The resistance of earth electrodes

This paper, which is an abridgement of a report¿ prepared by the E.R.A., deals briefly with the most important aspects of the resistance of electrodes used for earthing electrical installations and apparatus. After comparing the practice in various countries, details are given of the effect of the resistivity of the soil and the size and lay-out of electrodes on their resistance. It is shown that in order to have a low resistance the electrodes should cover a large area by consisting of either strips or, alternatively, a number of small electrodes connected in parallel. To facilitate the latter arrangement it is recommended that driven rod or pipe electrodes be used. A low resistance may also be obtained by salting the soil around electrodes, and this is considered together with the effect of using coke breeze.