Service Panel - Greenlee CMGRT-100 Instruction Manual

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.
Ground
Electrode
PHONE
CATV
Electric Utility
A B NEUTRAL
Service Panel
CMGRT-100
240 VAC
WH
BK 120 VAC
Bare
11