Quantcast Soil Resistivity - hdbk419a_vol10093

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MIL-HDBK-419A
2.10.4 Corrosive Atmospheres. In regions exhibiting low soil resistivity, in corrosive atmospheres such as
might be encountered near seashores, or near sources of large direct currents such as electroplating facilities,
cathodic protection may be necessary to prolong the life of foundations, underground cable facilities, or other
elements of a facility in contact with the soil. For additional information on the galvanic series of common
metals see Table 7-7.
2.11 GROUNDING IN ARCTIC REGIONS.
2.11.1 Soil Resistivity. The problem of electric earth grounding in cold regions is primarily one of making
good contact with high resistivity soils. Where frozen high resistivity materials are encountered, optimum
grounding of power and communication circuits can only be accomplished by special attention to both surface
and subsurface terrain. The fact is that resistance of frozen soils can be ten to a hundred times higher than in
the unfrozen state. Seasonal changes in temperature and moisture will therefore extensively affect the soil
resistance. Table 2-9 provides information on the effect of moisture content on earth resistivity, while Table
2-10 provides the effect of temperature on earth resistivity (2-16, 2-17).
Table 2-9. Effect of Moisture Content on Earth Resistivity
Resistivity, ohm-cm
Moisture Content
% By Weight
Top Soil
Sandy Loam
x 104
x 106
1,000
1,000
0
2.5
250,000
150,000
5
165,000
43,000
10
53,000
18,500
15
17,000
10,500
20
12,000
6,300
30
6,400
4,200
Table 2-10. Effect of Temperature on Earth Resistivity *
Temperature
Resistivity
ohm-cm
20
68
7,200
10
50
9,900
0
3 2 (water)
13,800
0
3 2 (ice)
30,000
-5
23
79,000
-15
5
330,000
*For sandy loam, 15.2% moisture.
2-66





 


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