Page 58 - BCCGA Best Practices Version 3.0

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3-11 LOCATE METHOD PREFERENCES
PRACTICE STATEMENT: When locating a single target facility electro-
magnetically, an active/conductive locating method is usually preferable to a
passive/inductive locating method.
PRACTICE DESCRIPTION: The preferred method of actively applying a signal
onto a facility is to use direct connection. This method involves connecting a
direct lead from the transmitter to the target facility and connecting a ground
lead from the transmitter to a ground point in order to complete a circuit.
A direct connection usually provides the strongest signal on the line and is less
likely to “bleed over” to adjacent facilities than other methods of applying a
signal. Direct connection allows for a greater range of frequency and power
output options. It is a good practice to use the lowest frequency possible at the
lowest power output possible to complete the locate.
If direct connection is not possible, the use of an induction clamp (coupler) is
the most effective method of applying a locate signal onto the target conductor.
However, this method limits the choices of frequency and power outputs than
offered by direct connection. Using an induction clamp is not as effective at
transmitting a signal as direct connection, can only be used within certain
frequency ranges, and must use a higher power output.
The least preferred method for locating a single target facility is usually
induction or broadcast mode on a transmitter. This method usually results in a
weaker signal that may “bleed over” to another conductor in the area. There
are situations where inductive locating gives the best results, such as on poor
conductors with no access point. When searching an area for all conductors
present, an inductive sweep using an ultra-high frequency is the preferred
method to avoid damages.
When using any of the above three methods, the locator should trace the
entire line from the point of signal application through the proposed work area.
ORIGIN/RATIONAL: It is very important that locators do not apply a signal
application to a target underground facility and begin locating prior to isolating
the grounding wire. Tracing continuously from the isolated grounding point of
signal application past the end of the work area improves the accuracy of the
locate.
Best Practices Version 3.0