The additional electrode is used in earthing when the resistance to the ground of a single electrode is
Right Answer is:
Any single rod, pipe, or plate electrode not having a measured resistance to earth of 25Ω or less shall be supplemented by the installation of an additional electrode.
The supplemental electrode is used to help lower the total resistance to the earth by providing additional discharge paths for lightning. When multiple grounding electrodes are installed at a single structure, they shall be spaced not less than 6 ft from each other, and bonded together. Bonding conductors shall not be required to be larger than 6 AWG copper.
The reason for the 6 ft (1.8 m) Separation requirement is so that lightning does not potentially are between the electrodes; it also prevents the radiation patterns into the earth from overlapping so that they can independently dissipate the incoming energy surge.