Earthing System Components – Part Two

In Article " Earthing System Components – Part One ", I indicated that:

Earthing System Components Earthing system in an installation is normally comprised of the following components: Earth wells and accessories Earthing grid conductors Marshalling earth buses (earthing distribution buses) Earthing wires and cables.

1- Earth Wells and Accessories the prime components and accessories of an earth well will be: Earth Rod, Earth Plate, Earthing Clamp, Earthing Rod Coupling, Earthing Rod Tip, Earthing Rod Driving Head with driving sleeve, Earth Access Pit, Earth Pit Cover, Earth Enhancement Materials.

Also in this Article, I explained the first six items; Earth Rod, Earth Plate, Earthing Clamp, Earthing Rod Coupling, Earthing Rod Tip and Earthing Rod Driving Head with driving sleeve.

Today I will explain continue explaining other Components of Earthing Well and Earthing Systems as follows.

You can preview the following Articles for more info:

• Introduction to Grounding System Design – Part One

• Introduction to Grounding System Design – Part Two
• Types of Earthing System – Part One
• Types of Earthing System – Part Two
• How to Select the Best Earthing System

Earthing System Components – Part Two

1.7 Earth Access Pit To provide access to the earth rod and its corresponding connection to the earthing grid at the top section of the rod, a small pit-like space is fabricated over the earth well, which is referred to as “earth pit”. For periodically measuring the electrical resistance of a buried ground system, inspection pits are used as a means of access to the ground conductor. To make electrical resistance measurements, remove the cover and attach a lead from a resistance measuring instrument to the ground conductor. 1- Earth Pit Sizes: Inspection pits are available in various sizes and materials. 2- Earth Pits Main Types: A- According to location: a- Light Weight Duty Light-duty units are generally used. For example Plastic Light weight duty earth pits are schedule 40 PVC. b- Heavy Duty For areas of high vehicular traffic, you should use heavy-duty inspection wells. For example Plastic Heavy duty earth pits are schedule 80 PVC. B- According to Material Earth pit’s side walls are constructed of insulating material to appropriately isolate the earth rod’s top connection from the surrounding soil and protect it for furture reference test and maintenance practices. The materials used for fabrication of Earth Pits are: Polymer Concrete: Polymer Concrete reinforced with heavy weave fiberglass resulting in high strength and minimal weight. Enclosures and covers rated for 10,000 lbs. maximum load. Light weight Polymer Concrete, HDPE (High Density Polyethylene). Note: Earth pits are essentially, constructed flush with respect to the surrounding finished ground.

1.8 Earth Pit Cover To protect the earth pits against ingression of foreign material, an appropriate concrete cover is provided to be placed atop the earth pit. The cover is equipped with a rigid handle for convenient removing and replacement practices. 1- Earth Pit Cover Sizes: Inspection pits covers are available in various sizes to accommodate the size of their earthing pits. 2- Earth Pit Cover Materials: The materials used for fabrication of Earth Pits Covers are: Cast iron grated cover, Flat steel cover, Plastic covers, Concrete covers. the ASTM specifications for Earth Pit Covers are as in the below image.

1.9 Earth/ Ground Enhancement Materials (GEM) Only rarely do grounding system designers and contractors get to work on a site with good grounding conditions. Even under ideal circumstances, soil structure can vary and make it difficult to achieve uniform, low levels of resistivity across a wide area. Under almost all soil conditions, the use of a ground enhancement material will improve grounding effectiveness. Some are permanent and require no maintenance. 1- Where and when Earth Enhancement Materials should be used? Earth Enhancement Materials improves grounding effectiveness regardless of soil conditions and provides excellent permanent conductivity: For areas with high resistance, such as rocky ground, mountain tops, and sandy soil, As a backfill when you have to drill because the ground is too hard to drive, or where ground rods cannot be driven, when used as a backfill for earth electrodes, soil conditioning agents effectively act to increase the electrodes surface area thus lowering its resistance to earth. Where limited space makes adequate grounding difficult by conventional methods. 2- Types of Earth Enhancement Materials Many types of Earth Enhancement Materials are used improves grounding effectiveness regardless of soil conditions and provides excellent permanent conductivity, Like: A- Carbon and Salt Bedding Depending on the technical design specification of the earthing system and primarily for soil conductivity reasons of the area where the earth wells are to be installed, the earth rods are embedded in carbon bedding. To install the carbon bedded earth wells, pre-excavation of the ground, to sufficient size and dimension, would be carried out to provide room for the carbon bedding and the earthing components (rods, plates, etc.). To achieve the maximum conductivity for the earth well, an appropriate amount of salt is added to the carbon and mixed before charging into the earth well. B- Marconite Compound Marconite forms a permanent solution when mixed with cement and is used when certain ground conditions make it difficult to obtain a reliable earth resistance or installation might require a low resistance. C- Bentonite Compound: Bentonite can be supplied in powder or granular form and is a moisture retaining clay which is used to reduce soil resistivity. It has two types: 1- Granular: It’s easier to handle in granular form, the powder can cause dust in windy conditions and below away, granular is the preferred option for filling trenches where the conductor is covered with bentonite and the water poured over and mixed in the trench. 2- Powder Powder is the preferred method for pouring into bore holes to ensure the mixture is a thin enough to reach the bottom of the bore hole, if diamond drilling is required for deep holes possibly 40 meters and deeper and the bentonite is to be pumped through the core into the hole, powder will be the preferred option. The above image clearly shows, GEM has a resistivity factor more than 20 times lower than bentonite clay. 3- How to Specify GEM? Ground enhancement material must be permanent and maintenance-free (no recharging with salts or chemicals which may be corrosive) and maintain its earth resistance with time. It must set up firmly and not dissolve or decompose or otherwise pollute the soil or the local water table. The ground enhancement material shall be suitable for installation in dry form, or in slurry form. The ground enhancement material shall not depend on the continuous presence of water to maintain its conductivity. Ground enhancement material in its set form shall have a resistivity of not more than 20 ohm-cm. Note: When selecting a ground enhancement material be sure it is compatible with the ground rod, conductor and connection material. 4- GEM Installation GEM is supplied in easy-to-handle bags for one-man installation. GEM can be installed dry or wet (recommended). GEM quickly absorbs moisture from the soil when used dry, to reach its maximum conductivity in days. To accelerate curing time, water can be added after GEM is installed, or it can be pre-mixed with water. A- Trench Installation Dig a trench at least 4 inches wide x 30 inches deep or below the frost line, whichever is deeper. Spread out enough GEM to uniformly cover bottom of trench-about 1 inch deep. Place conductor on top of GEM. Spread more GEM on top of conductor to completely cover conductor about 1 inch deep. Carefully cover the GEM with soil to a depth of about 4 inches, making sure not to expose the conductor. Tamp down the soil, and then fill in the trench. For various trench widths and GEM thicknesses, see the below table. B- Ground Rod Backfill Installation Auger a 3 inch or larger diameter hole to a depth of 6 inches less than the length of the ground rod. Place ground rod into augered hole and drive one foot (if possible) into bottom of the hole. The top of the ground rod will be approximately 6 inches below grade. At this time, make any connections to ground rod using CADWELD connections. Pour the appropriate amount of GEM around the ground rod. To ensure the GEM material completely fills the hole, tamp around the ground rod with a pole. Fill remainder of augered hole with soil removed during augering. For various augered-hole diameters and depths, see the below table. Notes: If premixing GEM into a slurry form, use a standard cement mixer or hard-mix in a mixing box, wheelbarrow, etc. Use 1-1/2 to 2 gallons of clean water per bag of GEM. Excess standing water must be removed from the hole.

Enhanced Ground Rod An Enhanced Ground Rod is a conductive hollow tube ground rod, usually manufactured from 300 stainless steel or copper.  They contain special hygroscopic, electrolytic salts. These salts form a saline solution by absorbing moisture out of the atmosphere.  This saline solution leaches out of the bottom of the rod, which gradually lowers resistivity of the surrounding soil, forming "electrolytic roots" over time. To increase the efficacy of the Enhanced Ground Rod, a very low resistance ground enhancement material is placed around the rod. A conductor is exothermically attached to the enhanced ground rod. This conductor is called the tail. The tail direction is very important. Enhanced Ground Rod design allows the current, either lightning or electrical fault, to maintain a downward sloping path to ground. There are two basic styles, vertical and horizontal (L-shaped) as in above image. Enhanced Ground Rod includes a variety of lengths, sectionals and different kits to meet many specific requirements.

In the next Article, I will continue explaining the Earthing Systems Components. Please, keep following.

Back To Course EE-5: Grounding System Design Calculations