Finding My Invisible Dog Fence, How Much Detector Do I Need?

[Tron]

All,

I have a use case for a metal detector that doesn't involve treasure hunting like I suppose most of you do, but I am sure you have the expertise to be able to tell me how much of a metal detector I really need.

I'm going to start core-aerating my lawn, and have some obstacles there that I don't want to damage. Namely an invisible dog fence (solid-copper single strand wire, rather thick gauge) and a signal cable going out to a weather station (a little thinner, but two strands). Both of them are just grown into the turf, but on top of the ground, so maybe an inch deep, if that, and not even covered by soil. So I thought that maybe I could locate the cables with a metal detector.

I suppose I don't need any fancy discrimination modes or coils capable of finding stuff several feet deep underground. But how much detector do I really need? If the pinpoint accuracy lets me reliably detect the cables with an accuracy of a foot or so, that's all I need.

As that's something I intend to do once a year only, I obviously don't want to break the bank. It's probably easy to overspend on a device that offers way more than I actually need.

So I'd probably want to stick with a reputable manufacturer (Minelab/Nokta?) but go low-end on one of theirs. So is, say, a GO-FIND 11 going to do the job? Or do I need something along the lines of a low-end Vanquish, a 340?

Yes, I'm aware that cable finders exist, but those require access to the cable for the signal injector, which is a bit difficult and nothing I'd want to do every year.

Thanks!

[Tron]

Additionally, I can certainly turn the fence off during searching for it, as I've heard the signal can severely mess with metal detectors.

The other cable is a 5V signal cable, which doesn't carry any relevant current.

[MD4V.org]

You could even go with the Minelab Voyager

https://usa.minelab.com/x-terra-voyager 

[PimentoUK]

This 'dog fence' issue came up a couple of years ago over on Tom Dankowski's forum.

The buried wire is essentially invisible to metal detectors ..... unless you short-circuit the ends together to make it into a complete loop. Then it should give a decent signal. So disconnect the electric generator  doohickey , then using whatever you have,  join the loop ends together.

Searching in non-motion mode ( eg. pinpoint mode ) with the coil 30cm / 12" above the ground, may be an easier way to locate the wire, as you won't be getting signals from other small junk etc buried in the ground.

The weather-station cable is trickier. If you make a loop by shorting both wires at both ends, you will create a loop .... but the wires are so close, that any current in one wire will have its magnetic field near-cancelled by the other. Better to use a separate length of wire, to join the station end to the 'home?' end, keeping them 3 metres apart.

[Johnnysalami1957]

Rent a cable locator and you can inject the frequency into one end of the fence connection. Works faster and more accurate than a metal detector. get some markout flags too.

[Johnnysalami1957]

2 minutes ago, PimentoUK said:

This 'dog fence' issue came up a couple of years ago over on Tom Dankowski's forum.

The buried wire is essentially invisible to metal detectors ..... unless you short-circuit the ends together to make it into a complete loop. Then it should give a decent signal. So disconnect the electric generator  doohickey , then using whatever you have,  join the loop ends together.

Searching in non-motion mode ( eg. pinpoint mode ) with the coil 30cm / 12" above the ground, may be an easier way to locate the wire, as you won't be getting signals from other small junk etc buried in the ground.

My Tesoro Compadre finds it okay in all metal. It's buried shallow. Mines 12 ga copper searched with fence deenergized.

 

[PimentoUK]

It depends on how the fence is energised, I suppose. It could be a transformer output, it could be capacitively coupled from some electronic switch. That's my reason for saying make the connection yourself, the generator/pulser unit is an unknown.

[GotAU?]

You could put the dog collar on and run around the yard mapping it out that way…just kidding!

A cable tracer would be most useful, and then as you map it out, put a nail with a large rounded head into the ground next to the wire. That way you could use an inexpensive metal detector to find it next in the following years. As far as cable tracers,  stores like Harbor freight have a rather inexpensive one that works well.

[Tron]

The thing is that especially the weather-station cable is hardwired, so it would be quite a hassle to disconnect and reconnect everything to inject the frequency for a cable finder. Thus the idea of a metal detector.

To give you some numbers, the cable is 12AWG (total overkill, I know), so 3.3 mm^2, and two strands. If the search coil has a diameter of, say, 10"/25cm, that would give a copper volume of 16.5cm^3 or 1.84g of copper underneath the search coil.

I've read people frequently find iron/aluminum bottle caps and can tabs, which weigh probably in the same ballpark...