Understanding Grounding for WeatherTRAK Systems

Grounding refers to a direct physical connection to the earth. While electrical engineers may use the term "ground" to describe a reference point for measuring voltage or a return path for electrical current, this guide focuses on grounding as a physical earth connection. Proper grounding is critical because lightning energy entering a system can cause serious equipment damage and potential personal injury. 

🚨Improperly grounded WeatherTRAK systems void the warranty. Grounding protects both personnel and your investment in the WeatherTRAK system.

Types of Ground Connections

Two primary types of ground connections are used in irrigation systems.

System Ground: A system's connection to the earth, which terminates at a grounding point (either a single electrode or grounding grid).

Equipment Ground: The connection that a piece of equipment or part of the system has to the system ground.

Ground Resistance Requirements

Ground resistance measures how effectively you've created a connection to the earth. The goal is to achieve the lowest resistance possible. The National Electric Code requires less than 25 ohms earth-to-ground resistance. In the irrigation industry, the ASIC (American Sports Builders Association Irrigation Council) grounding guidelines recommend achieving less than 10 ohms for optimal protection.

Grounding Conductors and Electrodes

To achieve connection to the earth, grounding conductors must be in direct contact with the earth. Irrigation systems use either a single ground point or a grounding grid—a group of conductors connected together. These conductors are buried in the soil with intimate contact with the earth, providing the physical connection needed.

Factors Affecting Ground Resistance

Type and Installation of Electrode

The most important principle is maximizing surface area in direct contact with the soil. The more electrode surface area touching the earth, the better the grounding performance.

Several installation considerations affect ground resistance:

• Ground Rod Mushrooming: When installing ground rods in very hard ground, the bottom of the rod may mushroom, creating an air gap that reduces direct soil contact. This will eventually settle, but may cause higher resistance readings if tested immediately after installation.
• Rocky Soils: Rocky soils are particularly problematic. Similar to inserting a broom handle into a barrel of tennis balls, only small points of the rocks actually touch the electrode, reducing effective contact area.
• Soil Settlement: When installing grounding plates, disturbed soil contains more air space. Allow the soil to settle before testing ground resistance for accurate readings.

Sphere of Influence

Each ground rod or plate has a sphere of influence—the area of earth into which lightning energy will dissipate. The earth can absorb infinite energy without damage, and that energy travels into this sphere.

Ground Rod Sphere of Influence: For an 8-foot ground rod, the sphere extends 8 feet in every direction (equal to the rod length). The total depth of the sphere is two times the rod length (16 feet total), and it extends 8 feet horizontally in all directions from the rod.

Multiple Electrodes: Two electrodes provide double the surface area in contact with soil, making two electrodes always better than one. However, do not install ground rods so their spheres of influence overlap. Overlapping spheres reduce effectiveness.

Wire Path Placement: Install ground rods or plates so wire paths do not run through the sphere of influence. If lightning energy exits the system into the sphere and encounters a wire path, it can jump back onto the system, causing damage.

When installing a three-point ground grid, ensure the ground rods are spaced far enough apart that their spheres of influence do not overlap significantly.

Grounding Plate Installation

For grounding plates, the sphere of influence follows similar principles. A 4-foot by 4-inch grounding plate has a sphere extending 4 feet (the plate length) in the horizontal direction and 4 inches in the vertical direction.

Grounding plates must be installed at least 30 inches deep and below the frost line.

Bonding Connections

The weakest link in any grounding system is typically the bonding—the connections between different points. Connections are critical to system performance.

Connection Types
Three main connection devices are available:

• Clamps
• Split bolt connectors
• Exothermic welds (CAD welds)

All connection types can potentially fail over time due to vibration, corrosion, or mechanical failure, which decreases bond effectiveness. Exothermic welds are recommended as the best option because they are least likely to fail over time.

Annual Inspection: Check all grounding bonds or connections annually to ensure good bonding is maintained. A ground rod installed with 7 ohms earth-to-ground resistance (well below both the 25-ohm requirement and the 10-ohm ASIC recommendation) becomes completely useless if the copper wire is not properly connected to the ground rod with a good bond.

Soil Resistivity

Soil resistivity measures how resistive or conductive the soil is at your site. This factor is outside your control but will have the biggest effect on your ability to achieve low earth-to-ground resistance.

If you have poorly conductive soils or soil with high resistivity, consider amending the soil around your ground point with a product such as Powerset to improve conductivity.

WeatherTRAK Controller Grounding Specifications

Conventional Wire System Grounding

1. Connect the controller enclosure to a good ground. This can be either a system ground or a ground rod installed near the controller.

2. Achieve a grounding connection with less than 25 ohms earth-to-ground resistance.

Two-Wire WeatherTRAK Controller Grounding

Two-wire systems require additional grounding considerations using line surge protectors.

1. Install a line surge protector at the beginning of the two-wire path (within 25 feet of the enclosure).

2. Install a line surge protector at the end of each two-wire leg.

3. Install additional line surge protectors along the two-wire path for every 5 decoders or every 500 feet of total wire, whichever comes first.

4. In areas very prone to lightning, install line surge protectors every 300 feet instead of every 500 feet.

5. Connect each line surge protector to both the two-wire path and your ground point (whether a single point or grounding grid).

6. Install grounding rods or plates so the wire path is not inside the sphere of influence of any grounding point.

7. Ensure the grounding point achieves less than 25 ohms earth-to-ground resistance.

Testing Earth-to-Ground Resistance

The only way to know how effective your grounding is requires measurement. Two methods are available for measuring earth-to-ground resistance: the 62% method (also called a 3-point test) and the clamp-on test. Both require specific devices and proper testing procedures.

ASIC Testing Recommendations

The ASIC grounding guidelines recommend extensive testing schedules:

• Test grounding points after installation
• Test every three months for one year to determine the most critical times of year
• Test every six months during those critical times to ensure good soil contact is maintained

While not part of the WeatherTRAK specification, this is a very good practice to consider implementing into standard maintenance routines.

62% Method (Three-Point Test)

This method uses a three-point ground resistance tester and is a derivative of a fall-of-potential test.

1. Disconnect the ground rod from the service ground by disconnecting the six-gauge copper wire from the ground rod.

2. Connect point X of the ground resistance tester directly to the ground rod.

3. Calculate the distance for point Z by multiplying the ground rod depth by 10. For an 8-foot ground rod, point Z is 80 feet away. For a ground plate, measure the diagonal distance from one corner to the opposite corner, then multiply by 10.

4. Install the probe for point Z at the calculated distance from the ground rod.

5. Take three measurements at different positions for point Y:

• First reading: 72% of point Z distance (58 feet for an 80-foot point Z)
• Second reading: 62% of point Z distance (50 feet for an 80-foot point Z)
• Third reading: 52% of point Z distance (42 feet for an 80-foot point Z)

6. Compare the three readings. If all values are within a few ohms (less than 3% change), calculate the effective earth-to-ground resistance by averaging the three readings.

7. Add the three measurements together and divide by three to get the average.

8. Verify the result is less than 25 ohms (or less than 10 ohms following ASIC guidelines) for acceptable earth-to-ground resistance.

Clamp-On Test

This test uses a clamp-on ground resistance tester and is quick and easy, taking only a couple of seconds. However, the equipment is generally more expensive than a three-point ground tester.

🚨Important: This test requires a connection to the utility neutral to function properly. For some two-wire systems, you cannot use a clamp-on test to test the ground.

How the Clamp-On Test Works: When you clamp around the conductor of your ground point, the tester inducts voltage that travels up through the system, finds an upstream grounding point, and allows current to travel through the ground back to the tester. Because the tester knows how much voltage was inducted and measures the current, it calculates earth-to-ground resistance using Ohm's law.

1. Ensure the system has a connection to the utility neutral.

2. Clamp the tester around the grounding conductor.

3. Read the resistance value displayed by the tester.

4. Verify the result is less than 25 ohms (or less than 10 ohms following ASIC guidelines).

Grounding Best Practices Summary

To properly protect your WeatherTRAK system:

• Make the investment in proper grounding connections for your WeatherTRAK controller
• Be mindful of the sphere of influence of grounding points when determining placement and installation
• Make good bonding connections for the entire grounding system
• Measure grounding points after installation to verify they are protecting your WeatherTRAK system
• Conduct regular testing to ensure continued protection

Video Walkthrough

If you have questions, here are 3 ways to get answers:

1. Search within this HydroPoint knowledgebase

2. Visit the HydroPoint support page

3. Call 800-362-8774 or email support@hydropoint.com, hours are Mon-Fri 3:00 AM – 6:00 PM PT and Sat 9:00 AM – 2:00 PM PT.