Locating Underground Services: The Expert Guide to Utility Locating Equipment and Procedures


If you’ve been around construction sites you will often hear about the utility locating tool most a lot of people refer to as the “magic wand” or the “locator”. 

What to choose between passive or active locating during on-site utility locating
Image of utility locating equipment used by certified locators on-site

And possibly, you could be here because you’re one of them wondering how magic is these magic wands. 

The truth is, this utility locator tool by itself isn’t that “magic” at all. 

Yes, it works when you know how to apply the correct utility locating methods but the wand in the hands of the inexperienced is far from magic. 

In this article, we are going to uncover what methods professional utility locators go through on-site and the equipment they use. We’ll also touch on the different options and scenarios that we need to deal with to achieve our service locating accuracy to the Australian Standard AS5488.

We’ll often get comments from the tradies on site that go like “Locating looks like an easy job!”, and, “Are you guys hiring?” 

With most things in life, professionals make the difficult look easy. In this case with locating and surveying underground services, it’s the same with watching some professional locating technicians at work.

I mean, physically, locating underground services is not as demanding on the body as other trades on the construction site but the toll it can take mentally is hard to measure by standing side by side with us utility locating and utility surveyors.

It might look like we have a cruisey job walking around with a glorified metal detector although the mental drain with the thoughts running through our minds with our concern for the safety of the workers on site, the safety of plant and equipment, the safety of our community, the project timelines and efficiency, and everything that could go wrong with a damaged electrical cable or gas explosion.

Unfortunately, not everything is as simple as it seems, and there are many factors that need to be considered when choosing how to complete a comprehensive utility locating scan of a site.

If you are one of those people who think that locating underground utilities using a ‘magic wand’ is easy, then maybe we should go through the locating equipment and methodology and point out a few key areas. 

What utility locator equipment do professional locating companies use?

To start with, having an understanding of what we use will help you understand the methodology and steps we locators will go through on-site.

Equipment used on-site for underground utility locating in NSW
Image of equipment used in underground utility locating

Utility locators, not the actual individuals themselves but the instruments we use are also referred to as pipe and cable locators, or for our friends in the UK, a cat and genny.

CAT = Cable Avoidance Tool

Genny = Generator (aka transmitter)

All these terms above are forms of electromagnetic locating equipment. 

The components you will typically find in a bag of a utility locator kit are:

  • TX – transmitter
  • RX – Receiver
  • Direct connection leads
  • Earth stake
  • Induction clamp

Locator Transmitter

Let’s start with the transmitter.

These battery-powered devices look like compact boxes with coils and circuitry inside to generate electromagnetic fields and pulse a current into conductive utilities such as underground services.

Transmitters on their own are able to direct the focus of this electromagnetic energy into underground utilities using the induction locating method, although by carefully selecting accessories in the correct sequence of locating procedures such as using the direct connection leads or induction clamp to target utility we want to locate.

The transmitter has multiple frequencies built in which helps certified locators like us select the best frequency for the task at hand to generate a signal into the utility.

Too high frequency and we risk our signal bleeding onto nearby conductors. Too low a frequency we risk our signal not being traceable or detected.

There’s a happy medium you need to understand for all types of situations and occasions on site which you only get through experience in the field.

Utility Locator Receiver

The locator, the wand, the thing the guy waves which makes beep beep noises. That’s called the receiver.

Magic Wand or Utility Locator detector being used for passive and active locating on-site
Image of Utility Receiver

When we match our receiver frequency to the frequency output of the transmitter, a touch of magic happens where we are now picking up what the transmitter is putting down…into the ground that is.

For example, a common frequency we use is 33kHz. We would match the 33kHz on the transmitter and receiver and be able to actively locate an underground water pipe we have directly connected to very easily.

Locating utilities without a transmitter 

The utility locator receiver not only has the ability to detect electromagnetic signals from the selected transmitter output, but it can also receive passive signals from electrical and communication cables that emit their traceable signals without the need of the utility locator transmitter, leads or clamps.

These traceable passive signals can be cables that have 50Hz AC alternating current running through them which is the frequency that live power cables have or passive signals can also be radio waves which can be found in telecommunication cables such as copper Telstra and communications cables.

This passive utility locating method and procedure is very handy when we are unable to access a particular underground utility asset to directly connect to or use the induction clamp to induce our signal.

Passive scanning for utilities is also an important procedure to verify utility markings and findings to distinguish if utilities have a live power signal or are known to be metallic. 

Passive locating is also the perfect way to complete our final locating procedures to cover all the possible methods to locate any traceable underground services on a work site.

What is Active Utility Locating?

Active utility locating is a great way to detect the location of underground services by actively targeting specific pipes or cables within a work area by applying a signal using the direct connection leads or the induction clamp. 

With active locating, an active signal is transmitted and induced down a pipe or cable where it can be traced along the surface by a ‘magic wand’ or the locating receiver. 

The utility locators then trace the signal above the ground’s surface using the pin-pointing method to accurately detect the highest readings at the centre of the electromagnetic field.

Pros and Cons of Active Locating

Pros: When it comes to locating underground services, using the lead or clamp accessories is the best way to locate utilities other than physically exposing them.

Active locating allows a utility locator to isolate the target lines from other utilities so we know which lines we are working on within a congested area. 

Active utility locating is the go-to method when starting a utility locating investigation on a work site as we can provide the highest accuracy of information about the target utilities through the feedback of data we receive from the utility locator’s receiver.

By applying a trace signal to a utility, we are actively tracing an underground pipe or cable to the Australian standards AS5488:2019 to a location level QL-B or quality level B

The quality location level B is the highest level of confidence you can get with electromagnetic locating equipment before you actually physically verify a utility with non-destructive digging methods

Cons: Active utility locating is not all sunshine and lollipops when it comes to detecting all underground services where it also has some limitations. 

Locating repaired or broken utility lines can be difficult.

Damaged or broken underground utility line on-site
Image of locating broken utility line

For example, when a pipe, cable, or trace wire has been damaged, applying an active signal over the entire length of the utility can be challenging, making it difficult to trace the line completely.

It’s often why you will see markings on the ground or a utility mapping plan where an underground service has been ’unable to be located’ or ‘end of trace’.

For example, when a copper water pipe has been repaired with a non-metallic section of pipe, this typically is where the traceable signal applied from the utility locator transmitter will stop.

As a professional utility locating company in Sydney, NSW, the team at Geoscope will on the rare occasion get feedback from clients saying they had found a metal pipe in their excavation that had not been located. 

Not all pipes or cables are traceable and when there are situations where the utilities have been patched or capped off with non-metallic repairs we aren’t able to push our traceable current through the line.

Active locating requires access to underground utilities

Another limitation we face with active utility locating is the need to have access points to the utility asset, such as a water meter, stop valve or trace wire, for actively direct connecting or we’ll need to access a pit, cable tray or duct to induce our current for utility locating to be effective.  

Stop valve on-site taken by Geoscope
Image of stop valve

Without being able to access the utility, we just can’t get our direct connection leads or induction clamp onto the underground service to be able to trace it using the active utility locating process.

Every site is different and will require all electromagnetic locating methods to complete our utility mapping and survey works.

If we might not be able to locate a utility with active locating, we can still locate the utility using a quality level C location level with other locating methods in which we can further investigate with potholing or directly connect it at a later stage once access is available.

What is Passive Utility Locating?

Passive locating uses signals that are ‘naturally’ present on a select type of buried conductive or metallic pipes and cables.

Passive locating using magic wand or utility locator
Image of Passive Locating conducted by Geoscope

The passive method can be done at any time during the locating process. 

Passive locating is excellent for a quick sweep to verify an active utility locating trace at the middle of the service search process although it is best done at the completion of the search process to be sure we have detected all traceable utilities.

One of the examples of utilities detectable by passive utility locating is electricity cables which carry currents and emit a frequency of 50Hz as part of their normal duty.

With this passive utility locating method, the utility locator will passively sweep the area with the receiver in a grid and perimeter fashion and look for utilities that radiate power and radio EM frequencies. 

These passive signals are typically in the form of 50 Hz, which is usually emitted by electrical or communication cables that emit radio frequencies. 

Pros and Cons of Passive Locating

Pros: Passive locating can be used when there are no visible indications of buried lines and when information about what might be buried in the ground is limited—for example, unknown and abandoned underground services.

It’s a method that can be conducted when there are no active utility locating methods that can be completed.

Passive utility locating is the perfect end to a utility locating process on site for searching for all traceable services.

Cons: The passive underground services locating method is not a one-and-done magical method that will find everything. 

Not all utilities emit this passive frequency, even though they are electrical or copper communication cables.

Because a passive services search detects metallic services that emit their electromagnetic field, it means this method is not suitable to detect non-metallic materials such as plastic, clay, and concrete underground services.

Although I wish we just could walk over an area with the receiver locator and pick up a plastic water main, that just won’t happen, basically ever.

For this reason, we cannot, and as a professional utility surveying company, we do not turn up to a site with a utility locator receiver without the rest of the transmitter and kit.

You can’t just passively sweep a construction site and call it a day.

Although we have witnessed other utility locating companies in the Sydney areas turn up to the site without a transmitter, this is leaving a lot of risk without utilising the most effective and efficient locating tracing method in actively utility locating.

Passive utility locating can be difficult to pinpoint sometimes, especially in congested areas where there are two, three or more nearby underground services emitting the same, similar, or alternate signals. 

Having multiple underground services in an area emitting passive or high voltages can make it difficult for the operator to distinguish the difference between each utility line. 

Using all available utility locating methods and procedures including active locating, GPR, two-man sweeps etc will help to overcome the limitations of passive utility detection.

Which Should You Choose Between Active And Passive Locating?

What to choose between passive or active locating during on-site utility locating
Image of Active and Passive Locating method used on-site

Having gotten this far into this article on locating underground services and the methods and equipment that a professional company would use on a typical Sydney construction site, you would be able to see which method you should choose.

In my experience, I can say that both methods work great, and I wouldn’t be choosing one or the other in any utility locating project we ever attend.

The answer is always to use all utility locating methods. Every time.

Combining both underground service locating techniques gives us the best chance of success in locating all traceable underground services on site. 

For instance, if a Sydney construction site had incomplete or inaccurate as-built maps, passive locating can help locate utilities in the planned excavation area, while combined with active locating methods will help in detecting all traceable utilities to get the highest accuracy of subsurface utility information.

Regardless of the method used, locating and marking buried utility lines to prevent damages and accidental strikes is the goal of any utility locator and contractor project. 

Geoscope marking street for located underground utility in NSW
Image of Geoscope marking services for located utilities underground

I hope you are now well informed of the electromagnetic locating methods and instruments used and it will help you be informed and sure utilities are located on your site, whether it is done by Sydney’s leading utility survey specialist in Geoscope Utility Detection Services or it’s your trusted Certified Locator.

With the information in this article, you can now be armed to question if you are getting the value from your locating team and do all that is possible to detect traceable utilities on your site.

If you have any questions or thoughts, feel free to leave a comment or contact our team.

Geoscope are professionals here, so let us bring our state-of-the-art electromagnetic locating equipment and take care of the complete locating process flow. 

Sit back and concentrate on planning the design and excavation process and doing what you guys do best.

Geoscope. Keeping people safe!

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