TheScullster wrote:

I have been considering how to satisfy 17th Edition wrt cooker cable.
As I see it there are three options:
1 Fit RCBO in place of MCB for cooker feed
2 Use earthed steel conduit protection
3 Bury cable 50mm below wall surface.

That got me to thinking about the stability of the wall if option 3 is used.
Allowing for plaster covering, but also the cable thickness means you will
be chasing to a depth of half the inner leaf thickness.

There's guidance in the On-Site Guide about the maximum depth of chases.
The depth of vertical chases shouldn't exceed one-third of the wall
(leaf) thickness. For horizontal chases the max. depth is one-sixth of
same.

Using a 30 mA RCBO is unlikely to give any problems if the cooker's in
good condition (although actually fitting one in an older CU might). If
you really want to use a non-protected circuit, the only practical
options in most cases a

- surface wiring, where acceptable;

- use a cable to BS 8436 - Earthshield or Flexishield (with these the
OPD must be a Type B MCB meeting energy limiting class 3), or MICC cable
if you have the skills to install it.

--
Andy