3M CablePipe Locating Techniques Manual

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August 1998
80-6108-6216-3-C
Cable and Pipe Locating
Techniques
for use with 3Mª Dynatelª
Cable and Pipe Locators 
						

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Table of Contents
Section 1 The Basics of Cable Locating
1. Introduction ........................................................................................................................... 7
2. Applying the Signal: The Direct Connect Method ................................................................. 8
3. Applying the Signal:  The Induction Method ......................................................................... 9
4. Applying the Signal: The Dyna-Coupler Method ................................................................. 10
5. Other Locating Signal Sources ........................................................................................... 10
A. Passive Signals ............................................................................................................. 10
B. Power Frequencies ........................................................................................................ 11
C. Radio signals .................................................................................................................. 11
D. Cable TV Signals ............................................................................................................ 11
E. Other Transmitted Signal Sources ................................................................................. 11
6. Choosing Trace Modes ....................................................................................................... 12
7. One Touch Gain adjustment ............................................................................................... 13
8. Locating Techniques ...........................................................................................................14
A. Sweeping ....................................................................................................................... 14
B. Positioning ..................................................................................................................... 14
C. Tracing ........................................................................................................................... 14
D. Identifying Cable By Depth-Current Measurement ........................................................ 15
E. Tracing Currents ............................................................................................................ 16
9. External DC Power and 5 Watt Output ............................................................................... 17
A. External DC Power ........................................................................................................ 17
B. 5 Watt Output ................................................................................................................17
Section 2 Telephone Cable Locating Techniques
1. Introduction ........................................................................................................................... 9
2. Applying Signal to Telephone Cable: Induction Method ....................................................... 9
3. Applying Signal to Telephone Cable: Direct-connect Method ............................................. 20
4. Applying Signal to Telephone Cable: Dyna-Coupler Method .............................................. 21
5. Locating Slack Loops and Butt Splices ............................................................................... 23
6. Locating Unknown Laterals ................................................................................................ 23
7. Locating Cables from Pedestals ......................................................................................... 24
8. Locating Service Drops .......................................................................................................25
9. Locating an Open End ........................................................................................................ 25
10. Identifying Cables .............................................................................................................. 25
11. Pair Identification ............................................................................................................... 26
12. Locating Splits ................................................................................................................... 27
13. Fiber Optic Locating .......................................................................................................... 28
A. Can the Fiber Be Traced? ............................................................................................. 28
B. Applying the Trace Signal .............................................................................................. 29
Attaching at CO or Remote Terminal Office .................................................................. 29
Attaching at the Splice Point ......................................................................................... 29
C. Tracing the Fiber Optic Cable ........................................................................................ 30
Section 3  Power Cable Locating Techniques
1. Introduction ......................................................................................................................... 31
2. Applying Signal to Power Cables: Direct-connect Method ................................................. 31
A. Applying Signal to the Transformer ............................................................................... 31
B. Applying Signal at the Meter ......................................................................................... 31
C. Applying Signal to De-Energized Secondaries .............................................................. 32
3. Applying Signal to Power Cables: Induction Method .......................................................... 32 
						

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4. Applying Signal to Power Cables: Dyna-Coupler Method .................................................. 33
A. Applying Signal to Primary Cables ................................................................................ 33
B. Applying Signal to Secondary Cables ........................................................................... 34
5. Identifying Slack Loops .......................................................................................................35
6. Identifying A Cable Open End ............................................................................................. 35
7. Identifying Primary Power Cables ....................................................................................... 36
8. Locating Open Concentric Neutrals .................................................................................... 37
9. Locating Buried Streetlight Cables ..................................................................................... 38
Section 4  CATV Cable Locating Techniques
1. Introduction ......................................................................................................................... 39
2. Applying Signal to CATV Cables: Induction Method ........................................................... 39
3. Applying Signal to CATV Cables: Direct-Connect Method ................................................. 40
4. Applying Signal to CATV Cables: Dyna-Coupler Method ................................................... 41
5. Locating Cable Slack Loops ............................................................................................... 42
6. Locating Cables from Pedestals ......................................................................................... 42
Section 5  Pipe Locating Techniques
1. Introduction ......................................................................................................................... 43
2. Applying Signal to Pipe: Induction Method ......................................................................... 43
3. Applying Signal to Pipe: Direct-connect Method ................................................................. 44
A. Direct-connect Method on Tracer Wires ........................................................................ 45
4. Apply Signal to Pipe: Dyna-Coupler Method ...................................................................... 45
5. Locating Nonmetallic Pipe .................................................................................................. 46
6. Locating Pipe with Impressed Cathodic Protection ............................................................ 47
Section 6  Locating Faults
1. Introduction ......................................................................................................................... 49
2. Locating Sheath Faults .......................................................................................................50
A. Locating Sheath Faults Near Pedestals ........................................................................ 52
B. Locating Sheath Faults Under Pavement ...................................................................... 53
Perpendicular Method ................................................................................................... 53
Triangulation Method ..................................................................................................... 53
Extended Frame Methods ............................................................................................. 54
C. Finding a Fault without Tracing the Cable Path ............................................................. 55
D. Multiple Faults ...............................................................................................................56
3. Locating Aerial  Faults ......................................................................................................... 57
4. Locating Earth Faults Near the Meter Box .......................................................................... 58
5. Locating Earth Faults in Secondary Cable ......................................................................... 58
Section 7  Locating Active Duct Probes
1. Introduction ......................................................................................................................... 59
2. Locating the Active Duct Probe ........................................................................................... 59
3. Determining the Depth of the ADP ...................................................................................... 61
A. Determining ADP Depth with 500A/573A Cable Locators ............................................. 62
4. Locating Blockage or Collapsed Ducts ............................................................................... 63
5. Locating Sewer Pipe Problems Using a Video Camera ..................................................... 63
6. Locating a Flushing Hose Nozzle ....................................................................................... 63
Dynatel is a Trademark of 3M 
						

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This manual has been prepared to provide the most important written instruction material to date for
cable locating with 3MÕs Cable and fault Locating products.  It assumes a basic understanding of the
commonly used terms in telephone transmission and switching.  Whenever this manual is reissued, the
reason(s) for reissue will be listed here.  Comments concerning the contents or organization of this
document, as well as suggestions for improvement are welcomed.
3M Telecom Systems Division
Lab - Technical Communications
6801 River Place Boulevard
Austin, Texas  78726-9000
For Technical Service call: 800/426 8688
(outside the USA call 512/984 2575) Direct comments to:
Glossary
ACAbbreviation for Alternating Current.
AmplitudeThe maximum value of a varying quantity.  A signal on a buried cable will have a certain
amplitude which may be different from the signal on another buried cable.  The receiver
electronics can detect and display the difference.
AttenuatedA general term used to denote a decrease in the magnitude of a signal from one point to
another.
AudioA signal which can be heard by the human ear, typically from about 15 Hz to 15 kHz.
ConductiveProperty of a material which allows the passage of a signal or current.
HzAbbreviation for Hertz.  A unit of frequency equaling one cycle per second.
InductionA method of putting signal on a buried conductor by using a varying current in one circuit
(the transmitter) to produce a voltage in another nearby circuit (the buried conductor).
kHzAbbreviation for kilo-Hertz.  Hertz times 1000;  Example: 2.7 kHz equals 2700 Hertz.
k ohmAbbreviation for kilo-Ohms.  Ohms times 1000; Example: 2.5 kohms equals 2500 ohms.
LCDLiquid Crystal Display.
MegohmsAbbreviation for mega-Ohms.  Ohms times 1,000,000.  Example: 2.5 megohms equals
2,500,000 ohms.
ModeMethod of operation.
NullA receiver trace mode where the receiver will respond to signal on a buried cable by
indicating minimum signal directly over the cable.
OhmmeterDevice for measuring electrical resistance.
PeakA receiver trace mode where the receiver will respond to signal on a buried cable by
indicating maximum signal directly over the cable.
ResistanceProperty of a conductor which determines the current which will flow through it when a
particular voltage is applied. Measured in Ohms.
RMSAbbreviation for root-mean-square.  Used to designate the measurement of a voltmeter
when measuring 60 Hz.  Example: 110 volts RMS.
SecondaryA cable transmitting approximately 600 volts or less.
TriangulateA method of finding the location of a point by taking observations at two of the corners of a
triangle.  The point where the two observations cross is the third corner of the triangle and
the target location.
VoltmeterDevice for measuring electrical potential difference. 
						

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Section 1 The Basics of Cable Locating
1. Introduction
1.1 Cable locating is not an exact science, yet. To do a good job, you must know your equipment, and
use your intuition and good judgment.  Certain techniques can alert you to potential problems and
make the difference between a good locate and a bad one. In this manual, we discuss the basics of
locating buried cable or pipe by using a Transmitter to apply a signal to the conductor, and tracing
the conductorÕs path using a Receiver.
1.2 There are three methods of applying signal with a 3MÔ DynatelÔ Transmitter:
lDirect connect method
lInduction method
lDyna-Coupler method
1.3 With any method of applying signal, frequency choice is important to get the ÒmostÓ signal on the
cable. Any signal applied to an insulated, buried cable or pipe leaks off to ground; as it gets farther
away from the transmitter, the signal gets weaker and finally disappears. How fast it leaks off is
determined by:
lCable diameter,
lwet or dry soil conditions, and
lsignal frequency.
Since these conditions vary, the Dynatel Transmitters offer more than one frequency choice:
Low (
						

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2. Applying the Signal: The Direct-connect Method
2.1 Connecting directly to the cable or pipe you want to trace (power cables only if they can be de-
energized) is the most accurate method of cable locating. Connecting the Transmitter directly
isolates the signal to one cable.
Danger! Voltage greater than 240 volts will damage equipment and cause personal injury and death.  Make all
direct test connections before turning on the Transmitter.   Then activate the Transmitter in the Ohms
mode and check the display for voltage readings.  Follow standard procedures for reducing the voltage.
2.2 Set the Transmitter frequency to a lower frequency (where applicable); low frequencies do not
couple to other grounded cables as easily as higher frequencies, and they travel further down the
cable.
2.3 There are several methods for direct-connecting the transmitter, depending on your application.
These may include applying signal to a telephone or CATV pedestal, a power transformer or
meter, or directly to the cable or pipe. You can find detailed instructions for your application in
later sections of this manual.
A Few Important Points About Grounding
2.4 Grounding can Òmake or breakÓ a locate when you are using the direct-connect method. The
Transmitter connects electrically to the cable or pipe to be located and sends signal current
through it.  The signal goes to ground at the far-end, and returns to the Transmitter through the
ground rod. If the conductor is not well grounded, or if the Transmitter connection to the ground
rod is poor, the signal will also be poor and not detectable. The better the ground, the stronger the
signal.
2.5 Place the Transmitter ground rod as far from the far-end ground and as far from the trace path as
possible. In general, this means placing the ground rod at a ninety-degree angle to the suspected
path, as shown above. If necessary, you can extend the ground lead with any insulated wire. 
						

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3. Applying the Signal:  The Induction Method
3.1 The simplest way to put signal on a buried cable or pipe is with induction, where you merely set
the Transmitter on the ground directly over the cable and turn the Transmitter on. The Transmitter
induces signal current (tone) into any parallel conductor within range.
3.2 It is important to place the unit directly over the cable, with the hinge parallel to the cable path, as
shown above. The signal drops off rapidly if you place the Transmitter even 5 or 10 feet to either
side of the path.
Note: In congested situations where services such as gas or water pipes, cable TV, and lawn-watering
control circuits are all buried nearby, you should not use the induction method to apply signal.
The induction mode applies signal to all nearby conductors and confuses the trace.
3.3 The strength of the induced signal depends on three things: the Transmitter frequency, how well
the conductor is grounded, and how deep the conductor is buried.
3.4 From the Transmitter, a higher frequency travels farther than lower frequencies and couples to
nearby conductors (such as the cable or pipe to be traced). When using the Induction method, set
the Transmitter frequency to 33 kHz or higher frequency. Keep in mind that higher frequencies
and the high output level setting also put signal on conductors other than the one you are tracing.
Also, the Receiver can pick up signal from the Transmitter up to about 50 feet away, even if no
cable exists between them. For best results, keep the Receiver away from the Transmitter by at
least that distance.
3.5 The conductor must be well-grounded at both ends to produce a good locate. In all methods,  the
better the ground to the conductor, the stronger the signal.
3.6 You can find detailed instructions for using the Induction method in your application in later
sections of this manual. 
						

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4.1 The easiest way to put signal on a cable is with the Dyna-Coupler. When its jaws close around a
cable or pipe, the Dyna-Coupler couples the Transmitter signal onto it. As with the other methods,
the cable or pipe must be grounded to form a complete circuit path for the signal to follow.
4.2 When you apply the Dyna-Coupler between grounds, signal will be on the section between the
grounds.
4.3 You can find detailed instructions for using the Dyna-Coupler in your application in later sections
of this manual.
5. Other Locating Signal Sources
A. Passive Signals
5.1 Passive signals are naturally present on many conductors and allow you to locate cables without
using the Transmitter. For example, power cables carry 50 or 60 Hz currents. Less obvious are low
frequency currents resulting from local broadcast radio transmissions that penetrate the earth and
flow along metallic cables.
5.2 Passive signals let you locate conductors but not identify them because the same signals may
appear on all conductors. Their value is in enabling buried conductors to be detected and avoided
using only the Receiver. Be aware that all passive signals may change without notice.
5.3 When you plan to excavate to a conductor that has been located and identified with an active
signal, you should give the area a passive sweep to check for other nearby lines that are at risk
during the excavation. Lines that you locate during a passive sweep can then be traced and
identified with an active signal.
4. Applying the Signal: The Dyna-Coupler Method