extending black and red circuit with blue and brown ?

Is it allowed to extend an old circuit using black and red wiring with new blue and brown. (the grey cable, not the rubbery black stuff)
Isn't the CPC wire size bigger in blue and brown?
I have several circuits (sockets and lights) running from a 'submain' fusebox, I'd like to use them but powering each from a separate MCB and blue and brown cable coming from the consumer units at the other end of the house.
Thus all fuses and trips will be in one location.
But is it allowed to mix different cables in one circuit? And how would I calculate the maximum size of MCB per circuit?
And for lighting circuits can I run the main power line in 1.5mm and then spurs to individual lights in 1mm squared?
Eventually I want to do full paperwork and testing and try to get it all approved by the council under building regs.
George
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On Friday, 29 December 2017 14:01:13 UTC, George Miles wrote:

Yes.

No.

Yes

Maximum demand after diversity, but if you're not an electrician you probably don't need to go beyond the standard circuits:
6A lighting on 1 or 1.5mm 20A radial sockets on 2.5mm 32A ring sockets on 2.5mm 32A radial sockets on 4 mm

No, cable should be the same size throughout the circuit. 1mm is actually adequate for most 6A lighting circuits in houses where the cable length isn't too long.
Owain
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snipped-for-privacy@gowanhill.com wrote:

But you should put a warning sticker on your CU(s)
<https://www.labelsonline.co.uk/electrical-labels/bs7671-cable-colour-harmonisation-labels
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On 29/12/2017 14:37, Andy Burns wrote:

Which has always seemed a little superfluous in domestic premises with single phase supplies.
Red - Brown Black - Blue
There's no mistaking which is live or neutral in either case.
SteveW
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On 04/01/2018 23:05, Steve Walker wrote:

Slight possibility of confusion when 3&E is used; Red, Blue, Yellow, or Black, Grey, Brown - all of which can be lives.
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On Friday, 5 January 2018 01:01:55 UTC, John Rumm wrote:

If an electrician can't handle working with the common standard cables, where does the fault really lie? As said the note on domestic CUs is senseless.
NT
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On 05/01/2018 05:06, snipped-for-privacy@gmail.com wrote:

Which has always seemed a little superfluous in domestic premises with

Is everyone who works on domestic electrics an electrician?
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It's still perfectly legal for non-electricians to work on house wiring. And some young persons may be mystified if they come across red and black in a house they've moved into.
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Roger Hayter

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If you came across wiring colours you didn't recognise, wouldn't you ascertain what they referred to before going further?
At one time is was quite common to find imported goods with just about any flex colours you could shake a stick at. So before fitting a mains plug you'd check which did what. If you valued your health.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Friday, 5 January 2018 14:18:35 UTC, Dave Plowman (News) wrote:
NT:

then what are they doing working on electrics?

either that's obvious, or the person concerned should be backing well away from anything as tricky as replacing a plug.

Maybe we should litter roads with 'caution: pothole' signs. Taps with 'caution: wet' signs. And microwaves with 'caution, food may be hot' signs. Oh, they do that apparently. Next it'll be 'caution, coffee is hot.'
NT
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On 05/01/2018 15:48, snipped-for-privacy@gmail.com wrote:

It called DIY.
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Adam

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On Friday, 5 January 2018 19:57:28 UTC, ARW wrote:

You don't say.
Either they're capable or they're not. A bit of paper on the CU saying what they will see with their own eyes is hardly useful.
NT
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On 06/01/2018 05:58, snipped-for-privacy@gmail.com wrote:

While true, it does rather ignore Dunning Kruger... i.e. all those who are not quite capable, but don't know it.

This is one of those pointless conversations really. One should (i.e. its a wiring regs requirement) fit the sticker when appropriate, its costs next to nothing to do it. It might help someone at some point. That's all there is to it really.
You obviously won't fit the sticker, that's your prerogative, and in the grand scheme of things the world is unlikely to end (at least for that reason).
There are a whole bunch of "soft" rules that don't alter the fundamental electrical safety of the installation, but potentially make life easier for either users or future maintainers. Lots of people don't label the MCBs, or fit a "live" sleeve on the switched wires on a lighting circuit - one could argue it doesn't matter since if you know what you are doing, you can work it all out from first principles anyway. However these are things that gives an insight into the attention to detail possessed of the installer. While its no guarantee, IME if you can see that the installer has shown attention to the small details, then you usually also find the big picture stuff is right as well.
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John.
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On 06/01/2018 17:16, John Rumm wrote: <snip> > You obviously won't fit the sticker, that's your prerogative, and in the

It seems to me the sticker was more clearly of value at the time of the change of colour schemes. But changing the regs. to remove the requirement raises the (all too common) issue of asymmetric rewards and penalties for the people responsible. Hardly anyone would praise them for saving 30 pence or so per CU. Many would call for their heads if someone were killed where the blame could be put on the lack of a label. (It's what made the MPs who backed the relaxation of Part P all the more praiseworthy IMO.)
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Robin
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On Saturday, 6 January 2018 17:16:47 UTC, John Rumm wrote:

it isn't, it's a simple statement of fact.

it's already been explained why it has no way to help anyone. It's as useful as a sign saying 'caution square pin plugs in use.'

I'm not aware of any fact or reason to base that on

that is a different situation and a different argument to the colours sign

yes, until the installation is altered later.
There are useful constructive rules and useless ones. Caution red & black does not look the same as blue & brown is one of the latter.
NT
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If anyone is confused by the new wiring colours over the old, get a pro in to do any work.
With 3&E in domestic use, I'd not assume what any of the colours are used for anyway.
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*I'm not your type. I'm not inflatable.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 05/01/2018 10:57, Dave Plowman (News) wrote:

That was made worse with the new colours when old timers used the black as the neutral and the grey as switched live.
I would however say that over 99% of the work I see now has the black as the switched live.
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Adam

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On 05/01/2018 20:19, ARW wrote:

TBH, I am pretty sure I have done that one one early installation with new colour 3&E as well.

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On 29/12/2017 14:14, snipped-for-privacy@gowanhill.com wrote:

With some exceptions? 2.5mm² T&E had only 1mm² CPC in the 70s
http://wiki.diyfaq.org.uk/index.php/Dating_Old_Electrics

Is that a "should" as in "best practice" rather than as in "must"?
I hope so as I've rewired lighting circuits using 1.5mm (for robustness and to keep voltage drop low) but left some switch drops in 1mm where it is in good nick, has a CPC and meets the conditions for overload etc - just to avoid having to channel the walls. And of course noted it on the form.
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Robin
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Robin wrote:

In Australia we can go up not down, the cable size can not be smaller than the size at the fuse or breaker but can be bigger elsewhere .

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