In uk.d-i-y, N wrote:
Well It is all sorted now. Basically, there was enough slack in the cable to
cut out the damaged portion and fit a 30/40 Amp junction box to join the two
sides of the cable. It was the old feed for the cooker which now just feeds
3 sockets as we have a gas cooker.

Super; hadn't realised it was in the floor rather than in the wall; that's
better for accessibility. Which is both a practical requirement (you did
replace the floorboard nails with screws when you put them back down,
didn't you? Makes lifting them next time *so* much easier; *and* gives you
another opportunity to put a screw right through the cable you only just
saw. Been there, done that, saw the flash, felt a total prat, still remember
it though it was just about 20 years ago!) - and (breathlessly recovering
back to the "both" where we started this sentence ;-) a requirement of the
Regs when using junction boxen. I claim that under a screwed-down floorboard
is accessible within the meaning of the Regs here, though I'll admit that
it rather depends on the floor covering - vinyl you can peel back to reveal
a nice hardboard with pipe and cable runs clearly labelled and access
hatches is one end of the spectrum, while gert big sheets of marine ply,
screed, and big-ass slate tiles would be quite the other ;-)

Is/was this normal practice? I always thought following the joists was quite
safe, I am begining to wonder if any of the other boards I have screwed down
over the years, about half the house, may have screws perilously close to
wiring. Although where possible I have always tried to look and work out the
routing of wiring piping etc. I just got carried away yesterday as it was
one of the last boards along the line of the joist.

Ah, you *have* been screwing the boards back - good man! Joist notching
*was* normal practice, judging by the couple of older houses I've lived
in and worked on, and comments in older installation guides. Except when
I didn't, I usually played safe by putting any screws to replace lifted
boards into, or pretty damn close to, the existing nail holes. These days
notching's frowned upon, both because it weakens the joist, and because it
makes it too unsportingly easy for Sod to guide your drill bit to them, as
you discovered ;-) The current On-Site Guide says it's OK for cable to go
*through* joists; holes a minimum of 5cm away from top and bottom surface,
and (for structural reasons) close neither to the centre nor the edges of
the span. It's also OK to run the cable in earthed steel conduit, which
provides good mechanical protection; the conduit can go in notches in
the top of joints, and again there's guidance on max depth of notches
(no more than 1/8th the depth of the joist) and position (away from
center of span, not right close up to edges either). As a third alternative,
it says you can try to provide "protection sufficient to prevent penetration
of the cable by nails, screws and the like", and immediately pooh-poohs its
own suggestion by saying that it's "difficult to meet" that requirement for
protection! Hunky steel plate (2-3mm thick or more) is sometimes fitted
over existing joist notches as a nod towards this "mechanical protection"
requirement, but by the time you've done the chiselling around the notch
to install and secure such plates, you could probably have rerun the
cable through holes deeper down the joists anyway.

Hope that helps, and glad to hear you got a proper job done on the
damaged bit of cable...

cheers, Stefek