Adding two spur sockets to Ring Final

[JohnW2]

Amendment 2 allows this. ... The useless 'power vs lighting' shambles is gone, minimum size for any circuit is 1.0mm² copper.

At last, something approaching common sense. Thanks for telling us!

Kind Regards, John

 

[EFLImpudence]

I presume the minimum size T&E for ring circuits is still the same - i.e. ≥20A CCC except 1.5mm² T&E.

 

[securespark]

You can still use 1.5mm² MICC for ring finals, I believe.

Praise the Lord that the power/ lighting shenanigans is gone!

All hail the new rule!

We did calculations at college on how small we could go with the CSA. One such calc was 1 milli on an immersion circuit.

I think we even did a stand-alone cooker on a 25A breaker using 2.5 milli.

 

[EFLImpudence]

You can still use 1.5mm² MICC for ring finals, I believe.

Yes, that was why I mentioned T&E with regard to the inconsistencies:

For T&E, 433.1.204 states a 2.5mm² csa minimum but then goes on to state that "Such circuits are deemed to meet the requirements of Regulation 433.1.1 [protection of conductors] if the current-carrying capacity (Iz) of the cable is not less than 20 A" - i.e. 1.5mm² T&E.

 

[JohnW2]

Yes, that was why I mentioned T&E with regard to the inconsistencies: For T&E, 433.1.204 states a 2.5mm² csa minimum but then goes on to state that "Such circuits are deemed to meet the requirements of Regulation 433.1.1 [protection of conductors] if the current-carrying capacity (Iz) of the cable is not less than 20 A" - i.e. 1.5mm² T&E.

I suppose it depends upon exactly how one reads it but, whilst (as we have often discussed) it doesn't seem rational, I wouldn't say that it is 'inconsistent' ...

... It starts by saying that the circuits must be wired in cable with a CSA of ≥2.5mm² (or ≥1.5mm² for MICC) and then goes on with the "Such circuits are deemed to ...." which you quote above. If, as I do, one takes that "Such circuits" to be those which satisfy the previous sentence (i.e. CSA-wise) (in other words, if one considers the two sentences together, with a logical 'AND' between them), then I don't think there is any inconsistency.

However, why on earth 1.5mm² T+E which (with its installation method) has a CCC of ≥20A is not "deemed to satisfy 433.1.1", whereas 1.5mm² MICC which (with its installation method) has a CCC of ≥20A is "deemed to satisfy 433.1.1" is anyone's guess. It almost seems is if they believe that MICC is in some way more able to tolerate currents in excess of its CCC than is the case with T+E, but I don't know that such is even necessarily true.

Kind Regards, John

 

[JohnW2]

All hail the new rule! ... We did calculations at college on how small we could go with the CSA. One such calc was 1 milli on an immersion circuit. ... I think we even did a stand-alone cooker on a 25A breaker using 2.5 milli.

Quite so. I can but assume that what flameport has told us is true (I'm still waiting for my Amd3 to arrive!) in which case, as I recently wrote, it seems to open up the possibility (maybe for "Europhiles"!) to have 16A radials wired in 1.0 mm² cable!

That may possibly shift some people's views about radials vs. rings. Whilst, as I've said, I personally do not favour 16A (or 20A) sockets circuits, those who are happy with such a concept could use 2 x 1.0 mm² 16A radials in place of one 2.5mm² 32A ring, using slightly less length of cable with only about 40% of the copper than would be needed for the ring!

Kind Regards, John

 

[securespark]

Well, I'm not happy. FFS, you think Brexit would take us away from Euroing our British regs, not add more mindless Eurotrash regs.

I won't be happy until we've gone back to red/black imperial sized cable with VOELCBs.

Proper British stuff!

Britannia rules the waves. Hurrah!

 

[JohnW2]

Well, I'm not happy. FFS, you think Brexit would take us away from Euroing our British regs, not add more mindless Eurotrash regs.

I doubt that was the intention - I was merely observing that the change means that anyone with 'European inclinations' probably could now install 1.0mm 16A radials if they wanted to!

Loss of the silly distinction between 'power' and 'lighting' circuits is surely welcome, isn't it?

I won't be happy until we've gone back to red/black imperial sized cable with VOELCBs. ... Proper British stuff! Britannia rules the waves. Hurrah!

I fear you will never be happy, then

I must say that brown always seemed to me to be a strange choice of colour for identifying line/phase conductors, given that, intuitively, it 'smells of' earth!

Kind Regards, John

 

[EFLImpudence]

Well, I'm not happy. FFS, you think Brexit would take us away from Euroing our British regs, not add more mindless Eurotrash regs.
I won't be happy until we've gone back to red/black imperial sized cable with VOELCBs.
Proper British stuff!
Britannia rules the waves. Hurrah!

D'oh, you and your quaint little British ways.



What about one of the forum members doing an experiment?

Replace one of the ring circuit 32A MCBs/RCBOs with a 25A one (yes, I know they are not available for all CUs, but that just leads to the question of why not? - So only do it if one is available and of course installation method allows).
Heavens above; perhaps you could even try a 20A one if not a massive demand.
I suppose the kitchen circuit would be best for the experiment but others might be even more appropriate.

Carry on as normal and see if anything noticeable happens.
If not then this would indicate that the British ring final circuit with all its special dispensations and restrictions is indeed redundant as it really was with the introduction of circuit breakers and save many hours of needless debate every time the subject arises.

You would of course still have a ring circuit but it would not require any dedicated regulations as it would just be a conforming radial circuit connected to the OPD at both ends - which, of course, you may do with any other circuit - or it could be split in the middle and made into two radials to give 50A capacity for the power-hungry.

 

[JohnW2]

Replace one of the ring circuit 32A MCBs/RCBOs with a 25A one (yes, I know they are not available for all CUs, but that just leads to the question of why not? - So only do it if one is available and of course installation method allows).
Heavens above; perhaps you could even try a 20A one if not a massive demand. ... Carry on as normal and see if anything noticeable happens.
If not then this would indicate that the British ring final circuit with all its special dispensations and restrictions is indeed redundant ...

Indeed - or, conversely, as I recently suggested, if one took a standard UK ring final and replaced the 32A MCB/RCBO with a 40A or 50A one, I suspect that the chance of their ever being any significant/serious problems would be incredibly small.

However, as I also said, to some extent one probably has to consider 'what is possible', even if extremely unlikley - so (in common sense terms) it all comes down to where one draws the line in the sand.

Kind Regards, John

 

[EFLImpudence]

Indeed - or, conversely, as I recently suggested, if one took a standard UK ring final and replaced the 32A MCB/RCBO with a 40A or 50A one, I suspect that the chance of their ever being any significant/serious problems would be incredibly small.

I agree, but that is not allowed in the regulation - with separate rules for conductors in parallel.

However, as I also said, to some extent one probably has to consider 'what is possible', even if extremely unlikley - so (in common sense terms) it all comes down to where one draws the line in the sand.

Lines removed with what I have suggested.
Yes, I know - installation methods - but that is the same for every circuit.


Incidentally, something I have never been quite sure about:
Is oval conduit buried in masonry regarded as method B?

 

[plugwash]

Yes, I know - installation methods - but that is the same for every circuit.

The question is how many real-world circuits are "Method C with no grouping or other derating factors" throughout. A particular elephant in the room that seems to be widely ignored is the grouping of conductors as they converge on the CU/DB. Granted not all of the circuits entering a CU/DB will be under full load at any given time but it's not improbable that several of them will be.

 

[JohnW2]

I agree, but that is not allowed in the regulation - with separate rules for conductors in parallel.

Sure - but, as I presume you understand, what I was suggesting was that it's pretty (probably very) unlikely that a 2.5mm ring (or even, probably, a 2.5mm radial) would, 'in real-world practice', be likely to be subjected to a current high enough, and for long enough, top result in any significant harm/[problem, even if the 'overload protection' was way above the Iz of the cable (or even if there were no 'overload protection' at all) - so very probably 'no problem provided that there were adequate fault protection (which a B40 or B50 would probably provide).

I was not suggesting that such is allowed by regs, or even that it 'should be allowed'. I suppose I was just reminding people that the regs are (perhaps reasonably) very cautious/conservative.

Incidentally, something I have never been quite sure about: Is oval conduit buried in masonry regarded as method B?

I would have thought so. Isn't the point that if cable is within any sort of 'conduit' which is buried in masonry, then at least some of the cable will be surrounded by air, rather than being in direct physical contact with the masonry? ... and that's as true with oval conduit as it is with any other sort of conduit/'tube'/whatever.

Kind Regards, John

 

[JohnW2]

The question is how many real-world circuits are "Method C with no grouping or other derating factors" throughout. A particular elephant in the room that seems to be widely ignored is the grouping of conductors as they converge on the CU/DB. Granted not all of the circuits entering a CU/DB will be under full load at any given time but it's not improbable that several of them will be.

At risk of attracting flak, I would personally say that this is where most people probably exercise 'common sense' - i.e. 'ignore' such small local instances of what is technically 'grouping' (which would lead to a high proportion of circuits, which were otherwise Method C, strictly not being Method C throughout their entire length). ... and it's not just in the vicinity of CUs/DBs - cables can often be in very close proximity, sometimes contact, for s very short distance when they enter accessories/equipment etc.

As you imply, de-rating for grouping is deemed to be adequate when all the grouped cables are 'fully loaded' (to their CCCs) for an indefinite period of time and for their entire length (which could be tens of metres), so, in common-sense terms, the 'grouping' for a few inches of cables which will almost never be 'fully loaded (to their CCC) for appreciably periods does not really require anything like as great, if any, de-rating than in the 'worst case' scenario completed (all cables continuously fully loaded and 'grouped for many metres).

It's really another example of what I recently wrote, about the regs being extremely 'conservative'/'cautious' and where, I would personasally suggest, a certain amount of 'common sense' is probably appropriate.

Kind Regards, John

'

 

[EFLImpudence]

The question is how many real-world circuits are "Method C

Most ?

Do you propose we discuss things assuming all the cables are wrapped in thermal insulation and state things like:
"For that shower you will required 25mm² cable unless it is not installed surrounded by thermal insulation".

with no grouping

In a domestic situation as far as grouping - all ?

or other derating factors" throughout.

Very few - or install them another way.

"Cables installed in such a way must be derated by x%" also means "install them by another method so that they don't".

A particular elephant in the room that seems to be widely ignored is the grouping of conductors as they converge on the CU/DB. Granted not all of the circuits entering a CU/DB will be under full load at any given time but it's not improbable that several of them will be.

In a usual domestic situation then if the cables are side by side flat on a wall in free air or buried in masonry, then grouping factors are unlikely to be necessary.