Dado 3 compartment or Maxi trunking - home office - use singles?

[SimonH2]

I think the basic problem is that BAS takes the view that a ring constitutes a single CPC while the rest of us take the view that the "earth wire" in an RFC constitutes two CPCs back to the earthing bar.

Being pedantic again, if we consider a radial and install two "earth wires" to the outlet then what do we have ?
Do we have one CPC in the form of a ring with both ends terminated at the earth bar, or do we have two CPCs ?

If you argue that we have two CPCs because they are separate wires, then you can't argue that the two legs (from any individual accessory to the earth bar) of of an RFC aren't two separate CPCs. If you argue that these two legs are one CPC (because they are all joined together into one circuit), then you can't argue that running two "earth wires" with a radial circuit don't also constitute a single CPC formed in a ring.

Of course, if you consider that any "earth wires" that are wired together into a single conductive circuit (as in the radial example) form a single CPC, then it's also impossible to comply with the regs as written since you can run 4 10, 100 separate "earth wires" and you'll still have a single CPC from the terminal in the outlet to one or more terminals in the earth bar.

 

[SimonH2]

Simple question for BAS - how many CPCs in this diagram ?

 

[JohnW2]

543.7.1.203(iii) requires two individual cpcs, each complying with the requirements of Section 543, and in Section 543, 543.2.9 requires that the cpc be in the form of a ring. So if 543.7.1.203(iii) requires two individual cpcs, each in the form of a ring, that means two individual rings.

You must be having a quiet day, since you appear to just be trying "to be clever" for the sake of it. The fact that the CPC of a ring final is required to be a the ring does not alter the fact that, when viewed from any point in the ring, there are two individual CPCs (which happen to be part of a ring) from that point back to the origin of the circuit. In other words, a single ring satisfies all of the regulations.

If you think you have two separate cpcs then you must be able to completely remove one separate one and have one separate one remaining. Can you do that?

Yes, as far as a particular socket is concerned, one can do that (although one would then be non-compliant with 543.2.9). If there are multiple sockets, one cannot "completely remove" one of the CPC paths (back to origin) from any but the first/last sockets - but that's because other sockets require it.

Kind Regards, John

 

[JohnW2]

Simple question for BAS - how many CPCs in this diagram ?

I've asked him that repeatedly and, more particularly, asked him whether you are showing "two separate CPCs" (which he accepts would be compliant) or "a (single) CPC ring" (which he apparently believes would be non-compliant)!

Kind Regards, John

 

[JohnW2]

I think the basic problem is that BAS takes the view that a ring constitutes a single CPC while the rest of us take the view that the "earth wire" in an RFC constitutes two CPCs back to the earthing bar.

Indeed, and since the view of "the rest of us" makes sense in relation to the presumed point of the regulations (whereas, as we've both pointed out, BAS's view results in anomalies, and doesn't make particular sense), BAS seems to be arguing for the sake of it!

However, if he really wants 4 CPCs running from each of the sockets in his computer room back to the CU, then he's free to do that, and it certainly won't do any harm!

Kind Regards, John

 

[ban-all-sheds]

I think the basic problem is that BAS takes the view that a ring constitutes a single CPC while the rest of us take the view that the "earth wire" in an RFC constitutes two CPCs back to the earthing bar.

If it constitutes 2 cpcs, can you remove one, leaving one, which has the both form of a ring having both ends connected to the earthing terminal?

If not, why not?

Being pedantic again, if we consider a radial and install two "earth wires" to the outlet then what do we have ?
Do we have one CPC in the form of a ring with both ends terminated at the earth bar, or do we have two CPCs ?

You could have either. The requirements for HI earthing are different for radial circuits.

If you argue that we have two CPCs because they are separate wires, then you can't argue that the two legs (from any individual accessory to the earth bar) of of an RFC aren't two separate CPCs.

I can, actually, when the requirement is that each cpc be a ring, and each one has to have both of its ends connected to the earth bar.

If you argue that these two legs are one CPC (because they are all joined together into one circuit), then you can't argue that running two "earth wires" with a radial circuit don't also constitute a single CPC formed in a ring.

The requirements for HI earthing are different for radial circuits. All along I've been talking about HIE for ring finals.

Of course, if you consider that any "earth wires" that are wired together into a single conductive circuit (as in the radial example) form a single CPC, then it's also impossible to comply with the regs as written since you can run 4 10, 100 separate "earth wires" and you'll still have a single CPC from the terminal in the outlet to one or more terminals in the earth bar.

The requirements for HI earthing are different for radial circuits. All along I've been talking about HIE for ring finals.

 

[ban-all-sheds]

Simple question for BAS - how many CPCs in this diagram ?
View attachment 82943

That is as easy to answer as would the question "is this a ring or a radial with parallel conductors?" be had you shown 2L and 2N connections as well.

Which is it? Please don't try to pull the wool over people's eyes by claiming it doesn't matter - you might fool some people, but not I, as I know it matters very much indeed.

 

[Iggifer]

//www.diynot.com/diy/threads/high-integrity-earthing-and-ring-final-circuits.142565/

 

[JohnW2]

The requirements for HI earthing are different for radial circuits. All along I've been talking about HIE for ring finals.

Ironically (in terms of your attempted argument), all of the methods indicated as acceptable for radial circuits [in 543.7.2.201(ii) ] amount to turning the CPC of the radial circuit into a (single) ring If that's OK for a radial, why do you imagine that two rings are needed for a ring final circuit???

Kind Regards, John

 

[JohnW2]

Which is it? Please don't try to pull the wool over people's eyes by claiming it doesn't matter - you might fool some people, but not I, as I know it matters very much indeed.

Perhaps you can explain why you feel that it "matters very much" for a HI ring final circuit to have four paths to earth (CU/MET) from each socket (which I don't think anyone but you believes) whereas two paths (including the situation in which those two paths exist as a single CPC ring) is acceptable for a radial circuit?

I think that you are probably "really on your own" on this one, more so than ususal.

Kind Regards, John

 

[EFLImpudence]

I would query the wording as usual.

543.2.9 states "THE circuit protective conductor of every ring final circuit shall also be run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit".
I.e. ONE cpc.

543.7.1.203(iii) states "TWO individual protective conductors ...


I don't know what they meant but that IS what they wrote.

 

[JohnW2]

I would query the wording as usual. 543.2.9 states "THE circuit protective conductor of every ring final circuit shall also be run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit". I.e. ONE cpc.

That's the BAS argument. As you know as well as I do, "the CPC" of a ring final circuit is, in fact, several separate protective conductors which are connected together (at sockets or other accessories) so as to form a ring. Call that "ONE cpc" if you wish - but I think you (and BAS) are talking pure semantics.

543.7.1.203(iii) states "TWO individual protective conductors ....

Yep - and once they are connected (at a socket), they become a (single) 'CPC ring'. Are you going to say that those "TWO individual protective conductors" are actually "ONE cpc". If not, why does a 'CPC ring' constitute "ONE cpc" in one case and two CPCs in the other case?

But what about the 'bottom line'? Are you really going to joint the BAS camp and say that a HI ring final circuit has to have two CPC rings - i.e. 4 paths to CU/MET from each socket???

Kind Regards, John

 

[EFLImpudence]

I would query the wording as usual. 543.2.9 states "THE circuit protective conductor of every ring final circuit shall also be run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit". I.e. ONE cpc.

That's the BAS argument. As you know as well as I do, "the CPC" of a ring final circuit is, in fact, several separate protective conductors which are connected together (at sockets or other accessories) so as to form a ring. Call that "ONE cpc" if you wish

That is what it says in 543.2.9.
THE cpc of a radial is many small lengths but cannot be two cpcs.

but I think you (and BAS) are talking pure semantics.

Not semantics, as such; more pointing out what it states.

543.7.1.203(iii) states "TWO individual protective conductors ....

Yep - and once they are connected (at a socket), they become a (single) 'CPC ring'. Are you going to say that those "TWO individual protective conductors" are actually "ONE cpc". If not, why does a 'CPC ring' constitute "ONE cpc" in one case and two CPCs in the other case?

That is the subject of the discussion.
If not, all they had to write was "THE cpc must be connected to individual terminals".

But what about the 'bottom line'? Are you really going to joint the BAS camp and say that a HI ring final circuit has to have two CPC rings - i.e. 4 paths to CU/MET from each socket???

Perhaps it is so that in the case of one terminal being disconnected it is still left with what it should have.


For HI earthing a radial has to have double the cpc of a normal radial.
Perhaps the requirement for a ring is the same.

 

[JohnW2]

If not, all they had to write was "THE cpc must be connected to individual terminals".

I think that you and BAS are over-interpreting "the CPC'. You presumably accept that we are talking about two protective conductors (two 'cut ends') - maybe, to avoid the ambiguity you seem to see, they should have written "The protective conductors (or even "wires"!!) must be connected to individual terminals"? Let's face it, if one took 'CPC' totally literally (as a single word 'conductor'), it would have to be a single continuous conductor, so there is no way it could be "connected to individual terminals".

For HI earthing a radial has to have double the cpc of a normal radial. Perhaps the requirement for a ring is the same.

For a radial sockets circuit, all one has to do is to turn the 'single CPC' into a 'single CPC ring' to satisfy the regs. OK, it's still not a ring in terms of L and N, but that's not relevant - there is no conceivable electrical reason I can think of that a string of sockets only needs one 'CPC ring' if the L&N don't return to the CU from the last socket but does need two CPC rings if the L&N do return to the CU - can you?

What I don't understand is that BAS (and now maybe you) are arguing about the words of the regs in a manner that results in him (and now maybe you) concluding that there is a requirement to do something which I strongly suspect no-one, or virtually no-one, does, or has ever done.

I suppose it was me that started out, but I was talking about something that seems to be far more of an anomoly - that for a non-sockets circuit, one can satisfy the requirement for HI earthing simply by having a (single) 10mm² CPC - which sounds neither sensible nor safe to me, since mechanical breakage of the CPC (which is about the only useful issue a high-CSA CPC would address) is a very unlikely cause of a hazard arising.

Kind Regards, John

 

[Iggifer]

I think somebody needs to give the IET a call!