Baseline's Grounding Resources

Earth

What is grounding?

The National Electric Code®, Article 100 defines a ground as "a conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth".

 

Why is grounding necessary?

Grounding protects people, protects equipment, and fulfills Baseline's extended warranty requirements. The grounding system provides a safe path for current to dissipate.

Why does Baseline have specific grounding requirements?

Proper installation of grounding rods, grounding plates, and wire connections is essential to providing good surge suppression. While there is no technology currently available that can fully protect an irrigation system against damage from massive surges such as those caused by direct lightning strikes, outfitting your Baseline system with grounding and surge arrestors as outlined in our Surge Arrestor and Grounding Spec will protect from most, if not all, naturally occurring electrical surges.


What is ground resistance?

Ground resistance is the measurement of the conducting connection between the grounding system and earth.

 

After you have installed your grounding system, Baseline requires that you measure the ground resistance in order to prove that each grounding point meets Baseline's specifications. Resistance readings of 5 to 10 ohms are desirable, and a reading of no more than 25 ohms is required. You should measure the system at least once a year to ensure that the resistance readings remain constant.

Ground resistance is affected by the following factors:

  • Type of grounding electrode
  • Contact with the soil
  • Soil resistivity
  • Contact resistance
  • Conductor/bonding

Soil Resistivity

Soil resistivity is a measure of how much the soil resists the flow of electricity (or inversely, a measure of the earth's ability to conduct electricity).

 

There is a direct relationship between ground resistance and soil resistivity, i.e., lower soil resistivity results in lower ground resistance.

 

Soil resistivity is the key factor that determines what the resistance of a grounding electrode system will be and to what depth the electrodes must be driven to obtain low ground resistance. The resistivity of the soil varies widely throughout the world and changes seasonally.

 

Soil resistivity is affected by the following environmental factors:

  • Moisture content
  • Electrolyte content (minerals and dissolved salts)
  • Temperature

 

What is a grounding electrode?

Testing Ground Resistance

Ground resistance can (and should be) measured using a 3-point ground resistance tester and the 62% Method (aka Simplified Fall of Potential Test).

Resources

Testing Soil Resistivity

Soil resistivity testing is not always required, but it can be a very effective and cost/labor saving tool. The test can help you determine the rod depth required in order to achieve your desired ground resistance.

Soil resistivity can be tested using a 4-pole Ground Resistance Tester using the Wenner Method.

four-point test

Testing Irrigation Wire Grounding

We recommend that you test the irrigation wire grounding at your site with a clamp-on ground resistance tester. Follow the appropriate procedures for the type of tester you are using.

Resources

A grounding electrode is a conductor in intimate contact with the earth for the purpose of providing a connection with the soil

 

The following types of grounding electrodes can be used:

  • Rods
  • Plates
  • Electrolytic electrodes
Electrode

Tips for Installing Grounding Rods

  • Increasing the depth to which a rod is driven can substantially reduce resistance. Doubling the rod depth reduces its effective resistance by as much has 40 percent.
  • Increasing the diameter of a rod does NOT materially reduce its resistance – in fact, doubling the diameter reduces the resistance by less than 10 percent.
  • You can use a soil resistivity test and a Grounding Nomograph to estimate the rod depth required to achieve the necessary resistance.
  • A grounding rod driven into rocky soil will only make contact on the edges of the surrounding rock, which does not provide the required intimate contact. Take steps to ensure that intimate contact is achieved and maintained. Also keep in mind that ground rods may not be practical on job sites with rocky soils.
  • When a grounding rod is driven into compacted or rocky soil, "mushrooming" can occur on both the top of the rod and the end that is being driven into the soil. A ground rod sleeve may prevent the top of a ground rod from mushrooming. However, if the end of the ground rod is mushrooming, you might need to use an advanced driven rod that is installed with a standard drill hammer.
  • After a grounding rod is driven into the soil, allow the soil to settle in order to eliminate air pockets.

Tips for Installing Grounding Plates

  • To determine the distance from the two-wire path a ground plate needs to be installed, measure the diagonal distance from one corner of the grounding plate to the opposite corner. So, if the grounding plate has a diagonal measurement of 32 inches, you will install the grounding plate 32 inches from the two-wire path. After you have that measurement, install the grounding plate accordingly with its longest side parallel to the two-wire path.
  • Install grounding plates a minimum of 30” below ground level and below the frost line. Position the plate flat at the bottom of the trench.
  • To test the resistance for the grounding plate, use the same diagonal measurement of the grounding plate and multiple that by 10. If the diagonal measurement of the grounding plate is 32 inches, the testing distance you will use is 320 inches. You can then use the 62% testing method to test the resistance.
Note: The chassis ground on the irrigation controller can be connected to the building system ground, but DO NOT connect the two-wire ground to the building system ground. This creates a loop that causes noise and damage on the two-wire.

 

The goal is LOW ground resistance

 


connectors

Bonding Connectors

All points of connection in the grounding system must have some type of bonding connector. These can be compression connectors, mechanical connectors, or exothermic weld connectors. All compression and mechanical connectors must be suitable for direct burial.

 

The weakest link in a grounding system is usually the bonding.

 

Test the bonding connectors yearly with a micro-ohm meter. The resistance reading on these connections should be less than one milliohm.

 


Equipment for Testing and Measuring

ground resistance tester

AEMC Digital Ground Resistance Tester (Models 4620 & 4630)

Clamp-On Ground Tester

AEMC Clamp-On Ground Resistance Tester (Model 6417)

For more information about AEMC's products, please visit the AEMC website. To purchase products, visit your Baseline distributor.


Other Resources

AEMC's Soil Resistivity Report (used to plot the data gathered in the Fall of Potential Test)

 

AEMC's Technical Documentation for Ground Testers

 

AEMC's Tech Support Contact Information

  • 1 (508) 698-2115 (Ext. 351)
  • 1 (800) 343-1391 (Ext. 351)
  • techsupport@aemc.com