Understanding the Unlocatable: Navigating the Limits of Utility Locates

When it comes to underground utilities, there's a hard truth many clients overlook, not everything can be located with standard locate methods. This reality often comes as a surprise, especially to those who have relied on quick scans or induction sweeps that gave them an "all clear."

In the early days of my career in the 1990s, I saw firsthand how limited those methods could be. Back then, we’d often rely on a simple passive signal scans or a quick induction sweeps. The results were often misleading, and I had my share of incidents where something hidden or non-conductive was struck.

That experience taught me an invaluable lesson. Instead of relying on shortcuts, I began thoroughly mapping each private property site. If we were only working in a small section of the property, I needed to know where everything was, even if the appurtenance for a utility line was on the opposite side of the building. I wanted to account for every buried facility, and more than once, that approach saved my bacon. I’d locate gas lines, communication cables, street lights, water lines, identify sewer invert directions, and even locate sewer lines when needed. This comprehensive approach gave our clients a true underground map and greatly reduced the risk of unexpected hits.

But even with the best technology and the most diligent process, there are still some utility lines that simply can’t be detected. For example, open-ended cables that aren’t grounded or lines made of non-conductive materials, can remain invisible to electromagnetic locate equipment. In other cases, the soil composition, such as clay and silt, can eliminate the effectiveness of ground penetrating radar.

Example of Unlocatable Communication Lines

These photos show a security and public address tower equipped with cameras and speakers. Despite being in service, the communication cables for this tower could not be located using standard electromagnetic locating equipment.

In this case, the communication cables were open-ended and unpowered, with no termination access inside the building. Without a continuous metallic path from one end to the other, or a return path to ground, the locator’s transmitted signal could not travel through the cable. Clamping a transmitter around a single open-ended conductor simply induces a signal locally, but without a complete circuit, that signal rapidly dissipates and becomes undetectable even a short distance away.

Additionally, if portions of the cable are non-metallic (such as fibre optic segments) or shielded in a way that prevents coupling, the electromagnetic signal will not propagate. This combination of factors made the cables effectively invisible to EM locating equipment.

This is a textbook example of why visual inspection, site mapping, and clear communication with the property owner are essential when planning excavation — especially when service points or terminations are inaccessible.

What we do is identify these limitations and communicate them clearly. In the example shown above, the photo captures a tower equipped with cameras and speakers. The communication lines run between this tower and the building’s communications room, which houses all the equipment. These lines could not be traced using standard locating methods. In situations like this, we designate the area between the tower and the building as a Critical Zone. We might not be able to pinpoint the exact path of the line, but we can advise the client to use hand digging or vacuum excavation within that zone. This ensures they understand exactly where extra caution is required before breaking ground.

The key takeaway is that a proper locate isn’t just about producing a map or giving an “all clear”, it’s about understanding and respecting the limitations of the tools we use. Clients who appreciate this are far less likely to face unexpected surprises.

If you want to learn more about the limitations with locate equipment, and what locate technicians can and cannot do, take Know Before You Dig – Private & Public Utility Infrastructure Awareness training created by your truly and Own Your Safety Inc.

In next week’s post, we’ll take this a step further and show you exactly how to define Critical Zones for water and sewer lines on private property when those lines can’t be located. We will show you scenarios, diagrams, and the safety measures that every excavator should follow before breaking ground.