I don't know. Are you saying that they're all fools?
You are losing whatever plot you originally had.BAS you protest too much
High integrity earthing
- Thread starter ban-all-sheds
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If your inability to read and understand who's posting which words is anything to go by, then I don't have any faith in your ability to read BS7671. And I shudder to think what kind of contribution you could make on an IEE committee.
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Softus
I think we may have our wires crossed here - probably my fault, and if so I apologise
My comment about 'proving wrong' is direct solely to BAS.
I think we may have our wires crossed here - probably my fault, and if so I apologise
My comment about 'proving wrong' is direct solely to BAS.
It was this post I was referring to
Well at least I have one to blow BAS
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It was entirely your fault, so I accept your apology. Thank you. However, at no point did I have any wire crossed (or cut, or terminated, or duplicated).
Yes, I know that, and I continue to question the wisdom of making personal comments. Not that I've never done it myself, but I have to be concerned at your apparent readiness to reach a wrong conclusion after such careless consideration of what you're reading.
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Softus wrote
I have re-read the posts and I have mistakenly read one of your posts as if it came from BAS - so once again I apologise.
As to personnel comments I agree but I don't make any claims on perfection.
I would point out that it was BAS who used the term fools to describe the BS 7671 committee.
The way this topic has developed serves no useful purpose.
I have re-read the posts and I have mistakenly read one of your posts as if it came from BAS - so once again I apologise.
As to personnel comments I agree but I don't make any claims on perfection.
I would point out that it was BAS who used the term fools to describe the BS 7671 committee.
The way this topic has developed serves no useful purpose.
Water under the bridge, but thank you.
I see. You were being ironic then. I missed that one.
I completely disagree.
It has highlighted a possible widespread misunderstanding of the intent of BS7671, and conflicting requirements within it. It has questioned the role of the CPC in some special cases, and provoked thought about that issue.
Nobody can afford to be so closed-minded as to believe that their interpretation of BS7671 is correct, all of the time, or in any way that prevents them examining their own understanding of the impact upon installing safely.
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OK for what its worth this is my view of the 'how and why' confusing and conflicting text has appeared in BS 7671.
This confusion began with the 2001 amendments. This is when 607-02-04 was changed to refer to Final Circuits in general without an explicit exemption for the ring final circuit.
I believe that this probably occurred because a word for word version of the CENELEC equivalent to 607-02-04 was used rather than a specific UK version.
The CENELEC document probably would not have an equivalent to 607-03-01 (i) because ring mains are not widely used outside the UK.
Further confusion arose because the explicit reference to 1.5mm² conductors was dropped. This has resulted in uncertainty even for people 'in the BS 7671 circle'.
To illustrate - GN7 edition 1 included the cpc size on its diagram of a compliant ring final circuit whilst edition 2 does not give any size. GN 8 likewise does not commit to a size and Paul Cooks commentary actually gives a size of 2.5mm² but with no detailed explanation.
In all cases the high integrity protective conductor connection consists of a cpc starting from a DB and terminating at each socket outlet with the ring final circuit - then returning to the DB - a single loop. All connection points use two independent terminations.
As I have said elsewhere in this topic - IMO the technical detail of the problem and its solutions has not changed.
This confusion began with the 2001 amendments. This is when 607-02-04 was changed to refer to Final Circuits in general without an explicit exemption for the ring final circuit.
I believe that this probably occurred because a word for word version of the CENELEC equivalent to 607-02-04 was used rather than a specific UK version.
The CENELEC document probably would not have an equivalent to 607-03-01 (i) because ring mains are not widely used outside the UK.
Further confusion arose because the explicit reference to 1.5mm² conductors was dropped. This has resulted in uncertainty even for people 'in the BS 7671 circle'.
To illustrate - GN7 edition 1 included the cpc size on its diagram of a compliant ring final circuit whilst edition 2 does not give any size. GN 8 likewise does not commit to a size and Paul Cooks commentary actually gives a size of 2.5mm² but with no detailed explanation.
In all cases the high integrity protective conductor connection consists of a cpc starting from a DB and terminating at each socket outlet with the ring final circuit - then returning to the DB - a single loop. All connection points use two independent terminations.
As I have said elsewhere in this topic - IMO the technical detail of the problem and its solutions has not changed.
Any reason why the earths are terminated like that.
This thread was created by ban, after I noted it in another thread and spark 123 replied.
I have never done any HI Earthing but aware of the two earth terminal sockets.
From what I read fom the regs, previous too this post, for a ring, if I had ever removed a HIE socket, I would have expected FOUR earth wires, two in each terminal.
Am I alone, or would anyone else have expected that, from reading the regs, (not the OS quide, which as we all now know, what that shows).
I think that is how ban also reads it, so two of us maybe.
I also understand how NHA says it should be done as shown in the OSG. (even though it may not be wrote like that in the regs).
The original question/observation was posed by ban in response to what I wrote on mdbalsons kitchen topic, but as high integrity earthing turned into a topic on its own I asked for it to be split from mdbalsons topic.
I only expected to see the two protective wires, just like in the pic into two separate terminals for high integrity earthing which is why I made the comment. The brown OSG on page 61 does show a single ring CPC which is consistant with the above photo, and everyone agrees the regs do call for 2 independant protective conductors when talking of conductors of this size.
Even though a ring has one CPC, each point does have two independant protective paths connecting it to the MET.
Wether or not a single ring CPC can be classed as two protective conductors or not seems to be the aim or this debate.
I only expected to see the two protective wires, just like in the pic into two separate terminals for high integrity earthing which is why I made the comment. The brown OSG on page 61 does show a single ring CPC which is consistant with the above photo, and everyone agrees the regs do call for 2 independant protective conductors when talking of conductors of this size.
Even though a ring has one CPC, each point does have two independant protective paths connecting it to the MET.
Wether or not a single ring CPC can be classed as two protective conductors or not seems to be the aim or this debate.
so in md balson's case we do not know how he connected the CU.
IF he has connected on the same terminal in the CU this would not now be a HIE ring,
The reason I first asked really ,
would a NORMAL ring now be wired wrong due to this, as the cpc does not now consist of solely 1.5 cable, but also sections of the socket earth bars.
Afaik,
There is no reg that says the earths have to be in the same terminal for a normal rfc
IF he has connected on the same terminal in the CU this would not now be a HIE ring,
The reason I first asked really ,
would a NORMAL ring now be wired wrong due to this, as the cpc does not now consist of solely 1.5 cable, but also sections of the socket earth bars.
Afaik,
There is no reg that says the earths have to be in the same terminal for a normal rfc
I can't see any reason why mdbalsons kitchen will require high integrity earthing. He connected as in the pic, someone asked why he connected it that way, and I said high integrity earthing (with a laughing smilie after it). Ban disagreed with the comment I made and it just went from there!
If it is good enough for high integrity earthing then there is no reason I can see why it isn't good enough for a normal RFC.
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This is a reminder / explanation of the problem for anyone who may benefit.
Why do we need it - some types of electrical equipment cause a current flow to earth. This may be deliberate, as in the case of a low pass supply filter (functional earthing current), or just as a consequence of their operating characteristics (leakage current).
The cause is not really important here - it is the fact that this current flow exists that is of concern.
Just a word or two on the magnitude of the current - we become particularly concerned when currents of 10mA or above might flow. This concern has nothing to do with the current carry capacity of the circuit protective conductors (cpc) - they can easily carry more than 1000 times 10mA.
10mA is based on shock protection data - in particular the 'let go' threshold for the average person. If a current of 10mA (ac) or more pass through your body muscle contraction may prevent you from 'letting go' or breaking free.
How does the hazard occur - if the cpc path is broken then the current flow must stop, however, the potential for the current flow remains and this manifests itself as a potential difference on any class 1 (earthed metal case etc.) appliance that is downstream of the break in the cpc.
So what - I here someone say. well we now have a potentially lethal shock risk (the actual current flow may be greater than 10mA) and it has occurred because of a SINGLE failure in the system.
Contrast this to the series of events necessary to be in the same position for a class 1 appliance without these standing earth currents.
ONE we need a fault to occur within the equipment that cause the metal case to become live. TWO we need the normal shock protection measures (usually EEBADOS) to fail to clear the fault within the specified safe time and voltage limits. (You see I can count).
So we got into all this trouble because of a SINGLE failure in the system. We want the TWO fault tolerance of the normal system so how might we achieve it - well in the case of a radial circuit we could simply provide a SECOND route to the means of earthing by adding a cpc. The ring circuit already has TWO routes so we don't need another, however - for both ring and radial we do want TWO independent terminations for the TWO routes to the means of earthing. Hence the socket outlets with two terminals and the instructions to use two terminals at the DB.
This was often called duplicate earthing. There are other methods, such as using larger conductors for example, which seek to use more robust connections that are less likely to fail.
Why do we need it - some types of electrical equipment cause a current flow to earth. This may be deliberate, as in the case of a low pass supply filter (functional earthing current), or just as a consequence of their operating characteristics (leakage current).
The cause is not really important here - it is the fact that this current flow exists that is of concern.
Just a word or two on the magnitude of the current - we become particularly concerned when currents of 10mA or above might flow. This concern has nothing to do with the current carry capacity of the circuit protective conductors (cpc) - they can easily carry more than 1000 times 10mA.
10mA is based on shock protection data - in particular the 'let go' threshold for the average person. If a current of 10mA (ac) or more pass through your body muscle contraction may prevent you from 'letting go' or breaking free.
How does the hazard occur - if the cpc path is broken then the current flow must stop, however, the potential for the current flow remains and this manifests itself as a potential difference on any class 1 (earthed metal case etc.) appliance that is downstream of the break in the cpc.
So what - I here someone say
. well we now have a potentially lethal shock risk (the actual current flow may be greater than 10mA) and it has occurred because of a SINGLE failure in the system.Contrast this to the series of events necessary to be in the same position for a class 1 appliance without these standing earth currents.
ONE we need a fault to occur within the equipment that cause the metal case to become live. TWO we need the normal shock protection measures (usually EEBADOS) to fail to clear the fault within the specified safe time and voltage limits. (You see I can count
).So we got into all this trouble because of a SINGLE failure in the system. We want the TWO fault tolerance of the normal system so how might we achieve it - well in the case of a radial circuit we could simply provide a SECOND route to the means of earthing by adding a cpc. The ring circuit already has TWO routes so we don't need another, however - for both ring and radial we do want TWO independent terminations for the TWO routes to the means of earthing. Hence the socket outlets with two terminals and the instructions to use two terminals at the DB.
This was often called duplicate earthing. There are other methods, such as using larger conductors for example, which seek to use more robust connections that are less likely to fail.
Whether it is the 16th or 17th the following applies (17th nomenclature):-
543.7.1.3
The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment , such that the total CPC current is likely to exceeed 10mA, shall have a high integrity protective connection complying with one or more of the following:-
(i) A single protective conductor having a cross-sectional area of not less than 10mm squared complying with the requirements of regulations 543.2 and 543.3
(ii) A single CPC of not less than 4mm squared complying with 543.2 and 543.3, the CPC being mechanically protected, eg; within conduit
(iii) Two individual CPC's each complying with section 543. The two CPC's may be of different types eg; metallic conduit together with a cable CPC. One of the CPC's may be formed by metallic sheath , armour or wire braid within the cable.
(iv) An earth monitoring system may be installed...........
(v) Use of a double wound transformer......................
543.7.1.4 Where two CPC's are used the ends shall be terminated independently of each other................
Which leaves us to conclude:-
(a) High integrity CPC's which are not mechanically protected and do not have conduit/armour etc acting as a second CPC need to be 10mm squared.
(b) High integrity CPC's which are mechanically protected need to be a minimum of 4mm squared
(c) Two individual High integrity CPC's can be used with one being provided by a core in the cable or by the armour/braid etc or can be two cables
(d) Where two High integrity CPC's are used they shall be terminated at separate points. In the example of the socket wiring shown in the picture above then you would expect to see four green and yellow conductors with two terminated at each end of the socket outlet (assuming that the CSA of each CPC is 1.5mm squared - if not then the other conditions listed above apply).
Regards
543.7.1.3
The wiring of every final circuit and distribution circuit intended to supply one or more items of equipment , such that the total CPC current is likely to exceeed 10mA, shall have a high integrity protective connection complying with one or more of the following:-
(i) A single protective conductor having a cross-sectional area of not less than 10mm squared complying with the requirements of regulations 543.2 and 543.3
(ii) A single CPC of not less than 4mm squared complying with 543.2 and 543.3, the CPC being mechanically protected, eg; within conduit
(iii) Two individual CPC's each complying with section 543. The two CPC's may be of different types eg; metallic conduit together with a cable CPC. One of the CPC's may be formed by metallic sheath , armour or wire braid within the cable.
(iv) An earth monitoring system may be installed...........
(v) Use of a double wound transformer......................
543.7.1.4 Where two CPC's are used the ends shall be terminated independently of each other................
Which leaves us to conclude:-
(a) High integrity CPC's which are not mechanically protected and do not have conduit/armour etc acting as a second CPC need to be 10mm squared.
(b) High integrity CPC's which are mechanically protected need to be a minimum of 4mm squared
(c) Two individual High integrity CPC's can be used with one being provided by a core in the cable or by the armour/braid etc or can be two cables
(d) Where two High integrity CPC's are used they shall be terminated at separate points. In the example of the socket wiring shown in the picture above then you would expect to see four green and yellow conductors with two terminated at each end of the socket outlet (assuming that the CSA of each CPC is 1.5mm squared - if not then the other conditions listed above apply).
Regards
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