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?

 

[HappyHippyDad]

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.

It's not strange at all really Dave. It can be different assessor each time and they all have there little pet hates and ideas of what is right and wrong. My last assessor stated it needs to be 25mm tails whereas the Stroma tech line said use your knowledge as an electrician to determine the size.

 

[davesparks]

To be fair to the 25mm² people, there is a certain logic in using the largest reasonable cable size in a situation where it's slightly more of a pain to alter for future upgrades (due to being (theoretically) sealed in the meter) than if they were entirely within the customer's equipment.

In a new installation where the service cable is 35mm and the tails 25mm yes.
It's the insistence on breaking that same seal you mention and/or damaging decorations etc to replace 16mm tails with 25mm that I object to.
[automerge]1577660087[/automerge]

It's not strange at all really Dave. It can be different assessor each time and they all have there little pet hates and ideas of what is right and wrong. My last assessor stated it needs to be 25mm tails whereas the Stroma tech line said use your knowledge as an electrician to determine the size.

They should all be working to the same regulations,their personal opinions should be kept out of it.

I've made a formal complaint about one of their assessors for this in the past. We got in to a bit of a row over something, I proved him wrong using the regulations and asked him how I could make a formal complaint about him and he suddenly backed down and signed off the assessment.
He seemed to think that signing off the assessment would somehow change my mind about making a complaint, it didn't.

 

[GaryH]

Hi,
Fairly new to posting on the forum so be gentle with me! I agree entirely with the comments of previous posts that there seems to be this wish to upgrade to 25mm tails regardless.
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 with RCBO unit. 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?!

 

[static zap]

comments of previous posts that there seems to be this wish to upgrade to 25mm tails regardless.

a) This may be foresight for the future without Petrol/Diesel !
--Short high demand charging cycles--

b) (Surely a lead covered cable 14.5mmsq sheds heat
much better -- than similar sized pvc insulated-sleeved )

 

[Wilko]

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 .

 

[Andy78]

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.

 

[Julie.]

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!

 

[suffolkspark]

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

 

[Julie.]

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

 

[Andy78]

Why would the ESQCR have relevance to a customer's installation ?

 

[123]

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.

 

[Mark Wright]

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?

 

[pc1966]

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.

 

[telectrix]

had so many arguments with other sparks on this issue. 16mm as tails, separate singles in free air will carry 100A till the cows are sofas.

 

[Mark Wright]

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