UK Phone line question

If it's a coax, you can force an audio-frequency current into the shield (it's probably grounded somewhere out there) and snoop for the magnetic field. I've found wires inside walls, by listening for the 60 Hz field when there was current in the wires.

It would probably work with an unshielded pair, too.

Silly questions first. Will the utility company do it? Is there a tool rental company that has underground wire locators somewhere close? This article mentions using an AM radio to find invisible fencing for pets. NO idea about how well it would work or if it's suitable for the wire you want to locate. Just an idle thought.

UK uses 2 twisted pairs( 1 is spare for residential use) in plastic outer. No shield.

They may do, at a 'silly' price...

You can probably force AC current into at least one wire. Audio amp and a series capacitor maybe.

There is probably some wire tracing gadget that you can buy, if you don't want to do it all yourself. Looks like Amazon has a bunch.

They don't have commercials for the equivalent of "call before your dig" on the TV all the time over there..?! Hard to avoid over here. Please check the web, or the phone book, before planning something so reckless!

Seems to be something like this over there,

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website:

Those sense E fields because they find network wires with one end disconnected. The main objective in using those is to find the connector at the other end when you have an array of 1000 jacks, so you can't put a load on the far end until after you find it. Each twisted pair is isolated in the networking case they are designed for. Consequently there can be no current, and they don't sense anything beyond a couple of inches. The most sensitive ones work to about 6 inches. Most of them don't work even at zero distance if there is a device plugged into the other end because it might allow current but it keeps the voltage down.

Could you sense E fields farther out?

tility company do it?

Around here it's free, Miss Utility. They don't want you mucking up their wiring either. Are you sure they charge for that?

I've used -- what we called -- a "tone generator" and "receiver" many times to do this type of thing inside buildings.

I'm sure that something like that, or a bigger version if it, could work. You might even be able to rent one as opposed to buying it.

I don't know how well the smaller units that I used would work through concrete. But I do know that with a fresh battery I could detect through walls multiple feet away. I usually had to turn the volume up quite a bit to hear a faint signal and then as I got closer turn the volume down to be able to differentiate as I got closer.

You should be able to repair the cable fairly easily yourself if that happens. Even a bad splice (involving wire nuts and electrical tape) is better than an open. Your broadband might be slower, but should still function while waiting on the phone company to do a more proper repair.

A couple more silly questions. Would it cost much to have a spare cable laid out in case you do cut the existing one? Would the utility let you reconnect both ends yourself?

An underground wire won't generate useful e-fields. Magnetic fields would work if the wires aren't too deep. As someone suggested, call the phone company.

What sorts of data rates do you get over an unshielded buried twisted pair?

I'm getting 120/40 Mbits at home from the cable TV provider, which is shockingly better than what we got over old soggy twisted pairs from AT&T.

About 8 years ago I caught them removing the buried cable outside my mother's house in a big well-connected city.

It was enamalled wire with wax paper insulation, and a lead sheath. They gave me ~1ft of it, as a curio, conversation piece, and cosh.

They are now installing fibre to the pole.

That seems a plan...

Residential cables are supplied as at least two twisted pairs in case one goes O/C. Sometimes it's 4 pairs... Saves pulling a new cable. In 'old' installations, they burried the cable in the ground when houses were built. Now they put them inside tubular trunking so a new cable can be pulled through....same for fibre/coax.

being prepared to repair it is probably the best guarantee against cutting it :)

The failure, here, is more commonly a reduced impedance to ground as water eventually infiltrates the cable. Phone line does not require burial in "shaded" ditches so ground subsidence leads to all sorts of wondrous surprises!

When requesting new service, TPC just lays the new cable on TOP of the ground, waiting for their crews to come along at a later date. I.e., that's an alternative for you if you shoot yourself in the foot and don't want to live without network access. (lay cable in expansion joint and cover with a layer of duct tape)

If you are anywhere near Bath, get in touch with me (contact details on website), I may be able to help.

It used to be the case that when your phone rang the exchange supplied enough power to operate a loud bell. I don't know the specification. I presume they are still capable of doing that even though most phones are locally powered now and use efficient sounders. So if you can find an old mechanical phone and ring your own number maybe that would put enough current through your cable to detect with a coil and audio amplifier even if it's a twisted pair...

Mike.