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6
TRACING TECHNIQUES AND HELPFUL INFORMATION
Many variables affect the process of locating a pipe or cable. The following information gives guidelines for various problem
situations.
6.1 Soil
Conditions
Generally, the effect of soil types on line tracing is as follows:
Soil Type
Effect on Line Tracing
moist,
compact
ideal
dry, sandy, or rocky
little or no moisture content creates
A
poor
tracing
environment
alkaline, high iron content
poor tracing environment
6.2 Adjacent
Conductors
If the field strength reading drops off more on one side of a conductor than it does on the other, the Receiver may be picking up
interference from an adjacent or parallel conductor. Confirm the exact location of the adjacent conductors. Place your ground
lead so that it does not cross over any adjacent conductors, but is as far away from your target conductor as possible, and is
extended perpendicular to the direction in which you are tracing.
6.3 Metroclamp:
Ground
Requirements
If you are using the Metroclamp around a cable, both ends of the target conductor must be grounded to insure sufficient field
strength. Power lines and telephone sheaths are assumed to be grounded.
If the conductor is a pipe which had an insulated joint, such as a gas pipe with a meter, use the jumper cable. Attach each end of
the jumper cable on opposite sides of the insulator.
6.4 Grounding:
Safety
If you use the Direct Connect method, be sure that there is no power flowing through the target conductor. If you use the
Metroclamp on energized lines, follow established safety procedures.
6.5 Distribution
Systems
To locate gas services on a gas distribution system, you must be sure that the service is grounded. This can be accomplished by
temporarily connecting a jumper cable to a ground spike at the end of a service, where the pipe comes out of the earth.
6.6 Deep
Conductor
Signals picked up by the Receiver from deep buried cables are weaker and not as directional distinct as those from cables closer to
the surface. The meter reading will only change by small increments in relation to moving the Receiver antenna.
Using the Inductive (indirect) Method of coupling signal to the conductor may be difficult if the target conductor is buried three
feet or more, or is set in recent backfill. For best results, use the Direct Connection method of coupling signal to the targeted
conductor. (Section 4.1)
6.7 What is Field Strength of the Signal?
When the signal is applied to the conductor using any of the three methods described in Section 5, an electromagnetic field is
created on the conductor. The Receiver measures the strength of this field, displaying it on the digital meter.
The field strength decreases as you move away from the target conductor and as you go farther away from the Transmitter. For
optimum tracing accuracy, the field strength should be between 975 and 500.
Measurement accuracy is affected by the ratio of the conductor diameter compared to how deep the conductor is buried. For
example, a conductor with a diameter of one foot should have two feet of top fill to endure an accurate measurement.
6.8 “Ghost” Conductor Due to Adjacent Conductor
If there is another conductor near the target conductor, it too may pick up the signal from the Transmitter. When this occurs, there
will seem to be a trace – a “ghost” trace – between the two conductors.
A ghost trace can be detected by noting the following:
