Triplett Fox 2 – PN: 3382 - Manual (Page 42)

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Miscellaneous Multiwire Cables:
Some general principles are important to keep in mind when
locating and tracing wires and cables.
Any wire with a signal on it, which runs parallel to another
wire or wires tends to couple its signal to the other wires.
The closer the wires are together, and the longer the parallel
run, the more signal that is coupled. This situation occurs in
multiwire cables, and when cables are bundled together when
installed.
Luckily, if the other wires are low impedance (they have loads
on them), the coupled signal will be lower in level. So, in
general its best to disconnect the cable being traced from
its loads, leaving other paralleling cables still connected to
their loads. If the other cables do not have loads (like when
they are being installed), it helps to temporarily connect one
end of the cable to earth ground, so that they do not inter-
fere with the trace.
The loading effect can also be used when trying to locate an
open fault in a wire in a multiwire cable. By leaving the loads
on the unfaulted wires, the tracer tone will be reduced in
level on the unfaulted wires, and make locating the open
easier. In fact, if the other wires are unconnected, it helps to
temporarily connect them to earth ground, so that they sup-
press the effect of the coupled signals. It may also help to
connect the far end of the open faulted wire to earth ground.
Doing this will produce the most distinct change in tracer
tone level when the HOUND or HOUND 2 passes over the
location of the open.