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

[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