bilbo*baggins wrote:

While screwing home the faceplate screws on a ringmain twin socket
outlet after easing them for painting, I had a 'flash-bang' moment,
for one of the screws had trapped - then penetrated - the live cable.
Doh! After I'd isolated the whole shooting-match and replaced the
fuse, I discovered that the spur socket, fed from the original
ringmain socket, was dead. So I disconnected the spur cable
completely, isolating the ends properly.

Chances are you had a poor connection at the spur socket, and it is that
which failed rather than the cable.

What sort of fuse do you have - re-wireable or cartridge?

What size is the cable on the circuit - and in particular is it old T&E
with a 1mm earth?

Now I want to identify the point of breach of the ~6 metre spur
circuit cable, and repair it. However I do this, there will be some
plaster to cut away, somewhere, and make good. This, I want to
minimise.

I have a Newlec multimeter and simplistic instructions
( appropriate! ), and expect I'm going to do a 'Continuity test' at
intervals along the cable, but I'm uncertain about what I'm looking to
see, to identify the point of breach.

Can someone kindly advise?

First make sure your cable under test really is isolated at both ends.

Set your meter to its lowest resistance range. Then measure the
resistance with the test leads shorted together, so you can factor this
out of your results.

If you twist all three wires together at one end and then measure
resistance between all combinations of them at the other end, you should
get some useful information.

The Live to earth resistance, and Neutral to earth resistance should be
equal. The Live - Neutral resistance should be lower. See the table here
for expected values:

http://wiki.diyfaq.org.uk/index.php?...stance_tab le

So for a modern 2.5mm^2 cable with 1.5mm^2 earth at six meters, you
would expect to measure values of:

6 x 14.82 = 0.088 ohms L to N. and 6 x 19.51 = 0.117 ohms L or N to E.

(your meter will need to be reasonably decent to measure to sufficient
accuracy here)

See more of the above article for details on tests.


--
Cheers,

John.

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