Camille Bauer GOSSEN METRAWATT GEOHM C, Operating Instructions Manual

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GMC-I Messtechnik GmbH 23
Figure 8 Soil resistivity
ρ
E in as influenced by season
without taking precipitation into consideration
(earth spike depth < 1.5 m)
The following table shows typical soil resistivity for several types of soil.
Table 1 Soil Resistivity
ρ
E
for Various Types of Soil
5.6.2 Calculating Dissemination Resistance
The following table includes formulas for calculating dissemination
resistance for various types of earth electrodes.
These rule-of-thumb formulas are entirely adequate for practical
application.
Table 2 Formulas for the Calculation of Dissemination Resistance R
A
for Various
Types of Earth Electrodes
R
A
= Dissemination resistance (
Ω
)
ρ
E
= Soil resistivity (
Ω
m)
I = Earth electrode length (m)
D = Ring earth electrode diameter, diameter of the equivalent circular area of a
mesh earth electrode or diameter of a hemispherical earth electrode (m)
F = Surface area (square meters) enclosed by a ring or a mesh earth electrode
a = Edge length (m) of a rectangular earth plate, a is defined as follows for rectan-
gular earth plates:
√
b x c, where b and c are the two sides of the rectangle.
J = Volume (cubic meters) of an individual foundation
Type of Soil
Soil Resistivity
ρ
E
[
Ω
m]
Wet bog soil 8
…
60
Arable fields, loam and clay,
moist gravel
20
…
300
Moist, sandy soil 200
…
600
Dry sandy soil,
dry gravel
200
…
2000
Rocky ground 300
…
8000
Bedrock 10
4 …
10
10
+
ρ
E
(%)
10
20
30
-10
-20
-30
Jan. May Sept.
March July Nov.
Number Earth Electrode Type Formula Auxiliary Information
1
Earth strip (crow’s foot
earth electrode)
—
2 Earth rod —
3 Ring earth electrode D = 1.13 ·
4 Mesh earth electrode D = 1.13 ·
5 Earth plate —
6
Hemispherical
earth electrode
D = 1.57 ·
RA
2 ρ
E
⋅
I
----------
=
RA
ρ
E
I
----
=
RA
2 ρ
E
⋅
3D
----------
=
F
2
RA
2 ρ
E
⋅
2D
----------
=
F
2
RA
2 ρ
E
⋅
4,5 a
⋅
-----------
=
RA
ρ
E
π D
⋅
--------
=
J
3