Triplett Hound 3 – PN: 3392 - Manual (Page 28)

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7.2.7: Resistance Heating Wires
The FOX or FOX 2 and the HOUND 3 can be used to trace the
path of a resistance heating wire in a plaster wall or ceiling.
This is usually performed to find an open in the wire. It is
best if the user is familiar with resistance heating techniques,
particularly in regard to the typical patterns used for the wire
path. The wire is usually in a serpentine pattern, with the
wire spacing and orientation varying depending on the
amount of heat needed in different areas of a room.
Finding the open can be a challenge. Several techniques can
be, and should be, used.
It helps if the user performs a few experiments before trying
to find the open. See Figure 6. Attach a few pieces of wire
(any kind) more than several feet long to each clip of the
FOX or FOX 2. Lay the wires out on a non-conducting sur-
face (a wood floor with no metal in the vicinity . . . nails are
OK, but make sure there’s no metal furnace duct below the
floor) parallel to each other, about 4 “ apart. Using the HOUND
3, trace along one of the wires, in normal fashion, noting
how the tracer tone becomes stronger as the wire is ap-
proached. Now trace along the other wire, noting that it be-
haves just like the previous wire. Now, slowing move the
HOUND 3 from one wire to the other wire. Notice that at
approximately the midpoint between the wires, the tracer
tone becomes very weak. This is the “null point”...... the place
where the signal from one wire cancels the signal from the
other wire. Notice how this null differs from simple loss of
signal . . . that is, there’s a very narrow zone where the null