When it comes to selecting a ground rod, engineers must avoid a one-size-fits-all approach. Different factors—material, soil resistivity, location, facility type, size, among others—play into the overall efficiency and service life of both the ground rod and overall grounding system.
Below we provide key considerations for ground material selection and then compare the most common types.
Potential Factors to Ground Rod Material Selection
Once the soil and environmental conditions have been assessed, materials should be compared according to their individual performance in the following areas, and their compatibility with your unique situation.
Corrosion Resistance: Perhaps most influential to the service life of the ground rod, assess materials based on their inherent corrosion resistance to your soil conditions. Depending on salt, sulfate content or pH, different materials will work best.
Cost: The upfront cost of one ground rod material should not be compared directly to another material. Rather, the lifecycle value of two materials should be compared. If one rod is $20 and another costs $30 but the cheaper rod will only last one-quarter as long as the other, the more expensive rod is the more cost-effective choice.
Ease of Driving into the Earth: This relates to the material’s strength and the soil’s hardness. If a ground rod is bent or broken when driven into the ground, it may be more likely to corrode. Also, a damaged ground rod will less reliably provide the most direct path for electrical currents to travel and dissipate.
Copper Theft: Some have called copper theft an “epidemic” at different times, and ground rods are not exempt. Depending on your proximity to a population and local theft rates, consider the potential cost of replacing stolen copper ground rods and the immediate system inefficiency it would cause. Typically theft is related to conductors and other above-grade materials, but ground rods are not completely exempt.
Conductivity: As a ground electrode, a ground rod’s purpose is to provide a physical connection to the earth and provide the most direct path for a current to dissipate. Though conductivity differences are typically minimal between the most common materials, certain conductivity levels are required in specific regions and are important for providing that path to ground.
Comparing Common Ground Rod Materials
Copper-bonded and galvanized ground rods are the two most common types of ground rods throughout most of the world. In certain situations, stainless steel or solid copper ground rods may be installed to meet unique environmental conditions. What is commonly overlooked, however, is the life expectancy of the grounding electrode system compared to the life expectancy of the facility.
Copper-Bonded Ground Rods
Copper-bonded steel ground rods are manufactured through a continuous electro-plating process of copper over a steel core, resulting in a permanent molecular bond between the two materials. This should not be confused with copper-clad steel, as that method is no longer employed for ground rods due to a less reliable bond.
- Advantages: Based on the extensive National Electrical Grounding Research Project (NEGRP) by the National Bureau of Standards, rods with 10 mils of copper will likely perform well for 40 years or more in most soil types. It offers the best annual cost advantage of available materials in most situations.
- Disadvantages: Though copper-bonded ground rods exhibit great corrosion resistance in most environments, under highly unique environments high in salts or corrosive chemicals, an upgrade to stainless steel may need to be made.
Stainless-Steel Ground Rods
Stainless steel is not a naturally occurring metal like copper, but it is an alloy of iron with at least 10.5% chromium and varying amounts of carbon, silicon, manganese and sometimes other materials. A stainless steel ground rod is created with a layer of oxide to help prevent corrosion.
- Advantages: Due to the oxide layer, stainless steel is more resistant to corrosion than copper. Stainless steel is also very strong and unlikely to bend or break when installed, even in rocky soil.
- Disadvantages: The primary disadvantage of stainless steel is cost. It is primarily used in industrial processing, saltwater environments and other highly corrosive situations when greater corrosion resistance and/or strength is needed. It is also less conductive than most alternatives, although the variance is relatively small in reality.
Solid Copper Ground Rods
Solid copper ground rods are very corrosion resistant (except when faced with salts) and are also very conductive. However, you will rarely see solid copper outside of the Middle East or similar environments because copper is a ductile, soft metal that often bends when driven into soil other than sand.
Another issue with solid copper is that it is extremely expensive when compared to alternatives. Also, copper theft can be a huge problem for solid copper, making it costly to replace these ground rods.
Galvanized Steel Ground Rods
Zinc-coated steel ground rods are on the opposite side of the cost scale from solid copper ground rods. These are the cheapest of common ground rod materials, offering limited reliability in the long term.
The problem, according to the NEGRP corrosion study mentioned previously, is that galvanized rods with 3.9 mils of zinc should only be expected to last for 10 to 15 years reliably (compared to 40 or more years for copper-bonded rods). Salts, in particular, are likely to corrode the zinc coating.
Because a lightning protection system is one that installers would prefer to “install and forget,” only 10 or 15 years of performance is poor. Constant replacement, including material and labor costs, can cause long-term issues and costs for galvanized ground rod users.
Dig Deeper on Grounding Systems
Choosing the appropriate ground rod is only one important factor in a comprehensive grounding system. View the ERICO Grounding, Bonding and nVent ERICO Cadweld Solutions Guide for an overview of facility electrical protection and where grounding fits in.
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