Using the BuzzBox in Conductive Mode
Plug the cable set into the jack on the side of the BuzzBox. Connect the red
clamp to the line, that is, the cable or cord you are using for this exercise. It
must make a good electrical connection, so clean off any rust or insulation that
might compromise this (on an extension cord, just clamp it to the prongs on
the male end of the cord). Shove the ground rod into the ground and connect
the black clamp to it. The ground rod also needs to make a good electrical
connection with the earth; deeper is better and wetter is better. You might
want to pour a cup of water around your ground rod if the earth is very dry.
The better your ground, the more blue LEDs will be lit. In practice, it is best to
maximize the distance between the ground rod and where you attach to the
“line”, keeping it at a 90° angle to the run of the line.
The technique for locating a line energized conductively is the same as for in-
ductively, so go ahead and walk the line again to see how it works. In general,
you will find that the signal is stronger and more distinct in the Conductive
mode.
Determining Depth
The LF2200 uses the same method to determine the depth of a line as it does
for determining the depth of a sonde.
The screen looks much the same too. When you are
directly over the line (indicated by solid tracks and
vibrating handle), hold the LF2200 up by your chest,
where you can still see the screen. We do this when
practicing because the line is on top of the ground and
we want to establish a distance we can measure. When
doing actual tracing, you will set the foot of the LF2200
on the ground for this step. When ready, click the
rocker switch to the right to get to the Depth Screen.
In a second or two, the depth will be displayed in feet
and inches or meters and decimeters, if you have set
your defaults that way), and the red LED will light.
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For best results in conductive mode, the far end of your test line
(cable, extension cord, etc.) should also be grounded, in order to make
the best electrical path back through the ground rod to the BuzzBox.
Recognizing and Dealing with Field Distortion
It is becoming increasingly rare to have only a single power line running
underground in an area where you are going to be working. The presence of
other power lines in the vicinity, or even other buried metallic material (such
as pipes) can distort the apparent magnetic field around a power line and give
misleading results if you are not prepared to expect it.
If the magnetic field produced around an energized power line is perfectly
circular, as it would be in total isolation, the locations indicated by both Peak
and Null modes would be the same, and they would be accurate. However, the
presence of field distortion tends to make the Null mode indicate off to the side
of the actual location.
With what you have learned here, you should be able to go out and be suc-
cessful at tracing a line you can connect to inductively or conductively without
knowing in advance where it is. Be sure to read “At the Jobsite” for practical
considerations when doing actual field locating with this equipment. Good luck!
This illustration shows the influence of a
distorted field on Null mode. The lines of the
magnetic field around the wire are not circular,
and skew to one side. The blue horizontal lines
in the figure show where a receiver in Null Power
mode will indicate the location of the line. The
deeper the line, the further off this reading
will be. Fortunately, Peak Power mode is not
particularly influenced by field distortion, and
although it is less precise than Null mode, it will
show the correct location regardless of depth.
You can detect the presence of field distortion
by raising the LF2200 a foot or two when you
have located the line in Null mode. If the field
is distorted, the location indication will appear to
move right or left. If this is the case, establish
the actual location using Peak mode and proceed
to the Depth screen from that point.
Be aware that “active” locating, using the LF2200 in conjunction with the Blue
BuzzBox in Inductive mode, is not affected by field distortion and will always
be more accurate.
will appear to be somewhat “shorter” than a shallow line of the same length.
You’ll need to experiment to see how much you should compensate for this.
This effect will be noticed in both Inductive and Conductive modes.
The LF2200 does not have a Depth screen for Power.
As we have said, locating power using passive methods is at
best an approximation, and the lack of accuracy extends to
the determination of depth to the point that we don’t want to
mislead you by suggesting unwarranted precision. Use the
Power features only for an initial survey of an area; use with
your BuzzBox inductively for precision locating of power lines.
