Poll - Ring final circuits with high integrity earthing

[JohnW2]

Well - maybe I was putting too much store by my memory of this:

As I wrote yesterday, I think one of the confusions is resulting from the fact that BAS seemingly perceives a difference between "Protective Conductor" and "Circuit Protective Conductor", accepting that the former represents "A path" back to the CU (hence there are two), but regarding the latter ('CPC') as referring to the entire ring of protective conductors (with joints) - in which case there is only one. Where he got those different 'definitions' from, I haven't got a clue.

If the rings in question are cpcs then I would call two separate ones "two cpcs". Or even "two individual cpcs"

I think the main problem here is that the a deficiency in the usual terminology, which frustrates attempts at clarity in anything other than very simple situations ...

A simple ring or radial final circuit will have a number of physical conductors ('wires'), joined together at accessories etc., and it is common to describe the totality of those joined wires as "the CPC" of the circuit - but that leaves one needing a word/phrase (other than 'CPC', since that is now spoken for) to describe those individual component 'wires' - unless one just calls them 'wires', I can't think of anything other than "protective conductor" - can you?

If, as in the system you postulate, there are two 'rings', a problem of terminology arises. If one is normally using "the CPC" to represent the totality of the system of 'connections to earth' then there would still only be 'one CPC' when there were two rings. Indeed, if one uses "CPC" to have that meaning, then no circuit could ever have more than one "CPC", could it?

If one removes any possible quibbles by postulating a hypothetical socket with four earth terminals, then, if one had 'two rings', it would actually be impossible to say which 'wire' belonged to which ring - so it would really be a question of 'doubling up' conductors in parallel, rather than having two physically distinguishable discrete rings.

Of course, this is all tangential to the actual issue under discussion, but an inadequacy in available terminology clearly doesn't help at all if one wishes to work strictly to the word of what the regulations "actually say". In fact, in the absence of adequate, properly defined, terminology, all one can really hope to work to is what the regulations "appear to say" - and that obviously opens up the possibility of varying opinions.

Kind Regards, John

 

[EFLImpudence]

I think the main problem here is that the a deficiency in the usual terminology, which frustrates attempts at clarity in anything other than very simple situations ...

It may be a deficiency or a difference of opinion.

A simple ring or radial final circuit will have a number of physical conductors ('wires'), joined together at accessories etc., and it is common to describe the totality of those joined wires as "the CPC" of the circuit -

I think the emphasis is on 'THE' as normal circuits only have one, so THE cpc is the totality.

but that leaves one needing a word/phrase (other than 'CPC', since that is now spoken for) to describe those individual component 'wires' - unless one just calls them 'wires', I can't think of anything other than "protective conductor" - can you?

What about just 'conductor' if you don't like 'wires'?
After all, until they are connected to earth, they are not really protective conductors, are they?
I know we would call the bare wire in a roll of cable the CPC and the others, Line and Neutral but until connected those descriptions aren't actually what they are.

As with all trades, we have to know what is meant but it seems here that we don't and are at crossed purposes.

If, as in the system you postulate, there are two 'rings', a problem of terminology arises. If one is normally using "the CPC" to represent the totality of the system of 'connections to earth' then there would still only be 'one CPC' when there were two rings. Indeed, if one uses "CPC" to have that meaning, then no circuit could ever have more than one "CPC", could it?

I am not sure. Are you not now wriggling?
How many line conductors are there in a two-way lighting system?

If one removes any possible quibbles by postulating a hypothetical socket with four earth terminals, then, if one had 'two rings', it would actually be impossible to say which 'wire' belonged to which ring

We haven't so it is possible.

- so it would really be a question of 'doubling up' conductors in parallel, rather than having two physically distinguishable discrete rings.

Except there are two distinguishable rings.

Of course, this is all tangential to the actual issue under discussion, but an inadequacy in available terminology clearly doesn't help at all if one wishes to work strictly to the word of what the regulations "actually say". In fact, in the absence of adequate, properly defined, terminology, all one can really hope to work to is what the regulations "appear to say" - and that obviously opens up the possibility of varying opinions.

It may - but if the regulation states a circuit must have 'two individual' CPCs, would that not imply, whatever you may think, that the normal arrangement should be doubled.
You cannot say that that is impossible because whatever you do there will still be only one CPC.

 

[ban-all-sheds]

A simple ring or radial final circuit will have a number of physical conductors ('wires'), joined together at accessories etc., and it is common to describe the totality of those joined wires as "the CPC" of the circuit - but that leaves one needing a word/phrase (other than 'CPC', since that is now spoken for) to describe those individual component 'wires' - unless one just calls them 'wires', I can't think of anything other than "protective conductor" - can you?

How about "conductor"?

But once installed, each one is not necessarily a protective conductor according to the definition on p33

If, as in the system you postulate, there are two 'rings', a problem of terminology arises.

I still think this is pointless.

If one is normally using "the CPC" to represent the totality of the system of 'connections to earth' then there would still only be 'one CPC' when there were two rings.

No, there would be two.

Indeed, if one uses "CPC" to have that meaning, then no circuit could ever have more than one "CPC", could it?

Yes.

If one removes any possible quibbles by postulating a hypothetical socket with four earth terminals

That creates problems, not removes them.

Of course, this is all tangential to the actual issue under discussion, but an inadequacy in available terminology clearly doesn't help at all if one wishes to work strictly to the word of what the regulations "actually say". In fact, in the absence of adequate, properly defined, terminology, all one can really hope to work to is what the regulations "appear to say" - and that obviously opens up the possibility of varying opinions.

How many rings are there in Audi's logo?

Or The Olympics?

 

[JohnW2]

I think the main problem here is that the a deficiency in the usual terminology, which frustrates attempts at clarity in anything other than very simple situations ...

It may be a deficiency or a difference of opinion.

Essentially the same, IMO. If the terminology were "non-deficient", and properly defined, there would be no scope for differing opinions, would there?

A simple ring or radial final circuit will have a number of physical conductors ('wires'), joined together at accessories etc., and it is common to describe the totality of those joined wires as "the CPC" of the circuit -

I think the emphasis is on 'THE' as normal circuits only have one, so THE cpc is the totality.

Exactly. As I said, that is the common use of "the CPC" (although it's slightly less clear what it means when there are spurs from a ring, or a branching radial)

What about just 'conductor' if you don't like 'wires'? After all, until they are connected to earth, they are not really protective conductors, are they?

As I said before, it's others who I feared would criticise me for talking about 'wires', and I also feared that I would also be criticised for saying just "conductor" without saying what sort of function (e.g. L, N or E) that conductor fulfilled!

If, as in the system you postulate, there are two 'rings', a problem of terminology arises. If one is normally using "the CPC" to represent the totality of the system of 'connections to earth' then there would still only be 'one CPC' when there were two rings. Indeed, if one uses "CPC" to have that meaning, then no circuit could ever have more than one "CPC", could it?

I am not sure. Are you not now wriggling?

I wouldn't call it wriggling. One can't really have it all ways. If, as above, one is going to 'define' the phrase "THE CPC" to be referring to the totality of 'wires connecting to earth' in a circuit, then there could (per that definition) only ever be one "THE CPC" per circuit, couldn't there?

If one removes any possible quibbles by postulating a hypothetical socket with four earth terminals, then, if one had 'two rings', it would actually be impossible to say which 'wire' belonged to which ring - so it would really be a question of 'doubling up' conductors in parallel, rather than having two physically distinguishable discrete rings.

Except there are two distinguishable rings.

As I said, they wouldn't be distinguishable. In the following, which four lettered wires do you think constitute 'distinguishable ring No. 1' and which constitute 'distinguishable ring No. 2'??

... in the absence of adequate, properly defined, terminology, all one can really hope to work to is what the regulations "appear to say" - and that obviously opens up the possibility of varying opinions.

It may - but if the regulation states a circuit must have 'two individual' CPCs, would that not imply, whatever you may think, that the normal arrangement should be doubled.

To echo your comment, "it may", but the lack of clarity means that there can, and will, be differing opinions. Although I understand BAS's argument that it doesn't matter what was the intent (all that matters being what the regulations "actually say"), my belief is that the intent was to require "two independent paths to earth" - non-clearly expressed in the regs as "two individual CPCs".

Kind Regards, John

 

[ban-all-sheds]

It may - but if the regulation states a circuit must have 'two individual' CPCs, would that not imply, whatever you may think, that the normal arrangement should be doubled.

I've posted this twice before:

He either genuinely cannot see the consistency and logic, or he can but cannot bring himself to admit it.

 

[JohnW2]

I've posted this twice before: ..... He either genuinely cannot see the consistency and logic, or he can but cannot bring himself to admit it.

I fully understand (and accept, per se) your logic, but I believe it to be based on a false premise.

I believe that (in the context we are discussing) 'high integrity' relates to redundancy of 'paths to earth' - i.e. that two or more 'paths to earth' constitutes 'high integrity earthing'. I therefore believe that a standard ring final (if it has 'separate terminals') is already 'high integrity', and therefore does not require anything to be "doubled" to create 'high intensity earthing' - and I believe (subject to confirmation from IET) is that is what 543.7.2.201(i) is trying to say. In other words, I would present your table as:

Kind Regards, John

 

[JohnW2]

If one removes any possible quibbles by postulating a hypothetical socket with four earth terminals

That creates problems, not removes them.

Not IMO. With only two terminals, people could attempt to argue that 'what was connected to which terminal' somehow identified which conductor was part of which ring.

One thing I'm not clear about is what you feel about a radial converted to HIE by turning its CPC into a ring (which I think you agree is acceptable as HIE). Since you would presumably regard that ring as being "one CPC" do I take it that you would therefore believe that 543.7.1.204 doesn't apply - i.e. that there is no 'separate terminals' requirement?

Kind Regards, John

 

[SimonH2]

Just out of interest, would someone like to post the official (BS7671) definitions of "protective conductor" and "circuit protective conductor" ?
I have a feeling it may be pertinent to the arg.. err I mean discussion.

 

[JohnW2]

Just out of interest, would someone like to post the official (BS7671) definitions of "protective conductor" and "circuit protective conductor" ? I have a feeling it may be pertinent to the arg.. err I mean discussion.

I've dealt with this in prose before, without literally posting the regs. As I said, "circuit protective conductor" is just a subset of "protective conductor" (essentially applicable when its not a bonding conductor or earthing conductor). Specifically:

Circuit protective conductor (cpc). A protective conductor connecting exposed-conductive-parts of equipment to the main earthing terminal

Protective conductor (PE). A conductor used for some measures of protection against electric shock and intended for connecting together any of the following parts:
(i) Exposed-conductive-parts
(ii) Extraneous-conductive-parts
(iii) The main earthing terminal
(iv) Earth electrode(s)
(v) The earthed point of the source, or an artificial neutral​

So, a CPC is a type of protective conductor, being one that is present to connect exposed-c-ps of equipment to the MET. "Protective conductors" include CPCs, but also bonding and earthing conductors
... [and I'm not too sure about (v) - does it perhaps relate to 'local' {generator etc.} supplies?].

FWIW, both of those definitions could apply to any 'wire' (or 'wires') in the path to earth. Hence, by those definitions, each of the 'paths to earth' from a point on a ring final could be correctly described as either a "CPC" (or, strictly, "cpc"!) or a "protective conductor" ("PE" !).

Kind Regards, John

 

[SimonH2]

I've dealt with this in prose before, without literally posting the regs. As I said, "circuit protective conductor" is just a subset of "protective conductor" (essentially applicable when its not a bonding conductor or earthing conductor). Specifically:

Circuit protective conductor (cpc). A protective conductor connecting exposed-conductive-parts of equipment to the main earthing terminal

Protective conductor (PE). A conductor used for some measures of protection against electric shock and intended for connecting together any of the following parts:
(i) Exposed-conductive-parts
(ii) Extraneous-conductive-parts
(iii) The main earthing terminal
(iv) Earth electrode(s)
(v) The earthed point of the source, or an artificial neutral​

​

So we agree then that a protective conductor is a conductor - not a "complete circuit". So for a ring final, there are 2 or more protective conductors - 2 if there is one socket, 3 if there are 2 sockets, 4 if there are 3 sockets, and so on.
Thus, for a ring final, 543.7.1.3(iii) is satisfied by a standard ring final layout "Two individual protective conductors". This is explicitly confirmed by 543.7.2.1(i).

Just so long as that single cpc ring is compliant with either 543.7.1.203 (i) or 543.7.1.203 (ii).

Now, where in the regs does it say that the ring "as a single conductor" must comply ?

 

[JohnW2]

So we agree then that a protective conductor is a conductor - not a "complete circuit". So for a ring final, there are 2 or more protective conductors - 2 if there is one socket, 3 if there are 2 sockets, 4 if there are 3 sockets, and so on.

Well, that's what the BS7671 definitions say, and what you and I believe, but as for "we agree", that depends on what 'we' you had in mind, because BAS seems unchangeable in his view that there is just one thing called "the CPC" (which BS7671 says is a type of "protective conductor) of a ring final, and that is the totality of all conductors in the paths from points on the ring to earth.

I think what I wrote two or three posts ago is probably the simplest clearest way of expressing my belief, and one of the main reasons for the difference in view between BAS and the rest of us. My belief is that (because every point has two independent paths to earth) a standard ring final, if it has 'separate terminals', already represents HIE - so, unlike the situation with a radial, nothing has to be done to 'turn it into' HIE.

Kind Regards, John

 

[SimonH2]

That's my interpretation as well.
I'd also add that if you argue (as I believe BAS does) that you cannot consider the "ring" cpc as consisting of two protective conductors from any arbitrary point on it back to the CU/DB ... then a logical extension is that you cannot consider the arrangement BAS proposes as having more than one protective conductor (it's several "pieces of wire" all in parallel, but still one protective conductor).

 

[JohnW2]

That's my interpretation as well. I'd also add that if you argue (as I believe BAS does) that you cannot consider the "ring" cpc as consisting of two protective conductors from any arbitrary point on it back to the CU/DB ... then a logical extension is that you cannot consider the arrangement BAS proposes as having more than one protective conductor (it's several "pieces of wire" all in parallel, but still one protective conductor).

I agree on all points. Furthermore, as I recently wrote, if BAS believes that a radial circuit converted to HIE by turning its CPC into a (single) ring has just "one CPC" that would presumably mean that it did not have to comply with the 'separate terminals' requirement - which, again, I do not believe is meant to be the case!

Kind Regards, John

 

[JohnW2]

The voting is interesting. We all know BAS’s view, and therefore would expect him to vote ‘No’ (once!). Of the others who have participated in the discussions (this thread or the original one), EFLI is about the only person who has ‘hovered’ in the direction of BAS’s view, although I doubt that even he feels strongly/certainly enough to have voted ‘No’ (I would rather have expected a “Don’t know” from him).

Whatever, since there are currently 5 ‘No’ votes, 3 or 4 of them are seemingly ‘unaccounted for’ in terms of the discussants. If any of those 3 or 4 voters are people other than BAS, I would be very interested to hear (by PM if they would prefer) what they believe is required for an HIE ring final.

Kind Regards, John

 

[ban-all-sheds]

First, I must apologise for this:

He either genuinely cannot see the consistency and logic, or he can but cannot bring himself to admit it.

I realised after I'd posted it that I'd done wrt you exactly what I'd asked you not to do wrt me, but I was out all day yesterday and couldn't do anything about it.