standards and guidelines for communication sites - Radio And ...

STANDARDS AND GUIDELINES FOR COMMUNICATION SITES SITE PREPARATION CONSIDERATIONS
B.3.3.2 TESTING THEORY AND ROD ARRANGEMENT
Figure B-4 shows the rod arrangement required for testing. The test requires inserting four test rods into
the test area, in a straight line, equally spaced and all at a depth of 229 mm (9 in.). A constant current is
injected into the earth from the earth resistance tester through the two outer test rods. The voltage drop
resulting from the current flow through the earth is then measured across the inner two test rods. Most
testers are designed to provide a direct reading in ohms. This value is then used in one of the following
formulas to calculate the soil resistivity (ρ) of the tested area.
ρ =191.5 × A × R
Where:
ρ = soil resistivity in Ω-cm
A = Distance between test rods (in feet)
R = Resistance obtained from tester (in ohms)
OR
ρ =628 × A × R
Where:
ρ = soil resistivity in Ω-cm
A = Distance between test rods (in metres)
R = Resistance obtained from tester (in ohms)
The calculated soil resistivity is the average soil resistivity between the soil surface and the depth of the
soil equivalent to the rod spacing.
68P81089E50-B 9/1/05 B-7