In recent months we have been getting high numbers of enquiries from contractors, some from large corporations, and some from much smaller businesses regarding the recent changes to Telstra Plant Locator Accreditation. Previously it was a case of attending a course, being signed off as competent and being Telstra accredited. However, recent changes to this accreditation process have meant that those contractors who are renewing their accreditation, or applying for a new Telstra accreditation have had to undergo a completely new process as required by Telstra to become one of their Accredited Plant Locators.


This new process is now part of a process known as Dial Before You Dig (or DBYD) accreditation, and the requirements to being signed off are far stricter than they previously were. Contractors must now undergo both the theory and practical testing and assessment required by Dial Before You Dig. For those contractors wishing to undertake the theory testing, which is done as the first part of the process, a short two day NULCA (National Utility Locating Contractors Association) course is offered by a limited number of training organisations, which is useful to brush up on the knowledge required to undertake the theory assessment, and is also useful in that this information will also better place you to undertake the practical assessment, the second part of the Dial Before You Dig Accreditation process. Although we get asked by many contractors, who are new to the industry, or are intending to add it on to an existing business, some experience is invaluable and really quite essential to undertake the testing.


With this new process, the part that is least understood is what sort of equipment is required. Many contractors contact us, or drop in to our office with a cheap underground service locator, which they have managed to get hold of, but the basic fact of the matter is that it just will not comply with the required list of equipment. The most expensive thing on that list is your underground services locator, or underground utilities locator or underground cable and pipe locator – whatever name you might know it by. Gone are the days when you may have been able to buy any underground service locator, get signed off and be let loose as an accredited locator. The underground service locator in particular has a very strict set of requirements, and these must be adhered to strictly in order to undertake the practical assessment. There’s nothing worse than having the wrong equipment, having to outlay thousands of dollars to get the right underground service locator kit and then also have to be re-assessed again (at an additional cost usually) because of a decision based on cost rather than requirements.


The underground service locator must meet the following requirements:

It must have a minimum of 2 frequencies, although 3 is preferable. Saying that, the more frequencies you have – to an extent, the more services you may be able to precisely locate. Nearly every underground service locator on the market will have the standard 33kHz frequency that is familiar to those of us who are used to using the equipment. Something like the Radiodetection C.A.T4+ and Genny 4 Cable Avoidance Tool is a single frequency underground service locator, and while they are very good at basic buried utilities locators, they will not meet the requirements of the Dial Before You Dig Accreditation. Technically, although the Radiodetection C.A.T4+ and Genny4 is marketed as a single frequency locator system, it is actually a two frequency machine, as it outputs what Radiodetection call a “small diameter locate signal” which is used to locate small diameter cables, such as twin pair, telecoms cables and so on. Although the frequency is not advertised, it is most likely to be 131kHz, or a suitably high frequency. Nevertheless, regardless of the number of frequencies on the C.A.T4+ and Genny4, it will not meet the stringent equipment requirements of the Dial Before You Dig Accreditation because of other locator requirements.


The next requirement of a suitable underground service locator is that it is required to have separate Peak and Null modes. Although to many prospective buyers of cable and pipe locators, these modes are somewhat confusing, they actually serve a very useful purpose. In modern buried infrastructure, cables and pipes often lie close together. Telephone lines in particular can be in crowded pits, buried alongside other cables and other buried services. When these buried services are close together, the transmitter signal can easily couple to a nearby line and be present on that, as well as the target cable (or pipe). This is where the Null mode comes into the equation. An undistorted magnetic field is more or less round in shape, but if signal coupling to another nearby cable or pipe has occurred (and this is more likely with a higher frequency – the sort that are used more for Telstra locates), the magnetic field will be distorted – in other words it is no longer round but an elongated shape, due to the signal being coupled onto more than one cable or other buried utility, as in the example here:



If peak mode was used here, there would most probably be a maximum response which would not correspond to the location of the target line. Changing the locator to Null mode can verify whether the signal is distorted. If the null response and peak response locations match, then it can be assumed that the signal is undistorted and that the locate is precise. If on the other hand, the null point (minimum response) does not match the location of the peak response, then the chances are that the EMF around the cable is distorted, most likely by the presence of another cable or buried service in the vicinity. One thing to note is that some of the available locators, such as the RD7100SL or the RD7100DL and the RD7000+DLM have a combined peak and null mode. This is not acceptable, as the modes MUST BE SEPARATE. What is noticeable right now is that a lot of the required functions are conducive to more difficult locates, particularly in dense infrastructure, which is becoming more common. As buried services become more congested, it is essential that accredited locators have equipment which has suitable functionality to work in modern infrastructure.


In addition to the above requirements, any underground service locator is required to have automatic gain, which must also be able to be disabled as the need arises. Automatic gain is a function designed to allow the locator to adjust it’s signal response in order to keep it on the target line. In guidance mode, the Radiodetection RD7100, RD8100 as well as some of the RD7000+ and RD8000 marker models are able to continually adjust their sensitivity. In a nutshell what this automatic gain does is prevents the operator from having to continually make manual adjustments, due to changes in the target line, such as changes in depth, or high resistance joints. In automatic gain mode, or guidance mode, the locator automatically adjusts the gain, or sensitivity in order to keep the locator on the target line, with no input or manual control from the operator. Of course there are times, such as checking a peak and null point where the automatic gain needs to be disabled and the operator needs manual control of the receiver, so changing mode out of guidance mode switches off the automatic gain function and returns the locator back to manual control. Guidance mode is fast and easy to use, but when there are changes in a buried cable or pipe, it is not always practical to have automatic control of the locator, hence the requirement to have the option of manual control.


Any locator being used to gain Telstra Accredited Plant Locator status, via the Dial Before You Dig practical assessment needs to be able to display current measurement. The reason for this is quite simple. For example, imagine you are doing a locate and you have a few buried services in the vicinity. Current measurement is used to confirm that the signal you are tracing is from the target line (in other words the buried cable or pipe that you are applying the signal to). Sometimes it is possible to be following an induced signal, which is not the one from the transmitter connected to your buried service, but instead is a signal which has coupled onto a nearby service by jumping off the original line. To overcome this, and more to the point to confirm that the trace being followed is the correct one, precision locators are able to measure current, such as the Radiodetection RD7100 series, RD8100 range as well as the RD7000+ and RD8000 marker ball models.


Suppose you were performing a locate, and there were three buried cables or services being picked up by the locator. How would you know which one was the cable to which the signal is being applied, as the other two of them are unwantedly coupling the signal to them (it is jumping off the target line) Nearly everyone who gets asked this question will invariably assume that the target line is the one with the strongest response, but what if the strongest response is simply due to the buried service being shallower than the target line – it would exhibit a stronger response. This is why precision locators measure current, because the target line that you are locating will always be the one with the highest current flowing through it. Regardless of signal strength. The cheaper underground service locators, such as the Radiodetection C.A.T4+ and the RD2000 do not have this current measurement, so will not be up to the standard required for the equipment.


As far as the underground service locator goes, the last thing on the list of requirements, and the one thing that narrows the suitable service locators right down to a much narrower range of equipment is the fact that a transponder is required. The main purpose of a transponder is to locate something known as RF marker balls. There are nine different frequencies of marker balls which are universally available, and for Telstra purposes, the telecoms marker balls operate at 101.4kHz, however, the latest equipment list states that the locator should be able to locate “all frequencies”. All of the Radiodetection Marker Locators have the ability to locate all frequencies of marker balls. We did hear stories of some utility providers using different frequency marker balls, but regardless of this the Radiodetection Marker Models can locate all frequencies of marker balls.


The marker locators have a pull down loop antenna, which sits in the up position, against the main body of the service locator. With the transponder antenna in this position, the locator works just the same as any standard underground service locator would. When you pull down the transponder, the locator can be set to either go into marker ball mode, or combined mode where it works as a combination marker ball and standard service locator. Push the transponder loop back up into it’s folded position, and the locator just functions as a standard service locator again.


So in conclusion to the requirements for a cable and pipe locator, the above requirements must be met, for candidates undertaking their practical assessment to be signed off as competent in order to gain accreditation. There are a small number of underground locators which will meet all requirements, and they are as follows:

Radiodetection RD7000+ PLM

Radiodetection RD7000+ TLM

Radiodetection RD8000 PXLM

Radiodetection RD8000 PDLM

Radiodetection RD8000 PTLM


These 5 service locators are the only ones to have a minimum of 2 frequencies (preferably 3). All have 5 or more. The above all have separate peak and null locate modes (the lower end of the RD7000+ markers only have combined peak and null mode which is not acceptable). All of the above have automatic gain (which can be disabled), current measurement and a transponder. If it was not for the transponder requirement, the RD7100 and RD8100 could be used. Technically they still could be, but a separate transponder would have to be sourced, which usually would involve a higher cost than the ones built into the Radiodetection Marker Locators.


Once you have the correct underground service and utility locator, then there are a few other things on the list, which you need to have, mainly for personal safety, such as a 4 gas confined space detector. This is not a sniffer, which is used for combustible gas leaks, but it is a detector which has to detect Oxygen (O2), Carbon Monoxide (CO), Hydrogen Sulphide (H2S) and Combustible Gas Lower Explosive Limit (LEL) in %. As well as this and protective clothing, you will need lid lifters and safety barriers etc. Dial Before You Dig have a published list.


The final thing related to the underground cable and pipe locator, that is required is duct rodding equipment and a sonde. This is used for pushing up plastic conduits, and the sonde (sometimes called a mouse) sits on the end of the duct rod, allowing non-metallic services to be located. These rods are available in various thicknesses with 6mm being the most popular, but you can also get 4.5mm ones and 9mm ones. However, the recommendation would be to use the Radiodetection FlexiTace if possible, which is a powered rod. You attach the signal transmitter to is and it applies a trace signal up the whole of the rod, making it easier to follow the signal right from the source. With the non-powered rods, only the sonde emits a signal, making the locate more difficult. Although the FlexiTrace is more expensive, the time it saves is generally well worth the extra investment. These are available in a 50 metre or 80 metre length, supplied on a purpose built frame.


As for the Sonde, the standard 33kHz sonde is the cheapest option, but does have some drawbacks. Firstly, it’s almost 40mm in diameter, which is quite large. Secondly, it’s 33kHz signal will be no good in cast iron, as the cast iron screens or masks the signal. For tracing in cast iron, one of the 512Hz sondes is usually recommended, as it can be located far more easily. Also the 512Hx signal is less likely to couple onto nearby services. The S13 Sonde is the most popular, as although it is around $200 more than the standard sonde, it is much smaller, at around 12mm in diameter, so as a result will fit into conduits and ducts far more easily.


Obviously all of the above considerations only really are worthwhile considering if you are intending to apply for Dial Before You Dig Accreditation with a view to gaining Telstra Plant Locator Accreditation. However, in saying that, due care and attention should still be given to selecting the right service locator, whether applying for accreditation or not. The cable avoidance tools, such as the Radiodetction C.A.T4+ and Genny4 and the Radiodetction RD2000 have their place and are very popular for basic asset location. They are also simple and easy to use with fewer settings than the more advanced underground service locators. Whilst they give an indication of the presence of buried services and utilities, they lack the precision features of the more expensive locators, and therefore are not always as effective, especially if you need to do a precision locate. The RD2000 is available in three different kits (one for power and two for telecoms, each with three active frequencies).


With the precision locators, the RD7100 and RD8100 are the two ranges which are the most popular. The Marker Locators are typically supplied to customers who may be applying for Telstra accreditation or Dial Before You Dig accreditation. For contractors wanting a precision locator, but not intending to undergo assessment for Telstra accreditation, the RD7100 and RD8100 service locators represent an excellent choice in equipment.


As a minimum requirement, I would normally recommend that if performing professional locates, and by that I mean beyond the scope of basic asset locates, then the chosen underground service locator should have:

  1. A suitable number of frequencies (a mix of low, medium and high between 512Hz and 65kHz of higher)
  2. Peak and Null modes in order to check distortion of the signal
  3. Current Measurement – to confirm that the target line is being followed
  4. Automatic Gain is useful for quickly following buried services, which may change depth
  5. Simple and easy to use
  6. Ease of servicing. Preferably within Australia via the supplying distributor
  7. Ability of the distributor to provide training and support on the equipment

Frequencies, or more to the point a variety of frequencies are more or less essential because they have different characteristics. A high frequency is easier to apply by various methods, but due to capacitance in the soil, which surrounds the buried cable or pipe, a high frequency signal also bleeds into the soil more easily, so travels over shorter distances than a low frequency locate signal. On the other hand, a low frequency signal is harder to apply (anything less than 8kHz can usually only be applied via direct connection – signal clamping or induction will not work). A lower frequency signal such as 512Hz or 640Hz though can travel much longer distances, because it is less affected by the capacitance in the soil, so these low frequency signals lend themselves well to longer distance locates.


In situations where you may be tracing something, such as a small diameter twisted pair cable, such as a phone line, the soil may need to allow the signal to return as the ground, especially where the cable is not earthed at the far end. Most power cables will be earthed at both ends, so these don’t pose the same problems. For instances where that cable is not earthed, then to use the soil as the ground, a higher frequency is usually used, as they travel more readily into the soil to complete the flow of signal current. The problem with this is that when locating something that is longer, and using a higher frequency signal, a sufficiently long enough locate may not be possible. To overcome this, Radiodetection transmitters for the RD7100, RD8100 and RD7000+ and RD8000+ locators are available in a higher 5-watt and a 10-watt version, both with a higher voltage output, which allows more current to be pushed into the target line, and therefore allowing the signal to flow further before completely decaying. For this reason, when supplying any of the underground service locator kits, we generally tend to recommend the higher power 5-watt and 10-watt transmitters. The RD2000 and C.A.T4+ use different transmitters which, at 1 watt maximum are less powerful, but as mentioned on a number of occasions in this article, they are good for basic asset location.


As far as the precision locators go, there are differences between each of them, but to detail the exact differences would make this article very long and drawn out. Basically the RD7000+PLM and TLM plus all of the RD8000 Marker Locators are compliant with Telstra’s requirements. The RD8000 has more frequencies than the RD7000+, plus optional GPS, Bluetooth (for remote control of the transmitter) and current direction (for which the 10-watt transmitter must be used). The RD7100 and RD8100 have similar differences, and then within each of those ranges there are 3 or 4 models. Each one of these models is optimized for a different industry. As an example, in the RD7100 series the DL has multiple sonde frequencies, so is good for drainage and plumbing contractors who need to locate various pipes. The PL is more geared towards power and electrical with certain functions such as power filters for more precise locating of live power cables, and depth in power mode which allows depth readings to be displayed when tracing live cables without applying a signal, and the TL is aimed at the telecoms market as it has 2 very high frequencies and more sonde frequencies (for tracing plastic ducts in congested infrastructure), but with the TL you lose depth in power mode and the power filters.


The RD8100 has three models, the most popular being the PDL version as it has quite a few frequencies, current direction, Bluetooth, power filters, depth in power mode to name a few.


My personal choice for non-Telstra accreditation customers would be either the 5-watt or 10-watt kit of the RD7100PL or the RD8100PDL. Both can be specified with GPS and usage logging if required.


For the Telstra Accreditation customers, the most popular are the 5-watt and 10-watt kit versions of the RD7000+PLM and the RD8000PDLM, but ultimately the choice is made by each individual customer, based on their requirements, and budget.


We do a fair amount of training for customers on the Radiodetection range of service locators, but can advise on generic location techniques if necessary. All underground service locators supplied by us here are fully backed up with our expert knowledge and support, so by all means feel free to give us a call or email if you would like some further assistance .