).
As such, it has to comply with all the rules for a PEC; in this case option (c) requires that it be connected to an earthing terminal / bar.
But if we do that, we end up with load current flowing in the E-bar & submain PEC of DB1 - which is non-compliant.
True there's a parallel fault current path via DB2's MEC & electrode.
But it's minor and unlikely to be capable of meeting EFLI disconnection times on its own.
Same for the MEN / MEC / electrode at MSB.
The primary fault current path is via the supply PEN conductor.
So the answer you were given was correct: once we've made a change from TNC to TN-S, we can't change back.
Indirectly this is from IEC 60364 series (though not from the stated part 1 ).
But the direct path is via ESRs & "3000".
Doesn't matter that the principle isn't set out plainly, . Standards are not text-books, they're not primarily about education.
Primary purpose is setting minimum requirements. So they don't always explain the 'why".
What matters is that the requirements, if followed, have the desired effect.
As for 5.5.3.1 ; the reason PEN submains are only permitted for outbuildings is because of the risks of simultaneously accessible conductive parts being at significantly different potentials, due to being connected to different earthing system.
Without the physical separation between the structures, the risk would be unacceptably high.
As it is if there are any other conductive paths between the two, eg a water pipe.
If you look at 2018 edition; there are a number of changes relating to earthing and bonding for outbuildings, all about avoiding different potentials between simultaneously-accessible parts.
And likely more change in next edition; after a case where the separation of a small outbuilding from a large main building was small enough that, when power was needed at far end of main building; it was closer to take the supply from the outbuilding than from MSB at other end of main building.
- Rating: 50%
Re: Once a PEN is separated can it be combined again in one installation
Not boring at all. Very useful.
As always greatly appreciated
Cheers
As always greatly appreciated
Cheers
Re: Once a PEN is separated can it be combined again in one installation
Firstly, I think Alec's idea that a PEN submain and MEN switchboard in an outbuilding requires inspection is incorrect.
ESR6(2)(b) - is mains work on an installation
Definitions:
Mains work - work on mains / work on main earthing systems
Mains - means those fittings forming part of an installation that are used for the supply of electricity to the MEN switchboard of the installation that is closest to the point of supply.
> so only the first MEN switchboard.
Main earthing system > the definition isn't as clear cut.
Then in - 3000 - 5.5.3.1
Wording like "shall be regarded as a main switchboard for the purpose of effecting the MEN connection."
Seems to imply it is only for that purpose, not for any other purpose/reason. The same with the wording for the earthing conductor to the electrode. Of course 3000 doesn't care about any particular ESR wording, but definitions do apply.
But besides all that, I don't know of any inspectors that believe a MEN switchboard or earthing system in an outbuilding requires inspection. And I don't remember seeing any EWRB cases where failure to have it inspected was one of the charges?
If the PEN submain and MEN switchboards were more problematic, wouldn't there be evidence from EWRB cases?
-----------
Onto the original question.
Alec already states that " "3000" doesn't specifically say PEN submain must be fed from an MEN swbd"
I'm not sure why you confuse the issue, by referring to 5.5.2.1 requirements for earthing? The PEN neutral obviously isn't connected to any earth conductor/bar. So that's irrelevant.
In 5.3.3.1(b) it states:
---
The submain supplying the outbuilding shall be run either—
(A) directly from the main switchboard; or
(B) from the main switchboard via distribution boards in one or more other outbuildings, to one distribution board only in the outbuilding.
---
That clause has no other qualification regarding the type of switchboard or submain to the DB in the outbuilding supplying the PEN submain.
5.5.3.1(b)(v) has been in the book since at least 3000:2000 version. So they are well covered for ensuring that the PEN neutral is properly connected back to the main switchboard regardless of that intermediate board being a PEN or PEC supply. From that point, it is subject to the usual problems associated with our normal TNC supply system.
ESR6(2)(b) - is mains work on an installation
Definitions:
Mains work - work on mains / work on main earthing systems
Mains - means those fittings forming part of an installation that are used for the supply of electricity to the MEN switchboard of the installation that is closest to the point of supply.
> so only the first MEN switchboard.
Main earthing system > the definition isn't as clear cut.
Then in - 3000 - 5.5.3.1
Wording like "shall be regarded as a main switchboard for the purpose of effecting the MEN connection."
Seems to imply it is only for that purpose, not for any other purpose/reason. The same with the wording for the earthing conductor to the electrode. Of course 3000 doesn't care about any particular ESR wording, but definitions do apply.
But besides all that, I don't know of any inspectors that believe a MEN switchboard or earthing system in an outbuilding requires inspection. And I don't remember seeing any EWRB cases where failure to have it inspected was one of the charges?
If the PEN submain and MEN switchboards were more problematic, wouldn't there be evidence from EWRB cases?
-----------
Onto the original question.
Alec already states that " "3000" doesn't specifically say PEN submain must be fed from an MEN swbd"
I'm not sure why you confuse the issue, by referring to 5.5.2.1 requirements for earthing? The PEN neutral obviously isn't connected to any earth conductor/bar. So that's irrelevant.
In 5.3.3.1(b) it states:
---
The submain supplying the outbuilding shall be run either—
(A) directly from the main switchboard; or
(B) from the main switchboard via distribution boards in one or more other outbuildings, to one distribution board only in the outbuilding.
---
That clause has no other qualification regarding the type of switchboard or submain to the DB in the outbuilding supplying the PEN submain.
5.5.3.1(b)(v) has been in the book since at least 3000:2000 version. So they are well covered for ensuring that the PEN neutral is properly connected back to the main switchboard regardless of that intermediate board being a PEN or PEC supply. From that point, it is subject to the usual problems associated with our normal TNC supply system.
Re: Once a PEN is separated can it be combined again in one installation
WRT the original question;
A PEN conductor has 2 functions (by definition.
It functions as a neutral (carrying return / balance current.
And it also functions as a protective earthing conductor.
As such, it has to comply with 5.5.2.1 - which is why I referred to that clause.
and connecting the supply end of a PEN submain to a n-bar of a non-MEN swbd does not comply.
True 5.5.3.1(b) allows a PEN supplying an outbuilding to run via intermediate swbds .
And yes, item (iv) doesn't restrict what type of swbds they may be;
beyond requiring that they must be in other outbuildings (so not in same structure as MSB0.
However there is a further restriction [item (v)] that you appear to have ignored.
it requires that where this is done, the integrity (continuity) of the PEN conductor must NOT depend on any connections within the intermediate swbd(s). So you can pass a PEN through an intermediate swbd, and tap off it to connect to the N-bar.
But you can't connect the incoming and outgoing PENs to the n-bar ; either separately or together.
it is not valid to regard an incoming N and an outgoing PEN connected separately or together to the n-bar of an intermediate swbd, as complying with this restriction.
-------------
As regards the requirement for inspection of outbuilding earthing systems installed under this clause; it's very simple.
And it doesn't depend on any wording in "3000".
There's no denying that the combination of electrode, MEC, and N-E link in the outbuilding meet (exactly) the definition of "main earthing system".
which is perfectly clear - and far better than what was in original ESRs back in 2010
And work on any "main earthing system is, by definition, "mains work.
Therefore installation of this system is high risk PEW.
It's as simple as that.
And while you are correct that many inspectors believe otherwise; they are simply wrong.
The only way such an issue would come before EWRB is if someone lodged a complaint.
Though - as we've seem on many occasions, EWRB decisions can be way off the mark.
Then saying black is actually white doesn't make it true; regardless of which side of the particular issue one is on.
And anyone who understands the safety issues must accept that they are exactly the same for an outbuilding as for a MSB.
making it entirely logical that it be classified as high risk;
regardless of whether that was the intent of the writer(s) of ESRs.
A PEN conductor has 2 functions (by definition.
It functions as a neutral (carrying return / balance current.
And it also functions as a protective earthing conductor.
As such, it has to comply with 5.5.2.1 - which is why I referred to that clause.
and connecting the supply end of a PEN submain to a n-bar of a non-MEN swbd does not comply.
True 5.5.3.1(b) allows a PEN supplying an outbuilding to run via intermediate swbds .
And yes, item (iv) doesn't restrict what type of swbds they may be;
beyond requiring that they must be in other outbuildings (so not in same structure as MSB0.
However there is a further restriction [item (v)] that you appear to have ignored.
it requires that where this is done, the integrity (continuity) of the PEN conductor must NOT depend on any connections within the intermediate swbd(s). So you can pass a PEN through an intermediate swbd, and tap off it to connect to the N-bar.
But you can't connect the incoming and outgoing PENs to the n-bar ; either separately or together.
it is not valid to regard an incoming N and an outgoing PEN connected separately or together to the n-bar of an intermediate swbd, as complying with this restriction.
-------------
As regards the requirement for inspection of outbuilding earthing systems installed under this clause; it's very simple.
And it doesn't depend on any wording in "3000".
There's no denying that the combination of electrode, MEC, and N-E link in the outbuilding meet (exactly) the definition of "main earthing system".
which is perfectly clear - and far better than what was in original ESRs back in 2010
And work on any "main earthing system is, by definition, "mains work.
Therefore installation of this system is high risk PEW.
It's as simple as that.
And while you are correct that many inspectors believe otherwise; they are simply wrong.
The only way such an issue would come before EWRB is if someone lodged a complaint.
Though - as we've seem on many occasions, EWRB decisions can be way off the mark.
Then saying black is actually white doesn't make it true; regardless of which side of the particular issue one is on.
And anyone who understands the safety issues must accept that they are exactly the same for an outbuilding as for a MSB.
making it entirely logical that it be classified as high risk;
regardless of whether that was the intent of the writer(s) of ESRs.
- Rating: 16.67%
Re: Once a PEN is separated can it be combined again in one installation
Alex with all due respect your argument relies heavily on PEN being regarded as a PEC.
Only definition I found was 2018
"1.4.99 Protective earth neutral (PEN)
* Neutral and protective earth functions combined in a single conductor."
Is there anything else?
I do agree best practise is certainly once PEN is separated not to re combine on the other hand what Doug says regarding risk are only general risks associated with any MEN Install is also true
Im starting to think this is a situation not covered by 3000 or esr and we may just be clutching at straws...
The fact that sub PEN doesn't require Inspection but the sub main earthing system arguably does seems to make no sense to me.
I do appreciate both inputs, personaly as an inspector I will always try to lean on side of caution and best practise for situations like this....
Only definition I found was 2018
"1.4.99 Protective earth neutral (PEN)
* Neutral and protective earth functions combined in a single conductor."
Is there anything else?
I do agree best practise is certainly once PEN is separated not to re combine on the other hand what Doug says regarding risk are only general risks associated with any MEN Install is also true
Im starting to think this is a situation not covered by 3000 or esr and we may just be clutching at straws...
The fact that sub PEN doesn't require Inspection but the sub main earthing system arguably does seems to make no sense to me.
I do appreciate both inputs, personaly as an inspector I will always try to lean on side of caution and best practise for situations like this....
Re: Once a PEN is separated can it be combined again in one installation
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.
-------------
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.
----------------
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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Re: Once a PEN is separated can it be combined again in one installation
As always, your explanation is in depth and well reasoned Alec. However, if the requirement was so prescriptive, I would expect that it would be more clearly explained in 3000 and not require two full pages of explanations with additional non-cited points in them.
I don't have time for a huge amount of detail. Just a couple of points.
- 5.5.2.1 already refers you to 5.5.3.1 in note 2.
- The wording "via distribution boards in one or more other outbuildings" doesn't specify if the via switchboards must be supplied by a PEN only and not PEC submain.
- I don't think your wording "the submain has to be continuous all the way back to MSB regardless of any connection(s) made at the intermediate swbd(s)" is correct.
I think you're referring to 5.5.3.1(b)(v) which says "the terminals on such distribution boards shall not be depended on for continuity of the combined protective earthing and neutral (PEN) conductor" which has a simple meaning. You can't use terminals in the switchboard for the continuity.
So not in separate terminals on the bar. But making a permanent joint of the incoming and outgoing neutrals would comply. Such as being in the same crimp lug or a link.
I don't have time for a huge amount of detail. Just a couple of points.
- 5.5.2.1 already refers you to 5.5.3.1 in note 2.
- The wording "via distribution boards in one or more other outbuildings" doesn't specify if the via switchboards must be supplied by a PEN only and not PEC submain.
- I don't think your wording "the submain has to be continuous all the way back to MSB regardless of any connection(s) made at the intermediate swbd(s)" is correct.
I think you're referring to 5.5.3.1(b)(v) which says "the terminals on such distribution boards shall not be depended on for continuity of the combined protective earthing and neutral (PEN) conductor" which has a simple meaning. You can't use terminals in the switchboard for the continuity.
So not in separate terminals on the bar. But making a permanent joint of the incoming and outgoing neutrals would comply. Such as being in the same crimp lug or a link.
Re: Once a PEN is separated can it be combined again in one installation
Yes the Note in 5.5.2.1 alerts readers to the provisions of 5.5.3.1;
but that doesn't mean 5.5.3.1 applies instead; it means it applies in addition.
Remember a not cannot alter a requirement;
Notes can only provide additional guidance.
It's the combination of these requirements that convinces me that the scenario in the OP is non-compliant.
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WRT connecting incoming & outgoing submain Ns at an intermediate swbd;
when I said had to be "continuous", I was referring to permanent continuity, not necessarily the same conductor continuing through.
I agree single crimp lug or link , or any similar permanent connection between incoming & outgoing, would comply.
This permanently connection can then be connected to the n-bar either directly or by use of a "tee" connection (eg using a line tap)
But simply putting both conductors into same terminal does not comply.
This same requirement for integrity of connections is also required - by "3001-1: 2022" - for all "common submains";
for all conductors not just PENs.
And i fully expect it will be spelled out across the 'library" as the Standards get reviewed
In fact it doesn't matter greatly for Actives;
but it absolutely does for any conductor performing protective earthing functions,
and to a lesser extent for neutrals
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So yes it would be possible for an incoming N of a PEC submain, and on outgoing N of a PEN submain,
to be permanently connected together in a manner compliant with 5.5.3.1(b)v).
Doing that would mean the incoming N becomes a PEN.
I'll have to think about that further - it may actually comply.
Certainly the connection of the PEN at origin, to main N-bar at MSB, is no less 'connected to MEC' than a perfectly normal 'individual submain' PEN.
It is unfortunate that Fig 5.3 doesn't show any PEN examples.
but that doesn't mean 5.5.3.1 applies instead; it means it applies in addition.
Remember a not cannot alter a requirement;
Notes can only provide additional guidance.
It's the combination of these requirements that convinces me that the scenario in the OP is non-compliant.
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WRT connecting incoming & outgoing submain Ns at an intermediate swbd;
when I said had to be "continuous", I was referring to permanent continuity, not necessarily the same conductor continuing through.
I agree single crimp lug or link , or any similar permanent connection between incoming & outgoing, would comply.
This permanently connection can then be connected to the n-bar either directly or by use of a "tee" connection (eg using a line tap)
But simply putting both conductors into same terminal does not comply.
This same requirement for integrity of connections is also required - by "3001-1: 2022" - for all "common submains";
for all conductors not just PENs.
And i fully expect it will be spelled out across the 'library" as the Standards get reviewed
In fact it doesn't matter greatly for Actives;
but it absolutely does for any conductor performing protective earthing functions,
and to a lesser extent for neutrals
-------------
So yes it would be possible for an incoming N of a PEC submain, and on outgoing N of a PEN submain,
to be permanently connected together in a manner compliant with 5.5.3.1(b)v).
Doing that would mean the incoming N becomes a PEN.
I'll have to think about that further - it may actually comply.
Certainly the connection of the PEN at origin, to main N-bar at MSB, is no less 'connected to MEC' than a perfectly normal 'individual submain' PEN.
It is unfortunate that Fig 5.3 doesn't show any PEN examples.