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Typical Applications (cont'd)
Central Office Locations
The main ground conductor from a ground window or a ground plane is usually the location to clamp the
unit. Due to the wiring practices within the central office, there are many locations at which you can look at
the water pipe or counterpoise from within the building. An effective location is usually at the ground bus in
the power room or near the backup generator.
By measuring resistance and current at several points and comparing the readings, you can identify neutral
loops, utility grounds, and central office grounds. The test is effective and accurate when the ground window
is connected to the utility ground at only one point.
Service Panel
At a service panel, several sources may be grounded at a single grounding point. As shown in the following
illustration, those sources could be electric neutral, telephone, CATV, and water.
The primary return path should be electric neutral. After taking the first measurement, disconnect one source
and take a new measurement. Continue in this manner until all other sources have been disconnected. Any
higher measurement may indicate that the electric neutral is defective or open.
Electric Utility
A B
NEUTRAL
240 VAC
Phone
WH
CATV
BK
120 VAC
Bare
Service Panel
Ground
Electrode
26
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