Using a multimeter to measure earth resistance
In many cases, it is necessary to bury the grounding body and lead to the grounding level in order to reliably ground the instruments and equipment. In order to ensure that the grounding resistance meets the requirements, usually need a special grounding resistance tester to measure.
But in practice, the special grounding resistance tester price is high, it is difficult to find, can you use a multimeter to measure grounding resistance? I use a multimeter in different soil on the grounding resistance of soil experiments, and will be measured by the multimeter data and dedicated grounding resistance tester measured data for comparison, the two are very close. Specific measurement methods are as follows:
Find two 8mm, 1m long round steel, one end of the grinding tip as an auxiliary test rod, were inserted into the grounding body to be tested on both sides of the A 5m away from the ground, the depth should be more than 0.6m, and make the three keep a straight line.
Here, A for the grounding body to be tested, B, C for the auxiliary test rod . Then use a multimeter (R * 1 stop) to measure the resistance between A and B; A and C, respectively, recorded as RAB, RAC, RBC, and then calculated to find the grounding resistance value of grounding body A.
As the grounding resistance refers to the contact resistance between the grounding body and the soil. Let the grounding resistance of A, B, C are RA, RB, RC. and then set the resistance of the soil between A and B is RX, because AC, AB distance is equal, it can be A and C between the soil resistance is also RX; and because BC = 2AB, so B and C between the soil resistance approximated as 2RX, then:
RAB=RA+RB+RX......
①RAC=RA+RC+RX......
②RBC=RB+RC+2RX......
(iii) ① + ②? ③It is: RA=(RAB+RAC?RBC)/2...... ④
④ type is the formula for grounding resistance.
Example of measurement: today measured the following data of a grounding body: RAB = 8.4 ∩, RAC = 9.3 ∩, RBC = 10.5 ∩. Then:
RA=(8.4+9.3?10.5)/2=3.6(∩)
Therefore, the value of ground resistance of the measured grounding body A is 3.6∩.
It is worth noting that: before the measurement, you need to polish the three grounding bodies A, B and C with sandpaper shiny to minimise the contact resistance between the meter pen and the grounding body to reduce the error.
