Measuring the resistance of the earth electrode.
It is very important to measure the resistance between the grounding rod and “true Earth”. Every ground rod must prove to have a low resistance to the earth. Different methods are used to test and confirm soil resistivity to ensure that it meets NEC 250.56 requirements. The most common methods used in the industry are listed below. 1) 3-point or Fall of potential Method, 2) 4-point Method or Wenner method, 3) Clamp-On Method. 3-Point Method – This is the most common method used when measuring the earth's resistance of a ground rod. It is used to effectively measure the ability of the ground rod to dissipate energy from a site. Three electrodes used in this test. the three electrodes are; The ground rod Under Test, The Voltage electrode (P) and the Current electrode(C) The ground rod under test must first be disconnected from the earth bus, then the auxiliary test electrodes would now be driven into the ground in a straight line away f