Cable tracing equipment - what sort of things are there?

[cl]

I have three boats (shortly going to sell one of them, we hope!).

I've spent happy (?) hours clearing up the awful mess previous owners had made of the wiring and as a consequence I'm coming to the conclusion that some sort of cable tracing equipment would be very useful.

I'm currently trying to fathom out where some of the wires run on one of the boats and I'm having a hard time doing so.

So what is there out there for tracing wires? These are nearly all low voltage DC (12 volts) so things that detect 50Hz aren't going to do me much good. What I'd *really* like is some sort of "non invasive" signal injector with a probe to trace where the signal goes. I suspect that is going to be expensive though.

Even some simple way of connecting to cables without cutting or disconnecting would be useful. For example I'm trying to find what feeds some lights which have flying leads from the light fitting crimped onto wires emerging from the nether regions of the boat so there's no easy way of getting at them electrically.

Any ideas would be welcome.

[Jabba]

[e-mail] scribbled...

[Andrew Gabriel]

I use a "pair tracer", designed for tracing telecoms pairs. I picked it up cheaply at a computer fare some 20 years ago. They're not cheap new, but can sometimes be found secondhand at electronics fares or car boot sales for under £10.

I'm not sure if it's supposed to be used on connected cables; I've never tried doing that, although it's probably OK at telecoms voltages.

[Peter Andrews]

I bought one of these

not from this supplier though. Not used it very often but invaluable proving to an electrician that the copper tape of a hearing aid loop under a newly installed lino floor had been cut. 90' of tape and I was able to locate the break to within 5mm! If you can get to one end of a wire it's easy to track it through.

Peter

[Dave Plowman (News)]

Ebay search - cable tracer. Lots of different ones there. Although you do normally need to connect the transmitter to the required wire. Dunno if there are inductively coupled ones.

[Harry Bloomfield]

[e-mail] submitted this idea :

BT engineers use a gadget which injects a signal into a wire, you can then follow the cable with a none contact probe, which has adjustable sensitivity. They are very, very good. You can inject the signal (contact required) on a pair of wires in a multi-core cable and pick out the actual cores at the other end 20 metres away. I suspect they are limited to being safe for voltages below 50v only, but with mains off should work just as well.

I paid £10 for them second hand a few years ago.

[Brian Gaff]

I still don't see how you can trace wires that have no ac on them though. You would just pick up the signal induced into other wires if you put an hf oscillator on them I'd have thought, though at least you might be able to figure out which ones were not the ends of the wires!

Brian

[cl]

That seems to be specifically for co-ax cables.

[cl]

That seems the sort of thing that would be useful, thanks, not too expensive either.

[John Williamson]

I use one of the screwdriver shaped testers with a bulb and a sharp point on the end instead of a screwdriver it. They're sold in Halfords and other motor factors for tracing car wiring. You do leave a pinhole in the insulation, but unless it's exposed to constant water, it's not normally a problem in the short to medium term.

The problem you should have on a boat with one of these is that they use chassis return, and boats must have isolated wiring, athough you can clip the return to the negative or positive according to taste.

A cheap possibility is to buy a pair of small crocodile clips with screw fastenings, and attach them to the end of your existing meter probes, wrapping the joint with tape according to how paranoid you are. I also wired up a piezo bleeper using a bridge rectifier and cables terminated with small crocodile clips many years ago, and I could hear it easily from the wrong end of an articulated lorry with the engine running when I needed to check the brake light circuits.

[John Rumm]

The tone injector and tracers used for telecoms and networking can help and work well in some cases - although you need to be able to get close to the wire. If its buried too deep you may not get a reliable result.

Automotive probe sets like:

can be useful - there are a set of fine long sharp probes which will slip up the side of cable sleeves and boots etc. There are also a couple of vampire taps that will pierce the insulation with a very small probe tip for a reading.

[cl]

Aha, I had trawled through the lead sets at CPC but missed the specific insulation piercing probes in this set, thank you. I've ordered a set.

[John Rumm]

I have never used the piercing ones in my set yet, but the fine probes are very handy for probing into the back of connectors and PCB headers of all sorts.

[Dave Liquorice]

make that 2,000 m or more away...

But that is on a balanced pair, fed balanced. My tone tracer doesn't work over any sensible distance on coax but I have used it succesfully over T&E with the mains off.

If the OP is tracing power circuits with a wired return rather than using the boats hull (proper inland boats are long, narrow and built of steel these days). Mind I'm not sure that using the hull as power return would be "Good Idea" in a boat due to electrolytic reasons.

[John Williamson]

It's forbidden by the Boat Safety Scheme regulations on boats used on British inland waterways.

240 volt supplies must have a solid, bolted, earth connection to the (steel) hull, and may have a galvanic isolator for the earth or isolating transformer (Recommended to reduce galvanic corrosion on the hull) at the input from any shore supply. They are also required to have an RCD and consumer unit as close as possible to the shore supply connection point.

Low voltage DC supplies *must* have a wired return to the batteries, and it is permitted to have a bond from the battery negative and the engine block to the hull. You still need to run a direct earth wire from the engine block to the battery, though. It is forbidden to intentionally use the hull as a part of any electrical circuit on a boat.

[Adam Funk]

Surely that's the "water" connection?

(couldn't resist)

[John Williamson]

Grone.

[Adam Funk]

...& at sea, groyne.

[cl]

It's definitely frowned upon, there should just be a single common earthing point to the hull and two wires supplying all electrical devices around the boat.