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

STANDARDS AND GUIDELINES FOR COMMUNICATION SITES FALL-OF-POTENTIAL METHOD TESTING PROCEDURE
• Several photocopies of Table D-4 on page D-21. This is needed to record and keep track of several
measurements across the site.
• Several photocopies of Figure D-5 on page D-12. This is needed to plot a graph of the resistance
profile across the measurement area.
D.3.3 PREPARATION FOR TESTING
D.3.3.1 TESTING AREA REQUIREMENTS
This test requires a reference test rod (outer reference test probe Z) which shall be placed outside the
field of influence of the grounding (earthing) electrode system. In many cases, this required location
will be outside of the site property line. shows a typical site layout and its required spacing distance
between the site and the reference test rod. As such, the following stipulations apply:
• For a single grounding electrode system, the distance of the reference probe shall be minimally 5
times, to preferably 10 times, the depth of the grounding electrode from the surface of the soil to the
bottom of the buried electrode. For fall-of-potential testing distance measurements, the planar
center of a single grounding electrode system is the electrode connecting point above ground.
• For a multi-bonded/multi-grounding electrode system, the distance of the reference probe shall
be minimally 5 times, to preferably, 10 times the diagonal distance of the grounding electrode
system. For fall-of-potential testing distance measurements, the planar center of a multi-bonded/
multi-grounding electrode system is the extreme edge of the system in the direction of where the
test probes are inserted. See Table D-1 for a resistance accuracy versus reference probe spacing
(MIL-HDBK-419A).
TABLE D-1 RESISTANCE ACCURACY VS. PROBE C SPACING
Accuracy (%) Probe Spacing
90 5 x diagonal under test
95 10 x diagonal under test
98 25 x diagonal under test
99 50 x diagonal under test
Use Table D-2 or Table D-3 to obtain the value for 10-times spacing distance between the site and the
outer reference test probe (Z). (Table D-2 provides values in feet; Table D-3 provides values in metres.)
For the minimum 5 times distance; divide the resulting numbers by 2.
NOTE: Any required permissions shall be obtained for accessing and placing a test probe on adjacent property
before testing is attempted.
68P81089E50-B 9/1/05 D-5