3M CablePipe Locating Techniques Manual

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2.2 To verify the fault location, insert the frameÕs red probe directly on the spot between the legs.
Pivot the frame in a circle around the red leg, reinserting the green leg in the ground every few
degrees of the circle.  The bar graph should always be on the left (red), indicating that the fault is
directly below the red leg. 

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A. Locating Faults Near Pedestals
2.3 The placement of the ground rod can have unfavorable effects on locating a fault that is very close
to a pedestal.  The pedestal is the access point for applying the Transmitter signal.  If the fault is
very close (a few feet, at most), and the ground rod is also very close, it may be impossible to find
the fault.  The returning currents from the fault are so distorted by close ground rod placement that
the earth contact frame cannot recognize the fault. A good...

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B. Locating Faults Under Pavement
2.4 When the cable is routed beneath and in line with a paved surface, you can locate the fault using
one of the following methods.
Perpendicular Method
2.5 Hold the frame parallel to the cable path but several feet to the side of the cable path.  Bar graph
reversal occurs when the frame center is directly perpendicular to the fault.
Triangulation Method
2.6 To check the accuracy of the Perpendicular method, move back several yards from the point of bar
graph...

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Extended Frame Methods
2.7 Where a cable passes under a roadbed or other narrow stretch of pavement, and a check on both
sides with the frame proves the fault to be under the roadway, triangulating the fault from both
sides of the road gives a general indication of the fault location.  A more accurate method is to
extend the distance between the probe tips:
Insert the green leg in earth on the far side of the fault, but do not insert the red leg.  Strip
about ten inches of an insulated conductor such...

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C. Finding a Fault without Tracing the Cable Path
2.8 Since the green leg of the Earth contact Frame points to the fault, tracing the path before or during
the fault finding process may not be necessary.  This technique uses 90 degree turns to pinpoint
the fault. It usually requires at least three such turns and is called the Ôthree-ninetyÕ method:
Start in the normal manner by holding the Receiver in one hand and the Earth Contact
Frame in the other with the green-banded leg towards the fault.  Near...

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D. Multiple Faults
2.9 The problem with multiple faults on a cable is finding the major fault.  Digging a hole to fix a
pinhole in the sheath when a fault that disrupts service is farther down the cable can be frustrating.
The procedure below will prevent this from happening:
When setting up the transmitter to find faults be sure to set the output level to high so that
the fault sensitivity will be highest.  You want to find all the faults on the cable. Do not
change the output level setting during...

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3. Locating Aerial Faults
3.1 Shorted pairs, crossed pairs, and grounds on aerial cables can be pinpointed using an exploring
tone coil.  To locate a fault with the exploring tone coil, use this procedure.
3.2 Determine if the fault is a short or cross or if a conductor is grounded to the shield.  This will
determine how the Transmitter is attached to the faulted conductors.  If the resistance of the fault
is greater than 1800 ohms as measured between the faulted conductors or between the conductor...

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4. Locating Earth Faults Near the Meter Box
4.1 When the meter box is the access point for applying the Transmitter signal to locate a fault in
secondary cable, be careful where the ground rod is placed.  If the fault is very close (a few feet, at
most), and the ground rod is also very close, it may be impossible to find the fault.  The returning
currents from the fault are so distorted by close ground rod placement that the earth contact frame
cannot recognize the fault.  A good practice is to always...

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Section 7  Locating Active Duct Probes
1. Introduction
1.1 The 3MÔ Active Duct Probe (ADP) is a self-contained, small, waterproof transmitter (sonde). It
can be attached to a push-rod or pull-tape and inserted into a buried nonmetallic sewer, duct,
drain, or pipe. A cable locator of the same frequency will find the exact surface location. There are
several ADPs available from 3M. Models 3236, 3237, and 3238 Active Duct Probes transmit at
frequencies detectable by 500A/573A cable locators. 3236 is for...

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2.5 With the receiver handle perpendicular to
the path, locate the ADP position by
moving along the suspected path until a
peak or maximum is found. Adjust the
receiver gain as needed.
2.6 At the peak, rotate the receiver
horizontally to maximize the signal.
This ensures that the receiver handle is
perpendicular to the path.
2.7 Next, move the receiver across the path
searching for a peak.  Mark the spot
where the peak along the conduit path
coincides with the peak across the path.