Poll - Ring final circuits with high integrity earthing

[SimonH2]

Lets assume for a moment that you are correct, would you please state how the single YELLOW ring in your earlier diagrams meets 543.7.1 (specifically 543,7,1,203(iii)), and also how the single green ring in the same diagrams also meets 543.7.1 ?

On it's own it doesn't. It's only as a pair that it works.

So you agree that the yellow cpc does not meet 543,7,1,203(iii)
So how does it meet the requirements of 543 ? Where 543,7,1,203(iii) says "2 conductors, each complying with 543"

Because, according to your logic, each of those rings must on it's own meet the requirements of 543. And since you are adamant that a single ring cannot comply, then neither can either of your two rings individually. So each one, on it's own, must be two rings - so now a total of 4 rings. But then, each of those rings must on it's own comply with 543, and therefore must be two separate rings - so now a total of 8 rings. I think we can all see where this is headed.

Is it headed towards an increasingly ridiculous argument from you?

You keep shouting "read what they actually say", I'm simply applying your standards. You have claimed (against all reasonable interpretations and discussions) that your arrangement is the only reasonable way to comply with 543,7,1,203(iii). I've pointed out that your method does not in fact comply unless both the yellow and green lines individually meet 543. So either both yellow and green lines meet 543,7,1,203(i) or 543,7,1,203(ii) which you have never suggested, and in any case if either did then only one would be needed; or they must each meet 543,7,1,203(iii) which requires two conductors each complying with 543 - that means the yellow pc must meet 543,7,1,203(iii) and the green pc must meet 543,7,1,203(iii).

If we stick with your definition, then 543,7,1,203(iii) is recursive - no quantity of parallel conductors will meet it.

 

[ban-all-sheds]

You're being silly. You know that no individual has the authority to amend BS7671.

Then his opinion is of no relevance to what the regulations actually say.

 

[ban-all-sheds]

if we stick with your definition, then 543,7,1,203(iii) is recursive - no quantity of parallel conductors will meet it.

And if we stick with that belief regulations become recursive as a matter of basic principle.

Stripped of extraneous words, with one word changed to an alternative from its dictionary definition and with the relevant parts merged the requirement is:

The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective conductor current is likely to exceed 10mA, shall have two separate circuit protective conductors, and each shall be in the form of a ring with both ends connected to earth at the origin of the circuit.

What do you think that means?

 

[bernardgreen]

such that the total protective conductor current is likely to exceed 10mA,

Is that exceed 10 mA when the circuit is functioning normally ( current in CPC being due to filters and other capacitive effects ) or only during fault conditions before the protective devices operate to cut the power on the faulty circuit.

Does this have any influence on manufacturers to design double insulated equipment ( no earth required ) that when powered up has a metal case parts that gives a "tingle" to the touch ? If the case was connected to earth via an amp meter and the leakage found to be higher than 10 mA then ( apparent ) the equipment would require a mains supply with a high integrity earth system. Do manufacturers choose to go double insulated ( albeit with a tingle touch ) so they can avoid restricting use to supplies with high integrity earths.
( And without an earth how do the manufacturers filter out mains borne voltage spikes. ? ? )

 

[SimonH2]

such that the total protective conductor current is likely to exceed 10mA,

Is that exceed 10 mA when the circuit is functioning normally ( current in CPC being due to filters and other capacitive effects ) ...

Yes, it is specifically for equipment with high leakage current - typically lots of filtering (eg capacitors between line(s) and earth). With such equipment, there is a risk that the exposed conductive parts of that (or other equipment on the same circuit) could rise to a dangerous voltage with sufficiently low impedance to cause a shock hazard.
Hence the "high integrity" earth connection to ensure that such a loss of earth fault is "unlikely".

In the specific context, with a standard RFC (all cpcs into single terminals), then a single terminal coming loose could lose earthing for a double socket or even the whole ring if it's at the earthing bar in the CU. By requiring every cpc to use a separate terminal, you need two such faults before there is complete loss of earth to any point.

Does this have any influence on manufacturers to design double insulated equipment ( no earth required ) that when powered up has a metal case parts that gives a "tingle" to the touch ? If the case was connected to earth via an amp meter and the leakage found to be higher than 10 mA then ( apparent ) the equipment would require a mains supply with a high integrity earth system.

Yes, I believe that would be the case. But I don't think it's related to going DI.

Do manufacturers choose to go double insulated ( albeit with a tingle touch ) so they can avoid restricting use to supplies with high integrity earths.
( And without an earth how do the manufacturers filter out mains borne voltage spikes. ? ? )

"Small" equipment doesn't usually have much leakage - some years ago I came up against this when my employer was having a new warehouse built. The electrical contractor was being "a bit anal" over the electrics - claiming he could only fit single sockets (not double) and would not fit extra (to give the number of outlets requested) without significant extra costs. So I knocked up a test rig (extension lead with multimeter in the earth connection) and tested a representative sample of all our kit - I couldn't find a single item with any significant leakage.

On the other hand, once you go up in size a bit ...
I dismantled our old failed UPS from the server room - cable went in the copper box, steel in the steel pile, only a relatively small amount of "electronic waste" left). That had some very sizeable input filters in the bottom of the cabinet - I think I'll see if we still have them lying around and test them.

I suspect the main reason for going DI is simply to avoid the need for an earth at all. Allows the use of a "figure of 8" 2 pin inlet, and no worries about (eg in the case of hand tools, lawn mowers etc) the risk of exporting an earth to a location where it may not be "earth". Not to mention, if you are holding a metal cased drill at the end of a very long extension lead, in the event of a fault it's possible to get s situation where the body goes to half the mains voltage (so 120V around here) but the upstream fuse could take a while to blow.

And without an earth - you don't filter out any spikes ! If there are no other connections to the equipment then you gain a lot of immunity to common-mode surges and spikes. An example of this is phones.
An ex boss lived in the country, all overhead services, and prone to thunderstorms. They would lose the fax machine and computer modems on a regular basis - but never any "ordinary phones". The phones weren't affected by the common mode surges because there wasn't a path for any current. Fax machines, modems, cordless phone bases all had a path via earth for incoming surges and so suffered.
I had suggested he really needed to route the phone lines close to the mains supply, and fit "whole house" surge protection at that point - but it never happened.

With the stack of kit under the TV ...
Well that's all linked by cables - so if any item is earthed then everything else will be earthed through it. Potentially one lot could be earthed up the aerial lead, via the LNB or dist amplifier, and down another aerial lead to another set of AV equipment that is earthed !

 

[SimonH2]

if we stick with your definition, then 543,7,1,203(iii) is recursive - no quantity of parallel conductors will meet it.

And if we stick with that belief regulations become recursive as a matter of basic principle.

Not at all.
Taking a simple case, if there is a requirement for A, and a requirement for B, that doesn't make either A or B recursive - either on it's own or mutually.

Stripped of extraneous words, with one word changed to an alternative from its dictionary definition

Or in other words, if I ignore what's inconvenient, and redefine things in my favour

and with the relevant parts merged

and an important bit left out - or as you put it, ignore what's inconvenient to your argument

the requirement is:

The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective conductor current is likely to exceed 10mA, shall have two separate circuit protective conductors, and each shall be in the form of a ring with both ends connected to earth at the origin of the circuit.

What do you think that means?

It means you either cannot read, or are simply ignoring what doesn't fit your argument - in the context, we are talking about meeting 543.7.1.203(iii) which you have been very vocal previously that each separate pc must comply with. Let me re-introduce the bit you've left out and then see how well it works :

Your original with the missing bit re-instated :
The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective conductor current is likely to exceed 10mA, shall have two separate circuit protective conductors each complying with the requirements of Section 543, and each shall be in the form of a ring with both ends connected to earth at the origin of the circuit.

So what does that mean ? Well filling in the requirement to meet Section 543 with the expanded text of 543.7.1.203(iii), we have :

The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective conductor current is likely to exceed 10mA, shall have two separate circuit protective conductors having two separate circuit protective conductors each complying with the requirements of Section 543, and each shall be in the form of a ring with both ends connected to earth at the origin of the circuit, and each shall be in the form of a ring with both ends connected to earth at the origin of the circuit.

 

[ban-all-sheds]

Not at all.

Why do you say that, and then immediately proceed on the basis that they are recursive?

Or in other words, if I ignore what's inconvenient, and redefine things in my favour

No, just concentrating on what is relevant to the situation where the chosen method of provision of a high integrity protective connection for a ring circuit is two separate cpcs. I've ignored nothing.

and an important bit left out - or as you put it, ignore what's inconvenient to your argument

Well, it seems I did leave out an important bit, given how you are now carrying on. Not because it was inconvenient to my argument though, but because it had no bearing on it. It had no bearing, and I thought that omitting it would make things clearer for you. I apologise if it didn't, but in my defence I will say that it really never occurred to me that you, or indeed anybody, would be so {whatever} that they would think that regulations could be recursive.

If I were to put it in we'd see that it is inconvenient to you, not me, and that it is you who is ignoring it because it doesn't fit with your claim that the regulations should be read recursively.

It means you either cannot read, or are simply ignoring what doesn't fit your argument

No - it is you who hasn't read it properly. I'll leave it for others to speculate whether you actually can't read properly, or are just ignoring something doesn't fit your argument.

I'm not actually going to re-write the condensed requirement, just point one thing out.

in the context, we are talking about meeting 543.7.1.203(iii) which you have been very vocal previously that each separate pc must comply with. Let me re-introduce the bit you've left out and then see how well it works :

543.7.1.203 applies to high integrity protective connections, not individual cpcs (clue - the second 'c' dpes not stand for 'connection'.

...shall have a high integrity protective connection complying with one or more of...

(i) A single cpc which is...
(ii) A single copper cpc which is...
(iii) Two individual cpcs, each complying with...
.
.

Your original with the missing bit re-instated :
The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective conductor current is likely to exceed 10mA, shall have two separate circuit protective conductors each complying with the requirements of Section 543, and each shall be in the form of a ring with both ends connected to earth at the origin of the circuit.

They did not write "each complying with the relevant requirements of Section 543", but I struggle to see how that means that you can force the application of regulations which themselves do not apply.

The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective conductor current is likely to exceed 10mA, shall have two separate circuit protective conductors having two separate circuit protective conductors each complying with the requirements of Section 543, and each shall be in the form of a ring with both ends connected to earth at the origin of the circuit, and each shall be in the form of a ring with both ends connected to earth at the origin of the circuit.

Nonsense, because 543.7.1.203 does not say it applies to cpcs, it says it applies to protective connections, and defines what form of cpc(s) or other measures qualify as high integrity protective connections.

 

[JohnW2]

such that the total protective conductor current is likely to exceed 10mA,

Is that exceed 10 mA when the circuit is functioning normally ( current in CPC being due to filters and other capacitive effects ) or only during fault conditions ....

As Simon has explained, it relates to the 'leakage' (due to filters etc.) during 'normal functioning'.

Does this have any influence on manufacturers to design double insulated equipment ( no earth required ) that when powered up has a metal case parts that gives a "tingle" to the touch ? If the case was connected to earth via an amp meter and the leakage found to be higher than 10 mA then ( apparent ) the equipment would require a mains supply with a high integrity earth system.

I'm not quite sure how one would get 10mA flowing to earth from the exposed-c-pc of non-faulty DI equipment. Whatever, as Simon quoted, the regs are talking about >10mA total in a circuit - in a sockets circuit that could be, for example, 5 bits of equipment each of which, individually, resulted in a leakage only just over 2mA.

Do manufacturers choose to go double insulated ( albeit with a tingle touch ) so they can avoid restricting use to supplies with high integrity earths.

I rather doubt it, at least in terms of consumer equipment, since they would presumably only have to 'impose' such a restriction for individual items with >10mA leakage - which is most unlikley to happen. (most modern equipment is required to have <3.5mA leakage, anyway).

( And without an earth how do the manufacturers filter out mains borne voltage spikes. ? ? )

I confess that I've never really thought about that, and when I do start thinking I get a bit confused! My first reaction is to say that (whether one is talking about 'incoming' or 'outgoing' spikes), all that may matter (in the absence of an earth connection) are any 'spikes' of L-N potential difference, and that they could be 'dealt with' by L-N capacitors. However, if it were as simple as that, I presume that no-one would bother with L-E or N-E filter components - so I'm not sure!

Kind Regards, John

 

[JohnW2]

543.7.1.203 applies to high integrity protective connections, not individual cpcs (clue - the second 'c' dpes not stand for 'connection'. ... ...shall have a high integrity protective connection complying with one or more of...
(i) A single cpc which is...
(ii) A single copper cpc which is...
(iii) Two individual cpcs, each complying with...

I must confess that I hadn't previously noticed that - so now we have "protective connection" as well as "protective conductor" and "circuit protective conductor", and, to give us more to speculate about, BS7671 does not provide a definition of "protective connection". As a matter of correctness, the three abbreviations I have highlighted in red in your quote are incorrect. The regulation does not say "cpc(s)" or "circuit protective conductor(s)" but, rather "protective conductor(s)".

I am still not always totally sure how people are using these various terms. Which of these terms would you use to describe the length of conductor between an earth terminal on one socket and an earth terminal on the 'next' socket in a circuit (ring or radial)?

Kind Regards, John

 

[ban-all-sheds]

BS7671 does not provide a definition of "protective connection".

Yes it does.

543.7.1.203 says "... a high integrity protective connection complying with one or more of the following ..." and then goes on to describe 5 alternative followings.

As a matter of correctness, the three abbreviations I have highlighted in red in your quote are incorrect. The regulation does not say "cpc(s)" or "circuit protective conductor(s)" but, rather "protective conductor(s)".

As a matter of correctness:

The wiring of every final circuit and distribution circuit ... shall have ... a single protective conductor ... or ... or two individual protective conductors ...

In the interests of brevity and focussing on what is relevant I do not think it was wrong or misleading to talk about "circuit protective conductor".

Above, I did not claim that this was an actual quote from the regulations, I said it described the requirement:

Stripped of extraneous words, with one word changed to an alternative from its dictionary definition and with the relevant parts merged the requirement is:

The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment, such that the total protective conductor current is likely to exceed 10mA, shall have two separate circuit protective conductors, and each shall be in the form of a ring with both ends connected to earth at the origin of the circuit.

I am still not always totally sure how people are using these various terms. Which of these terms would you use to describe the length of conductor between an earth terminal on one socket and an earth terminal on the 'next' socket in a circuit (ring or radial)?

Just that piece?

Certainly not a "circuit protective conductor" - it clearly isn't what Part 2 defines one of those as.

And unless it can be shown that that length on its own is being used to provide some measure of protection against electric shock, and on its own is intended for connecting together exposed- or extraneous-conductive parts, I would say not a "protective conductor".

On its own it's just a bit of wire, a length of cable, a conductor. On its own it may well be part of a (C)PC, but unless on its own it is intended to be, and is on its own performing the function(s) defined for a (C)PC then it can't be one. But a CPC can be a number of those, plus screwed connections, plus metal straps across the backs of sockets.

 

[SimonH2]

Nonsense, because 543.7.1.203 does not say it applies to cpcs, it says it applies to protective connections, and defines what form of cpc(s) or other measures qualify as high integrity protective connections.

OK, just so we are 100% clear, you are saying that your interpretation of 543.7.1.203(iii) is that it requires two circuit protective conductors, but those two conductors do not themselves individually need to meet the requirements of 543.7.1.203, and nor does 543.7.1.203(iii) specify that either of them has to be a ring.

Ignore all other regs for the moment, this is only about 543.7.1.203(iii).

 

[JohnW2]

BS7671 does not provide a definition of "protective connection".

Yes it does. 543.7.1.203 says "... a high integrity protective connection complying with one or more of the following ..." and then goes on to describe 5 alternative followings.

I terms of what the regulation "actually says", that doesn't really qualify as a definition. It could easily mean "... shall have a high integrity protective connection..." (as defined somewhere, except that it isn't) which also "...complies with one or more of the following....".

By analogy, if I wrote: "...shall have a Low Voltage supply complying with one of the following: (i) TN-S earthing system ... (ii) TN-C-S earthing system", that would not constitute a definition of "low voltage" or "low voltage supply".

As a matter of correctness: The wiring of every final circuit and distribution circuit ... shall have ... a single protective conductor ... or ... or two individual protective conductors ... In the interests of brevity and focussing on what is relevant I do not think it was wrong or misleading to talk about "circuit protective conductor". Above, I did not claim that this was an actual quote from the regulations, I said it described the requirement:

You did, indeed, not explicitly claim that it was a quote from the regs (although that's what it looked like it was meant to be). However, given that so much of this discussion centres so much on the meanings of these words and phrases, it seemed a bit odd that you changed "protective conductor" in the regulation to "cpc" in what you wrote. If you were just trying to save typing, you could have used the BS7671-specified abbreviation for "protective conductor" (which is "PE"!!).

I am still not always totally sure how people are using these various terms. Which of these terms would you use to describe the length of conductor between an earth terminal on one socket and an earth terminal on the 'next' socket in a circuit (ring or radial)?

Just that piece?

Yes - or any other individual 'piece'.

Certainly not a "circuit protective conductor" - it clearly isn't what Part 2 defines one of those as. And unless it can be shown that that length on its own is being used to provide some measure of protection against electric shock, and on its own is intended for connecting together exposed- or extraneous-conductive parts, I would say not a "protective conductor".

But what about what the definition in Part 2 of BS7671 actually says? The words in bold italics you have written above do not actually appear in that definition. In any event ....

On its own it's just a bit of wire, a length of cable, a conductor. On its own it may well be part of a (C)PC, but unless on its own it is intended to be, and is on its own performing the function(s) defined for a (C)PC then it can't be one. But a CPC can be a number of those, plus screwed connections, plus metal straps across the backs of sockets.

Fair enough. Let me rephrase the question, then. What about the collection of wires/conductors, screwed connections and metal straps which provide an electrical path from a socket back to the main earthing terminal - do I take it (on the basis of what you've written above) that your view is that, when all those things are taken together, their totality qualifies as "a CPC"?

Kind Regards, John

 

[ban-all-sheds]

OK, just so we are 100% clear, you are saying that your interpretation of 543.7.1.203(iii) is that it requires two circuit protective conductors, but those two conductors do not themselves individually need to meet the requirements of 543.7.1.203,

Does 543.7.1.203 say that they do? I can't see it.

and nor does 543.7.1.203(iii) specify that either of them has to be a ring.

How can that be my "interpretation" of it when it does specify that?

Ignore all other regs for the moment, this is only about 543.7.1.203(iii).

I can't see how it is either valid or helpful to do that when 543.7.1.203(iii) refers to other regulations.

 

[ban-all-sheds]

I terms of what the regulation "actually says", that doesn't really qualify as a definition. It could easily mean "... shall have a high integrity protective connection..." (as defined somewhere, except that it isn't) which also "...complies with one or more of the following....".

By analogy, if I wrote: "...shall have a Low Voltage supply complying with one of the following: (i) TN-S earthing system ... (ii) TN-C-S earthing system", that would not constitute a definition of "low voltage" or "low voltage supply".

OK, but that does not alter the fact that whatever it is it is required to comply with one of the 5 listed requirements.

You did, indeed, not explicitly claim that it was a quote from the regs (although that's what it looked like it was meant to be).

It was meant to be what I said it was. If it looked like something else to people who did not read what I wrote that's not my fault.

However, given that so much of this discussion centres so much on the meanings of these words and phrases, it seemed a bit odd that you changed "protective conductor" in the regulation to "cpc" in what you wrote. If you were just trying to save typing, you could have used the BS7671-specified abbreviation for "protective conductor" (which is "PE"!!).

So if, in another context, a requirement said "dining tables shall have at least 4 legs" you would quibble with someone calling them "table legs".

Fair enough.

But what about what the definition in Part 2 of BS7671 actually says? The words in bold italics you have written above do not actually appear in that definition.

No, they don't, but I wanted to stress that you were talking about an individual piece (which you have confirmed you are), i.e. a piece on its own. Again I do wonder, wrt 543.7.1.203(iii), whether you are having problems understanding what "individual" means.

What about the collection of wires/conductors, screwed connections and metal straps which provide an electrical path from a socket back to the main earthing terminal - do I take it (on the basis of what you've written above) that your view is that, when all those things are taken together, their totality qualifies as "a CPC"?

Yes.

 

[SimonH2]

OK, just so we are 100% clear, you are saying that your interpretation of 543.7.1.203(iii) is that it requires two circuit protective conductors, but those two conductors do not themselves individually need to meet the requirements of 543.7.1.203,

Does 543.7.1.203 say that they do? I can't see it.

So is that a yes or no to the question ?
The question is very simple, really really simple ...
Do we agree that 543.7.1.203(iii) requires two protective conductors ?
Do we agree that 543.7.1.203(iii) does not require either of those conductors, on it's own, to be a high integrity protective conductor as defined in 543.7.1 ?
Simple questions, that have simple yes or no answers. Surely it can't be that hard for you to read just one line of text and answer those questions ?

and nor does 543.7.1.203(iii) specify that either of them has to be a ring.

How can that be my "interpretation" of it when it does specify that?

EDIT: So you agree that 543.7.1.203(iii) does not in any way require either of those conductors to be a ring ? Yes or No

Ignore all other regs for the moment, this is only about 543.7.1.203(iii).

I can't see how it is either valid or helpful to do that when 543.7.1.203(iii) refers to other regulations.

It is valid and useful to define what 543.7.1.203(iii) means.