In message , Steve Firth
writes

There are places where I'm not sure that the horizontal/vertical rule
improves safety. I

I'll second that. I was working in a cellar that had twin 13A socket
all around the wall spaced about 10' apart at about 4' above the floor,
I opened a couple and the wiring was horizontal. Fair enough, the unit
I was mounting was at about 6' above the floor and half way between 2
sockets,

Turns out that the ring came from above and then split left and right,
half way between 2 sockets. No prizes for guessing where I
drilled........... Why they didn't fetch it down above a socket I'm not
sure and why I didn't use my cable detector I'm even less sure.......

--
Bill