Stefek Zaba wrote:

Moving up to 4mmsq pushes you usefully further away from
that dividing line - though with the UK cables the earth conductor's no
bigger in "normal" 4mmsq than in 2.5mmsq, so the earth loop impedance
isn't helped away from the margin as much as one might like.

Good point, sir.

Andy's further suggestion of changing the MCB for a 32A is a further
Win.

With 32A protection and a 1.5mm^2 CPC the situation is the same as the
unfused ring spur, so there's not very likely to be a problem.

With split-appliance ovens and hobs being as common as they are, you'd'a
thunk the IEE might get round to putting out a Note about wiring 'em to
existing cooker circuits.

Funny, there's an article covering good practice in kitchens in the
current edition of the IEE's "Wiring Matters" which completely fails to
address this point.

Nor would MK, Contactum and friends do us a
disservice by marketing a dual 45A switch (in both "landscape" and
"portrait" orientations!) with neat little "hob" and "oven" labels, to
fit existing deep double boxes, which would give us two sets of switch
terminals to wire our 2.5/4/6/10mmsq final-leg cable to.

Something similar went through my mind while I was writing that piece
yesterday. I'm not sure there's a need for a double-gang switch
(Appendix 8 allows one switch to control two 'cooking appliances'), but
ISTM that there is a clear need for a double-gang cooker outlet.

--
Andy