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 warranty requirements. The grounding system provides a safe path for the current to dissipate.

Why does HydroPoint have specific grounding requirements?

Proper installation of grounding rods, grounding plates, and wire connections are 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 WeatherTRAK system with grounding and surge arrestors as outlined in our Surge Arrestor and Grounding Spec will protect you 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 the earth.

After you have installed your grounding system, HydroPoint requires that you measure the ground resistance in order to prove that each grounding point meets HydroPoint’s specifications. Resistance readings of 5 to 10 ohms are desirable, and 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
• Conductor/bonding

What is 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?

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
  
  
  
  

Tips for Installing Grounding Rods

The key factor to consider is the amount of surface area of the electrode(s) you’re installing that is in direct contact with the earth. 

• 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.
• Using multiple grounding electrodes, such as multiple rods, multiple plates, or a combination of rods and plates is an effective way to ensure low earth-to-ground resistance.  We recommend all installations follow the ASIC grounding guidelines whenever possible. 

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.

Soil amendments such as power set or power fill increase the conductivity of the soil around a grounding electrode and are effective additions to any grounding application.

Tips for Installing Grounding Plates

To determine the distance from the two-wire path a ground plate needs to be installed, measure the horizontal distance from one corner of the grounding plate to the opposite corner. So, if the grounding plate has a horizontal 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 horizontal measurement of the grounding plate and multiple that by 10. So if the horizontal length of the grounding plate is 32 inches, the testing distance you will use is 320 inches. You can then use the Measuring Ground Resistance with the 62% Method to test the resistance.

Soil amendments such as power set or power fill increase the conductivity of the soil around a grounding electrode and are effective additions to any grounding application.

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

AEMC Clamp-On Ground Resistance Tester

(Model 6417) AEMC Digital

 
 

  Ground Resistance Tester

  (Models 4620 & 4630)

 

For more information about AEMC's products, please visit the AEMC website