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

CLAMP-ON OHMMETER TESTING PROCEDURE APPENDIX D: GROUNDING (EARTHING) ELECTRODE SYSTEM TESTING/VERIFICATION
NOTE: The neutral wire is used for a measurement because it is the only point in a site where all of the site
grounding connections are common over a single conductor. As such, measuring at this point allows the
clamp-on ohmmeter to “view” all of the various connections as one single grounding electrode.
In many cases, the first neutral-ground bonding point may not be at the site building electrical
service panel, but rather at the meter box where the neutral is bonded to the conduit that enters the
building. As such, service that uses a PVC conduit typically has the first neutral-ground bonding
point at the electrical service panel; service that uses metallic conduit may have the first neutralground
bonding point at the meter.
If a measurement is attempted at the electrical service panel where neutral-ground bonding is at the
meter, an erroneous closed-loop reading on the meter will result instead of a reading of the
grounding electrode system.
NOTE: See the meter user's manual to determine a meter indication, if any, showing that the meter is reading a
closed loop rather than the actual grounding electrode system. The closed loop reading may be caused
by a ground loop through a conduit, electrical service meter base or any other electrical panel board. It
can also be an indication that there is another utility connected, such as a water pipe or the Telephone
Company ground.
Ground Bus
4. Depending on location of first neutral-ground bonding point, attach the clamp-on ohmmeter around
the neutral wire as shown in Figure D-9 or Figure D-10.
5. Set the meter to the Amps scale and verify there is no significant current on the neutral wire.
6. Set the meter to the Ohms scale and note the reading; if no noise or other errors are indicated on the
meter, this is the resistance of the grounding electrode system under test.
Record the reading on the photocopy of the clamp-on ohmmeter/ammeter test worksheet
(page D-25).
Main Panel
To Master Ground Bus
Neutral Bus
First Point of Neutral-Ground Bond
Neutral-Ground Main Bonding
Jumper
Ground Connection to Multi-bonded/Multigrounding
Electrode System
FIGURE D-9 CLAMP-ON OHMMETER PLACEMENT FOR MULTI-BONDED/MULTI-GROUNDING
ELECTRODE SYSTEM (NEUTRAL-GROUND BOND AT SERVICE PANEL)
D-18 68P81089E50-B 9/1/05