The Key Parameters of an Efficient Earthing System
- Excellent electrical conductivity
- Low Earth Resistance and Impedance
- In order to achieve a low resistance and impedance earth, all connections should be as short and direct as possible.
- Maximizing the surface contact between the soil and all electrodes and conductors is essential for efficient performance.
- Conductors capable of withstanding high fault currents
- Robust Mechanical Connections
- All connections should be robust to facilitate a long working life.
- High Corrosion resistance Materials chosen for earthing systems should offer an acceptable compromise between cost and longevity. It is essential that compatible metals are used in the installation of an earthing system to minimize corrosion.
- Equipotential Bonding
- The elimination of dangerous step and touch potentials is achieved through equipotential bonding of all earths.The Importance of Low Soil Resistivity While many factors influence the effectiveness of an earthing system, it is the resistance of the earth itself (earth / soil resistance) which has the greatest influence on the overall impedance of an earthing system. Several factors such as soil composition, moisture content, seasonal weather, mineral content and possible contaminants determine the resistivity of the soil. Soil types and composition vary greatly from one site to the next.
- Rich dark soils high in organic content are typically good conductors due to the retention of moisture which aids in the dissipation of electric currents.
- Sandy soils are ineffective in retaining moisture content due to the high drainage effect of sand and typically have a higher impedance.
- Rocky ground retains virtually no moisture content and as a result is very high in resistance.Moisture content is the single largest influence on soil resistivity and in most cases the higher the moisture level of the soil the lower the soil resistivity. The installation of a deep driven earthing electrode which reaches the water table beneath the surface represents an ideal earthing system.Seasonal weather conditions play a significant role in influencing soil resistivity levels over an extended period of time.
- Areas which are subjected to high annual rainfall will typically have lower soil resistivity levels in comparison to areas which are prone to sustained hot temperatures and drought like conditions, which will result in increased soil resistivity levels. Regions where temperatures fall below freezing will see sharp increases in soil resistivity as the moisture content within the soil freezes.
LPI offers a wide selection of earthing products which are used in the installation of low resistance earthing systems. Earth Rods, Tapes and Clamps LPI copperbonded, solid copper and stainless steel earth rods in combination with copper tapes and connecting clamps form the key components of an earthing system, which provides for the safe and efficient transfer of fault currents and lightning energy into the earth mass. See pages 9-27, 52-55. Exothermic Welding Permanent Connections The use of exothermic welding is a safe and efficient way of providing a permanent connection between conductors.