High integrity earthing and ring final circuits.

[ban-all-sheds]

ok, writing aside, the diagram in the photo above shows a high integrity earth..

It might do. It says it's the diagram of a ring final, so if that cpc is at least 10mm², or 4mm² with additional mechanical protection then it would comply with 543.7.1.3 (i) or (ii).

If it doesn't comply with 543.7.1.3 (i) or (ii) then it is not a high integrity earth for it clearly does not comply with 543.7.1.3 (iii) or (iv) or (v).

if the sockets were part of a radial then the last socket is connected back to the earth bar... yes?

But they are not.

so by it's very nature of already having the earth at the last socket connected back to the earth bar, a ring also has a high integrity earth

If there is only one ring, it only qualifies as a high-integrity cpc if it's at least 10mm², or 4mm² with additional mechanical protection.

( assuming that the earths are in seperate terminals at the socket and board, and leaving the 1.5mm cpc in T+E issue asside since I don't do domestic and generally wire in singles.. )

The 1.5mm² issue can't be left aside - it's fundamental to this whole problem, because if you only have one cpc ring it can't be 1.5mm².

which is exactly what you have in a ring if you use the dual earth terminal sockets and terminate one cpc into each terminal.. if you take one out, you still have the other..

No you don't.

You don't have two rings to start with, you only have one, so if you break it you then have no ring cpcs.

1) For a ring final the cpc must also be a ring.

2) Unless oversized you need two separate ring cpcs.

you yourself above have agreed with my statement that you have 2 cpc's at each socket.. but then insist on adding "neither of which is a ring".

No - I never said you had two cpcs at each socket - if you undo a connection as you suggested then each socket only has one path back to earth. The circuit has 2 cpcs, each one is a radial serving only some of the sockets. So no longer compliant as the cpc for a ring final.

do you then terminate the additional earth from the end of a radial into each and every socket on it's path back to the board?

No, because with the radial circuit you only have a single cpc. In the form of a ring.

so if I looked in the back of any of your sockets that you have wired to have high integrity earth, I would see 4 earth wires, 2 into each earth terminal?

You would if I

a) were to wire one

b) were to choose not to use a cpc of at least 10mm², or 4mm² with additional mechanical protection

because that is what the regulations say you must do.

543.7.1.3 (iii) two separate protective conductors, distinct from each other, each one of which is a ring.

 

[ColJack]

that drawing is perfectly acceptible as an example of a radial with a high intergrity earth is it not? ( which is what I meant by "writing asside" )

could you post a scan of the 17'th regs regarding this please.. it seems that it has changed fundamentaly in it's wording from the 16'th I have beside me..

 

[jockspark]

bas lets just take this back a little bit you want to quote books words
paragragh phrase when i guided you towards publications you told me in your personal attack on a previose thread i could not think for myself but you are happy to do this
now lets stop and you start from the top give us your interputation of
high integrety earththing and we will follow on with our comments
go BAN ALL SHEDS its all yours

 

[Jaymack]

The CPC's are shown using two ways of the earthing terminal block inside the CU. How does this relate to the sequence numbering allocation for the MCB ways?

Regards

 

[Spark123]

You need to clearly ID the each end of each ring CPC with alphanumerics.
As an aside, we had a similar discussion about high integrity earthing a while back - only got to 20 pages here
The regs call for there to be 2 individual protective conductors at each point. In a ring as in RFs picture there are 2 protective conductors which are independant of each other at each point.

 

[ban-all-sheds]

The regs call for there to be 2 individual protective conductors at each point. In a ring as in RFs picture there are 2 protective conductors which are independant of each other at each point.

No - the regs call for the circuit to have two separate protective conductors, distinct from each other, each one of which is a ring.

If a circuit has two separate cpcs, each one of which is a ring, then you must be able to completely remove one of the two separate ring cpcs, leaving one remaining ring cpc. If you can't then unless you're going to tear up the dictionary, and declare fundamental rules of topology wrong then you did not have two separate ring cpcs to start with.

In the diagram that RF posted, can you completely remove one separate ring cpc and leave yourself with one remaining separate ring cpc?

 

[ban-all-sheds]

now lets stop and you start from the top give us your interputation of
high integrety earththing and we will follow on with our comments
go BAN ALL SHEDS its all yours

1) For a socket final circuit, 543.7.2.1 calls for a high integrity protective conductor connection complying with the requirements of 543.7.1.


2) 543.7.1.3 goes on to say that the circuit has to have a high integrity protective connection complying with one or more of:

(i) a single protective conductor of at least 10mm² complying with 543.2 & 543.3.

(ii) a single protective conductor of at least 4mm² with mechanical protection, complying with 543.2 & 543.3.

(iii) two individual protective conductors each complying with the requirements of Section 543

(iv) & (v) not relevant here.


3) 543.2.9 requires the cpc of a ring final to also be a ring.


So when we add the requirement of 543.2.9 into 543.7.1.3, and take account of the meaning of the word "individual", which is not redefined anywhere and which therefore retains its normal meaning, our ring final socket circuit requires a high integrity protective conductor connection complying with one or more of:

(i) a single protective conductor of at least 10mm² run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit.

(ii) a single protective conductor of at least 4mm² run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit.

(iii) two separate protective conductors, distinct from each other, each run in the form of a ring, and each having both ends connected to the earthing terminal at the origin of the circuit.

There simply is no way that connecting the sections of a single ring-shaped cpc into different terminals on the sockets turns it into two separate ring shaped cpcs.

There is no getting away from the fact that if a circuit has two separate, distinct, cpcs you must be able to completely remove one of them and still have one left.


If you cannot do this then you did not have two separate, distinct, cpcs in the first place.

 

[holmslaw]

..

 

[Spark123]

The regs call for there to be 2 individual protective conductors at each point. In a ring as in RFs picture there are 2 protective conductors which are independant of each other at each point.

No - the regs call for the circuit to have two separate protective conductors, distinct from each other, each one of which is a ring.

If a circuit has two separate cpcs, each one of which is a ring, then you must be able to completely remove one of the two separate ring cpcs, leaving one remaining ring cpc. If you can't then unless you're going to tear up the dictionary, and declare fundamental rules of topology wrong then you did not have two separate ring cpcs to start with.

The regs call for 2 individual protective conductors, not 2 individual circuit protective conductors. The CPC for the circuit needs to be installed as you say in the form of a ring.

In the diagram that RF posted, can you completely remove one separate ring cpc and leave yourself with one remaining separate ring cpc?

I can remove a protective conductor and show the remaining 2 individual protective conductors like this:

(ok, that is the pic I drew last April )

 

[ban-all-sheds]

The regs call for 2 individual protective conductors, not 2 individual circuit protective conductors.

543.7.2.1 - For a final circuit.... the circuit shall be provided with a high integrity protective conductor connection complying with the requirements of Regulations 543.7.1. The following arrangements of final circuit are acceptable:

(i) + 543.7.1.3 (i) and therefore + 543.2.9 a ring final circuit with a ring protective conductor having a cross-sectional area of not less than 10mm².

(i) + 543.7.1.3 (ii) and therefore + 543.2.9 a ring final circuit with a ring protective conductor having a cross-sectional area of not less than 4mm² with additional protection against mechanical damage.

(i) + 543.7.1.3 (iii) and therefore + 543.2.9 a ring final circuit with two separate ring protective conductors which are distinct from each other.

I can remove a protective conductor and show the remaining 2 individual protective conductors like this:

(ok, that is the pic I drew last April )

Each protective conductor has to comply with 543.2.9.

If you really had two separate protective conductors, each of which complied with 543.2.9 then you would be able to remove one separate protective conductor complying with 543.2.9 leaving one remaining separate protective conductor complying with 543.2.9.

You have failed to do that.

Therefore you did not start form a position of having two separate protective conductors each of which complied with 543.2.9.

Therefore you did not start from a position of having a circuit which complied with 543.7.1.3 (iii).

Forget circuits, cpcs, rings etc etc for a minute

Just think of the general situation where you have two separate {wossnames}, each of which having {some sort of property}.

You must be able to take one {wossname} away and be left with the one remaining {wossname}. Since each separate {wossname} had (some kind of property} your one remaining {wossname} has {some kind of property}.

If you cannot take one away as described then you did not have two in the first place.

 

[Spark123]

Each protective conductor has to comply with 543.2.9.

The circuit protective conductor needs to comply with 543.2.9 which is as it would be installed. As long as the 2 protective conductors at each point comply with the 543 for a protective conductor I don't see the problem.

 

[ban-all-sheds]

The regulations say that you need two separate and distinct protective conductors, each one of which has to be a ring with both ends of each one connected to the earth terminal at the origin.

If you'd never encountered anything to do with high-integrity earthing, but knew enough about ring circuits to know what "ring" meant, and someone said to you "please draw me a circuit with two separate and distinct protective conductors, each one being a ring with both ends connected to the earth terminal", what would you draw?

The circuit protective conductor needs to comply with 543.2.9 which is as it would be installed. As long as the 2 protective conductors at each point comply with the 543 for a protective conductor I don't see the problem.

"The" cpc is the problem You must have two of them, not one. And if you're going to argue that you do have two protective conductors at each point then you have automatically admitted that it's not complying with 543.7.1.3 (iii), because you can't count them as two AND show that EACH ONE is a ring with BOTH ENDS connected to the earth terminal at the origin.

 

[AndyOlds]

Followed all of this with interest. BAS's argument seems to be with the wording more than anything else?

However I look at it, to have two separate CPC rings to each socket in the diagram posted, you would need 4 CPC wire ends entering each socket. Yes? (You would also presumably end up with a shed load of CPC cables running exactly the same parallel route between the CU and whatever point in the ring you care to look at).

However, surely the fact that there are only likely to be two CPC terminals on the back of the socket renders the "two separate CPC rings" idea somewhat pointless?

If one end of one CPC ring becomes physically disconnected, it is likely to be because the screw in the terminal has loosened. Surely in this situation both CPC wire ends in that terminal are likely to have become disconnected?

Apologies if I'm talking ballcocks, but I just can't see how the requirement could be achieved in practice (unless there are such things as special high integrity sockets).

I must add that I'm not an electrician, so have absolutley no practical experience on which to base my thoughts! Just interested in the logic of the argument![/u]

 

[ban-all-sheds]

Followed all of this with interest. BAS's argument seems to be with the wording more than anything else?

I think my argument is with all the people who, for whatever reason, look at plain, unambiguous wording and decide that it doesn't actually mean what it actually says....

However, surely the fact that there are only likely to be two CPC terminals on the back of the socket renders the "two separate CPC rings" idea somewhat pointless?

Why?

One terminal for one ring, the other terminal for the other.

If one end of one CPC ring becomes physically disconnected, it is likely to be because the screw in the terminal has loosened. Surely in this situation both CPC wire ends in that terminal are likely to have become disconnected?

Yes, so one of your separate and distinct cpc rings is no longer a ring. But your second separate and distinct one still is,

Apologies if I'm talking b*****s, but I just can't see how the requirement could be achieved in practice (unless there are such things as special high integrity sockets).

Yes - they have two cpc terminals.

 

[Grizzly]

So BAS, just to clarify things, is this picture more in agreement with what you are saying?

Untitled

• Grizzly
• 24 Jul 2008
• 1

*Apologies to Spark123 for my rather massy Paint butchering of his nice picture*