TENTECH MTD 20KWe Manual De Uso página 13

5. Wenner's equation simplified form can be applied whenever the
insertion depth of each rod is not significant compared to the D
distance. This condition can be difficult to fulfil when D is small, due
to the need of ensuring a good contact between the rod and the soil.
If this were the case, the full form of the equation must be applied:
Where:
ρ = soil resistivity [Ωm]
D = distance (spacing) between rods [m]
p = insertion depth of the auxiliary rods [m]
R = value shown on the display
When D >> p, the simplified form is obtained.
6. In order to properly evaluate soil resistivity, measurements must
cover the whole area to be occupied and influenced by the future
grounding system. For an area of up to 10,000 m
recommended resistance measurements to be performed in at least
five points, arranged as shown in figure 04. Two sets of
measurements should be needed for the central point (each set of
measurements with its corresponding spaces between rods of 1, 2, 4,
8 and 16 m).
Larger areas can be divided in areas of 10,000 m
measurements in 5 points can be carried out as shown in figure 04.
Besides, in the case of different forms, there will always be the
possibility of limiting a rectangle and proceed as in the previous case.
4 RD
=
2D
1 +
2
D + 4 p
14
D
-
2 2 2
D + p
2
, it is
2
each, and