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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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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) |
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#3
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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 |
#4
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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 |
#5
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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 |
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"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. |
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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 |
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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 -- Please note that the email address used for posting 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 need to contact me please visit my web site and submit an enquiry - http://www.kazmax.co.uk |
#9
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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 |
#10
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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 |
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#12
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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 |
#13
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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 |
#14
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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 |
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