Earth pit Resistance checking by Fall of Potential method or 62 percent method using 3 poles Tester:
Connection: Terminals E1 and P1 are shorted and the lead wire is connected to the earth electrode under test. Terminal E2 lead wire is connected to a spike driven at a minimum distance of 10 times the depth of earth electrode. Terminal P2 lead wire is connected to another spike driven at 62 percent of the distance between Earth electrode and E2 spike. The 0 or ref point is always the earth electrode spot for single electrode.
Example : Assume Earth electrode length or buried depth is 1 meter.
Then E2 spike distance is minimum 10 times of earth electrode depth. So the distance is 10 meter away from earth electrode.
P2 spike distance is 62 percent of 10 meter so it is driven at a distance of 6.2 meter away from earth electrode. So P2 spike will be in-between earth electrode and E2.
As far as possible Earth electrode, P2 spike and E2 spike should be in a straight line.
All lead wire size should be minimum 1 sq mm in order to avoid resistance errors.
To get accurate results spike P2 can be shifted 1 meter forward and backward and the readings observed at these 3 spots are averaged. If the resistance value of 3 readings difference is more than 2 ohms then the E2 spike should be moved further ie more than 10 times earth electrode buried depth.
The spike and earth electrode spots can be wetted by pouring water in order to reduce resistance due to dry earth. The depth of the electrode can also be increased to reduce resistance. Another method to reduce resistance is to use multiple electrodes linked together maintaining a minimum distance of twice the depth between each.
8 сен 2024
