Why oh why 25mm meter tails?

[sparc]

Does anyone understand the logic of 'mandating' 25mm meter tails when upgrading a CU, when the sizing of other cables are left to the electrician's discretion?

I'm again having to explain to a little old lady with not a lot of money that she's need new meter tails with with tiny 6-way board, for her tiny 2-bedroom flat.

Massively cooking range to feed? Nope! 10.8Kw Powershower? Nooooh!

When copper is becoming an increasingly rare resource shouldn't we be fitting what's needed?

My guess is that the IET are simply 10 years out of date, plus someone somewhere calculate the specification, then a sub committee adds 10% to that, and the main committee thinks - let's be in the safe side, and adds another 10%.

Craziness gone mad!!!

(Rant for the day over - thank you for listening)

 

[telectrix]

if main fuse is 80A or less, you can use 16mm tails.

 

[Rockingit]

Trouble is Tel, that's not actually written anywhere that I know of, so peeps just looking at the pretty pictures in the OSG take it as granted.

 

[JulianC]

According to the ESC:

In an existing domestic installation, are 16 mm2 single-core pvc/pvc meter tails (having a current-carrying capacity of 87 A clipped direct) adequate if the rating of the distributor’s cut-out fuse is 100 A? This size of tails may be adequate provided the maximum demand of the installation, taking into account the load characteristics (diversity and load profile), does not exceed the current-carrying capacity of the tails, and also provided that the requirements of Regulation 434.5.2 for protection of the tails against fault current are met.
As a practical tip, the current-carrying capacity of the meter tails is likely to be adequate if they have been in service for several years and there are no signs of thermal damage at the terminations or to the cable sheath or insulation.
Regulation number(s)

• 311.1
• 433.3.1(ii)
• 434.5.2

 

[JulianC]

Interesting article on Page 18 here:

http://www.esc.org.uk/fileadmin/user_upload/documents/public/switched_on/SwitchedOn-Issue-15.pdf

 

[sparc]

Trouble is Tel, that's not actually written anywhere that I know of, so peeps just looking at the pretty pictures in the OSG take it as granted.

You're absolutely correct - I've always take the pretty picture in OSG as a summary of what is 'Gospel'. So it's very helpful to be educated otherwise.

 

[Octopus]

Does anyone understand the logic of 'mandating' 25mm meter tails when upgrading a CU, when the sizing of other cables are left to the electrician's discretion?

I'm again having to explain to a little old lady with not a lot of money that she's need new meter tails with with tiny 6-way board, for her tiny 2-bedroom flat.

Massively cooking range to feed? Nope! 10.8Kw Powershower? Nooooh!

When copper is becoming an increasingly rare resource shouldn't we be fitting what's needed?

My guess is that the IET are simply 10 years out of date, plus someone somewhere calculate the specification, then a sub committee adds 10% to that, and the main committee thinks - let's be in the safe side, and adds another 10%.

Craziness gone mad!!!

(Rant for the day over - thank you for listening)

I was under the impression that the 25mm was "mandated" for new builds and rewires.

 

[GLENNSPARK]

3 ways to do this...
1) 80A bullit....16mm tails
2) max demand at the c/u (after diversity)
3)direct measurement (clamp)
....well just my thoughts on it anyway.....

 

[sparc]

Interesting article on Page 18 here:

http://www.esc.org.uk/fileadmin/user_upload/documents/public/switched_on/SwitchedOn-Issue-15.pdf

Whether applying to inspectors or electricians with job of upgrading the CU, the question is whether there's really an 80A or 100A in the cut-out? So that old chestnut about not fiddling with supplier's side is raised. Personally, I've never been worried about open it up to isolate the installation - my safety trumps the supplier's ownership as far as I'm concerned.

 

[Octopus]

3 ways to do this...
1) 80A bullit....16mm tails
2) max demand at the c/u (after diversity)
3)direct measurement (clamp)
....well just my thoughts on it anyway.....

4. remove 100A DNO fuse and replace with 80A fuse

tin hat on