UK Why Are Incoming Live/Neutral 16mm and Tails From Consumer Unit 25mm

[OnlQQker]

I just can't seem to understand this and can't find a clear reason behind it either. I asked a chap on the DNO once and he didn't know either.

Anyone?

 

[xylophone]

Possibly worthy of consideration is that some cut outs don’t seem capable of taking 25mm tails. Mine has 16mm2 from cutout to meter, 25mm2 thereafter, upgraded onwards due to a split/Henley arrangement for some sub mains a couple years back.

 

[cloverman]

I don't disagree with any of the points made on 16mm tails, However I would say that most people don't probably want the confrontation with their inspector during the annual assessment and so just choose to install 25mm tails to get the boxes ticked and save themselves all the hassle.

 

[Mark Wright]

The only other interesting thing I found was this

A Practical Guide to The Wiring Regulations

This best-selling text has been revised to reflect the requirements of the 17th Edition of the IEEWiring Regulations (BS 7671: 2008). It includes essential information on the new rules applied to special installations or locations, such as bathrooms, swimming pool locations, camping/caravan...

books.google.co.uk

 

[pc1966]

I don't disagree with any of the points made on 16mm tails, However I would say that most people don't probably want the confrontation with their inspector during the annual assessment and so just choose to install 25mm tails to get the boxes ticked and save themselves all the hassle.

A perfectly good point, and if you are not sure (see @Mark Wright post) then simply fitting 25mm is the easy solution.

But that does not make 16mm inadequate, just likely to cause arguments based on the specific thermal assumptions made, and it is not a reason for the trouble & risk of replacing them with 25mm if no other reasons exist.

 

[cloverman]

I don't think I said that 16mm tails were inadequate, I was agreeing with the comments made by others that under the correct circumstances they would be more than suffice for the job.
My point was that for a lot of people out there who perhaps feel under pressure, or somehow don't have the knowledge/courage to stand up to their assessor during the inspection will install 25mm because they feel to do otherwise will result in them been failed.
Over the years I have had some really great assessors who took on board what your views were and some who wanted it their way.
Most electricians/companies that I know will set aside certain works completed to steer their inspector towards during the assessment process and ensure they don't rock the boat so to speak by putting things that could be debated one way or the other depending on your view point.
Rightly or wrongly most will want to avoid that and will know from past assessments what that individual is keen on.

 

[Simon47]

There is an argument that using 25mm where 16mm would do is a safety issue in itself. Given the near universal acceptance of 6181Y, IMO there's an argument for saying that many installations are "a bit iffy" due to the strain such stiff cable puts on the terminations and component mountings. With 6381Y, different matter - but then you get into "discussions" with wholesalers who ask "what's wrong with 6181Y - everyone uses it"

 

[UKPN]

That's weird, our NICEIC assessor this year was happy with 16mm tails straight from a 200A supply to a switchfuse. I can't see any real difference.

I would get a new assessor, I take it you said ok, then promptly fitted 70mms?

 

[GBDamo]

Older installations had 16mm tails fitted because that all they need.
In recent years it has become the norm for people working in the domestic sector to fit 25mm tails regardless of what size is actually required.
This has been fuelled by the IETs picture book which shows diagrams of typical supply and CU setups where 25mm tails are fitted.
So now we have a lot of installations with shiny new CUs and 25mm tails, fed via 16mm tails from the cutout which in turn is fed via a 100 year old paper insulated lead sheathed cables of an imperial size a bit smaller than 16mm.

Why electricians these days seem to forget/ignore the theory, science and regulations and choose to follow the herd like a bunch of sheep I don't know.

Not about forgetting or ignoring it is a thing that just doesn't need thinking about, doesn't need remembering and doesn't need calculating doesn't need over complicating.

In domestic situations 25mm tails will never be wrong.

Just use them and leave the abacus in the van.
[automerge]1599258490[/automerge]

There is an argument that using 25mm where 16mm would do is a safety issue in itself. Given the near universal acceptance of 6181Y, IMO there's an argument for saying that many installations are "a bit iffy" due to the strain such stiff cable puts on the terminations and component mountings. With 6381Y, different matter - but then you get into "discussions" with wholesalers who ask "what's wrong with 6181Y - everyone uses it"

Its not a great argument though.

The equipment is designed for 25mm cables. If routing and entries are well planned no undue strain need apply.

 

[freddo]

There is an argument that using 25mm where 16mm would do is a safety issue in itself. Given the near universal acceptance of 6181Y, IMO there's an argument for saying that many installations are "a bit iffy" due to the strain such stiff cable puts on the terminations and component mountings. With 6381Y, different matter - but then you get into "discussions" with wholesalers who ask "what's wrong with 6181Y - everyone uses it"

Use the now widely available 19 strand stuff, much more flexible. Even the meter fitters have now started using it!

 

[Gavin John Hyde]

I feel like a rebel now for using 10mm tails out a Henley block to supply an RCBO in a small enclosure before a 4m cable run to an EV charger. All in the meter cabinet. I do like working with 16mm Flexi tails but few suppliers stock them around here

 

[davesparks]

I would get a new assessor, I take it you said ok, then promptly fitted 70mms?

No, the 16mm tails were already fitted and fully compliant.
I don't think it's even possible to fit 70mm into a 32A switchfuse!

 

[UNG]

Older installations had 16mm tails fitted because that all they need.
In recent years it has become the norm for people working in the domestic sector to fit 25mm tails regardless of what size is actually required.
This has been fuelled by the IETs picture book which shows diagrams of typical supply and CU setups where 25mm tails are fitted.
So now we have a lot of installations with shiny new CUs and 25mm tails, fed via 16mm tails from the cutout which in turn is fed via a 100 year old paper insulated lead sheathed cables of an imperial size a bit smaller than 16mm.

Why electricians these days seem to forget/ignore the theory, science and regulations and choose to follow the herd like a bunch of sheep I don't know.

Not quite sure on what you base some of your facts and why you choose to make the final comment you do
The tail size is more likely carried over from the Electricity Boards, in the board areas I worked MANWEB and NORWEB both specified 25mm² tails and a 16mm² earth for meter connections in the 80's I don't know what the other EB's around the country required at the time but it would seem likely they had the same requirements.
Since the privatisation changes to the electricity supply industry I'm not sure who specifies the size of tails required for a meter connection as the DNO's who replaced the Electricity Boards don't fit meters anymore