It is less efficient because there is no metal to metal contact
to transfer the current onto the line. A smaller portion of
the transmitter’s signal makes it onto the target conductor,
and that limits the distance you can trace the line.
2. Induction using just the transmitters
coils does not discriminate between utilities above ground
and utilities below ground. The higher the frequency, the
easier it is to induce a current onto all of the sorrounding
3. When using the transmitter coils Air Coupling
needs to be tested for and avoided.
4. Induction is less effective on deeper
To create a circuit inductively, the signal must be able
to travel in a both directions on a conductor. In other words,
the conductor needs to be grounded at both ends. Some conductors
do this better than others. As a rule of thumb, lines that
require electrical continuity in order to move their product
(electric, cable, phone) are better at this than those that
do not (gas, water).
Remember that you need a good circuit for current to flow.
Higher frequencies used while inducing may help but
Induction in practice will not make current flow in a bad
(high resistant) circuit.
Induction also requires a higher frequency than direct connect.
Nearly all transmitters work better at a frequency of 33kHz
or higher for induction. (The SeekTech ST-33Q “Q-ring”
is an exception. In many cases it can produce a locatable
signal at 8kHz on highly conductive utilities.)