Conduit with first fix wiring

[ban-all-sheds]

I hope you are not suggesting that the ring final needs to be 6mm² BAS.

Long answer:

In the absence of any credible data to the contrary, a sheathed cable in conduit which is totally surrounded by thermal insulation has a Ci of 0.5.

433.1.204 required that the cable for a ring final has an Iz of ≥ 20A.

Given both of those, the smallest compliant cable is 6mm².


Short answer:

Yes.

Designers who do things like that tend to be sent to site to help second fix ,

if the latter you'd need to use 6mm², which would be mightily impractical.

... And cause your electrician to curse you.

then they get a nasty note that the materials cost has gone over whats allowed for.

A problem in many fields when accountants are allowed to triumph over engineers.