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

OVERVIEW APPENDIX D: GROUNDING (EARTHING) ELECTRODE SYSTEM TESTING/VERIFICATION
D.1 OVERVIEW
Testing can be performed using one of the following three methods described in this chapter:
• Fall-of-Potential Testing
This method is the most widely accepted. However, performing the test may require access to areas
that may be beyond the site property lines. When testing a grounding electrode system consisting of
a multi-bonded/multi-grounding electrode system, the distance required for testing is directly
related to the effective diagonal distance of the buried grounding electrode system.
• Clamp-on ohmmeter
This method should be used when access to necessary space needed for the fall-of-potential test is
not available. However, the clamp-on ohmmeter test can only be performed after the AC utilities
have been connected to the site and various feed conductors are accessible.
• Combined Soil Resistivity Testing with Clamp-on Ohmmeter Testing
This method should only be used in special cases where fall-of-potential testing or clamp-on
ohmmeter testing cannot directly provide a suitable evaluation. The data obtained from soil
resistivity testing and clamp-on ohmmeter testing is then used by an engineering firm specializing
in grounding electrode system design to make determinations regarding the grounding electrode
system.
D.2 PREREQUISITES FOR TESTING
The following conditions must be met in order to perform grounding electrode system testing:
• Fall-of-Potential testing is possible only if the following conditions can be met:
• Sufficient land area must be available to perform a fall-of-potential test. The reference probe
may likely need to be inserted into soil that is beyond the site fence or property line. Testing
using a clamp-on ohmmeter may be an option in these cases.
• The grounding electrode system must be able to be isolated from the power company grounded
conductor (may be a neutral wire) and other utility grounds.
• Clamp-on ohmmeter testing is possible only if the following conditions can be met:
• The site must be supplied with commercial power. Sites supplied only by a generator or other
non-commercial power may not be suitable for clamp-on ohmmeter testing.
• A neutral wire must be present as part of the power company service.
• A neutral wire must be part of an extensive power company grounding system. In systems such
as 3-phase delta service, the neutral wire may not be part of the extensive power company
grounding system.
• The grounding electrode system must be connected to the power company grounded conductor
(may be a neutral wire).
• For sites using a multi-bonded/multi-grounding electrode system (commonly used at
communications sites), a point on the neutral wire before its first bond to the site must be
available for using the clamp-on ohmmeter.
• For a single grounding electrode system, the grounding electrode conductor must be accessible
to the clamp-on ohmmeter at a point between the grounding electrode and any other
connection (such as the telephone company ground or a metallic pipe).
D-2 68P81089E50-B 9/1/05