A correctly designed and installed earthing system is essential for the safe operation of protective devices under electrical fault conditions to safeguard the life of personnel. In addition it is essential to protect against the danger from touch and step potential.
Whilst the principle of providing an effective path and connection to the general mass of earth is relatively simplistic, the variety of individual circumstances and specific requirements are far reaching leading to the need for complex designs vital for the protection of life.
As such an earthing system could be as simple as a single earth electrode driven into the ground or as complex as a full underground grid of conductors covering thousands of square metres incorporating hundreds of connections to pile foundations, reinforcing bar, steel columns, equipment plinths and plant etc Strategically placed earth bars of a variety of configurations are installed as connection points from the below ground earthing grid to a comprehensive above ground equipotential bonding arrangement for the whole project. This would be typical of a new build power station, sub station or switchyard.
The continuity of welded, brazed or clamped joints are tested to a millionth of an ohm using a Megger DLRO 10 micro ohm meter.
Final fall of potential testing in accordance with BS7430 2011+A1:2015 is carried out from the basic single electrode earth system using an earth resistance tester through to the more complex slope method covering up to a 1000m using a Megger DET2/2 high performance earth tester.
The DET 2/2 is also used to carry out soil resistivity surveys via the Wenner four terminal method to gather accurate data of the resistivity of the ground strata from a depth of 60m to 0.5m in 2 – 0.5m increments. This information can then be used to assess the anticipated resistance of a single electrode at a specific depth, or for providing a detailed soil model through world renound earthing software CEDEGS in preparation for a detailed earthing design.