Openly identifying the technological challenges faced by private utility locators is probably not the most recommended approach to marketing a business. But frankly, it’s solving these problems for our customers that makes our job fun. Why do these challenges exist? There are two key elements to understanding how utility locating works, and thereby better understand the limitations of the technology. They are knowing what impedes the flow of electrical current, and how electromagnetic fields behave. Why? In reality, underground utility locators do not actually locate underground utilities. They locate electromagnetic (EM) fields that rise above the Earth’s surface and are produced when alternating electrical current flows on a utility.
Like gravity, EM fields are a fundamental law of nature. Whenever alternating current flows, EM fields are produced perpendicularly to the flow of that without interference, the electromagnetic field will be round in shape. When the peak of that round field rises above the ground surface, it can be easily detected, and will be centered directly above the underground utility. At properly spaced intervals, the technician will mark the location of the peak along the route of the utility using a dot of paint. Subsequently, line segments of paint are used to virtually join the dots together. The industry term used to describe this process is known as “horizontally designating” an underground utility.
The equipment used to search for utilities consists of two parts, a transmitter and a receiver. The preferred method of locating a utility is to create an electrical circuit using the target utility as an antenna that will carry the current along its entire route. There are two leads connected to the transmitter, and one lead is directly clamped onto the utility, typically via a surface feature of that utility, and the other lead is clamped to a grounding rod which provides a return path for the current and thereby completes the circuit. A separate hand held receiver is then tuned by the technician to the frequency of the applied current, and used to locate the peaks of the electromagnetic fields along the utility. Collectively, these tools are known as cable and pipe locating equipment, and is the optimal tool for finding metallic underground utilities.
While there are many other challenges that exist with private utility locating, at least one of these five common challenges exists on virtually every job site:
Utility Depth - Technically speaking, electromagnetic fields expand indefinitely throughout space, however they degenerate as they move further away from their original source. Their degeneration accelerates even further as they pass through resistance. Because soil is a conductor, the electromagnetic fields attenuate as they pass through it. Similar to a radio wave’s inability to reach your car’s antenna as you pass through a tunnel, depending upon the depth of a utility, it is possible for the electromagnetic field to never reach above the ground surface.
Utility Composition - The most obvious and widely known limitation of electromagnetic pipe and cable locating is that it cannot locate plastic, terra cotta, and other non-metallic utilities. This is simply because electrical current will not flow along non-conductive material. The lesser known challenge, however, falls under the same principle. Whenever an underground utility contains non-metallic joints, connectors, or is significantly corroded, it will impede the flow of current or even cause a “break” in the circuit. If current is not flowing, EM fields will not emit from the utility, rendering it non locate-able with standard cable and pipe locating equipment.
Non-Insulated/Poorly Insulated Utility - Current will travel back to the transmitter through the soil if the surface area of a metallic utility comes in contact with the surrounding soil, current will be lost as it travels along the utility through the soil and back to the transmitter. The greater the surface area that comes in contact with the soil, the greater the loss of current. For this reason, insulated utilities are typically easier to locate as they are able to carry current with minimal loss as it moves along the cable. EM fields will be stronger at longer distances along insulated utilities over non-insulated utilities. Deteriorated insulation causes a similar problem. If at any point the metal comes in contact with the soil, current will travel back to the transmitter through the soil. A significant loss of current will occur beyond that area, making it more difficult to locate the rest of the utility. Less current results in weaker EM fields.
Proximity to Other Buried Utilities - Remember the principle of “electricity follows the path of least resistance?” Instead of the current returning to the transmitter through the soil, at times, the path of least resistance will be along a nearby underground utility. The current flowing on the nearby utility will produce its own electromagnetic field, oscillating at the same frequency as our target utility. As the name suggests, electromagnetic fields are magnetic. Similar to bar magnets, EM fields have the potential to repel or attract one another. In either case, the interaction of the two fields cause distortions to the shape of the target utility’s field, and the peak will no longer be directly above the target utility. In some situations, nearby, parallel utilities can produce electromagnetic fields whose attraction can be so strong that they create a single electromagnetic field. No longer indicating the presence of multiple utilities.
Commonly Bonded Utility - Common bonds are points at which multiple utilities are grounded together in order to safely divert any high voltage electrical surges to the earth. When utilities are commonly bonded together, electrical current will flow on every utility that is connected to the electrical ground. Technicians are not able to program the transmitter to only energize the target utility. Therefore, if the common bond cannot be broken, the current cannot be isolated to flow only on the target utility. Since cable and pipe locating equipment cannot tell a technician the utility type they’re locating, it can make it more challenging to know whether or not they are on their target utility.
How are theses challenges solved? Any experienced underground utility locator will tell you that the challenges presented here can be overcome simply by making adjustments that are typically related to the “transmitter” component of the equipment. It was renowned scientist Michael Faraday who, in 1831, discovered principles of electromagnetic induction and that changes in electrical current will produce corresponding changes in the magnetic field. To solve complex locating problems, a technician will need to find creative ways to create an electrical circuit on the target utility, or alter the flow of current on the utility, so that it produces an EM field whose peak is strong enough to reach above the Earth’s surface and is directly above the target utility. Some examples are changing the frequency of the current, using electromagnetic induction methods of applying current, increasing the size or location of the ground antenna, or attaching the second lead to the far end of the utility instead of the grounding rod.
Since the equipment is not capable of making these changes to itself, it stands to reason that private utility locating technicians may be the ultimate limitation, and without the proper training and experience, this limitation can be impossible to overcome. Even still, there are other challenges that cannot be solved with cable and pipe locating equipment alone. That’s why other technology and equipment exist, like ground penetrating radar, duct rodders, sondes, etc. and should be required on all job sites where every utility needs to be found.
For Master Locators, every technician is trained to deploy a minimum of three different technologies when searching an area for all utilities types. Each one designed to address the limitations that would exist if they stood alone. This may mean that our technicians go through a longer certification process than most, but it’s one of the ways we are able to achieve the highest value for our customers.