New 4mm T&E feed to existing remote 2.5mm ring. OK or not?

[Mark42]

I'm building a small rental annexe at my own house, which will be supplied by a new local sub-main, with local metering. This includes one existing bedroom which will become part of the annexe.
This room has an existing ring final in 2.5mm, all in good condition. Rather than run two new 2.5s, a long way, in parallel to the new DB, may I run a single 4mm, then connect the existing 2.5mm 'tails' (now pulled back from the main house DB) to this locally? One less joint, and one less awkward run of cable. Protection would be a 25A RCBO.
I can think of no reason why this is not OK electrically, but I've never seen it done. It feels a bit 'bodgy' but so is running two great lengths of 2.5 in parallel for no particular reason.
Have I missed anything? Are there any regs about the CCA change within a circuit which might apply?

 

[ipf]

Ha Ha! You completely misjudge me. I'm a scientist by nature and training: it's always a pleasure to be proved wrong and hence to learn something new. That's how science works.

But rather than receive an ad hominem attack from behind anonymity, I'd prefer to hear why, technically, what I propose is 'wrong'. Explain that, clearly, and I'd be the first to thank you for teaching me something new.

Go ahead please.

Cheers, Mark

Keep learning, prof. We all are.
As I intimated, you've got all the answers....

 

[Charlie_]

Didn’t realise you had another thread.
I’ve posted onto there.
That cable is non compliant.
The standards are irrelevant for this country, my information is from the governing bodies..
Not my opinion, I have to comply with the use of standard cables as a responsible electrician.. insurance purposes, etc..

You are a diyer so perhaps you play by different rules.

 

[Mark42]

That cable is non compliant. ...

Interesting new evidence. What date is your BASEC e-mail please?
This must, by extension, mean that the wide supply of these cables by all the big suppliers*, obviously for inclusion in regulated installations in the UK, is effectively fraudulent. Any reasonable person would believe that cables sold by legitimate suppliers would be legally usable.
This is potentially a big story, with costs running into millions.
Taken at face value, it means that every installation which contains these cables should be condemned as non-compliant. It has massive insurance implications.

* EDIT: And the supplier I used is a major sponsor of this forum ...

 

[Charlie_]

My email is over a year old but still relevant.
Basec have rolled out a program to have these type of cables approved but as of yet none of the manufacturers have had them approved by Basec.

 

[ipf]

It's non compliant for your intended use. There are systems where it is compliant and, as a result, it can be acquired, legitimately. What it is used for is the buyer's choice....compliant or not.

 

[Toneyz]

The NICEIC did a technical bit in professional Electrician mag about this worth reading.

 

[Charlie_]

Prysmian do an interesting article

Prysmian Group | Cables, Energy & Telecom Solutions

Prysmian Group | Cables, Energy & Telecom Solutions

www.whyprysmian.co.uk

 

[GBDamo]

Prysmian do an interesting article

Prysmian Group | Cables, Energy & Telecom Solutions

Prysmian Group | Cables, Energy & Telecom Solutions

www.whyprysmian.co.uk

Good read, cheers for posting. I have been asked to use up some of this stuff the previous spark bought but have always kicked back.

 

[Wilko]

.

 

[telectrix]

i am just.......

 

[Pete999]

i am just.......

Whilst I'm not Thunderstruck, I am however

 

[l4urence]

Wow! What a thread - so different from the standard DIY question we see. The difference here is opinion. I’ve read lots of opinions here, I have my own as do others. There is nothing wrong with the ops opinion. The difference, and the thing that unites us here is being compliant with the regulations. Being able to sign off an installation as complying to those, good or bad. We even have opinions about the regs but we still comply. Your opinion is fine, I agree with many of your thoughts and comments but what you suggest is not compliant and that’s the problem here.