Grounding Earth Resistance Test is an important maintenance practice to verify the integrity of the grounding system. It analyses whether the ground system can safely carry fault currents to the earth without affecting the electrical assets. It is vital in preventing electrical hazards. So, how does grounding work, and why is it critical?
Proper grounding is the most fundamental thing in an electrical safety system, yet it is often overlooked. This single aspect can lay a strong foundation for building reliable electrical systems that will last longer.
This blog will explore why grounding earth resistance is important, how it works, and what guides its application. We will understand the basics of proper grounding, the importance of maintaining minimal ground resistance, various ground testing methods, and so on.
Electrical Grounding: An Overview
Electrical grounding, or Earthing, is building a connection or a path between the electrical system and the ground, through which the fault current, such as short circuit, lightning strikes, current surges, etc, flows to the ground without any interference. But, how does it work? A wire (grounding conductor) connects parts like the metal casing of electrical appliances to a ground plate submerged in the earth. The grounding wire dissipates excess electricity to the ground safely. For instance, if a live wire comes in contact with a metal surface, the fault current will flow to the ground, triggering the circuit breakers. This can otherwise be fatal if there is an ineffective grounding system, which can harm people or equipment.
The Importance of Industrial Electrical Systems Grounding
Grounding matters greatly in any context, but even more in industries because the scale, complexity, and risks are so much higher. For example, industrial operations mostly include equipment, motors, transformers, heavy machinery, etc, which run on high-voltage and power. A minor fault caused by improper grounding can result in significant damage. Equipment failures may necessitate the replacement of parts or even the entire unit, resulting in unplanned downtime that can cost anywhere from thousands to millions of dollars. Grounding is essential for standard compliance, and with QHSE policies mandated by law in various industries. Sensitive devices need clean and stable power, and finally, yet importantly, proper grounding is crucial in ensuring personnel safety.
Purpose of Ground Resistance Testing
Ground resistance testing measures how effectively the grounding electrode is connected to the earth. This understanding is vital for identifying potential faults or safety risks. Regular testing helps maintain the system’s performance, aids in preventive or proactive maintenance, and ensures long-term safety and stability of the grounding systems.
The key purpose of an effective grounding system is to keep people, equipment, and property safe from electrical threats such as electrocution, equipment crash, or fire. Proper installation and maintenance of the grounding system are essential to ensure a reliable and effective electrical system.
Multi-Grounded Systems
A multi-grounded system is a network of interconnected grounding points providing numerous paths for channelling fault currents. The main objective is to determine the effective ground resistance of the connected grounding points without interference from parallel ground paths. Analysing the resistance of this network of grounding points is slightly more complex than measuring the resistance of a single-point system.
Testing the ground resistance in a multi-grounded system needs proper planning, appropriate testing tools, knowledge of the system’s configuration and careful execution. Implementing ideal measurement techniques will ensure reliability and confirm that the grounding network will always work effectively.
Clamp-On Test Method
A non-invasive technique to evaluate the grounding resistance using a special clamp meter. Traditionally, the ground electrode was disconnected to conduct measurements, but with the advent of this approach, the technicians can measure the system while it remains fully live and operational.
The clamp-on test method is suitable for multi-grounded systems, where isolating single electrodes is usually impractical or disruptive. The clamp meter generates a test signal through a stake and measures the resulting current with the other, allowing it to calculate the loop resistance between the ground electrode and the earth through the existing grounding paths. This enables accurate and efficient resistance measurements without interrupting power or compromising safety. The clamp-on test method is beneficial in industrial settings, where operations happen around the clock and the equipment remains energised. By minimising unplanned downtime and avoiding de-energising procedures, the clamp-on technique aids in regular maintenance and continuous assessment of the grounding system.
Minimum Grounding Resistance specifics
Maintaining proper grounding is crucial for safety and system performance in network installations. Grounding resistance should ideally be within the range of 5 to 25 ohms, as this allows fault currents to be discharged into the ground. Staying within this range helps avoid system crashes or damage, electrical shocks, and signal interference.
A lower grounding resistance depicts a strong connection to the earth and quick dispersal of fault currents. Regular testing and maintenance of the grounding ensures the resistance value remains within the desired range, especially in changing seasons and soil conditions.
What impacts Ground Resistance?
Several factors, for example, soil texture, moisture content, soil minerals, temperature, etc., influence the grounding resistance. The grounding resistance should be minimal to conduct fault charges into the ground. The following are the general factors affecting the ground resistance.
- Soil Composition and Resistance: Understanding the soil texture and composition is crucial for installing grounding systems. Mineral and salt-rich soils are low resistive and project lower ground resistance. On the contrary, dry sandy or rocky soils have higher resistivity, making the ground resistance high.
- Moisture content: Dry soil is highly resistive and cannot efficiently conduct fault currents. Moist soil conducts fault current more easily. The varying weather conditions can affect moisture and ground resistance in soil. Periodic testing allows for monitoring these changes and helps maintain the efficiency of the grounding system.
- Electrode configuration: The choice of electrode material, such as copper, stainless steel or galvanised steel, significantly affects conductivity and durability. Copper, for example, provides excellent conductivity, while galvanised steel hinders corrosion in various environments. Depth and spacing also play an important role in achieving low ground resistance. Deeper and wider spaced installations between the electrodes result in better current dissipation.
- Mineral content: Mineral-rich soils, like igneous soils, are highly resistive, whereas soils containing ores exhibit lower resistivity. The mineral content in the soil must be evaluated before the grounding system is installed to improve the grounding effectiveness in different terrains.
- Contaminants: The soil contains various substances, minerals, metals, salts, or oil, which can affect the ground’s resistivity. High salt concentrations can significantly reduce resistance, whereas oil can increase it.
- Temperature: Frozen ground has high resistivity when compared to warmer terrain. Temperature fluctuations influence the soil resistivity and the effectiveness of the grounding system. Ensuring regular testing with changing seasons will improve the reliability of the grounding systems.
Analysing these factors and configuring a well-rounded system is essential to ensure a proper and reliable grounding. Regular ground resistance testing and maintenance must be carried out to verify the integrity of the installed systems.
Methods for Earth Ground Testing
Here is the list of commonly used methods for earth ground testing, each suited to individual site and testing requirements:
- Stakeless Testing: Stakeless or the clamp-on testing measures the ground resistance quickly without disconnecting the ground system. A clamp meter forms a test signal and measures the current and the voltage to find the resistance.
Stakeless testing is ideal for multiple ground rods testing in a system, or if disconnecting the system is difficult. For instance, in industrial plants where operations are continuous, halting operations to conduct testing may not be possible. Fluke 1630-2 Earth Ground Clamp is a tool that could do the job by providing temporary ground stakes.
- Fall-of-potential Testing: This technique, also called the three-point test, is generally used as a reliable approach for assessing the grounding resistance. Fall-of-potential testing involves a ground electrode, a current electrode and a potential electrode.
A controlled current is applied between the ground electrode. The voltage drop is measured between the ground and the potential electrodes. This method is beneficial for configuring new grounding systems, periodic testing in large installations and understanding effectiveness after big electric work or lightning strikes.
- Selective Testing: Selective testing focuses on specific details of components or sections of a grounding system, providing highly accurate resistance measurements. It is similar to the fall-of-point method, but uses a different conductor to avoid interference.
Fluke’s 1625-2 GEO is designed to bring precision to the testing, isolating and analysing the test current on individual electrodes. This gives a detailed measurement of the performance of the complex grounding system.
- Soil Resistivity Testing: Soil resistivity testing determines the soil resistances to understand the feasibility of the grounding system. It involves carefully placing probes equally spaced into the ground and determining the current and voltage at various spacings. This method gives data essential for setting grounding systems to maintain resistance levels within the safe range across different soil conditions.
Soil resistivity expressed in ohm-metres (Ω·m) varies depending on soil composition and moisture level. In highly conductive soils, values may be as low as 1 Ω·m, while dry or rocky terrain can show resistivity levels exceeding 10,000 Ω·m. A proper evaluation ensures the installed system maintains ground resistance within the thresholds (generally below 25 ohms) to facilitate easy fault current flow and improve electrical safety.
How to Improve Ground Resistance?
Developing a proper ground resistance system requires a structured approach to dissipating fault currents, ensuring safety, and optimal performance. Below are several important steps to consider for improving ground resistance.
Step | Explanation | How to Apply |
| Increase rod thickness | A thicker rod increases the contact surface area with the soil, allowing for improved electrical flow and reduced resistance. | Choose rods with a greater diameter to boost grounding efficiency. |
| Install multiple grounding rods. | Spreading the electrical load across multiple rods improves the system’s ability to conduct electricity effectively. | Place several rods in a straight line or a triangular layout, maintaining proper spacing as per recommended standards. |
| Extend the rod length. | Longer rods reach deeper earth layers, providing more conductive paths and improving grounding performance. | Use extended rods to tap into deeper, more conductive soil regions for better grounding. |
| Modify the soil to decrease resistivity. | Enhancing the soil’s conductivity lowers ground resistance, improving the effectiveness of the grounding system. | Improve soil properties by: – Using salts or compounds: Add calcium chloride or magnesium sulfate agents. – Applying conductive gels: Use gels specifically made to reduce soil resistance. – Watering: Keep soil moisture consistent through regular watering. |
| Upgrade the quality and type of electrode | Utilising superior materials improves electrical conductivity and extends lifespan. | Use premium materials such as copper or high-quality galvanised steel for manufacturing rods. |
| Enhance electrode positioning and layout | Proper arrangement and location help achieve more efficient grounding. | Adhere to recommended spacing and depth standards; place electrodes in highly conductive soil. |
| Conduct routine checks and maintenance | Regular inspections help maintain consistent grounding performance. | Frequently examine electrodes, their connections, and soil conditions; promptly address issues like rust or wear. |
What Is a Ground Earth Resistance Tester?
A grounding resistance tester is a crucial tool to measure the resistance of electrical grounding systems. It helps ensure the fault currents are safely diverted from equipment and people, guaranteeing safety and dependability. Typically using 3-point or 4-point test methods, this tool can measure resistance ranging from a few ohms to higher values. Ground earth resistance testers are essential for periodic inspections, maintenance, and compliance with grounding standards.
Earth Ground Resistance Testing from Ocean
Earth Ground Resistance, or earthing resistance testing, is critical for the safety and integrity of electrical assets. A reliable grounding system redirects the excess surge or fault current into the earth without causing physical threats to people, equipment and structures.
Periodic testing, maintenance and adhering to safety standards improve the effectiveness of ground resistance testing. It is essential to have a clear understanding of the aspects influencing the resistivity, the soil composition, changing demands and technology to successfully implement and execute the reliability of the ground earthing system.
Ocean, the leading engineering company in Oman, provides the most modern ground resistance testers to ensure high precision and reliability. Our expert engineers and technicians follow stringent practices to meet the quality standards. We employ earth ground testers from renowned manufacturers like Fluke Reliability, fostering the idea of best quality to sustainable solutions.
For more information on ground resistance testing, electrical switchgear safety, cable testing, and condition monitoring services, contact us to discover how Ocean can enhance the reliability of your electrical systems and machinery.