How to measure ground resistance with a multimeter
The grounding resistance was tested on soils with different soil qualities with a multimeter, and the data measured by the multimeter was compared with the data measured by a special grounding resistance tester, and the two were very close. The specific measurement methods are as follows:
Find two 8mm and 1m long round bars, sharpen one end of them as auxiliary test rods, and insert them into the ground 5m away from both sides of grounding body A to be tested. The depth should be more than 0.6m, and keep the three in a straight line.
Here, A is the grounding body to be tested, and B and C are auxiliary test rods
Then use a multimeter (R*1 gear) to measure A and B; the resistance values between A and C are recorded as RAB, RAC, RBC respectively, and then the grounding resistance value of grounding body A can be obtained by calculation.
Because the grounding resistance refers to the contact resistance between the grounding body and the soil. Let the grounding resistances of A, B, and C be RA, RB, and RC, respectively. Then let the resistance of the soil between A and B be RX, because the distance between AC and AB is equal, the soil resistance between A and C can also be RX; and because BC=2AB, the soil resistance between B and C is approximately 2RX, then:
RAB=RA+RB+RX. . . . . .
①RAC=RA+RC+RX. . . . . .
②RBC=RB+RC+2RX. . . . . .
③Compose ①+②-③ to get: RA=(RAB+RAC-RBC)/2. . . . . . ④
④ formula is the calculation formula of grounding resistance.
Measured example: The data of a grounding body measured today are as follows: RAB=8.4∩, RAC=9.3∩, RBC=10.5∩. but:
RA=(8.4+9.3—10.5)/2=3.6(∩)
Therefore, the grounding resistance value of the grounding body A under test is 3.6∩.
