It might not seem like it, but tracer wire systems are complex installations.
Everything needs to be connected to each other to create a working circuit. If that isn’t happening, the system is incomplete and will give you a weak or non-existent signal. The products should also be made of high-quality materials that will last for years. Cheap materials have no place in a tracer wire installation. If something goes awry, those materials could be a liability.
It may seem like installing tracer wire is a straightforward process, but that isn’t always the case. We can control the products we use and how we install them, but what about the things we can’t control – like the earth around us?
To the untrained eye, dirt is dirt. But soil resistivity can drastically impact how your underground installation performs.
With that in mind, can you improve the system by altering the soil where the tracer wire is buried?
Your typical tracer wire system works best in low-resistivity situations. However, as we’ve often learned, conditions are rarely perfect.
Soil conditions differ wildly from place to place, so it’s critical to optimize conditions as much as possible to reduce resistivity. Lowering the soil’s resistivity makes it easier to locate underground utilities through the tracer wire system and generates better results.
Low-resistivity soil isn’t always a nice-to-have. Sometimes, resistivity levels can be spec’d into a project, forcing crews to treat it with an additive or find another solution.
However, understanding resistivity can determine:
This information can help you determine the most efficient way of creating a safe, low-cost, and effective tracer wire system.
When we talk about soil resistivity, we’re talking about the soil’s ability to carry electrical currents.
Many materials can carry a current, but some allow electricity to flow much better than others. When we look at soil, its composition will determine how well it allows electricity to move.
If you took a shovel of dirt from the ground and looked at it closely, you’d see a lot of different bits and pieces. Soil contains many materials, including minerals, water, rocks, organic matter, and air. Depending on where the work is taking place, the soil makeup will be different, with some materials being more prominent than others.
Sand, silt, and clay are the most abundant materials in soil across the U.S., but what you’ll see depends on where you are. Silt is commonly found in the Northeast and Midwest, while sand makes up the soil in the Southeast and Southwest. Clay, meanwhile, is a common component of soil in Texas and other gulf states.
The easiest way to think about soil composition is by treating it like a recipe. Though it may be the same base ingredients, the ingredients will change based on the surroundings and what happens to be available.
Several factors help determine the soil’s resistivity. Some are within our control, but others are dependent on the environment, including:
Cold or frozen soil is more resistive, making it harder for electrical currents to flow. Resistance increases quickly once the temperature falls below the freezing point (32F or 0C).
The drier the soil is, the higher its resistance is. Resistance falls as you add moisture.
As the salt content increases, the electrical resistance is reduced.
If the ground is rocky or harder, resistance will be higher. Learn more about the resistivity of different soil types here.
Gas, oil, and metal materials can damage ground rods and eat away at tracer wire, resulting in weak or lost signals.
This is one factor we can control. Ground rods should be installed in moist soil layers because they carry lower resistance than drier soil layers. The ground rod should also avoid rocky or bedrock soil layers because they contain less moisture and will not generate a strong signal.
Although an eyeball test gives us clues to the soil’s composition, there are more accurate ways of measuring overall soil resistivity.
One commonly used soil resistivity test is the Wenner 4-Point Test. This involves driving four equally spaced spikes into the ground in a straight line. Usually, the test takes place as close to the final installation site as possible to get the most accurate reading and results.
After the spikes are inserted, a current is sent from one probe to another through the outer points. As the current moves through the testing system, resistance measurements are taken between each spike and to the same distance underground. For example, if the probes were placed 10 feet apart, the resistivity would be measured up to 10 feet underground.
You might think the measurements will be the same, or at least similar, across the testing sites, but that isn’t the case. Most soil is heterogeneous, meaning components are different across each section of the testing area. During testing, you will receive relative resistivity results that only apply to the section you’ve tested.
On the other end, homogeneous soil compositions feature similar soil composition across the testing area, resulting in less variation across measurements. These situations are uncommon, though.
If the soil has high resistivity, there are a few ways to reduce it naturally. Some are easier to maintain than others.
The first thing you can do to reduce resistivity is to make the soil moist. Adding water will decrease resistivity, but only while the ground is saturated. Consider this a temporary solution to a long-term problem.
Another option is to add salts like magnesium sulfate or sodium chloride to the soil. Salt is a great electrical conductor and adds ions that help move electricity more efficiently. However, salts are another temporary solution that needs to be replenished as they get washed away by groundwater. They may also eventually damage grounding systems.
Coke powder or bentonite clay are other options that can be mixed into the soil to promote better electrical current flow. Bentonite clay is porous and absorbs surrounding water in the ground to swell up several times its size. However, one drawback of the additive is its dependability on moisture and temperature. In hot, dry environments, bentonite dries out, limiting its usefulness.
If installed correctly and using high-quality materials, your ground rods, tracer wire, and other accessories should easily withstand the tests of time.
Although soil resistivity is important, it’s only one piece of the tracer wire puzzle. Kris-Tech’s team of tracer wire experts can explain your options and help you choose a solution to locate your underground utilities for years to come.