Grounding Rods - How They Work

Figure 1: Ground rod for mobile objects like vehicles

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Ground rods are critical in electrical grounding systems, providing a safe pathway for excess electricity dissipating into the earth. These rods protect people and electrical equipment from potential harm caused by lightning strikes or power surges. This article explores the design and installation of ground rods.

Table of contents

What is a grounding rod

A ground rod (Figure 2 labeled E) is a long metal rod driven into the ground to provide a path for electrical current to disperse into the earth. When a fault occurs, such as a lightning strike or a malfunction in the electrical system, the excess electrical energy needs a safe path to dissipate. A grounding rod helps to prevent the dangers associated with static discharge voltages, such as lightning, thereby reducing the risk of harm during storms. It is connected to the electrical system's service panel via a grounding wire (Figure 2 labeled F), ensuring a safe path for excess electricity to the earth. Read our grounding overview article for more details on how electrical grounding works.

Note: Earthing spike is a more specific term that refers to a device specifically designed for grounding mobile objects such as vehicles, power generators, and other similar devices.

Figure 2: Electric power distribution system: service wire (A), transformer (B), electric meter (C), lightning rod (D), ground rod (E & I), ground wire (F), electric breaker panel (G), and appliances load socket (H).

Materials

Ground rods can be made from different materials.

• Copper: Copper is typically the most commonly used material for a ground rod. These rods are created by coating a steel core with copper. Copper-clad ground rods have a longer lifespan than those made from other materials.
• Stainless steel: Ground rods made from stainless steel are expensive but highly corrosion-resistant. Therefore, it is ideal for environments with high salt content.
• Galvanized steel: Galvanized steel ground rods are produced by applying a protective zinc coating to a steel base to guard against rust. These represent a more economical alternative among ground rods, though they do not match the reliability of copper options. Factors such as salt exposure can erode the zinc layer, resulting in an estimated service life of about 15 years, significantly shorter than the approximately 40-year lifespan of copper ground rods.

How to install a ground rod

Materials required

Proper selection and usage of equipment and materials are crucial for a safe and successful ground rod installation.

• Ground rod: The primary grounding element
• Earth pit or inspection chamber: A protective housing that attaches to the ground rod, shielding it from the environment and facilitating future maintenance and inspections.
• Ground rod clamp: A component designed to affix the ground rod within the earth pit or inspection chamber. Often constructed from copper or similarly conductive material, the clamp ensures a secure connection with minimal electrical resistance.
• Earth-enhancing compound: A material that enhances the soil's electrical conductivity and decreases ground resistance. This compound is typically spread around the ground rod to boost the grounding system's performance.
• Shovel or post-hole digger: A shover or post-hole digger is necessary to dig the hole the rod will go into.
• Additional tools and materials might also be needed, such as a rod-driving hammer and high-conductivity couplers for extending the ground rod.

Figure 3: Inspection pit for buried earth rod

Installation process

Figure 4: Ground rod installation: ground wire (A), ground rod (B), control cap (C), access well (D), and ground enhancement material (E).

1. Location selection: Ensure the location is clear of underground utility lines to prevent any damage during installation. This site should be chosen based on various considerations outlined in the grounding system design.
2. Assessing soil resistivity: Evaluate the soil's resistivity and consider any necessary soil treatments. The higher the soil resistivity, the less effective the grounding will be, and additional rods or deeper penetration may be required. Depending on the soil's resistivity and the site's specifics, the ground rod may be directly installed into the earth, or an earth-enhancing compound might be used to decrease ground resistance.
3. Hole excavation: Use a shovel or post-hole digger to create a hole for the ground rod. This hole must be sufficiently deep to drive the rod at least 8 feet (2.45 m) below the surface. Typically, a hole with a diameter of 120 to 150 mm and a depth of 2.4 m is adequate for inserting the ground rod, although this may vary based on the rod's size.
4. Rod insertion: Position the ground rod in the prepared hole and drive it into place with a hammer or sledgehammer. Ensure the rod is driven straight to guarantee effective grounding. All packaging should be removed from the rod, and the pointed end should be oriented downward. After installing the rod, connect a grounding wire to its top using a grounding clamp. This wire should extend to the electrical panel or another grounding junction.
5. Using the grounding clamp: Extend the grounding wire to the electrical panel or an alternate grounding point and fasten it securely with the appropriate grounding clamp (Figure 5).
6. Applying earth-enhancing compound: Mix the earth-enhancing compound (Figure 4 labeled E) with water to create a slurry as instructed by the manufacturer. Thoroughly pour the slurry into the hole to ensure complete filling. Without a ground-enhancing compound, the hole may be refilled with the excavated soil. If a compound is used, allow it to cure or set within the hole. The grounding site is then ready for connection use after 1-2 days post-installation once the resistance value has been checked.
7. Installing ground pit/inspection chamber: Install the ground pit or inspection chamber (Figure 3) over the ground rod to offer protection against environmental elements and simplify future maintenance and inspections.

Figure 5: Connecting the grounding wire to the rod using a clamp

Ground rod installation requirements

Ground rod sizing

• Length: When installed vertically, the ground rod must be driven at least eight feet (2.45 m) deep into the soil, meaning the length of the rod extending below the ground surface should not be shorter than eight feet from the surface. This ensures that the rod is in contact with moist soil, which has lower resistance than dry soil. Grounding rod sizing regulations necessitate that the standard length for residential use is usually 8 feet, while for commercial or industrial applications or in areas with high soil resistivity, longer rods may be required for effective grounding.
• Diameter: Common diameters for ground rods range from 1/2 inch to 3/4 inch (15 - 23 cm). Larger diameters have a lower resistance to earth but are more expensive and more difficult to drive into the ground.

Other considerations

• Soil conditions: Soil resistivity plays a significant role in the effectiveness of a ground rod. In rocky or very dry soils, achieving an 8-foot depth for grounding rod may be challenging, and alternative methods like horizontal installation or using multiple rods might be necessary. Read our article on ground plate vs rods for different soil types to know more about how various soil types affect the selection of ground electrodes.
• Placement: While there are no exact rules for placing a ground rod, it is advisable to position it at a minimum distance of two feet from any building structure to prevent potential disruptions. Installing the ground rod near the home's electrical panel is also recommended. The ground rod location should be accessible and provide sufficient space for easy installation.
• Tools: The ground rod should be driven into the ground using a hammer or a driving rod. Do not use a digging tool, as this could damage the rod.
• Connection to the grounding wire: The ground rod must be connected to the electrical grounding system of the building or structure using a grounding conductor. The grounding conductor must be at least 8 feet long and made of copper or galvanized steel.
• Multiple rods: The total grounding system design might require more than one ground rod for adequate grounding. When multiple rods are used, they should be spaced at least 6 feet apart, according to the NEC.

FAQs

How deep should a ground rod be?

A ground rod should be driven into the ground to a depth of at least 8 feet (2.45 meters).

How far apart do ground rods need to be?

Ground rods should be spaced at least 6 feet (1.83 meters) apart.

Can rebar be used as a grounding rod?

Rebar is steel reinforcement used in concrete to provide strength. The rebar can be used as a grounding rod but is more prone to corrosion.

The purpose of a grounding system is to protect people, structures and equipment, and to ensure maximum safety from electrical system faults and lightning. A vital piece of the system is the ground electrode. The overall system&#;s reliability is dependent on this component. When using a ground rod for the ground electrode, the general performance or conductivity of available materials is minimal, but the service life of each material can vary by decades. In this post, we consider the 2 most important factors to weigh when selecting ground rod material.

Factors to Consider in Grounding System Design

Consider the relationship between expected service life and cost in order to receive the best value from your ground rod. Below, we uncover the top two most important factors to consider before selecting a ground rod material.

1) Corrosion Resistance and Longevity

The expected service life should be the first&#; and most important&#; factor considered when selecting ground rods for a grounding system.

A ground rod&#;s resistance to corrosion is directly related to service life and overall system effectiveness&#; the quicker a ground rod corrodes, the shorter the service life and overall cost will be. Because below-grade products are exposed to significant corrosion threats, the service life between two materials can vary by years or decades. The resistance of a ground rod will significantly increase when corroded and can result in a catastrophic loss of ground over time.

2) Cost

Cost generally comes into play when contractors are attempting to cut costs by using a cheaper material, or balancing cost and corrosion resistance between materials like solid copper and stainless steel. When a grounding rod specification does not reference a specific brand, product or material, a contractor may choose the cheapest allowable ground rod. However, to maximize value and produce the safest, most reliable system for users, that may not be enough.

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 clearly the more cost-effective choice.

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National Electrical Grounding Research Project

To appropriately balance service life and cost when comparing ground rod materials, we can point to established studies from reputable third-party organizations for proof.

In , the Fire Protection Research Foundation established the National Electrical Grounding Research Project (NEGRP), which studied the long-term performance of 18 different grounding electrodes in diverse geographical locations and soil types. It is the most extensive study on corrosion involving copper and galvanized material since a National Bureau of Standards study from -.

Comparing the Service Life and Cost of Common Ground Rod Materials

Common ground rod material selection is based on the corrosion resistance of the rod, balanced with the longevity of the system. Galvanized steel, copper-bonded steel and stainless steel are the most common materials considered for grounding systems in most parts of the world.

Galvanized steel rods are often the go-to material because they are cheap, allowed by the NEC and UL listed. However, in the NEGRP study referenced above, it&#;s been uncovered that galvanized rods are an inferior material choice in terms of service life longevity. Also note that choosing a material based solely on its upfront cost does a disservice to the grounding system&#;s users and their safety, and will likely cost more in the long term.

Copper-bonded ground rods are a major step up in terms of corrosion resistance. The NEGRP found that copper-bonded ground rods last an average of 40 years in most soil types, compared to 15 for galvanized rods. This is a larger return compared to galvanized rods for a marginal initial cost increase.

For certain situations, stainless steel ground rods may be specified. According to the NEGRP, these ground rods offer a service life of around 50 years. In highly corrosive environments&#;such as at industrial plants or salty environments (e.g. ocean beaches)&#;stainless steel outlasts copper-bonded ground rods.

The chart above articulates a clear gap in service life for zinc galvanized ground rods when compared to its alternatives.

To clearly evaluate the value of each material, we can compare each material in terms of annual cost. If we now know zinc galvanized rods may need to be replaced twice before a copper-bonded or stainless steel rod does once, how does that translate into cost?

From a value perspective, stainless steel is the clear loser, explaining why it is only specified when absolutely necessary due to its high initial cost.

When comparing galvanized and copper-bonded ground rods, both copper-bonded products offer an annual cost advantage.

Dive Deeper on Grounding Systems

Now that you know The Pros and Cons of 4 Common Ground Rod Materials and the 2 Most Important Factors to Weigh When Selecting Ground Rod Material, take the next steps and read the:

3 Reasons Engineers Should Choose Copper-Bonded Ground Rods

Download the nVent 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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