Clamp-On Ground Resistance Testing
A clamp-on ground resistance tester measures ground rod and small ground grid
resistance without the use of auxiliary ground rods. Clamp-on ground resistance testers
are used in multi- grounded systems without disconnecting the ground under test and with
electrical service connected.
To use a clamp-on ground resistance tester
1. Clamp the tester around the ground conductor and read the resistance-to-ground
directly from a digital display.
This type of measurement permits the quality of the grounding connections and
bonding to be verified.
2. Use certified Ground Resistance Testers for all clamp-on ground resistance
measurements.
Principle of Operation
In a typical grounded system, the neutral is bonded to ground at the service panel. There
are numerous neutral-to-ground bonds prior to this point, all in parallel. These bonds
create an effective earth resistance from the utility of virtually zero. A clamp-on ground
resistance tester uses this fact along with the connection between the utility service and
the grounding system under test. The clamp-on tester injects a known voltage into the
system and measures the current felt on the return path. Realizing the near "zero"
resistance on the service side, the meter reading indicates the resistance of the grounding
system under test.
TDC-0971-011 CCU 100 and Repeater 100 Installation Guide 119
Proprietary and Confidential
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