The motivators and practicalities of a change from isolated distribution earthing systems

The effective management of earthing systems associated with distribution networks supplying metropolitan areas is often restricted by constraints imposed by rigid policies. These policies are often established using rule of thumb earthing practices due to an absence of tools capable of assessing distribution earthing designs for individual assets. Policies based on rule of thumb targets are selected by addressing the problems associated with the dominant installation type. This means that those installations in the minority can represent significant risk to asset owners, even though they comply with standard construction practices. Installations within metropolitan areas, due to the greater diversity in surrounding infrastructure and use, can change the risk profile of the installation, making the implementation of the rigid risk management policies unfeasible. For ActewAGL, a change in the distribution earthing system paradigm to include common bonded earthing, is seen as a solution to a number of problems within the existing distribution system. This paper considers the motivators and the practicalities of the changes required in the context of a largely unique network; where the administration of an isolated system by one authority has resulted in a predominately separately earthed distribution system throughout.