The specific measurement method of the multimeter to test the grounding resistance
Regarding the method of testing grounding resistance with a multimeter, before measurement, the three grounding bodies A, B, and C need to be polished with sandpaper to reduce the contact resistance between the test lead and the grounding body. For reference.
How to test grounding resistance with a multimeter
In use, the special grounding resistance tester is expensive and inconvenient to purchase. Can a multimeter be used to measure the grounding resistance?
Using a multimeter to test the grounding resistance in different soil properties, and comparing the data measured by the multimeter with the data measured by a special grounding resistance tester, the two are very close.
Measurement methods:
Find two 8mm, 1m long round steel, sharpen one end as an auxiliary test rod, insert them into the ground 5m away from both sides of the 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 block) to measure the resistance value between A and B; A and C, which are recorded as RAB, RAC, RBC respectively, and then the grounding resistance value of grounding body A can be obtained by calculation.
Since the grounding resistance refers to the contact resistance between the grounding body and the soil, the grounding resistances of A, B, and C are respectively RA, RB, and RC. Let the resistance of the soil between A and B be RX, because the distance between AC and AB is equal, the resistance of the soil between A and C can also be RX; and because BC=2AB, the resistance of the soil between B and C is close
It seems to be 2RX, then:
RAB=RA+RB+RX.
①RAC=RA+RC+RX.
②RBC=RB+RC+2RX.
③ Combine ①+②—③ to get: RA=(RAB+RAC—RBC)/2. ④
The formula ④ is the calculation formula of grounding resistance.
Example: The measured data of a grounding body is as follows: RAB=8.4∩, RAC=9.3∩, RBC=10.5∩. Then: RA=(8.4+9.3—10.5)/2=3.6(∩), so the grounding resistance value of the measured grounding body A is 3.6∩.
Note: Before measurement, polish the three grounding bodies A, B, and C to shine with sandpaper to minimize the contact resistance between the test lead and the grounding body to reduce errors.
