Measurement of Earth Resistance (Three-point method)
In this method earth tester terminal C1 & P1 are shorted to each other and connected to the earth electrode (pipe) under test. Terminals P2 & C2 are connected to the two separate spikes driven in earth. These two spikes are kept in same line at the distance of 25 meters and 50 meters due to which there will not be mutual interference in the field of individual spikes.
If we rotate generator handle with specific speed we get directly earth resistance on scale. Spike length in the earth should not be more than 1/20th distance between two spikes.
Resistance must be verified by increasing or decreasing the distance between the tester
electrode and the spikes by 5 meters. Normally, the length of wires should be 10 and 15 Meter or in proportion of 62% of ‘D’.
