standards and guidelines for communication sites - Radio And ...
standards and guidelines for communication sites - Radio And ... standards and guidelines for communication sites - Radio And ...
GROUNDING (EARTHING) ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4: EXTERNAL GROUNDING (EARTHING) 2.4 m (8 ft) FIGURE 4-9 ANGLED GROUND ROD INSTALLATION WARNING When operating any kind of power tool, always wear appropriate safety glasses and other protective gear to prevent injury. • Hammer drills or electric jackhammers may be used to drive in the ground rods. Do not deform the head of the ground rod. See IEEE STD 142-1991, section 4.3.2. for additional information. • If rock formations prevent ground rods from being driven to the specified depth, an alternate method of achieving an acceptable grounding electrode system shall be engineered and implemented. See “Special Grounding (Earthing) Situations” on page 4-88 for additional information. • When the grounding electrode system design requires deeper ground rods (in order to lower the grounding electrode system resistance, penetrate down to permanent moisture level, or to penetrate below the frost line) two or more ground rods may be joined together by use of a coupling (threaded, compression sleeve, or exothermic weld). Threaded rods or compression sleeves shall be UL listed. (IEEE STD 142-1991, section 4.3.1). See Figure 4-10 for an example of splicing ground rods together. FIGURE 4-10 SPLICING TWO GROUND RODS BURIED GROUNDING ELECTRODE CONDUCTORS 45˚ maximum 76 cm (2.5 ft) 4-14 68P81089E50-B 9/1/05
STANDARDS AND GUIDELINES FOR COMMUNICATION SITES GROUNDING (EARTHING) ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS 4.4.1.2.3 EFFECT OF GROUND ROD SIZE ON RESISTANCE TO EARTH Increasing the diameter of a ground rod does not significantly reduce its resistance to earth. Doubling the diameter of a rod reduces its resistance to earth by approximately 10%. See Figure 4-11. Approximate Resistance to Earth in Ohms 50 45 40 35 30 25 20 15 10 5 0 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Ground Rod Diameter (Inches) 3 m (10 ft) Ground Rod in 10,000 ohm-cm soil FIGURE 4-11 RESISTANCE TO EARTH DUE TO GROUND ROD DIAMETER As the length of a ground rod is increased, its resistance to earth is substantially reduced. In general, doubling the length of a ground rod reduces the resistance to earth by 40%. See Figure 4-12. Approximate Resistance to Earth in Ohms 140 120 100 80 60 40 20 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Ground Rod Length (Feet) 15.9 mm (0.625 in.) Diameter Ground Rod in 10,000 ohm-cm soil FIGURE 4-12 RESISTANCE TO EARTH DUE TO GROUND ROD LENGTH 68P81089E50-B 9/1/05 4-15
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GROUNDING (EARTHING) ELECTRODE SYSTEM COMPONENT AND INSTALLATION REQUIREMENTS CHAPTER 4: EXTERNAL GROUNDING (EARTHING)<br />
2.4 m<br />
(8 ft)<br />
FIGURE 4-9 ANGLED GROUND ROD INSTALLATION<br />
WARNING<br />
When operating any kind of power tool, always wear appropriate safety glasses <strong>and</strong><br />
other protective gear to prevent injury.<br />
• Hammer drills or electric jackhammers may be used to drive in the ground rods. Do not de<strong>for</strong>m the<br />
head of the ground rod. See IEEE STD 142-1991, section 4.3.2. <strong>for</strong> additional in<strong>for</strong>mation.<br />
• If rock <strong>for</strong>mations prevent ground rods from being driven to the specified depth, an alternate<br />
method of achieving an acceptable grounding electrode system shall be engineered <strong>and</strong><br />
implemented. See “Special Grounding (Earthing) Situations” on page 4-88 <strong>for</strong> additional<br />
in<strong>for</strong>mation.<br />
• When the grounding electrode system design requires deeper ground rods (in order to lower the<br />
grounding electrode system resistance, penetrate down to permanent moisture level, or to penetrate<br />
below the frost line) two or more ground rods may be joined together by use of a coupling<br />
(threaded, compression sleeve, or exothermic weld). Threaded rods or compression sleeves shall be<br />
UL listed. (IEEE STD 142-1991, section 4.3.1). See Figure 4-10 <strong>for</strong> an example of splicing<br />
ground rods together.<br />
FIGURE 4-10 SPLICING TWO GROUND RODS<br />
BURIED GROUNDING ELECTRODE<br />
CONDUCTORS<br />
45˚<br />
maximum<br />
76 cm<br />
(2.5 ft)<br />
4-14 68P81089E50-B 9/1/05
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