Rod Earthing – Which Type Should You Use?

For safe electrical earthing and bonding, the choice of an appropriate Rod Earthing is pivotal for ensuring safety, reliability, and longevity of electrical installations. Rod Earthing  serve as a crucial component in grounding systems, providing a path for fault currents to safely dissipate into the earth. This blog delves into the earth rod specifications, comparing pure copper, copper bonded, and stainless steel rods to help you in selecting the most suitable option based on specific requirements.

Earth Rods or Rod Earthing have various functions & advantages. Their fittings are used for effective earthing systems in overhead and underground electricity distribution and transmission networks. These are used singularly or in groups to:

• Form a ground field.
• Create a path to dissipate static discharge voltages (lightning or other forms) to the earth.
• Provide the required interface to ground in all soil conditions and provide high-fault current capacity on low, medium, and high voltage substations, towers, and power distribution applications.

 

Rod Earthing Functions

Human Protection

Electrical equipment has exposed or covered metal parts with protective insulation. Earth rods protect humans from direct or indirect contact from exposed metal parts with damaged insulation even after the insulation wears off.

Protection to LV Installation

Reduces common-mode disturbances external to the LV installation, for example, 50/60 Hz overvoltage in the event of:

• MV/LV transformer breakdown
• Overvoltage due to lightning

In the case of LV breakdown, the potential of the power system rises concerning the earth. Without grounding, it creates a risk for the equipment and workers in the TT system. Apart from a lightning strike, the power system encounters pulsating overvoltage on all live conductors. It may result in high EMC risk; therefore  Earthing systems like Rod Earthing is required. Let’s understand it’s types in detail.

Types of Rod Earthing

The effectiveness of an earth rod is  influenced by its resistance and conductivity properties. These characteristics determine the rod’s ability to carry fault currents safely to the ground, a critical aspect of any grounding system. Let’s explore these properties in detail for pure copper, copper bonded, and stainless-steel earth rods.

Pure Copper Earth Rods

Pure copper earth rods set the standard for conductivity in grounding applications. Copper’s inherent electrical properties allow these rods to exhibit the lowest resistance among the three types, making them exceptionally efficient at conducting electricity. This high conductivity translates to a superior fault current carrying capacity, ensuring that electrical surges are effectively dissipated into the earth with minimal resistance.

Pure copper earth rods are ideal for environments where electrical conductivity is paramount. Their ability to handle high fault currents makes them suitable for industrial settings, high-voltage installations, and areas prone to lightning strikes. The premium electrical performance of pure copper rods, however, comes at a higher cost, both in terms of material and potential theft risk due to their value.

Copper Bonded Earth Rods

Copper bonded earth rods offer a compromise between the high conductivity of pure copper and the durability of other materials. These rods consist of a steel core with a copper coating, combining the strength of steel with the conductivity of copper. While their conductivity is moderate compared to pure copper, it is significantly better than that of stainless steel rods. This balance makes copper bonded rods a versatile choice, offering good fault current carrying capacity at a more economical price point.

These rods are well-suited for a wide range of applications, from residential to commercial and light industrial settings. They are particularly appealing in scenarios where cost considerations are as important as performance, providing a reliable grounding solution without the premium price tag of pure copper.

Stainless Steel Earth Rods

Stainless steel earth rods prioritize durability and corrosion resistance over pure conductivity. With the highest resistance among the three types, these rods have the least fault current carrying capacity. However, what they lack in conductivity, they make up for in longevity and resistance to harsh environmental conditions. Stainless steel’s non-corrosive properties ensure that these rods maintain their integrity over time, even in settings prone to moisture, chemicals, and salt.

Stainless steel rods are the material of choice for harsh or corrosive environments, such as coastal areas, chemical plants, and locations with high soil salinity. Their extended lifespan and minimal maintenance requirements make them a cost-effective solution over the long term, despite their higher initial resistance and lower conductivity.

Watch this video to understand different types of  Earth Rods

Design of Rod Earthing

In grounding systems, a metallic object is seamlessly integrated with the earth through an earth electrode system, ensuring electrical safety and stability. The efficacy of this system, characterized by the strength of the fault current, is directly influenced by the type of Earthing system deployed. Adherence to safety standards, such as maintaining contact voltage below 50 V as recommended by UL for AC systems, is paramount. This involves connecting the exposed metallic parts of electrical equipment to protective earth (PE) conductors, which in turn are linked to the earth, establishing a comprehensive Earthing arrangement.

Guidelines set forth by the National Electric Code (NEC) mandate that grounding electrodes exhibit a resistance-to-ground (Earth) of less than 25 ohms, explicitly prohibiting the use of aluminium electrodes in grounding, as per standards 364 and NF C 15-100 (1923).

To ensure safe, dependable, and enduring Earthing protection, earth rods must be meticulously selected based on the corrosive nature and electrical conductivity of the soil, alongside the rod’s mechanical durability to endure the rigors of installation without deformation, particularly at the head when driven into the ground.

For achieving the requisite depth and maintaining enduring electrical connectivity, copper couplers are utilized to link multiple earth rods together. This technique allows for reaching deeper, lower resistivity soil layers, enhancing the grounding system’s effectiveness.

Vertically-driven earth rods are recognized as the most efficient, particularly favored in compact substation areas or in conditions of low soil resistivity.

The performance of an earth rod is verified through a current probe encircling the conductor leading to the earth or ground rod. Any discrepancy, such as leakage current, is readily identified, indicating a potential flaw in the grounding system. This method underscores the critical nature of rigorous testing to ensure the grounding system’s integrity and functionality.

 

Types of Earth Electrodes

Rod Earthing

As discussed above, these rods are standard driven rods or copper-clad rods used as grounding devices. They are made of relatively low carbon steel, are 8 to 10 feet long, and have 254 Microns as per UL Standard. NEC mandates that that driven rod must be at least 8 feet in length, and it must be in direct contact with the soil.

Grounding Plates

These thin copper plates are placed in direct contact with the earth under poles or supplementing counterpoises. NEC advises that these plates should have at least 2 ft. of surface area exposed to the surrounding soil. The ferrous materials must be at least .20 inches thick. The non-ferrous materials (copper) need a thickness of only .060 inches. These should be buried at least 30 inches below grade level. The surface area of grounding plates increases over a driven rod; the zone of influence is relatively small. The zone of influence of a grounding plate can be as small as 17 inches.

Ufer Ground or Concrete Encased Electrodes

These electrodes channelize the faulty current to the earth through the concrete. These foundations are used when the concrete of the structure is in direct contact with the earth, i.e. there are no plastic barriers. One example is the concrete surrounding ammunition bunkers, building foundations. For building foundations, they consist of any concrete-encased electrode like the rebar (0.500 inches in diameter) or a wire or wire mesh in the concrete. There would be a direct metallic connection from the service ground to the rebar buried inside the concrete. The process depends on the conductivity of the concrete and the large surface area, which usually provides a grounding system to handle very high current loads.

But as per NEC guidelines, they use 20 feet (minimum) long No. 4 AWG copper wire that is encased in a 2 inches (minimum) of concrete; the zone of influence is not increased. So the resistance to the ground is only slightly lower than the wire without the concrete. As concrete retains a substantial amount of water, the moisture in it superheats and expands rapidly. A high current may cause steaming creating cracks. Cracked concrete pieces do not let the copper wire contact the surrounding soil. It increases the resistance-to-ground of the electrode. Therefore, relatively small electrical faults may damage the electrodes, which is risky to the building.

Besides, Ufer groundings are impossible to test unless there is a fault with a high current. Isolating the concrete slab to test resistance-to-ground is nearly impossible. Here’s a detailed blog on Ufer Grounding.

Water Pipes

Water pipes with plastic insulators are in use as grounding electrodes for a long time. Plastic insulators are used usually by city water departments in pipelines. It prevents the flow of current and reduces the corrosive effects of electrolysis. Also, the plastic or tar coating makes them unreliable. Therefore, NEC guidelines mandate that at least one additional electrode must be installed with the water pipe.

Thank you for reading the blog, Axis is a leading manufacturer and supplier of Earthing and Lightning Protection Solution. To get a quote or to talk to our industry expert visit our contact us section.

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