standards and guidelines for communication sites - Radio And ...
standards and guidelines for communication sites - Radio And ... standards and guidelines for communication sites - Radio And ...
SOIL RESISTIVITY VARIABILITY AND FACTORS AFFECTING SOIL RESISTIVITY APPENDIX B: SOIL RESISTIVITY MEASUREMENTS NOTE: “Gumbo” is soil composed of fine-grain clays. When wet, the soil is highly plastic, very sticky, and has a soapy appearance. When dried, is develops large shrinkage cracks. The resistivity of soil is primarily determined by the soil's electrolyte contents. Electrolytes consist of moisture, minerals, and dissolved salts. In general, soil resistivity decreases (improves) as electrolytes increase. Figure B-1 shows soil resistivity changes as a function of soil moisture content. The resistivity of the soil decreases rapidly as the moisture content increases from very little moisture to approximately 20 percent moisture. Moisture Content (% by weight) Resistivity (Ω-cm) 0 Top Soil Sandy Loam > 10 9 > 10 9 2.5 250,000 150,000 5 165,000 43,000 10 53,000 18,500 15 19,000 10,500 20 12,000 6,300 30 6,400 4,200 280,000 240,000 200,000 160,000 120,000 80,000 40,000 Source: Soares Book on Grounding and Bonding, 9th addition (ISBN 1890659-36-3). FIGURE B-1 SOIL RESISTIVITY CHANGES AS A FUNCTION OF SOIL MOISTURE The resistivity of soil is also affected by its temperature. In general, soil resistivity increases as temperature decreases. Figure B-2 shows soil resistivity changes as a function of soil temperature. As shown in the figure, the greatest rate of change in soil resistivity is at the point where moisture in the soil freezes. B-2 68P81089E50-B 9/1/05 0 Top Soil Loam 5 10 15 20 25 Moisture Content (% by weight)
STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SOIL RESISTIVITY VARIABILITY AND FACTORS AFFECTING SOIL RESISTIVITY S Temperature °C °F 20 68 7,200 10 50 9,900 0 (water) 32 (water) Resistivity (Ω-cm) 13,800 0 (ice) 32 (ice) 30,000 -5 23 79,000 -15 14 330,000 Source: Soares Book on Grounding and Bonding, 9th addition (ISBN 1890659-36-3). FIGURE B-2 SOIL RESISTIVITY CHANGES AS A FUNCTION OF SOIL TEMPERATURE Because the resistivity of soil is directly affected by its moisture content and temperature, it is reasonable to conclude that the resistance of any grounding electrode system will vary throughout the different seasons of the year. Figure B-3 shows the seasonal variations of the resistance to earth of a grounding electrode. Resistance (in ohms) of the test electrode 80 60 40 20 FIGURE B-3 SEASONAL VARIATIONS IN GROUNDING ELECTRODE RESISTANCE 68P81089E50-B 9/1/05 B-3 360,000 320,000 280,000 240,000 200,000 160,000 120,000 80,000 40,000 0 Sandy Loam 15.2% Moisture Influence of Change of State 10 20 30 40 50 T (˚F) 1.8 cm (0.75 in.) grounding electrode in rocky clay soil Depth = 91 cm (3 ft) 1.8 cm (0.75 in.) grounding electrode in rocky clay soil Depth = 3 m (10 ft) 0 Jan Mar May Jul Sep Nov Jan Mar May Jul Seasonal Variation Source: Soares Book on Grounding and Bonding, 9th addition (ISBN 1890659-36-3). 60 70
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- Page 405 and 406: APPENDIX A ELECTROMAGNETIC ENERGY I
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- Page 433: APPENDIX B SOIL RESISTIVITY MEASURE
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- Page 467 and 468: APPENDIX C PROTECTING AGAINST ELECT
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- Page 471 and 472: APPENDIX D GROUNDING (EARTHING) ELE
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STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SOIL RESISTIVITY VARIABILITY AND FACTORS AFFECTING SOIL RESISTIVITY<br />
S<br />
Temperature<br />
°C °F<br />
20 68 7,200<br />
10 50 9,900<br />
0<br />
(water)<br />
32<br />
(water)<br />
Resistivity<br />
(Ω-cm)<br />
13,800<br />
0 (ice) 32 (ice) 30,000<br />
-5 23 79,000<br />
-15 14 330,000<br />
Source: Soares Book on Grounding <strong>and</strong> Bonding, 9th addition (ISBN 1890659-36-3).<br />
FIGURE B-2 SOIL RESISTIVITY CHANGES AS A FUNCTION OF SOIL TEMPERATURE<br />
Because the resistivity of soil is directly affected by its moisture content <strong>and</strong> temperature, it is<br />
reasonable to conclude that the resistance of any grounding electrode system will vary throughout the<br />
different seasons of the year. Figure B-3 shows the seasonal variations of the resistance to earth of a<br />
grounding electrode.<br />
Resistance (in ohms) of the test electrode<br />
80<br />
60<br />
40<br />
20<br />
FIGURE B-3 SEASONAL VARIATIONS IN GROUNDING ELECTRODE RESISTANCE<br />
68P81089E50-B 9/1/05 B-3<br />
360,000<br />
320,000<br />
280,000<br />
240,000<br />
200,000<br />
160,000<br />
120,000<br />
80,000<br />
40,000<br />
0<br />
S<strong>and</strong>y Loam<br />
15.2% Moisture<br />
Influence of<br />
Change of State<br />
10 20 30 40 50<br />
T (˚F)<br />
1.8 cm (0.75 in.) grounding electrode in rocky clay soil<br />
Depth = 91 cm (3 ft)<br />
1.8 cm (0.75 in.) grounding electrode in rocky clay soil<br />
Depth = 3 m (10 ft)<br />
0<br />
Jan Mar May Jul Sep Nov Jan Mar May Jul<br />
Seasonal Variation<br />
Source: Soares Book on Grounding <strong>and</strong> Bonding, 9th addition (ISBN 1890659-36-3).<br />
60<br />
70
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