Finding a cable in the ground...
 

Hi.

My MIL has just moved house and it has a number of outside
lights. Some are 12v and some are 240v.

A couple of circuits aren't working and the cables are buried
underground. Does anyone know of a way of finding the route
and/or checking where a cable break might be, - without digging
up the entire lawn! ??

TIA.

H.

--
Howard Coakley
e-mail... howarddot}coakleyatcoakleydot].codotuk
ICQ:4502837. (Try ICQ at www.icq.com)

In article , "Howie"
lid says...
Hi.

My MIL has just moved house and it has a number of outside
lights. Some are 12v and some are 240v.

A couple of circuits aren't working and the cables are buried
underground. Does anyone know of a way of finding the route
and/or checking where a cable break might be, - without digging
up the entire lawn! ??

Some people reckon that dowsing works and that most people can do it
- doesn't hurt to try (unless the neighbours start taking the ****
too severely).

Howie wrote:
My MIL has just moved house and it has a number of outside
lights. Some are 12v and some are 240v.
A couple of circuits aren't working and the cables are buried
underground. Does anyone know of a way of finding the route
and/or checking where a cable break might be, - without digging
up the entire lawn! ??

1. Find yourself someone who does groundworks / pavement repairs and has
a C.A.T. (Cable Avoiding Tool) - a cable detector on steroids - and ask
him to wander over your lawn. You can hire them from about £6 a day[1].
That will get you the cable route.

2. Get a capacitance meter and measure the capacitance across each end
of the cable. The ratio of the two figures will show about how far along
the cable the break is. That will get you where to start digging.

3. Ask previous owners where they buried the figging stuff.

Owain

[1] Hire (7 day minimum)
http://isswww.co.uk/Test%20Equipment...ault%20Locator

[2] Hire
http://www.surveyexpress.co.uk/C-ScopeCat.htm

Harry Bloomfield wrote:
BT use an instrument which is basically an oscilloscope and a pulse
generator. The pulse goes down the cable and bounces back from where the
break is. The initial pulse followed by the 'echo' are displayed on the
'scope, from which can be determined the time between the two and thus
the distance to the fault.

Time domain reflectometer, I think. AIUI it has to be calibrated by
cable type.

Probably does not help with where the cable is located - though you
could do the same for both ends, add the two lengths together and it
would give the limits of where it could be.

Even better, if you have the distances from two points, draw the arcs of
the circles and where those arcs intersect is the point of break.
Assuming the cable runs in reasonably straight lines of course.

Owain

Howie formulated on Sunday :
Hi.

My MIL has just moved house and it has a number of outside
lights. Some are 12v and some are 240v.

A couple of circuits aren't working and the cables are buried
underground. Does anyone know of a way of finding the route
and/or checking where a cable break might be, - without digging
up the entire lawn! ??

TIA.

H.

BT use an instrument which is basically an oscilloscope and a pulse
generator. The pulse goes down the cable and bounces back from where
the break is. The initial pulse followed by the 'echo' are displayed on
the 'scope, from which can be determined the time between the two and
thus the distance to the fault.

Probably does not help with where the cable is located - though you
could do the same for both ends, add the two lengths together and it
would give the limits of where it could be.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org

"Harry Bloomfield" wrote in
:

Howie formulated on Sunday :
Hi.

My MIL has just moved house and it has a number of outside
lights. Some are 12v and some are 240v.

A couple of circuits aren't working and the cables are buried
underground. Does anyone know of a way of finding the route
and/or checking where a cable break might be, - without digging
up the entire lawn! ??

TIA.

H.

BT use an instrument which is basically an oscilloscope and a
pulse generator. The pulse goes down the cable and bounces back
from where the break is. The initial pulse followed by the
'echo' are displayed on the 'scope, from which can be determined
the time between the two and thus the distance to the fault.

Probably does not help with where the cable is located - though
you could do the same for both ends, add the two lengths
together and it would give the limits of where it could be.


Suggest a metal detector would help you plot the cable route.

What Harry described is a Time-Domain Reflectometer (aka TDR). Not
a lot of people know that.

It happens that Kinell formulated :
Suggest a metal detector would help you plot the cable route.

Only if the cable is no more than a few inchres deep in the ground.


What Harry described is a Time-Domain Reflectometer (aka TDR). Not
a lot of people know that.

I didn't ;-)

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org

Kinell wrote:
What Harry described is a Time-Domain Reflectometer (aka TDR). Not
a lot of people know that.

I remember when I did my HNC Electronics (30+ years ago now) we used an
oscilloscope to measure signal reflections in a cable of different length.

Never used that technique since, but I know it does work.

Andrew

--
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usenet messages is configured such that my antispam
filter will automatically update itself so that the
senders email address is flagged as spam. If you do
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submit an enquiry - http://www.kazmax.co.uk

BT use an instrument which is basically an oscilloscope and a
pulse generator. The pulse goes down the cable and bounces back
from where the break is. The initial pulse followed by the
'echo' are displayed on the 'scope, from which can be determined
the time between the two and thus the distance to the fault.

Probably does not help with where the cable is located - though
you could do the same for both ends, add the two lengths
together and it would give the limits of where it could be.


Suggest a metal detector would help you plot the cable route.

What Harry described is a Time-Domain Reflectometer (aka TDR). Not
a lot of people know that.

Not a lot know how expensive they are either. We use one for finding
faults on co-ax cables up transmission towers.....
--
Tony Sayer

In article ,
tony sayer writes:
BT use an instrument which is basically an oscilloscope and a
pulse generator. The pulse goes down the cable and bounces back
from where the break is. The initial pulse followed by the
'echo' are displayed on the 'scope, from which can be determined
the time between the two and thus the distance to the fault.

Suggest a metal detector would help you plot the cable route.

What Harry described is a Time-Domain Reflectometer (aka TDR). Not
a lot of people know that.

Not a lot know how expensive they are either. We use one for finding
faults on co-ax cables up transmission towers.....

I used to run about 3km of thick and thin Ethernet in ceiling voids, and
there was never a TDR on the market cheap enough for `them' to let me get one.
--
SAm. all sweeping generalisations are false

In article ,
(Sam Nelson) writes:
I used to run about 3km of thick and thin Ethernet in ceiling voids, and
there was never a TDR on the market cheap enough for `them' to let me get one.

I wrote an ethernet driver for the first ethernet chipset, the AMD LANCE
7990. That has a built-in TDR, and when the cable broke, our systems
(GEC 4000 minicomputers) output on the console the TDR values, which is
the number of 10MHz clock cycles which pass between transmitting the
preamble and seeing its reflection from a cable break. Customers found
this incredibly useful, and many picked a quiet time and went round
their networks breaking the ethernet every 10 metres or so to record
the TDR values the GEC 4000's generated, so when it broke for real, they
could instantly home in on the 10m region of suspect cable. To this day,
I remain amazed that no one else ever seems to have put this feature into
an ethernet driver (although with switched twisted pair networks, it's
now become redundant). OK, it's not as fine grained as a separate TDR
instrument, but it was damn useful on networks of 10base5 and 10base2
that were around for many years.

--
Andrew Gabriel

On Sun, 24 Apr 2005 22:13:13 +0100, Harry Bloomfield wrote:

It happens that Kinell formulated :
Suggest a metal detector would help you plot the cable route.

Only if the cable is no more than a few inchres deep in the ground.

Wouldn't that depend on the quality of the metal detector and the size of
the cable? Of course you wouldn't know whether your detector/cable
combination was working if you didn't find the cable! You could experiment
I suppose, if you knew what sort of cable you were looking for, but that
would involve a bit of digging up the lawn too :-) I'm sure there would be
someone knowledgeable on uk.rec.metal-detecting. Also a little Time Team
style trench at a right angle to your suspected cable run might be helpful,
you should find some marker mesh/tape above the cable. None of that would
help you find the damaged area of the cable though, if that is what causing
your problem.



--
Holly, in France
Holiday home in Dordogne
http://la-plaine.chez.tiscali.fr

Harry Bloomfield wrote:
It happens that Kinell formulated :

Suggest a metal detector would help you plot the cable route.


Only if the cable is no more than a few inchres deep in the ground.


What Harry described is a Time-Domain Reflectometer (aka TDR). Not
a lot of people know that.

I always thought that was the critical component of the TARDIS!

David

Sam Nelson formulated the question :
I used to run about 3km of thick and thin Ethernet in ceiling voids, and
there was never a TDR on the market cheap enough for `them' to let me get
one.

--

I often see the instrument on the surplus market at giveaway prices.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org