Cable tracing

[christopher]

Having had great support when looking for buried transformers , I thought i would ask the group for help to trace a wire.

I have a disconnected but modern cooker size wire running from my consumer unit into the wiring loom of the house. I can see it for a bit then it goes into trunking etc. I would like to trace this wire as I have to run a new supply to my kitchen and if the this existing wire goes part of the way it could be usefull. I assume i will have to have some sort of tone generator and a listning device.

Any thoughts ??

Chris

[meow2222]

That could work. A simple listener is a flat metal plate for capacitive pickup, a 3 stage cmos gate amplifier and a little piezo sounder.

NT

[Dave Liquorice]

On Sat, 21 Mar 2009 22:51:34 +0000, [e-mail] wrote:=

Well there a limited number of places that a cable of that size would go= in a normal house. Either a shower, a cooker or possible another CU in o= ut building/garage.

Yes but I'd have thought you'd be able to find the other end with a bit = of looking. A cooker cable would end in a cooker switch, a removed shower feed pulled back into the loft etc. Check for a short live/neutral on yo= ur free end and if open circuit connect a battery across the two wires and =

when you find the other end connect a suitable bulb, if it lights you ha= ve the same cable...

A decent tone tracer kit will put you back over =A350 but I see CPC have= a set for =A312.54 + P&P + VAT! Donno how well it will perform though. Don= 't let it come in contact with mains or you'll kill it. Fine on truely dead= cables though. Also handy

[Harry Bloomfield]

For £10, a few weeks ago at a radio rally, I picked up an ex-BT device. It has a generator in one unit with a couple of wires to connect onto the cable, then a separate unit to trace the cable back to source. The latter unit has a sensitivity adjustment allowing you to trace from around 18" distance from the cable, down to actually needing contact with the cable for it to be triggered. The generators tone cycles continuously, making it easier to identify it from other signals which might be picked up.

It works well on none live conductors, but I doubt it would survive being connected to a live cable L+N. I have yet to test it on E+N.

[Dave Plowman (News)]

Bought one off Ebay some time ago for about 20 quid. Meant as a telephone/network cable checker/tracer it comes with plugs for that - but also crock clips for any cable. Works very well. However, I've only used it for identifying one cable within a bunch so don't know how well it works at a distance.

[Frank Erskine]

If you connect the oscillator across a pair in a, say, telephone cable, you will pick up tone on other pairs by induction. To prove the pair you think you've picked up with the probe, you simply short that pair with, for example, a screwdriver. If you have the right one the tone level at the receiver will drop abruptly.

[Dave Plowman (News)]

Right. I've only used it for identifying a cable within a bunch. Once identified the colours identify the pairs?

[Frank Erskine]

Hopefully, assuming the pair is intact and hasn't been 'split' elsewhere along the route. And of course there are lots of repeat pair colours in a 'real' telephone cable :-)

[Dave Liquorice]

Even if it has you still get enough signal to identify the pair. I find that if you can separate the pairs by an inch or so that is enough to detrimin which is the one you want. Always assuming you've forgotten which colour pair you connected the sender to...

Modern telephone cable goes up to 30 pair with unique colours. Units 1-5 or 6-0 are Blue Orange Green Brown Grey. These 5's are then White Red Black Yellow Violet Pink.

that old telephone cable was a nightmare.

[Frank Erskine]

30 pair? That's just small stuff - I was thinking in terms of 3000 pair :-)

[Harry Bloomfield]

Frank Erskine brought next idea :

He said 'unique colours' - fun those 3000 pair :-)

[Bill]

In message , Dave Liquorice writes

If it, and you, light really brightly for a moment then you have found an unterminated length of live cable. Probably a good idea to switch off your consumer unit before checking any unknown cable.

[Dave Liquorice]

Do they still do cables with that many pairs? I can find up to 320 pair internal or 200 pair external.

These large cables are bundled into lumps of up to 30 pairs coded as above and the bundles are also coloured coded. I don't know if the bundles follow the same pattern but if they do we could have up to 30 bundles of

30 pairs = 900 fairly easily identifiable pairs.

[Dave Liquorice]

Valid point I found the bare cut end of a live cable under some floor boards by that method. It was at arms length and out of sight and I didn't know it was there, I was trying to reach something else. It is now wrapped in insulating tape with a note on a tape flag.

[Harry Bloomfield]

Dave Liquorice wrote on 22/03/2009 :

In my days it was done in layers, with a thin tape served over each layer.