On the other hand: if all HIE requirements can be met:
for a ring circuit by connecting the cpc to separate terminals and
for a radial circuit similarly by using four-core cable then
what is the point of all the other 'waffle'?
Poll - Ring final circuits with high integrity earthing
- Thread starter JohnW2
- Start date
for a ring circuit by connecting the cpc to separate terminals and
for a radial circuit similarly by using four-core cable then
what is the point of all the other 'waffle'?
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[the problem with using 'four core cable" for a radial is that it would have to be cable with a total CSA (L+N+CPCs) of at least 10mm² {e.g. four 2.5mm² cores}, which may not be the easiest thing to find. Hypothetical "4mm² 3C+E" would presumably do it, but I don't think that exists!) ]
Some of the other waffle is offering alternatives to those (simple) approaches. For example, either a ring or radial circuit could be wired with a single 10mm² (or mechanically-protected 4mm²) CPC ring, in either case removing the need for 'separate terminals' and, in the case of a radial, removing the need for a second CPC. .. or, of course, you could have an 'earth monitoring system' or an isolated supply!
Whatever, I've posed the question (essentially per the Poll question) to the IET technical help desk and will let you all know if/when I get some opinion or interpretation from them!
Kind Regards, John
Who is going to do that if all you have to do is put the existing cpc in separate terminals?
No-one with any sense, I imagine - I was merely pointing out the 'other options' which are offered by some of that 'other waffle'!
Kind Regards, John
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Yes, quite.
I was trying to show that the reason for the 'other waffle' may be because you could be incorrect in your deductions.
I was trying to show that the reason for the 'other waffle' may be because you could be incorrect in your deductions.
Who knows. It will be interesting to hear what the IET have to say - albeit even that will presumably only be 'an opinion', given that they may not find the regs any simpler/clearer than we do, and can't necessarily get inside the minds of JPEL/64 to ascertain the 'intended' meaning!
Kind Regards, John
Maybe because a spur is not a ring, and therefore the topology of two ring cpcs (if that's what's been used as the way to comply with 543.7.1.203) cannot/does not need to be carried through to the spur, but they wanted to remind people that HIE of some sort which complies with 543.7.1 will still be needed for the spur?
But in any event, it would be madness to assume that because a particular requirement is not repeated it doesn't apply. They don't repeat the requirement for the colour ID of the cpc either, but that doesn't mean you can use whatever colour you like.
It can't.
Because that is not what "all the other 'waffle'" says are the HIE requirements.
from drawings ive ever seen recently , I tended to agree with johns version, though using seperate terminals at the Dist board too, which I didnt see mentioned in your first post.
However reading some of the posts now, I have my doubts.
Must say when I iniatially see 2 earth terminal sockets, I did think of Two rings of earth, but on seing drawings and thinking how its practical using T+E cable, without actually reading the reg, i opted to assume 1 rings enough.
Unfortunately, if the debate was between Bas and anyone else, Id opt for bas as his understanding of reading regs IMO is second to none, However JohnW2 seems clued up on english grammar and common sense sides with Johns way as possibly being what was intended, even if the reg is poorly worded.
Therefore im on the fence and confused
However reading some of the posts now, I have my doubts.
Must say when I iniatially see 2 earth terminal sockets, I did think of Two rings of earth, but on seing drawings and thinking how its practical using T+E cable, without actually reading the reg, i opted to assume 1 rings enough.
Unfortunately, if the debate was between Bas and anyone else, Id opt for bas as his understanding of reading regs IMO is second to none, However JohnW2 seems clued up on english grammar and common sense sides with Johns way as possibly being what was intended, even if the reg is poorly worded.
Therefore im on the fence and confused
I was over-abbreviating, for the sake of brevity. 543.7.1.204 (which is what I was talking about) requires 'separate terminals' "...at all connection points throughout the circuit e.g. the distribution board, junction boxes and socket outlets".
I've always assumed and believed that one ring was enough. Those who produce the regs may not be very good at writing them clearly, but they are very far from being daft people. There is no disagreement that they are happy that turning the CPC of a radial into one ring is enough for HIE, so why on earth would they require two CPC rings for a ring final? That would mean that if one converted a radial into an HIE-compliant one, by turning the CPC into one ring (by adding a protective conductor from last socket back to CU), if one then also turned the L and N into rings (again, by taking conductors from the last socket back to the CU) it would suddenly become non-compliant as far as HIE is concerned - which sounds ridiculous, and I find very hard to believe the intention of the group of very intelligent and knowledge people who produce the regs!
I wonder if (outside of very special environments), anyone has ever seen a ring final circuit with two separate 'CPC rings' - i.e. 4 protective conductors attached to each socket etc.?? If any of you out there has seen such a circuit, please speak up!!
The one thing we are all agreed about is that it's badly worded, whatever it is trying to say. On the basis of common sense, and my belief in the intelligence (if not writing ability!) of those on the committee that produce the regs, I obviously am very inclined to believe my position as I have explained it! However, it will be very interesting to hear what the IET have to say, assuming they respond to my query!
KInd Regards, John
The thing I find most difficult to understand - if you are correct - is that it would have been so simple to say that all that was needed to achieve HIE for a ring circuit was to connect the cpc to separate terminals at each connection and for a radial circuit to make the cpc the same as a ring circuit but they did not.
Instead they wrote a full page of csa and protection requirements.
Why? It doesn't make sense - unless ...
Instead they wrote a full page of csa and protection requirements.
Why? It doesn't make sense - unless ...
I recently wrote:
The actual point of this is to illustrate how one can achieve the 'separate terminals' requirement when there are not enough ways in the CU's earth bar. However, it is clear that there are two, not four, protective conductors for the HIE ring final circuit - so definitely only one ring, not two. So, if one assumes that the IET would not publish an article which was incorrect in terms of BS7671, it sounds a bit like "John 1, BAS 0" However, I'll still wait for a reply from IET before getting too carried away with myself.
Kind Regards, John
Maybe I don't have to wait to hear from the IET. I've just remembered that the article in the IET's "Wiring Matters" about high integrity earthing (click here) gives a very clear opinion/view on the matter under discussion. It includes this ...
The actual point of this is to illustrate how one can achieve the 'separate terminals' requirement when there are not enough ways in the CU's earth bar. However, it is clear that there are two, not four, protective conductors for the HIE ring final circuit - so definitely only one ring, not two. So, if one assumes that the IET would not publish an article which was incorrect in terms of BS7671, it sounds a bit like "John 1, BAS 0"
However, I'll still wait for a reply from IET before getting too carried away with myself.Kind Regards, John
Good question. However, as I've said, I believe that what it says in 543.7.2.201 about both ring and radial circuits (essentially a 'deemed-to-satisfy' situation) is intended to 'short-circuit' the need to comply with (or even necessarily read!) all the CSA etc. options described in the various parts of 543.7.1.203, particularly in domestic installations. I suspect that those 'other options' in 543.7.1.203 primarily relate to non-domestic installations - when maybe 10mm² CPCs, earth monitoring systems or isolated supplies might sometimes be appropriate ways to go?
Kind Regards, John
That was the article and diagram that origanally convinced me john.
As an aside, i recall sockets that have an independant earth that is isolated, how would they have been earthed when used in conjunction with a metal backbox
As an aside, i recall sockets that have an independant earth that is isolated, how would they have been earthed when used in conjunction with a metal backbox
These are "clean earth sockets" and not to be confused with High Integrity Earth applications. With a clean earth the back box and fixing screws are earthed by the CPC in the twin and earth and the socket earths are connected to a separate earth terminal for connection to a clean earth ( NOT the CPC ).
There was a socket that was sold with the two earth terminals linked by a bridge. This bridge could be cut to separate the two earths when the socket was used in a clean earth installation. The CPC could then go either to the back box or to the "dirty" earth terminal on the socket while the clean earth cable went to the clean earth terminal on the socket.
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