Broadband Related > Telephony Wiring + Equipment

Finding a hidden underground joint

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aesmith:
Hi,

We've had two faults which turned out to be with a hidden joint on our local cable, where an old joint post had been driven over and pushed underground so effectively the line was just a bunch of crimps in the soil.   Both faults took a long time to fix, mainly because although they caused line noise the tester was still passing.  In fact in each case it took months.

I've just taken a walk along the line, and I can see that there's another buried joint somewhere, as counting from the house joint (5) has opaque grey cable about 15mm in diameter coming from it, and joint (6) has smaller cable around 8mm with a translucent outer sheath on that side (back to larger cable on the DP side).  So somewhere in between there's a joint which I'll call (5a) that joins large cable to small.

I'd like to find that joint, because if it's like the one I referred to I can report it as damaged plant in its own right.

Any clues as to how to locate a buried joint?   All this runs along a fairly narrow margin between the track and the cultivated field.  Where the cable is buried it is typically around 9" deep.

Thanks,  Tony S

burakkucat:
My first thought was "ground penetrating radar".  ::)

Thought number two was if you could map the buried cable(s), thus knowing exactly where it/they are located, close observation of the ground may then provide a hint. So what about one of those detecting devices, used by competent contractors, to locate other buried services before any excavation takes place? With the route clearly defined, you could then perform a sequence of test digs, using the classical "binary chop", to locate the hidden joint.  :-\

JGO:
Would a recreational Metal Locator do the job ?

burakkucat:

--- Quote from: JGO on May 18, 2017, 05:12:36 PM ---Would a recreational Metal Locator do the job ?

--- End quote ---

That's an interesting idea. It would certainly be worth a try.

Black Sheep:
There are various methods employed in finding a buried joint .................. it all depends on what you are presented with as an engineer as to which method you would use ??

If there are 'spare pairs' within the cable that are not used, the chances are they may be 'stumped' (disconnected) in the buried joint. So, we would measure these 'spares' and whilst tracking the cable using a 'Cat & Genny' (Google it  ;)), we also use a pedometer to wheel out the distance of the measured spare pairs.

The problem is, there could be a coil of cable left in the ground as sometimes happens that would throw ones measurement out quite a lot, so the key is to also listen to the CAT tools 'beep-beep' and start tweaking down the 'sweep' level. Where the spare pairs end, the 'beep-beep' will all but disappear. It needs a little bit of experience to get to grips with it.

Likewise, if there are no spare pair in the cable, ie: they are all used and jointed through, then we attach the Genny to the armoured wiring protecting the inner cable, this is a bit trickier to get to grips with as the induced signal from the Genny has a high chance of spreading to 'Earth' where the insulation has cracked over years of being underground. But, a good engineer will know a 'good signal' from a 'poor signal' and will follow the trace until the 'beep-beep' diminishes, which is where the armoured cable has been cut to fit the buried joint.

Many, many years ago, we were told to fit a metal plate to the joints so that we could use a metal detector to locate it again in the future, but that practice kinda dropped off over the following years.  ::).

Believe me when I say that when you are presented with mile after mile of rural buried cable, you become quite proficient in measuring, locating and digging down on buried joints.  :)

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