RD5100H
2
O+ Operation Manual
28
© 2018 Radiodetection Ltd
7.2 Signal & ground
connection
Manhole covers
Sometimes when locating, it is not possible to insert the
ground stake into the earth, for example, when locating on
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.
7.3 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 7.5 - Making double-ended connections