Stay up to date with Tempo Announcements and News

Utility worker in a hard hat and high-visibility vest using an orange Tempo electromagnetic line locator on a paved street beside a grassy sidewalk and shrubs

Line Locators: Application & Usage Guide

Tempo Articles
June 24, 2025•11 min read

Line Locators: Application & Usage Guide

Locating underground assets such as cables and pipes is part science and part art, and the challenge only increases when searching for points of interest, such as joints and tees. We’ll show you the equipment and techniques to detect what’s beneath your feet. 

Reasons to Locate: From Finding Faults to Damage Prevention 

You may be locating to determine where you need to dig or where NOT to dig! You could be searching for something you need to excavate to make a modification, repair, replacement, or removal, or you may simply need to know where you are free to bury a new addition without risk of hitting something dangerous or expensive. 

Safety and Damage Repair

An excavator bucket hovers over a freshly dug trench, revealing underground utility lines. The soil is damp, and the scene suggests a deliberate digging operation, emphasizing the need for careful locating to avoid damaging buried infrastructure.A powerful geyser of water shoots skyward from a burst water main in a city street, drenching nearby cars and causing street flooding. Emergency cones and a utility crew are visible, highlighting the urgency and disruption caused by accidental utility strikes.A massive plume of orange flames and black smoke rises from a gas line explosion in a green field near residential and industrial buildings. The aerial view shows the scale of the devastation and the serious safety risks associated with unlocated gas lines.A large water spray erupts near suburban homes, spraying over lawns and rooftops. The intensity of the water suggests a high-pressure line break, underscoring the importance of locating utilities before digging in residential areas.

Striking utility lines can create dangerous situations including explosions, electrocution hazards, or high-pressure jets of water that put lives at risk. 

Besides the destructive nature of gas, power, and water, even telecommunications lines require a great deal of manpower and equipment to bring back online if they are damaged Thus, the importance of locating buried utilities is widespread across all underground assets. 

Access 

There are points along buried lines that may need to be uncovered and manipulated by hand such as damaged lines, valves, or joints/fittings. 

A partially unearthed metal pipe with a valve is shown embedded in dry, sandy soil. The pipe appears corroded and is exposed for manual access, possibly for inspection or repair of a joint or damaged section.A network of blue-painted underground water pipes and valves is exposed in a construction trench. The joints and connectors are visible, highlighting complex infrastructure that may require manual manipulation or access for maintenance or inspection.

Line Locators: Transmitting and Receiving Signals 

Metal cables and pipes are conductive and well-suited for carrying electricity. We can apply alternating currents of electricity to these metallic lines to “sense” where they are located and which direction they travel. 

Line locating often relies on understanding how well a circuit can be made using the line being located and the surrounding soil. Changes in signal application method, positioning of the transmitter along the line, signal frequency, and even ground stake placement can all influence how well your signal corresponds to the line you’re locating. 

Having a basic understanding of electromagnetic fields and antennas can enhance your ability to interpret signal sources beneath your feet. 

A set of line locating tools displayed on a white background includes a handheld receiver wand, a signal transmitter unit with control panel, and an orange clamp-style signal injector. The tools are used to transmit and detect electrical signals in buried metallic lines for underground utility locating.

Transmitter Signals – Alternating Currents at Different Frequencies 

Circuits 

Signals can be thought of as rapid “vibrations” of electricity that travel out from the transmitter along a metallic line and are strongest when they can most easily move in a circular path back to the transmitter via ground stake. 

An electrical transmitter is connected to a red and blue cable laid across the ground. The cable ends at two orange ground stakes positioned on either side. Black arrows and AC symbols indicate current flow from the transmitter, through the cable, and into the earth at each stake, illustrating how the signal completes a circuit through the ground.

Earth (dirt/clay/sand) that contains moisture is conductive, so if the far end of the line comes into electrical contact with the earth, a simple circuit is created: out along the line, back through the earth in a widespread area and then concentrating around the transmitter’s ground stake once again. 

A simplified illustration shows a transmitter on the left and a ground contact point on the right, connected by a cable. Curved arrows beneath the cable depict multiple signal paths radiating outward and downward through the soil, labeled “Signal Paths through Dirt,” showing how electric current disperses and returns through the earth.

Even without direct electrical contact on the far end, the signal can capacitively “leak” little by little along the conductor and return to the transmitter through the earth and eventually back through the ground, creating little circuits of electricity along the way. 

A schematic shows a horizontal conductor (such as a buried cable) with several vertical arrows pointing down to ground symbols, each passing through a capacitor symbol. An AC signal source is connected to the left end, illustrating how signal current “leaks” capacitively to ground at multiple points along the cable’s length.A 3D illustration shows a person using a handheld line locator above a buried cable. Blue concentric arcs rise from the cable, representing electromagnetic signals radiating upward, which the device detects. The diagram emphasizes how the signal strength correlates with the cable’s proximity and length beneath the operator.

The longer the buried line extends away from you and the transmitter, the more signal will be carried through the portion of the line underneath you.

If you can, it is always better to ground the far end of the cable than to rely on capacitive leakage.

Frequency

This capacitive leakage or sometimes called “bleed” effect into the dirt increases as the frequency of your signal increases, so higher frequencies work well to travel along shorter lines as well as lines that are not directly grounded at the far end. The drawback is that a high-frequency signal generally won’t travel as far as a low-frequency signal.

In fact, there are other tradeoffs you can make with higher or lower frequencies:

 

The chart visually summarizes that low-frequency signals have better range and lower signal bleed, but are more prone to electrical interference and need a ground connection. High-frequency signals travel shorter distances but require less grounding, overcome resistance better, and induce signals more easily on nearby lines.

Higher frequency signals “bleed” not only to the ground but to other nearby conductive lines. This means you may detect signal on a nearby pipe, cable, rebar, or metal fence even though they’re not connected to the transmitter. 

Higher frequencies can also “bleed” through poor conductivity due to corrosion, bad connections, or even non-metallic gaskets. This can work in your favor when tracing damaged lines but against you when trying to pinpoint where the damage is located. Use the lowest frequency available to avoid “bleed” and to trace as far as possible, particularly when you have grounded the far end of a cable. 

Locator frequencies tend to range between around 500 Hz (cycles per second) on the lowest end and around 500,000 Hz (500 kHz) on the highest end). This is a logarithmic scale, so 1.75 kHz, 33 kHz, and 447 kHz are all roughly equally spread. 

The scale highlights the wide and logarithmically spaced range of typical line locator signal frequencies, showing how lower and higher frequencies are distributed across the spectrum. These frequencies are used in locating buried lines with varying penetration depth and signal behavior based on frequency selection.

Grounding 

Even the wettest dirt is not nearly as conductive as metal. Still, there is just so much dirt in the ground that electricity usually has no problem moving through it unless it’s very rocky, loose, dry, frozen, or a combination thereof. Attaching one of the transmitter’s leads to the line and the other to the earth via a Ground Stake is usually the most effective and efficient way of applying signal to a line. 

The ground stake connected to the transmitter sometimes causes a bottleneck in the signal circuit. There is a limited amount of dirt touching the surface area of the metal stake, so driving the ground stake as far into the dirt as possible and wetting the dirt around the ground stake can have a positive effect. But use care, you are pushing a sharp spike into the soil; do you know there’s nothing dangerous under there? 

A close-up photo shows a person’s hand placing a metal ground stake into dry, light-colored soil. The person appears to be pressing the stake in vertically by hand, demonstrating a proper method for establishing an electrical ground for signal transmission during underground utility line locating.

Even moving the ground stake from one spot to another can improve signal. It’s best to start with the ground stake a few feet off to one side of the buried line. Avoid placing the ground stake on the far side of any other buried lines in the area to avoid signal bleeding onto those lines. 

Induction 

Directly connecting to a line is preferred, but it’s not always possible. Since signals can “bleed” over to other lines, especially higher frequencies, we can use this to our advantage and “wirelessly” induce signals onto a line. 

By coiling wire, you can multiply the magnetic field and “broadcast,” making it possible to induce a signal to a line below ground that you don’t have direct access to. 

A small orange box labeled “Transmitter” rests above a buried utility line. Orange curved lines radiate downward from the transmitter to the cable, illustrating the inductive broadcast of signal from above ground. This demonstrates how signal can be wirelessly induced into an underground line without physical connection, useful when direct access to the conductor is not available.

Furthermore, creating an inductive antenna in the shape of a loop can more efficiently induce signal onto a line without needing to access the metallic portion. These Inductive Coupler Clamps can be very handy when cables are insulated or protected by plastic conduit. Not only that, but signals can even be safely applied to power lines carrying live voltage or signal cables that are in operation. 

A diagram shows an orange inductive coupler clamp secured around a buried cable. The clamp forms a closed loop through which alternating current (AC) signal lines are shown entering and exiting. This illustrates how signal is inductively applied to a cable without direct contact, often used when the line is live or insulated.

Directly connecting to a line will always give the strongest signal, followed by an Inductive Coupler Clamp, and lastly with a Broadcast Antenna. Keep in mind that it’s more difficult to use lower frequencies when using inductive methods, so you won’t have their long-distance and low-bleed benefits. 

EM Fields 

Locator signals are alternating currents that cause electromagnetic fields to alternatearoundthe lines they travel through. 

A visual representation of electromagnetic fields shows a wavy blue line symbolizing an alternating current flowing through a cable. Surrounding the cable are spiral-shaped blue lines (magnetic fields) with orange curved arrows looping over the top, indicating the directional flow of electromagnetic energy around the conductor. The diagram illustrates how locator signals generate alternating electromagnetic fields detectable by antennas.

This alternating electromagnetic field that an antenna can pick up is strongest nearer to the line and can also get stronger as more signal current flows through the line; hence why it is always best to ground the far end of the cable if you can. 

Receiver Antennas – Cylindrical Coils

A diagram shows a cylindrical coil of wire (receiver antenna) wrapped around a blue rectangular core. Radiating outward from the coil are symmetric field lines in light purple, representing the electromagnetic field that the antenna detects. The image demonstrates how receiver antennas are designed to sense electromagnetic vibrations moving across their windings.

Receiver antennas are essentially small coils of wire wrapped into cylindrical shapes that detect electromagnetic vibrations moving across them.

Peak Antenna

This means the most signal an antenna can receive is when the coil cylinder is oriented perpendicular to the line, as shown above. The “loops” of the magnetic field around the conductor pass directly along the main axis of the coil generating the strongest signal.

A small orange box labeled “Transmitter” rests above a buried utility line. Orange curved lines radiate downward from the transmitter to the cable, illustrating the inductive broadcast of signal from above ground. This demonstrates how signal can be wirelessly induced into an underground line without physical connection, useful when direct access to the conductor is not available.

Null Antenna

If the coil cylinder is oriented 90 degrees so that it is vertically pointed directly at the line above it, there are no magnetic field lines moving along the cylinder, and it receives no signal whatsoever.

A cylindrical coil antenna is shown vertically aligned (parallel) to a buried conductor encircled by blue electromagnetic field loops. A red arrow points toward the cylinder to indicate its vertical orientation. A nearby signal strength meter displays a very low reading with only one green bar, representing minimal to no signal reception. The diagram demonstrates that this "null" orientation causes the antenna to miss the magnetic field loops, resulting in no detectable signal.

If the antenna drifts slightly from this alignment, small amounts of signal will be received, so it is easy to tell when the antenna is pointed directly at the line.

Another Null

Keeping the Peak Antenna horizontal but twisting it around to be parallel with the line will also result in a Null (signal cancellation). This helps determine the direction of the line.

A cylindrical coil antenna lies horizontally and parallel to a buried cable, which is surrounded by blue circular magnetic field loops. Red arrows point outward from the antenna, indicating its alignment with the field. A signal strength meter shows a very low reading with only one green bar, signifying signal cancellation or "null." The diagram demonstrates that this orientation—while horizontal—results in minimal signal pickup due to alignment parallel with the magnetic field lines, aiding in determining line direction.

When using a Line Locator’s Receiver, remember that you may sometimes need to visualize not just the line but the interaction of the antenna with the round field lines around the line. 

Depth/Current 

Since Null antennas are very precise, one can triangulate the depth of a line quite accurately using only a Null antenna. When holding the Receiver vertically, a Null indicates the line is directly below. Finding the Null again at a 45-degree angle creates an imaginary triangle where the distance between the two points on the ground equals the depth of the line. 

A diagram shows a handheld receiver positioned at a 45-degree angle from the ground surface. An underground point labeled “DEPTH” lies directly beneath a vertical line. A dashed diagonal line from the receiver intersects the underground point, forming a right triangle. The horizontal distance on the surface equals the depth of the line, demonstrating how to calculate cable depth by locating a null signal at a 45-degree angle.

Sophisticated Line Locators will have Receivers with multiple Peak antennas stacked upon one another at set distances. With multiple antennas receiving different amounts of signal, the Receivers can compute not only the depth of the line but also the amount of signal current running through it.

receivers with multiple peak antennas can compute the depth of the line as well as the signal current running through it

Buried Markers: Highlighting Points of Interest

Many buried services are non-conductive; plastic gas and water pipes, optical fiber cables, concrete rainwater drains etc. Often these have been installed with “tracer wires” specifically buried directly above them for the past couple of decades, however, earlier ones may not have such aids. Also, when repairs are made do those tracer wires get reconnected reliably? Often not.

For electrical and telephone cables, being able to follow the signal from above ground can tell you the depth and position of the conductor underground but cannot identify where, for example, a buried splice joint is located.

Or for plastic pipelines, even if buried with tracer wire, it’s not good enough to know where a line is located and in which direction it’s going; you may also need to know where an access point to a shutoff valve is or where a repair was performed. Buried passive electronic markers put you back exactly where you need to be and will last as long as the buried assets they’re marking.

Points of Interest

A close-up view of a buried pipeline segment shows a yellow tracer wire and a valve partially exposed in a shallow trench. The wire is coiled and laid near the pipe to assist with future location using a signal transmitter.A blue electronic marker and vertical tracer wire post are installed in dirt, marked by a small orange traffic cone. This setup indicates a buried point of interest, such as a valve or splice, near the surface for easy identification.A deeper excavation reveals a section of blue plastic pipeline with a visible blue electronic marker disk placed beside it. The trench walls suggest a repair or maintenance site, with the marker indicating a key location such as a splice or repair point.

Many points along a utility line are of interest to utility companies or to anyone avoiding damage when digging, which won’t necessarily be locatable with a Line Locator alone:

  • Joints/Fittings

  • Wyes/Tees

  • Curves/Bends

  • Stubs/Ends

  • Depth Changes

  • Material Changes

  • Repairs

  • Valves

Resonant coils

Coming in various shapes, passive electronic buried markers are a clever technology that does not require any battery power but can still be detected multiple feet deep using coils tuned to resonate at specific frequencies when excited by a marker locator from above.

A red circular shell reveals an internal coil labeled “Resonant Coil.” The design illustrates the inner workings of a passive buried marker, which operates without batteries by resonating at specific frequencies when excited by a locator’s magnetic signal.Two side-by-side diagrams show how a locator above ground sends a magnetic signal downward. Below ground, the signal activates a yellow "OMNI MARKER II" placed near a buried pipe. The first panel shows the signal hitting the marker, and the second shows the signal being reflected back upward to the locator. This illustrates how buried resonant coils interact with surface locators to mark key underground locations.

Fields

These resonant coils create electromagnetic fields that give off a hot spot for Marker locators. Some markers need to be placed vertically to ensure a field is directly above (e.g., spike markers), some need to be placed flat (e.g., disk markers), while others are self-leveling (marker balls).

A cross-sectional diagram shows an "OMNI MARKER II" buried below the ground, emitting symmetrical electromagnetic fields above and below. The field creates a “hot spot” detectable by marker locators positioned on the surface.A transparent blue spherical marker is shown with internal components visible. It is designed to self-level regardless of how it lands underground, ensuring the electromagnetic field is consistently oriented toward the surface.

A vertically oriented spike marker is shown inserted into the ground above a pipe.A flat disk-style marker lies horizontally, positioned directly above an underground pipe.A spherical marker ball rests naturally above a pipe, self-aligning for optimal signal detection

Frequencies

There are different tuned frequencies for different color markers, each corresponding to a type of utility or asset:

  • Purple, Non-Potable Water, 66.35kHz

  • Orange and Black, CATV, 77kHz

  • Yellow, Gas, 83kHz

  • Yellow/Black, Fiber Optic, 92kHz

  • Orange, Telephone/Communications, 101.4kHz

  • Green, Sanitary, 121.6kHz

  • Red and Blue, Power (Europe), 134kHz

  • Blue, Water, 145.7 kHz

  • Red, Power (North America), 169.8 kHz

With a little bit of forethought, you can bury passive electronic markers and leave all the clues you need to pinpoint exactly what it is you may come back to search for.

Other Location Methods: From Pseudoscience to Cutting Edge

The vast majority of professional utility locators use transmitter/receiver line locators to do their work, and between line locators and buried markers, you can find just about everything you’d ever need to look for. Still, there are some other “technologies” out there as well.

“Witching” Sticks/Divining Rods

There is no scientific basis for it, and who knows how it began, but over thousands of years, people have believed that Y-shaped or L-shaped sticks would lead them to water, or other types of lines buried in the ground. Many folks today claim to be highly accurate and reliable with “witching” or “divining,” but you won’t find too many Utilities putting their trust in this method of locating.

A person stands on a grassy field holding two L-shaped metal dowsing rods in front of them, one in each hand. The rods are slightly crossed at the center, positioned as if in use for “witching” or “divining” — a traditional but unscientific method believed to detect underground water or utilities.

Metal Detectors

Metal detectors use various technologies that are very helpful in finding buried metal objects of all kinds. Because they find any metals, including random objects, Utility Locators will often use them with Ground Penetrating Radar (GPR).

A person dressed in outdoor work clothes operates a metal detector across a dry, grassy landscape. He scans the ground methodically with the device’s detection coil, likely searching for buried metal objects. The setting suggests fieldwork related to locating underground utilities or objects in a rural or undeveloped area.

Ground Penetrating Radar

A very effective and versatile tool for underground locating, GPR can find lines and objects that are metal or non-metal alike. The reason GPR is not used more often is the combination of being costly and producing data that is difficult to interpret.

A 3D illustration shows a ground-penetrating radar device scanning an underground area. The GPR emits radar waves into the ground, depicted as cones reaching buried objects like pipes or structures. The scan results are displayed in three formats: A-scan (a signal trace), B-scan (a side profile view with layer lines), and C-scan (a top-down image with colored anomalies). The diagram demonstrates how GPR collects and visualizes subsurface data.

Acoustic Resonating Locators (for locating non-metallic pipes like PVC)

A low-cost solution, Acoustic Locators allow users to find lines by ear. They have a limited range but work quite well for short water lines.

A worker in a safety vest and hard hat uses an acoustic resonating locator to scan the ground along a sidewalk near trees and residential homes. The locator device is held vertically and appears to be detecting underground non-metallic water lines such as PVC by sound.

Electrical Resistivity Tomography

One of the most sophisticated Underground Locating technologies, ERT will inject electrical current into the ground and measure variations in the earth’s resistivity, which paints a picture of the underground, from rock formations to groundwater locations to Utility and Infrastructure mapping. This technology is even more expensive and difficult to interpret than GPR while being substantially more difficult to set up.

A composite image illustrates components of an ERT system. At the top, a diagram shows electrodes inserted into the ground in a line, connected to orange data acquisition units. Below, an orange carrying case contains a laptop displaying a colored resistivity map of subsurface layers. Coiled cables, probes, and connectors are arranged beside the case, representing the complex hardware setup required for this underground imaging technique.

Conclusion

Locating underground assets is both a science and an art, at times requiring an understanding of electrical circuits, signal behavior, and field interactions. Whether you’re preventing damage, accessing key points for repair, or mapping buried infrastructure for future use, the right tools and techniques make all the difference. By leveraging the various complementary electromagnetic locating methods, buried markers, and emerging technologies, professionals can efficiently and accurately detect what’s hidden beneath the surface. While some traditional methods persist, modern advancements continue to refine and expand the capabilities of utility locating, ensuring safety, efficiency, and precision in every dig.

electromagnetic line locatorunderground utility locatorburied cable detectionirrigation valve locatorutility locating toolsTempo line locatorUSA utility locating
Back to Blog