Consumer Unit Replacement

[ban-all-sheds]

I didn't think you needed multiple cpcs if wiring in singles, just one large enough for the largest circuit carried.

what is the topology of a cpc shared between two ring finals, or a ring final and a radial?

Dunno - I've never wired in singles - so you'd have to ask someone else. However, if one did as you suggest, one presumably could not, for example, test the continuity of the CPC in a ring final circuit.

I still don't see why. Unless you're using conduit or trunking for the cpc it too has to be a ring. 543.2.9

Mind you, with singles, I suppose that there are not necessarily any (cable) CPCs at all - it could all be conduit. In that case, it would not have to pass through any hole, anyway - but I am again uncertain as to if/how would could/would do certain aspects of testing.

Loop impedance, just as with a cable cpc.

cpc continuity cannot be done as per "normal".

• https://www.voltimum.co.uk/articles/guide-verification-steel-conduit
• https://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=6205

I'm still unsure what an installation would look like if multiple circuits shared a single cpc.

 

[JohnW2]

If, as OwainDIYer seemed to be suggesting, there were just two CPCs "large enough for the largest circuit" (and serving all circuits) going to the CU, then showing continuity between those two would not in any way guarantee that the CPCs going around any ring final circuits in the installation were continuous. As I've said, I have no experience of wiring final circuits in singles, but I very much doubt that it is done as suggested.

 

[ban-all-sheds]

543.2.9

 

[JohnW2]

...As I've said, I have no experience of wiring final circuits in singles, but I very much doubt that it is done as suggested.

 

[securespark]

How are you suggesting it has been done?

 

[JohnW2]

How are you suggesting it has been done?

I am personally suggesting nothing. This all started with ...

I didn't think you needed multiple cpcs if wiring in singles, just one large enough for the largest circuit carried.

... and, as I've said, although I have no experience of wiring final circuits in singles, I really don't think anyone would do it like that (have just one CPC {or two if there were ring final(s) involved} entering the CU/DB, serving all the final circuits).

I therefore think this is a rather silly discussion, since, as I say, I don't think anyone would do it like that. However, in case they did, "543.2.9" keeps getting mentioned here, and I don't really think that changes anything. That reg merely requires that any ring final has a CPC arranged as a ring with both ends of the ring connected to the origin of the circuit. It says nothing that would preclude other circuits sharing part(s) of that CPC ring - so, if one were daft, one could have, say, two ring finals, one with the two ends of its CPC ring going to the CU/DB and with the CPC of the second one connected to the CPC of the first ring at, say, it's first and last sockets. Both ring finals would then have a CPC which was "arranged in a ring, with both ends connected at the origin of the circuit" - but it would be impossible, from the CU, to test the CPC continuity of either ring with confidence.

However, as I said, I think it would be plain daft to do that, and I doubt that anyone would!

Kind Regards, John

 

[securespark]

Well, trunking or conduit (assuming the ferric type!) is effectively one CPC. And it is plenty big enough!

And I have installed many ring final circuits in domestic properties (blocks of flats) that have had L & N arranged in the usual ring fashion in 2.5 stranded copper singles and the CPC provided by the steel conduit.I have actually seen a conduit system installed as a ring.

 

[JohnW2]

Well, trunking or conduit (assuming the ferric type!) is effectively one CPC. And it is plenty big enough! And I have installed many ring final circuits in domestic properties (blocks of flats) that have had L & N arranged in the usual ring fashion in 2.5 stranded copper singles and the CPC provided by the steel conduit.

Indeed - and the requirements of 543.2.9 do not apply if conduit is being used as the CPC of a ring final. However, as this all started, one cannot then ('usually' - see below!) test the continuity of a ring final's CPC, so I presume one has to confirm a satisfactory earth connection to each and every socket.

I have actually seen a conduit system installed as a ring.

Hmmm - if that were done for a ring final, I suppose that, with a bit of 'plumbing work', one could test the 'ring CPC continuity' - but I rather doubt that many people would

Kind Regards, John

 

[securespark]

You could, but you wouldn't really expect it to be installed in that fashion. I happened to see it before making good.

 

[sparkwright]

And I have installed many ring final circuits in domestic properties (blocks of flats) that have had L & N arranged in the usual ring fashion in 2.5 stranded copper singles and the CPC provided by the steel conduit.I have actually seen a conduit system installed as a ring.

I don't quite follow this bit.

Surely the conduit would nearly always be in the form of a ring, if the wiring is a ring circuit.

If the conduit went in just a line, then stopped, then the conduit would need four wires throughout, and wiring it would be a very complicated, and suspect a few T-boxes would end up being used, and make the system impossible to rewire.

Sorry if I have misunderstood.

 

[securespark]

No, used to do linear installs and those with tees. All depends on the situation.

 

[ban-all-sheds]

"543.2.9" keeps getting mentioned here, and I don't really think that changes anything.

It ought to change your perception of a problem if you read it properly.

That reg merely requires that any ring final has a CPC arranged as a ring with both ends of the ring connected to the origin of the circuit.

Yes, but I'm not sure that "merely" is an appropriate word to use.

It says nothing that would preclude other circuits sharing part(s) of that CPC ring - so, if one were daft, one could have, say, two ring finals, one with the two ends of its CPC ring going to the CU/DB and with the CPC of the second one connected to the CPC of the first ring at, say, it's first and last sockets. Both ring finals would then have a CPC which was "arranged in a ring, with both ends connected at the origin of the circuit"

No they wouldn't. The cpc of the second circuit would not be a ring with both ends connected at the origin if they are connected at not the origin.

 

[JohnW2]

The CPC of the second ring would be "a ring with both ends connected at the origin". The CPC ring will have multiple joints (most or all at sockets etc.), and the fact that the conductors from the first and last joints to the 'origin' are shared with the first ring does not alter the fact that the second circuit's CPC is a "ring with its ends connected at the origin".

 

[EFLImpudence]

Especially as what is being discussed is shared CPCs.

 

[JohnW2]

Especially as what is being discussed is shared CPCs.

That's the point. Although, as I've said, only a pretty daft person would do it this way, as far as 543.2.9 compliance is concerned ....

Those two red lines look very much like "CPCs arranged in a ring with the ends joint at the origin", don't they?

Kind Regards, John