General Machine Products RD7000 Traceable Rod Detection - Manual (Page 27)

RD7000 Operation Manual 21
Identify points where lines may be bonded or in
close proximity to each other. Work toward these
points rather than away from them. For example, if
gas and water pipes are bonded within a building,
apply the signal at the valves or access points in the
road rather than in the building.
Reduce coupling to a parallel line by using a low
signal frequency where available.
Return signal flowing on another line. Use a double-
ended connection to by-pass the ground return
if possible.
Choose a signal application point where the line is
furthest from other lines and not in a
congested area.
When using single-ended connection, site the
ground stake as far from the target line as possible
and away from other buried lines.
Avoid using existing structures for ground
connections; other buried lines may be bonded
to them.
A bad ground connection or just laying the ground lead
on the surface at right angles to the line may result in
less coupling than a good ground provided long distance
tracing is not required.
6.2 Signal grounding
6.2.1 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.
6.2.2 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 receiver to trace
cables feeding illuminated street furniture as well as other
street lights.
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WARNING! The live cable connector is for use
only by operators licensed or permitted to work on
live cables.
When the cable is not grounded at the column, open the
inspection door and connect the live cable connector to
the live or neutral conductor.
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 receiver 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.
6.2.3 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.
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