Poll - Ring final circuits with high integrity earthing

[ban-all-sheds]

Yes, that's what is says. However, what I said was that I believe 543.7.2.201(i) is trying (unsuccessfuly) to say something different.

So you have decided that it does not mean what it says or say what it means, and that therefore it is unsuccessful at saying/meaning something different.

Fair enough.

That's not really an answer to my question, because that would still be true even if none of 543.7.2 existed. So I have to ask again, what exactly in the point of 543.7.2.201(i)? To my mind, it is clearly trying (but failing) to give special consideration to a ring final with a single cpc ring which wouldn't exist if 543.7.2 didn't exist.

If it were trying to do that, why would it explicitly require compliance with 543.7.1 and therefore 543.7.1.203?

Again, you seem to be deciding that it doesn't mean what it says, and is trying to say something else, and therefore, as a result of your arbitrary decision it is failing.

Fair enough.

 

[JohnW2]

That's not really an answer to my question, because that would still be true even if none of 543.7.2 existed. So I have to ask again, what exactly in the point of 543.7.2.201(i)? To my mind, it is clearly trying (but failing) to give special consideration to a ring final with a single cpc ring which wouldn't exist if 543.7.2 didn't exist.

If it were trying to do that, why would it explicitly require compliance with 543.7.1 and therefore 543.7.1.203?

You tell me! 543.7.1 doesn't exclude sockets circuits, so compliance with 543.7.1.203 would be necessary even if none of 543.7.2 existed, so what is any of 543.7.2, including 543.7.2.201(i), trying to achieve? The only rational explanation is surely that 543.7.2.201 must be intended to be saying something which wouldn't be the case if it didn't exist - so what is that 'something'?

Kind Regards, John

 

[EFLImpudence]

There are several puzzling aspects to 543.7.2.201 which do not really make sense so I would think it is this section which contains the errors which are the cause of all the uncertainty.

 

[JohnW2]

There are several puzzling aspects to 543.7.2.201 which do not really make sense so I would think it is this section which contains the errors which are the cause of all the uncertainty.

Yes, it seems very odd. As I said, the bit in the pre-amble requiring compliance with 543.7.1 effective makes 543.7.2.201 totally redundant. Since that surely can't have been the intention, I strongly suspect that the preamble requiring compliance with (all of) 543.7.1 should not be there with its present 'blanket' wording.

If it were not for that blanket requirement for compliance with all of 543.7.1, this discussion would probably not be occurring, since 543.7.2.201(i) would probably then simply be saying that (as I believe) normal ring finals are deemed to be already HIE (provided they comply with 543.7.1.204, which would somehow have to be written in).

If that's what was intended, it would probably have been even better/ simpler/ clearer to do away with 543.7.2 and simply add the relevant bits (e.g. a ring final with a single CPC ring) to the list of options in 543.7.1.203.

Kind Regards, John

 

[EFLImpudence]

Yes, I know that is your argument for this subject but other parts are just silly.

For example -
543.7.2.201 For a final circuit ... 10mA, the circuit shall be provided with a HI protective conductor connection complying with the requirements of Regulation 543.7.1.
The following arrangements of the final circuit are acceptable:
(i) ...
(ii) ...
(iii) Other circuits complying with the requirements of Regulation 543.7.1.

Well, yes.

 

[JohnW2]

... other parts are just silly. For example - 543.7.2.201 For a final circuit ... 10mA, the circuit shall be provided with a HI protective conductor connection complying with the requirements of Regulation 543.7.1.
The following arrangements of the final circuit are acceptable:
(i) ... (ii) ... (iii) Other circuits complying with the requirements of Regulation 543.7.1.
Well, yes.

Maybe, but rather than just 'silly', I would say that tends to re-inforce the suggestion I've just made - that the blanket reference to compliance with 543.7.1 in the pre-amble probably should not be there. If it wasn't there, then your 'silliness' would go away, and it would all make sense, because it would then be saying that arrangements which were acceptable (as HIE) were ... (i) (rings with a ring protective conductor) .... (ii) (radials with (a), (b) or (c)) ... other circuits [i.e. other than those covered by (i) or (ii)] complying with 543.7.1. In other words, rings with a single pc or radials circuits complying with (a), (b) or (c) were 'deemed' to be 'acceptable' as HIE (with no general requirements to comply with 543.7.1) but any other circuits had to comply with 534.7.1.

If that were the case, 543.7.2.201(i) is particularly interesting since, after saying that ring finals with a ring pc were 'deemed' to be acceptable as HI (with no general requirement to comply with 543.7.1), it would be adding that spurs should have "HI conductor connections" which do have to comply with 543.7.1) ... so that would all fit - and make sense.

Kind Regards, John

 

[SimonH2]

Yes, I will claim that. "protective conductor (PE)" is not the same as "circuit protective conductor (cpc)". There are two different entries in the definitions - or hadn't you noticed that ?

Yes, I have noticed that.

I have not noticed, I must admit, 543.7.1.203 using the term "protective conductor (PE)". Is this because I've missed something which is there, or because you are seeing things which are not?

But I will tell you what I have noticed, and that is written English, which therefore construes as written English.

I have also noticed ".. every circuit .. shall have a .. protective conductor ..". So that makes it a circuit protective conductor.

But surely, according to you we must read the regs AS WRITTEN - and teh regs do not say circuit protective conductor. So by using that when the regs actually say something different, you are interpreting the regs as saying something they do not ?

Also, for the purposes of HIE, they may well have deliberately used the different terminology. As I see it, the cpc is there for fault protection, the PE is there for protection against shock due to the leakage current. As it is, in some or many cases the same conductor (or set of conductors, joints etc) will act as both.

Do you get it now?

Yes, I get that you are still using your diversionary tactics.

So you think it is logical that "high integrity" should mean "more integrity" for one sort of circuit but "same integrity" for another.

Yes, and it is strange that you seem unable to grasp that concept. It means that - that the END RESULT should be high integrity, not that any specific process must be followed to convert from one of several levels of integrity into one high level of integrity.

Taking the specific example, would you compare the PE redundancy of a radial where the end earth connection has been extended and taken back to the MET thus closing a ring, and that of an RFC (with one cpc) ?

Of course.

With the former you have done something to increase the integrity. In the latter you have not.

I'll give you the benefit of the doubt and allow that you misread the question.

Please compare the level of redundancy of the PE, not the process that arrived at the topology, but the level of redundancy as installed. In the case given, does the case of two radials with the PE ends linked together have higher redundancy, the same level of redundancy, or lower redundancy when compares with the PE of an RFC - assuming both are wired with the same techniques (ie using the separate earth terminals in accessories and so on).

Assuming both use the same termination methods - ie using separate terminals in both accessories and MET - is there any difference in either topology or redundancy between the resulting PE "rings" ?

No, there isn't. But in the former that topology represents increased integrity or redundancy compared to "normal", and in the latter it does not.

Ah, so you did read it then, and you agree that both provide the same high level of redundancy. Why does it matter that with one topology you started with no redundancy and so have to increase it, while with the other you started with almost the required level ?

You keep sounding like you think the process is more important that the end result.

In the former it makes a change which makes it reasonable for there to be the concept of "high integrity" as something distinct from "normal", in the latter it does not. But the concept of "high integrity" as something distinct from "normal" is applied by the Regulations to RFCs.

If you are right, and that actually there are no such requirements, do you have a logical, simple even, explanation of why they didn't just exempt RFCs in 543.7?

A standard RFC PE does not automatically, and in most cases as wired to "common practice" does not, meet the requirements for HI. It is normal, for example, to put both tails of the PE into the same terminal in the MET, and many people put both tails of the PE into the same earth terminal in the accessories - that does not meet the requirements for HI.
But an RFC starts off with higher integrity than a radial wired using the same practices.

543.7.2 seems (on it's own) to be saying that if you wire an RFC with some minor changes in practice - ie using separate terminals for the two ends at each point - then it does qualify as HI.

Also consider the specific statement that (with some conditions relating to circuit protection) that where two radial circuits are present, it is acceptable to link the earth terminations of the end points together so that the CP forms a ring. That is most definitely not "doubling up" the number of CPCs

Indeed it is not. It is changing the topology to increase the redundancy of connections. If the circuit started out needing that level of redundancy then when you need to increase it you need to change the topology. The way which the regulations say that shall be done is to double up the number of cpcs.

It really does. That's what "two individual" means - two is double the number one.

Hmm, so adding (say) 6" of earth wire to a large installation is "doubling"

So we have two radials, lets assume wired in T&E, and by choice or design we arrange for the last devices to be in close proximity so we can easily just drop a bit of earth wire between them.
Do we now agree that both radials (subject to separate terminations etc) now meet the requirements for HI earthing ? And that this has a single ring of protective conductors from the MET, via all the accessories, and back to the MET ?

I agree that it meets the requirements for HI earthing for radials, not rings.

And leaving aside for a minute the regs, do you see a logical reason why that topology is HI for the two radials, but ceases to be HI if you add L&N links and make it an RFC ? What is the change in integrity of the PE that is caused by the adding of the L&N links ?

 

[SimonH2]

Lets take our industry, IT. Suppose you are sat in a meeting with various people reviewing power supplies for a number of small installations.

At installation A you observe that while you have a modular UPS, it only has one power conversion module installed - so if this fails you will lose power to the supported equipment. You all agree that adding a single extra module, thus doubling the number of modules, will give you redundancy in the event of a power module failure.

At installation B you observe that there is a larger load, and this is supported (without redundancy) by a similar UPS which has 3 power modules installed. What do you agree is the required action to introduce redundancy in the event of a single power module failure ?
Do you :
a) Apply the logic that because you had to double the number of modules in A, you must double the number of modules in B - and thus install an extra 3 modules for a total of 6.
or b) Apply the logic that adding only 1 module (for a total of 4) will give you redundancy and therefore adding the extra 2 is not required ?

But what if the redundancy you seek is also against failure, or removal, of one of the two power supplies into the room?

As expected, diversionary tactics. Avoiding the question asked by answering a different one.

 

[EFLImpudence]

Have you noticed that Part 2 has separate definitions for Protective conductor(PE) and Protective earthing?

Where in the regulations does it mention "Redundancy"?

 

[EFLImpudence]

Does anyone who doesn't think illogically think they put "(PE)" after the wrong one?

 

[JohnW2]

Have you noticed that Part 2 has separate definitions for Protective conductor(PE) and Protective earthing?

Does anyone who doesn't think illogically think they put "(PE)" after the wrong one?

I've previously commented on the rather strange abbreviation they have used for "protective conductor" - not just that it is "PE", but also that it is in uppercase, whereas their abbreviation for "circuit protective conductor" ("cpc") is in lower case.

You might well be right that they put "PE" after the wrong entry in Part 2. However, unless/until they change/correct that, we would probably cause even more confusion if we didn't stick with what the regs "actually say" about the abbreviations. However, having said that, you will have seen that, when in autopilot mode, I sometimes use the abbreviation "pc" - which seems more logical, and more consistent with "cpc".

Kind Regards, John

 

[JohnW2]

Where in the regulations does it mention "Redundancy"?

I don't think it does actually use the word, but there is surely no doubt that redundancy of paths to earth is the most important electrical concept in achieving HIE (as you know, I don't personally feel comfortable with just large CSA <whatevers>) - and that, without using the word 'redundancy', that's what they are talking about in 543.7.1.203(iii), 543.7.1.204 and nearly all of 543.7.2.201?

Kind Regards, John

 

[SimonH2]

Does anyone who doesn't think illogically think they put "(PE)" after the wrong one?

Yes, I had noticed that, and I did think it rather odd. I wonder if they thought "pc" was liable to confusion with something else ?

I know it can be difficult coming up with abbreviations for a large quantity of terms without hitting some corner cases where the obvious abbreviations for 2 things are either the same or close enough to cause confusion.
I wonder if BAS has similar "discussions" over details with his work colleagues, because I know some (particularly some of the older ones) of our abbreviations and acronyms in the IT world don't really make sense - or are clearly very contrived.

 

[bernardgreen]

When the first buildings are built on the moon will people be mooning all electrical equipment and will lunacy take over the regulations.

 

[EFLImpudence]

You might well be right that they put "PE" after the wrong entry in Part 2. However, unless/until they change/correct that, we would probably cause even more confusion if we didn't stick with what the regs "actually say" about the abbreviations.

I appreciate the comment about "actually say" but in this case it is just wrong and not an interpretation of meaning.

Apart from the fact that PE not an abbreviation for two words beginning with P and C, a protective conductor is not even protective earthing when it is a bonding conductor.
So just wrong.


I was being a bit sarcastic when asking where it says 'redundancy' because Simon kept using the word yet asking where in the reg. it says 'ring' when that was one of the conditions.