Phil Addison wrote:


Isn't running it on the surface where its obvious to everyone also
allowed? And what does a 2" trench in a wall do to it's structural
integrity?

Yes, surface-run is also allowed, though not if it's likely to be
damaged. (So, in domestic kitchen behind cooker - fine; in busy
workshop/warehouse, unprotected T&E surface-run would be inappropriate).

As for digging a 2-inch trench - that's not really what the regs-writers
are trying to encourage! Rather, it's saying "if you must take a
non-obvious route, put the cable out of the way of normal little nails
and screws"; e.g. if in a partition wall, clipped to the centre line of
the studwork (makes it a b*g*r to replace, of course - and not many
studs-n-noggins running diagonally ;-); where not feasible to go that
deep, provide bad-ass degree of cable protection. Mostly, the
regs-writers would like you as an installer to reconsider running cables
other than in the Expected routes, imposing pretty onerous requirements
for such routes to sway the economics back in the direction of "obvious"
up/down/across routes.

Stefek