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.

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?

On Nov 23, 4:31 pm, "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.

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?

It's fairly unlikely that the cable has been damaged - are you
positive this is the case?

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.

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.

Well unless something *very* wierd has happened the break is going to
be in the box behind the twin socket where the 'flash-bang' occurred.

I suppose you *might* have pulled the cable to the spur socket so hard
that you've parted it somewhere under the plaster but there's still a
great likelihood that you've broken the wire (maybe inside the
insulation) very close to the end that is/was in the back box of the
socket you were working on.

My suggestion would be to remove the double socket from its box again
and unwrap the ends of the wires that go to the spurred socket and
give the wires (not the insulation) a tug with a pair of pliers, if
one is broken near the end it will pull out.


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?

If it gets to this you'll be checking between the point where you have
broken in to the cable and the end at the ring main socket, i.e. the
red wire should be continuous and the black wire the same. However if
there really is a break in the wire it might be less messy to give up
and replace it completely. (For 'Red' and 'Black' read 'Brown' and
'Blue' if this is modern installation). The damage you will almost
inevitably do to the cable while checking continuity will mean that it
needs replacing anyway!

--
Chris Green

On 23 Nov, 16:39, stevelup wrote:
On Nov 23, 4:31 pm, "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.

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?

It's fairly unlikely that the cable has been damaged - are you
positive this is the case?

Stevelup,

Having belatedly made safe, unscrewed, inspected and then replaced the
spur wiring most carefully - then reinstated power - the ringmain twin
outlets worked fine, but the spur outlet didn't. There was
'blackening' on the brickwork 'chase' adjacent to the spur cable
entry, spur live cable end, and adjacent metal box. The spur live
cable sheathing was visibly pierced, presumably by the faceplate
screw, for that was what I was tightening when the event occurred. I'm
guessing the 'flash-bang' damaged the spur live cable locally to the
ringmain box.

Bilbo

The spur socket outlet, some 6 metres away, seemed undamaged on visual
inspection.

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.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Nov 23, 4:53 pm, "bilbo*baggins" wrote:
On 23 Nov, 16:39, stevelup wrote:



On Nov 23, 4:31 pm, "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.

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?

It's fairly unlikely that the cable has been damaged - are you
positive this is the case?

Stevelup,

Having belatedly made safe, unscrewed, inspected and then replaced the
spur wiring most carefully - then reinstated power - the ringmain twin
outlets worked fine, but the spur outlet didn't. There was
'blackening' on the brickwork 'chase' adjacent to the spur cable
entry, spur live cable end, and adjacent metal box. The spur live
cable sheathing was visibly pierced, presumably by the faceplate
screw, for that was what I was tightening when the event occurred. I'm
guessing the 'flash-bang' damaged the spur live cable locally to the
ringmain box.

Bilbo

The spur socket outlet, some 6 metres away, seemed undamaged on visual
inspection.

Hi

I really cannot think of any possible way that a short circuit within
your twin socket box could damage the spur cable downstream of that
location.

The only possible place that damage could have occurred is within the
twin socket box.

Aside from that, the fault current would have had to be both huge and
sustained to damage 2.5mm T&E. I really think you should focus your
diagnostic energy into the double socket area. Did you also have the
spur off the wall for decorating? Are you positive the connections are
sound at the other end.

Steve

On Fri, 23 Nov 2007 08:31:23 -0800, 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.

snip

Examine the cable leading to the spur, at the ringmain end. As the screw
penetrated the wire it put an earth on the live conductor, which will
have blown a hole in the copper conductor at this end. You can test this.

First, MAKE SURE THAT THE SPUR IS REALLY DEAD - don't trust the obvious
disconnected wire! It sounds stupid, but mistakes can kill you. If you
don't, your meter will be damaged at best.

You then need to get a connection from the spur (probably using an
extension lead and a plug with 3 wires on it. Use the Ohms range (or
continuity buzzer if it has one) on your meter to verify L-L, N-N and E-E
between the end of the cable in the ringmain socket and the spur. Also
check for short circuits between the conductors.

Fixing it is more of a problem... If there is enough spare cable to
remake the connection you will be very lucky.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info http://mixpix.batcave.net

John Rumm wrote:
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.

Its ever the weakpoints in a circuit that go o/c during a heavy fault
current, ie connections & switches.


NT