Passive Power Mode - Fisher TW-82P Operating Manual

TW-82P RECEIVER

PASSIVE POWER MODE

While the Standard and Lateral Modes use the 82kHz signal injected
by the Transmitter, in some cases it is desirable to locate buried
utilities by tracing electric power currents running through them.
Buried utilities may be energized by the electric power currents
running directly through them, current coupling into them as a result
of leakage from power cable faults, defective electrical loads that leak
AC power into ground connections or from cathodic protection on
metal pipelines.
The Passive Power Mode detects both 50Hz and 60Hz electric currents
as well as harmonics of these frequencies resulting from distortions
caused by electrical loads being served by the utility. Cathodic
Protection (at 100Hz or 120Hz) is also detected. This mode will usually,
but not always, detect underground AC power lines. It does not detect
voltage and will usually not detect a power line which is not delivering
current, i.e. one that is not under a load. The operator must use his
knowledge of infrastructure and each specific area being located to
interpret the character of each underground utility.
ABSENCE OF A DETECTABLE POWER SIGNAL DOES NOT
GUARANTEE THAT NO POWER IS PRESENT.
Among the important uses of the Passive Power Mode is to check
ground connections being considered for use as a transmitter
connection to do a conductive trace. Many "grounds" are in fact
improperly grounded and/or have substantial AC power
flowing through them due to defective installation or defective
loads. Ground connections should always be treated as though they
have dangerous voltage or current on them. If the Passive Power
Mode detects power current flowing in a proposed ground connection,
it is usually advisable to use some other ground connection if
available. REMINDER: This mode does not detect voltage. A floating
ground with power voltage on it will probably not be detected. A
high-impedance AC voltmeter can be used to detect voltage provided
that another ground is available to measure the voltage differential.
Floating grounds with full line voltage on them can usually be detected
with a neon bulb line tester without the need for a second ground
connection; follow the instructions provided by the manufacturer.
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