© 2023 Radiodetection Ltd 42
hard ground such as roads. In this case, the ground return
can be made by attaching the ground lead to the metal
frame of a manhole.
Using lighting columns
Direct Connecting to a metal, street-lamp column is
almost as effective as connecting to the cable sheath
itself. Normally the cable sheath is bonded to the metal
column, therefore a simple connection onto the column
enables the user to locate the street lighting quickly and
safely without having to call out a technician from the
lighting company.
If the lighting column is made from concrete make the
transmitter connection to the cable sheath unless the
cable is earthed to the inspection doorframe. Connection
to the cable sheath applies the transmitter signal for a
considerable distance enabling the locator to trace cables
feeding illuminated street furniture as well as other street
lights.
WARNING! The live cable connector is for use only by
operators licensed or permitted to work on live cables.
The use of a street light column as a means of applying a
signal to other power cables on the same electric circuit is
a possibility. The signal may be weak using this method
because it may have travelled some distance back to the
sub-station and out again on the other system. With the
locator used on a high sensitivity setting it is often possible
to locate a cable, which would otherwise have been
difficult or inconvenient to energize with the transmitter
signal.
Finding a good ground point
When using a Direct Connection, it is important to get the
best possible grounding for the transmitter. This provides
the lowest resistance ground path and the best output
signal. If it is not possible to use the ground stake the
following are examples of good alternative ground points:
Metal manhole covers
Metal drainage grates
Metal railings
Metal fence posts
8.3 Double-ended connections
Large diameter water pipes and gas distribution pipes that
are laid in sections sometimes have insulated joints
between the sections and can be difficult to locate using a
single ended connect. This is because when using a
single ended connection ground return, signals can often
cause confusion by returning to the transmitter along other
lines. The problem sometimes occurs when return signals
appear stronger than on the target line, usually because
the target line is deeper than the line carrying the return
signal, or the return path may be a better electrical
conductor than the target line.
Applying a double-ended transmitter connection is a
useful technique for positively tracing and identifying a
target line in a situation such as a heavily congested
industrial site, provided there are access points at each
end of the line.
Making a double-ended connection
Connect the transmitter to an access point on the target
line. The transmitter ground is connected with a long cable
to another access point further along the line. A complete
circuit is achieved without using ground as a current return
path. The long cable should be kept as far away as
possible from the expected route of the line.
This method of applying the transmitter signal is ideal for
positive identification of a target line. When a connection
has been made to two points on the same line, the same
level of current should be detectable around the circuit.
The locator display should remain constant if the depth of
the line does not change.
Figure 8.5: Making double-ended connections
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