Digital Ground Resistance Tester Model 4500
21
Chemically treated soil is also subject to considerable variation of resistiv
-
ity with changes in temperature, as shown in Table 9 on the next page. If
salt treatment is employed, it is, of course, necessary to use ground rods
which will resist chemical corrosion.
20
10
0
-5
-13
110
142
190
312
1440
The Effect of Temperature on the Resistivity of Soil Contining Salt*
(sandy loam, 20% moisture; salt 5% of weight of moisture)
Temperature ˚C
Resistivity
(Ohm-centimeters)
Table 9
*Such as copper sulfate, sodium carbonate and others. Salts must be EPA or local ordinance
approved prior to use.
4.1.4 Effect of Ground Electrode Depth on Resistance
To assist the engineer in determining the approximate ground rod depth
required to obtain a desired resistance, a device called the Grounding
Nomograph may be used. The Nomograph, shown on the following page,
indicates that to obtain a grounding resistance of 20 ohms in a soil with
a resistivity of 10,000 ohm-centimeters, a 5/8" OD rod must be driven 20
feet. NOTE that the values indicated on the Nomograph are based on
the assumption that the soil is homogeneous and, therefore, has uniform
resistivity (Figure 8). The Nomograph value is an approximation.
