"Lurch" wrote
| You will also want to check that it is actually part of the ring, and
| not a spur from the ring before connecting anything to it. To do this
| you'll have to cut it and test it.
| A cheaper way is to turn of all power at the CU, cut the cable and
| make it off into a JB, repower the installation and test as above but
| with a multimeter at the junction box. If it's on the ring, add the
| new cable to it, if it's not, put the lid on and find the ring.

I think a slightly clearer way of putting that is "cut the cable and make it
off into a separate junction box for each end (or a 4-terminal with the two
lives separated, N and E), turn back on. If both ends are live it's on the
ring, if one end is live and one dead that is the supply and load side of a
spur"

Owain