If you have ever been on a site and heard someone say that plastic pipes are invisible to a CAT, then you have heard one of the most dangerous myths in the industry, because the answer is not as simple as yes or no.
While the literal answer is yes, a standard CAT does not detect a
plastic pipe on its own, as plastic does not carry an electromagnetic signal;
however, that is only half of the equation, and if you do not know how to
proceed from that point, then you are leaving your job and your safety to chance.
The real question is how you can use your equipment to make those
invisible services appear.
The Science of Why Plastic Stays Hidden
To understand the solution, one must first understand the problem. The
way a CAT works is by detecting the electromagnetic fields emitted by metallic
cables or pipes. Plastic does not emit an electromagnetic field because plastic
is an insulator. It also won't pick up a signal broadcast by a Genny through
induction. The mistake most operators make is when they run a standard sweep
and find nothing. They then assume the trench is clear. This is exactly why CAT
training is so important. During training, you will learn that a silent
device does not mean a clear trench.
How to Bring Plastic into Focus?
The most common professional means of accomplishing this feat is
through the use of a signal sonde or a traceable duct rod. This means that you
are providing the CAT something to see as it travels through the network.
Essentially, you are creating a temporary transmitter out of a non-conductive
plastic pipe. Thanks to your CAT training, you will be able to determine
the depth of this sonde as well as its path of travel through the network,
thereby providing a 3D image of the plastic assets.
The Role of Tracer Wires and Marker Tape
In many contemporary installations, the utility companies now run a
tracer wire with plastic gas and water mains. If one is informed as to where
the connection is, it is possible to apply an active signal directly onto this
wire. In some installations, detectable mesh or marker tape is buried above the
pipe. While these are useful, they are not infallible. One has to be skilled
enough to distinguish between the signal from a thin wire and bleed-through
from a nearby high-voltage cable.
The Bottom Line
The idea is to move away from that beep-and-dig mentality. By learning
how to effectively utilise accessories like dual frequency sondes or
flexi-traces, you guarantee that no plastic or other type of utility is left
lurking beneath your feet unseen.
Learning about the capabilities of your equipment is the first step to
becoming a competent user of it.
