Discuss Why Are Incoming Live/Neutral 16mm and Tails From Consumer Unit 25mm in the Electrical Forum area at ElectriciansForums.net

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3 circuits, 32A cooker, 32A ring and 6A lighting. The main cut-out fuse is 60A. New meter been fitted within the past year or two and the tails from the meter to fuse board were obviously replaced at the same time. They are 16mm tails. Personally I see no reason to replace them - Am I wrong?!

Hi - the 16mm conductors are rated above the 60A fuse and the load seems quite modest. So it seems fine to me.

Maybe I’m wrong too :) .
 
The bit that gets me is that within the OSG under 2.2.3.1 Consumer Tails it states on para 2 "Polarity should be indicated by the colour of the insulation and the minimum cable size should be 25mm." The reg no it refers to is 514.3.1 - however this doesn't mention anything about cable size.

I am currently in the process of replacing a customers old re-wireable fuse board. The main cut-out fuse is 60A. They are 16mm tails. Personally I see no reason to replace them - Am I wrong?!

You are not wrong.
Please remember that the OSG is a dummies guide to simple 'lectrics and if they can guide the masses to idiot proof their installations to cover up their ineptitude, then all will be safer. In theory.
 
If anyone has a copy of the napit EICR codebreaker book, in there under section 1.4 there is a point about the cross sectional area of the tail between the meter and cu having to be more than the minimum allowed of 25mm2, citing a FI code against a breach of the ESQCR.

Now, this is admittedly only a napit book, but is generally considered to be in line with the 'rules'.

In saying that, I cannot find any reference whatsoever to this in the ESQCR!
 
If anyone has a copy of the napit EICR codebreaker book, in there under section 1.4 there is a point about the cross sectional area of the tail between the meter and cu having to be more than the minimum allowed of 25mm2, citing a FI code against a breach of the ESQCR.

Now, this is admittedly only a napit book, but is generally considered to be in line with the 'rules'.

In saying that, I cannot find any reference whatsoever to this in the ESQCR!
People have already picked several holes in that napit book, it's got several things in like that
 
People have already picked several holes in that napit book, it's got several things in like that
Yeah, spotted a few others myself, or bits I disagree with, but just thought I'd mention it as there is lots of documentation out there which imply there is a rule somewhere leaning towards a minimum of 25mm2.

Not that I am aware of any rule in reality
 
Why would the ESQCR have relevance to a customer's installation ?
 
I can count on one hand the amount of times I have seen 25mm tails in domestic properties in these parts. It's always 16mm. The DNO here though generally fit an 80A Fuse in the head, 100A is not at all common.
 
maybe I'm being completely stupid but how are consumer tails sized? alot of people saying 16mm is fine also in the past/years it was acceptable 16mm and 100A fuse ? and just briefly flicked through current carrying capacity tables and 16mm is quite below 100A - what am I missing or doing wrong?
 
maybe I'm being completely stupid but how are consumer tails sized? alot of people saying 16mm is fine also in the past/years it was acceptable 16mm and 100A fuse ? and just briefly flicked through current carrying capacity tables and 16mm is quite below 100A - what am I missing or doing wrong?
Mostly the current rating you will see for 16A is part of a multi-cable assembly, even then if you look at 4D2A table method E 'free air' you see 16mm down as 94A and with two separate wires the rating is a bit more.

Table 4D1A lacks information on 16mm single wires, but if you look at 25mm for method F spaced by one diameter it is 130A-146A depending on orientation (i.e. air flow) so 16mm as used for meter tails is quite capable of taking 100A.
 
Thanks again for the replies.

looked at so many things for answers my heads spinning, ill have a closer look again at the tables.

obviously the main thing I'm finding is the OSG 2.2.3 and sizing recommended at 25mm current version and even going back to a 1992 copy.

So if theres any reading matter you know of on the subject let us know :)
 
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.
 
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.
 
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.
 
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.
 
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" :rolleyes:
 
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?
 
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.
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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" :rolleyes:
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.
 
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" :rolleyes:
Use the now widely available 19 strand stuff, much more flexible. Even the meter fitters have now started using it!
 

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