Webinar "How to make a good grounding?", page 2

Webinar #6 of Electric energy saving and quality improvement" series

Webinar text. Page 2

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—When selecting an earthing system, it would be more preferable to classify facilities  not by their load specifics, as Sergei Anatolyevich suggested at his webinars, but by the area they occupy. Therefore, another fundamental point is choosing a place to install an earthing system. Structures such as engineering works, factories, stadiums, supermarkets, railway facilities, substations, etc., can be equipped with a single earth loop installed around the perimeter which can immediately provide an earthing resistance of 1.2 – 1.4 Ohms or close to this value. On this slide, you can see an earth loop around the 30x50 m building. This loop provides the total resistance of 1.63 Ohm in the ground, such as, for example, loam with a resistivity of 100 Ohm*m.

Foundations in Aggressive Environments.

— The use of reinforced concrete foundations is not always possible, as the earth resistance can increase significantly with the use of bitumen, epoxy and surface coatings insulated with protective coatings. As a rule, bitumen and bitumen/latex waterproof coatings have a very little effect on the earth resistance. If a glued covering impedes the process, its natural earthing can always be supplemented with a man-made one. It means that an earth loop installed around a building is not sufficient. It may be radiating at some distance, or you can install an additional earth loop in the form of grid cells, etc. Earth rods may be vertically driven in the grid intersection points. But we are going to turn to it a bit later. The use of coatings significantly increases the resistance of the foundation earthing system. Using it as the only available solution can be rather complicated. The most appropriate solution is to use artificial earthing. However, the corrosive environment, which makes the use of coatings mandatory, greatly affects and corrodes materials, such as standard steel and carbon steel. Therefore, corrosion-resistant materials, such as stainless steel and copper bonded steel, should be used. The only advantage of the corrosive environment is that, as a rule, soil resistivity is rather low and, therefore, the artificial earthing is quite limited, despite the fact that the foundation is coated.

Options for Smaller Building Dimensions.

— As we can conclude by now, the 1.3 Ohm resistance provides a 40x60 m earth loop for soils with resistivity of 100 Ohm*m. The length of the horizontal earth loop may be less than 200 m for such buildings like laundries or any other small-sized facilities, for example, residential buildings or offices. 

Use of Vertically Driven Earth Rods

— Let's consider the options of vertically driven earth rods. Ten 6-meter earth rods were driven into the soil within a 15-meter area. As a result, the earthing system resistance was reduced from 1.72 Ohms to 1.4 Ohms, which is the recommended value for the energy-saving hardware. The resistance was reduced by 22%, which is quite good. Longer vertically driven earth rods can reach the water-bearing layers, thus reducing the earthing resistance even more. These ones were 6-meter long, but vertically driven earth rods can be 15 meters or more. In this case their number can be reduced. These are never installed along the whole loop, but only at four intersection points. This may be quite sufficient, but you'd better re-check it with calculations.

Lightning Protection

— The feasibility of the earthing system for the energy-saving hardware may be affected by a surge protection circuit. If a building is protected by vertical discharge interception rods mounted along its perimeter (they can be either installed on the building roof, or attached to the wall), and a surge protection circuit is installed around the building perimeter from the down conductor, downleads should be run through the building in 20-25 meters. A 20-meter distance meets the requirements of the industrial standard SO 153, and a 25-meter distance meets the requirements of the ruling document RD-34. 

Why Cannot Vertical Earthing Devices Be Installed Close to Each Other? Electrolytic Grounding in Permafrost Soils: Should Vertical of Horizontal Electrodes Be Used?