Top 3 Cable Tracing Technologies

Firstly, why would you need to trace network cabling? In a perfect world you wouldn’t need to, but even if a network begins life properly labelled, things have a habit of changing. Documentation and cable labelling don’t always keep up when changes are made.

Network Cable Mess
A jumble of network cables in a network cabinet.

When you need to re-arrange the cabling in your patch panel, can you be 100% certain that the label is correct? You can be reasonably certain if you installed and maintain the network yourself, but what if others are involved. Are they as fastidious as you are in keeping the network documentation up to date?

Before cable moves, it doesn’t do any harm to make sure the label is up to date. It is one thing to disconnect a single phone or workstation, quite another to disconnect the server.

A number of different technologies exist for tracing network cabling. Each technology has their plus points and their down sides too. A brief explanation of each technology will now follow outlining when each should be applied.

Tone Tracing

Tone tracing is pretty much as old as copper cabling itself. Tone tracing is the grand daddy of all cable tracer technologies. The basic idea is that at one end of the cable you place an electrical signal onto the cable, using a tone generator, and then trace that signal, using a tone tracer, in order to understand where the cable is located.

It could not really be much simpler. Well unfortunately, it is simple in theory, and usually it really is that simple in practice, but there are some things in network cabling especially that manage to make things a little more complex.

The design characteristics of the network cable are working against you. The design of Unshielded Twisted Pair (UTP) cabling is meant to reduce the interference between the pairs of copper wire that make up the cable as a whole. All of CAT5, CAT5e, CAT6 cable types have four pairs of copper wire carefully twisted together to minimise interference. This presents a number of problems to anyone attempting to trace a category 5, 5e or 6 cable because you wish to maximise the signal on the cable in order to increase the strength of the signal you can detect.

The best way to minimise the effective damping effect of the cable twists is to place the signal on a single wire within the cable whilst the other pair is earthed. If a signal is placed onto both pairs in a cable the twists in the cable will work to dampen the signal, placing the signal onto a single wire will help to avoid the dampening effect.

Tone tracers have traditionally been analog. More recently digital or asymmetric tone tracers have arrived onto the market. Asymmetric toners have a number of advantages over more traditional analog tracers.

Tone Generator and Trace Diagram
A diagram showing how a tone generator and tone tracer works.

Tone tracing provides the only cable tracing technology that can be performed on a live cable. More modern asymmetric tone tracers operate at frequencies well above the level that even very modern cable like CAT7 operate. Consequently, the tone signal does not interfere with a network signal.

Locating exactly where the fault lies can be very useful in deciding whether a cable run needs replacing or repairing. A fault close to the end of the cable may be repairable. Conversely, a fault in the middle of the cable would, in all likelihood, require a replacement. A tone tracer can be used to locate a fault, though it is a laborious process tracing each wire until the break is located. A full featured cable tester or TDR tester would be much faster and consequently a much better use of your time.

Continuity Testing

A continuity tester provides the ideal way to locate and label your network cabling. Whilst a toner can only work one cable at a time, a continuity tester can locate up to 20 cables at a time.

Each continuity tester is supplied with at least one remote. The remote fixes onto one end of your cable and you place the tester itself on the other end. When the tester and the remote are connected to the same cable, the continuity tester will show the number of the connected remote. Additional remotes can usually be supplied for most continuity testers or are included in the kit form of the tester. The additional remotes are numbered sequentially allowing you to locate and label a batch of cables at a time. If you have a large number of cables to locate, this can be a real time saver and will save you a lot of leg work.

In addition, a continuity tester is also capable of simple cable testing ensuring that all of the pairs of wires have no breaks and are connected correctly. It must be stressed that low end continuity testers can be fooled into giving a positive result when the cable is incorrectly wired.

Most continuity testers have a tone generator built in, so, with the addition of a tone tracer, can be used for tone tracing as well. Using the built in tone generator on a continuity tester can save you from carrying around a tool, saving you space and weight in your kit bag.

Hub Blink

Most modern hubs and switches have activity lights for each port indicating the traffic level and status. A recent addition to many cable testers and outlet identifiers has been the ability to blink the lights on a port. This feature is called hub blink.

Of course, this feature is only useful if the cables you wish to locate are connected to a live network. Hub blink is completely useless if you are trying to locate bare wire cables or before the network infrastructure has been installed.


Which technology you find a best fit is largely dictated by a few factors like how many cables you need to track and whether the cables are live.

If you are tracking cables that are not terminated, your options are traditional tone generator and tracer or continuity tester. Ditto if the cable is live, your only option is to use an asymmetric toner.

Hub blinking is also fine so long as your switch is relatively small. If you’ve got a huge switch with hundreds of ports, you may well struggle to identify exactly which port is blinking.

If you have a lot of cables to find, then a continuity tester with multiple remotes will allow you to identify cables in batches, speeding up the process of identification and labelling.

JDSU ValidatorPRO-NT NT1155 Box Opening

A series of box opening photos of the recently released JDSU ValidatorPRO-NT NT1155 all-in-one copper, fibre and wireless tester with active network features.

Video ahoy!

We’re in the process of producing a bunch of videos explaining the features on some of our more specialised products…what am I saying? They’re all specialised!

There are a lot of concepts in the cabling world that many IT workers haven’t come across before. We’re determined to make it as easy as possible for them to learn the dark secrets of cable testing and cable locating.

The video is hosted on YouTube because it is cheap and very, very available. We haven’t put a voice over on the video as yet, but being as over excitable as ever, I thought I’d jump the gun as usual.

As the recent extensive BBC website video integration has proved, all websites will be TV channels in one form or another soon, so we may as well try to be at the forefront of the trend rather than trailing behind. None of us has any experience of producing videos so it has been a steep learning curve. As usual in small companies you get to do everything with very little time and precious few resources. I guess that’s probably what makes things fun!

Equipment bought so far: 1x Sony DCR-SR55E & 1 x Vegas® Move Studio

Equipment required: 1 x PC microphone

If anybody has a recommendation for a good, moderately priced PC microphone, please leave a comment.

Update: Denis Laverty is the star of the show…we’ll have to get him an equity card if he carries on like this!

New 6 Point Checklist for Cables

A couple of weeks ago BASEC (The British Approvals Service for Cables) issued a 6 point checklist pre-empting the release of the 17th Edition Wiring Regulations in July. They are alerting cable installers that the need to ensure the correct specification of cables for major projects has now become critical.

Dr Jeremy Hodge, BASEC’s Chief Executive, said: “For any size of project, the last piece of news a contractor or specifier wants is that cabling has to be stripped out because the system is not working properly, there is a safety implication or the wrong cable has been installed.”

BASEC’s six-point Spec Check was designed as a quick-check guide to reducing the risk of things going wrong for specifiers and installers, the outlines are briefly:

  1. Get the installation design right. Good installation design reveals the technical specification for each circuit on the mode of use, accessories, current loading, physical protection needs, fire and smoke performance, operating temperature, future expansion and so on…
  2. Get the cable specification right. From the circuit specification, the cables should be specified by reference to the standard number and table / type
  3. Communicate specification. Use one of the standard specification packages or forms usable by quantity surveyors and procurement specialists.
  4. Check application of the spec. When changes are proposed make sure these are signed off by the designer to ensure continuing compliance with the design rules.
  5. Check product on delivery. This is important for both installer and client. When cable arrives on site check more specifically what has been purchased for you and inspect the product.
  6. Final check. Commissioning tests and inspections are the last opportunity to enforce the specification. Make sure these are rigorously carried out and if problems are found check what is installed against the original specification again. If there are problems found with or questions are raised about a cable, don’t automatically strip out the cable, but seek advice. If necessary get the cable tested – BASEC can provide advice in such circumstances.

If you would like to read the Full Alert, it’s available online at
The wiring regulation changes coming into force in July (BS 7671) are outlined at Voltimum.

ELEX Harrogate Pictures

Many thanks to everybody who attended the ELEX show in Harrogate last week. OPENXTRA had a stand and we enjoyed meeting you all.

Denis and Annie at ELEX

Denis and Annie did heroic stand duty ably assisted by Steve from JDSU.

Denis with the cable tester demonstrator box

One of the big hits at the show was the cable tester demonstrator box (as demonstrated by Denis above) with various cables exhibiting a number of different faults like shorts, miss wires and the like.

See you there next year!

Looking forward to 2008

We expect two main trends to continue to drive business throughout 2008:

  • Convergence — a lot of people not normally associated with computers and communications are being drawn in, most notably electricians working in the building industry. With things getting sticky in the housing market, it is likely that a lot of electricians will be looking for alternative sources of revenue;
  • Heat in the data centre — its not just the planet’s environment that’s warming up…servers keep getting hotter too with only modest signs that things are going to change any time soon. The data centre environment is going to be a concern for a while yet.

Mid March we will be going to the ELEX show in Harrogate. Given the first item above, you won’t be surprised to know that we’ll be showcasing cable testers aimed at the converged electrician.

Devices for measuring and alerting on environmental conditions keep getting better. We expect that trend to continue throughout 2008. In fact, Sensatronics have just released the first firmware upgrade for their rack-mount environment monitor. I’ll post more fully about that when I’ve collated all of the new features.

In addition, we’ve had good results with network enabled thermometers in non IT environments too. Warehouses and cold storage facilities gain the same benefits from convergence with the network as the IT industry has over the last decade or so.

At the top end of the cable tester market, Agilent continue to build a very fine platform with fibre, 10 gig and alien cross talk capabilities. We can look forward to more great products from them. The great thing with the Agilent approach is that you are freed from the buy, trade-in cycle. I suppose, for the more cynical reader, you replace it with the buy then perform repeated software upgrades cycle. 😉

With economic conditions uncertain, it looks like 2008 is going to be interesting to say the least. 🙂

Test-Um training roundup

JDSU were kind enough to invite myself and Denis to a Test-Um product training day at the JDSU offices in Basingstoke. Michael, the Test-Um trainer, is extremely knowledgeable about cable testing in general (as an ex-installer himself) and about the whole Test-Um range in particular.

One heads up. The Test-Um name is going to start disappearing soon. All of the Test-Um range will be re-branded as JDSU Network and Enterprise Test.

In no particular order, the news from the Test-Um world:

  • When toning, ground half of the cable pair if possible in order to increase the tone strength by around 3 times
  • Measuring the distance to break using impedance or TDR is only accurate to around 3%. If there’s a break in a cable a tone will generally stop at the break pinpointing it very precisely. However with some of the more powerful toners the tone may breach the break. Using the Banjo cable breakout box, LB68, you can split out each cable and earth them one at a time to detect very precisely where the tone stops and consequently the break. Expect to see the LB68 on our site real soon.
  • All of the Test-Um range of tone generators are digital, there are no analogue toners, and asymmetrical, so they do not disturb the traffic even on a live Ethernet network. Although hub flash will also work on a live network it’s sometimes hard to see the flash in among the normal network traffic. Tones are much faster and easier to pick up.
  • The Wi-Net can display wireless signal level as both a percentage value and as a dB level. You can toggle between the two quite easily
  • An update to the Testifier (to be called the Testifier Pro) is due in the UK in Q1 2008…features to follow closer to launch

We will be discussing a number of these items in greater detail in future posts.

Copper vs Fibre cabling costs


You might assume that because the technology involved in manufacturing optical fibre cable is more complex than copper, installation of fibre networks would inevitably be more expensive than using copper. However, with the advent of CAT6 cabling means that copper is getting faster — but at a cost.

There are environments where copper is at a severe disadvantage; take an industrial environment with a lot of electromagnetic interference; copper cable in this type of environment will need a lot of protection, incurring extra cost, fibre would be totally immune to such interference.

Environments requiring long cable runs of 180m or more can mean that the cost of repeaters and outdoor environment cabling will outstrip fibre costs. If you want to test this for yourself, an excellent resource is the TIA Fiber Optic LAN Section which provides a cost model (you need to give email details) to help you separate out the copper vs fibre dilemma.

Tracking live network cables

Category 5 cable

I’m often asked how to track live network cables. I have a confession: I don’t know how to do it! There, honesty is always the best policy!

More and more companies have systems that are in operation 24/7, that cannot in any circumstances be switched off. Sometimes the data centre cabling is poorly documented. So, how do you track cabling that is live?

I know how not to do it. Normally, I’d either use my ever faithful pair of tone generator & tone tracer. Or, I would use a something like an outlet identifier that blinks the lights on the hub or switch port.

Trouble is, both of the above methods can’t be used on a live network. If you put a tone on any of the pins on a network cable that’s going to interfere with the network traffic. Same with the port blinking method too.

Normally, in circumstances where toning on the cable pins is impossible, I’d use the cable sheath instead. Unfortunately, most deployed CAT5/6 cable is unshielded, so it doesn’t have a conductive sheath.

So, I don’t know how to track live network cables. I have a suspicion that it can’t be done. If you know how, please put this poor sap out of his misery. 🙂

Update September 2014: you can tone a live network cable if you use an asymmetric toner. An asymmetric toner produces tones well above those used by network traffic so does not interfere with it.

Data, Voice, and Video Cabling book

Data, Voice, and Video Cabling book cover

If you are involved in installing data, voice or video cabling then you won’t be disappointed by Data, Voice, and Video Cabling by Jim Hayes and Paul Rosenberg.

Jim Hayes, as we’ve recommended before, also has a couple of online tutorials available. Well worth a look!

The book gives a nice overview of the various technologies involved as well as more practical chapters on wiring installation, testing and termination. The book covers both copper and fibre cabling too.

The book has a good chapter about business issues too including labour rates for communications wiring. The rates are US centric, but are interesting nevertheless.

Whilst I doubt the experienced cable installer will find anything new, the less experienced will find much of interest. The book will be most useful for none specialist IT staff and electricians called upon to install communication cabling.