3M CablePipe Locating Techniques Manual

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Section 3  Power Cable Locating Techniques
1. Introduction
1.1 Read Section One of this manual to learn more general information about each of the following
signal application methods. The following paragraphs provide specific instruction on applying
signal for power cable locating.
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. Applying Signal to Power Cables: Direct Connect Method
2.1 There are several possibilities for direct-connecting the Transmitter to apply signal, including
applying signal to the transformer, meter, and cable to be located.
A. Applying Signal to the Transformer
2.2 The transmitter signal can be applied to all neutrals (both primary and secondary) that are
grounded at the transformer by simply connecting the Transmitter to the transformer cabinet.
There is no need to open the transformer or to de-energize any of the cables.  However, all the
neutrals are carrying signal and it may be difficult to identify a single cable.
B. Applying Signal at the Meter
2.3 Since the secondary neutral connects to ground at the meter as well as the transformer, you can
locate energized secondary cables by connecting the Transmitter directly to the meter box.  The
meter box is the preferred point to apply signal because the transformer usually has better
grounding to earth than the meter.  The locating signal is weaker if applied at the transformer.
2.4 You must place the Transmitter ground rod as far away from the meter ground as possible.  If
necessary, extend the ground lead with insulated wire.  This technique is fast since you do not
have to open the transformer, or break the meter seal.  Select the lower frequency; it does not
couple to other grounded cables as easily as a higher one. 
						

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3. Applying Signal to Power Cables: Induction Method
3.1 The Induction method broadcasts signal into an area.  No access to the cable is necessary.  Use
this only when there are no other buried conductors present, or when locating all conductive
buried services in a general area.  Perform the following procedures to use the Induction method.
3.2 Place the Transmitter on the ground over the cable to be located. The Transmitter hinge should be
in line with the cable path, as shown above.  Be certain that the Transmitter is directly over the
cable to be located.
3.3 Turn the Transmitter on and choose a frequency of 33 kHz or higher.
3.4 Use the Receiver to test the signal level by placing the Receiver 50 feet away from the Transmitter
on the ground near the cable. Move the Transmitter back and forth across the path. Listen for
strongest signal from the Receiver. If the Receiver has trouble picking up the cable path, return to
the Transmitter and switch to a higher frequency.  Recheck the signal level using the Receiver. If
the highest Transmitter frequency will not give satisfactory Receiver response, then boost the
Transmitter output as instructed in the units Operating Instructions.
C. Applying Signal to De-Energized Secondaries
 2.5 On de-energized cables with the far-end grounded, connect the Transmitter directly to the center
conductor of the cable to isolate signal to that one cable. Use the direct-connect method as shown
to apply signal. 
						

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4. Applying Signal to Power Cables: Dyna-Coupler Method
Warning: A potential for electrical shock exists when using the Dyna-Coupler on energized cables.   Use
appropriate safety procedures. DO NOT USE ON CABLES CARRYING IN EXCESS OF 600 VOLTS RMS.
A. Applying Signal to Primary Cables
4.1 Use the Dyna-Coupler method to put tracing signal on the neutral of either primary or secondary
cables and energized cables. The neutral and its grounds form a circuit path for the signal to
follow. When you apply signal with the Dyna-Coupler to the neutral anywhere between grounds,
signal will be on the section between the grounds.
4.2 Where you clamp the Dyna-Coupler on the
concentric neutral is very important. On three-
phase primary cable, clamp the Dyna-Coupler
on all the concentric neutrals as close to the
earth ground as possible. The signal is
coupled onto each cable equally.
4.3 It is important not to place the Dyna-
Coupler around one of the individual
primary cables.  Since the cables are buried
in the same trench, this causes a canceling
effect as signal goes one way on one cable
and the opposite way on the other.
4.4 On single-phase primary cable used in
a loop configuration, canceling is not a
problem. You can apply signal with the
Dyna-Coupler to the individual
concentric neutral of the cable to be
located as shown.
Note: Always use high output level with the coupler. 
						

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B. Applying Signal to Secondary Cables
4.5 To locate secondary cables, the easiest access to
the neutral is at the meter box.  There are several
ways to put signal on the neutral.  If the riser pipe
is nonmetallic (usually PVC), clamp the Dyna-
Coupler around the pipe as shown.  The jaws of
the coupler must fully close for signal
transmission.  This may be impossible if the riser
is flush with the mounting structure.
4.6 If the riser is flush with the mounting structure, it
may be impossible to clamp the Dyna-Coupler
around the riser. If this is the case and access is
permitted, break the seal and open the meter box
and clamp the Dyna-Coupler around the neutral in
the box as shown.
4.7 Some meters may have an external ground wire from
the meter box to the ground rod. Clamp the Dyna-
Coupler around the wire as shown.  This puts signal
on the neutral since the ground wire is connected to
the neutral in the meter box. Make sure you place the
Dyna-Coupler above other utilities grounded at the
ground rod, or signal may be coupled to them also. 
						

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5. Identifying Slack Loops
5.1 To identify the presence of a slack loop in the cable path, first locate and mark the cable path.
Then find the maximum response over the marked cable path and press the gain adjust key.
5.2 Retrace the cable path with the Receiver held so the handle is perpendicular to (across) the cable
path, as shown. When the Receiver passes over a slack loop, the signal increases and the bar graph
closes. Mark each response.
6. Identifying A Cable Open End
6.1 It is sometimes necessary to locate the open end of a buried cable. The cable could have been
severed or buried intentionally as in new construction.  If the cable end is insulated from earth
ground, use the following technique.
6.2 Connect the Transmitter using the Direct Connect method.  Use the continuity function to see if
the buried end is in contact with earth ground (low resistance).  If the resistance is high, choose
the highest frequency available.
6.3 Set the Receiver to match the Transmitter frequency and trace the cable path. The signal decreases
suddenly at the site of the ungrounded end. 
						

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7. Identifying Primary Power Cables
7.1 This procedure uses the Receiver and a Dyna-Coupler to identify a particular primary cable in a
group of similar cables.  This operation is sometimes called phasing.  The Transmitter is used to
apply tone to the target cable using the direct-connect method.
7.2 Follow standard procedures and remove the source elbows and park them at ground.  Remove the
load elbows and park at ground. After all phases have been de-energized and discharged, at the
load end, remove the cable to be identified from ground.
7.3 Apply Transmitter signal using the direct-connect method to the center conductor of the primary
cable carrying the phase to be identified. Use the lowest trace frequency available.
7.4 At the access where the cable is to be identified, connect a Dyna-Coupler to the Receiver with the
Extension Cable.  Select the PEAK selection of trace mode and select the same frequency as the
Transmitter.
7.5 Check the first cable in the group by clamping the Dyna-Coupler around the cable.  Press the
GAIN ADJUST key and observe the numeric display for relative signal strength.  Remember the
number and continue by clamping the Dyna-Coupler around the next cable in the group.  If the
signal strength is greater than the previous observation, press the GAIN ADJUST key.  If the
signal strength is less than before, ignore it.  After checking all the cables in the group, the cable
with the highest reading is the target cable.  Without pressing the GAIN ADJUST key, verify by
re-clamping the Dyna-Coupler around each cable.  Only the target cable should have tone on it.
Transmitter Transmitter connected
to center conductor of
target cable Primary Load Elbows
parked at ground Primary Source Elbows
parked at groundReceiver
Dyna-Coupler 
						

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8. Locating Open Concentric Neutrals
8.1 Open primary concentric neutral conductors will cause the normal neutral current to seek a path
around the open.  This path is usually through the adjacent earth and will cause a voltage gradient
around the open.  The 60 Hz voltage can be detected at the surface using the earth contact frame.
If you are confident that an open concentric neutral exists, follow the procedure below to locate
the open.
IMPORTANT
Neutral current may find a path around the open which is not through the earth.  A bare CATV
splice or other utility services which are common-bonded (grounded at the same point as the
power utility) may be carrying the neutral current.  In which case, this method may not work.
a. Carefully trace and mark the path of the cable so that it can be followed easily.
b. After tracing the path, connect the Earth Contact Frame to the Receiver.  Turn the
Receiver on and select the tone mode.  Next, press the frequency key to select the power
frequency selection (50/60 Hz).
c. Hold the Receiver in one hand and the Earth Contact Frame in the other.  Starting at least
20 feet away from the transformer, insert the frame probes fully into the ground parallel
and as close as possible to the marked cable path.  Press the gain adjust key.
d. Continue along the marked cable path, reinserting the frame probes every few steps while
watching the receiver bar graph.  You may also listen to the speaker audio.  Remember to
keep the frame parallel to the cable path.
e. When the bar graph and speaker indicate an increase in signal strength,  proceed slowly,
inserting the frame probes every few inches.  Locate a point on the marked path where
the bar graph indicates maximum closure.  If the bar graph completely closes, press the
gain adjust.  The maximum indication may be rather sharp. In other words, frame
movements on the order of 5 or 6 feet may go from one side of the maximum to the other.
The open neutral will be located beneath the center of the frame at maximum closure. 
						

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9. Locating Buried Streetlight Cables
9.1 Buried cables that bring power to streetlights are normally not energized in the daytime. Each
streetlight has a light sensitive switch that will open during daylight hours. Trying to locate these
cables using the passive power frequencies (either 50 or 60 Hz) will not work.
9.2 Street light cables appear to be floating (no grounds) since the supply is a transformer and the
light sensitive switch is open. This means there is no return path for a tracing signal to return to
the transmitter. To put a tracing signal on the cable, use the Dyna-Coupler and the highest
frequency available (200 kHz). The easiest point to apply the signal is at the base of the light.
Before you dig, check all the nearby streetlights to keep from excavating a dangerous power
cable. 
						

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Section 4  CATV Cable Locating Techniques
1. Introduction
1.1 Read Section One of this manual to learn more general information about each of the following
tone application methods. The following paragraphs provide specific instruction on applying tone
for CATV (cable television) cable locating.
2. Applying Signal to CATV Cables: Induction Method
2.1 The Induction method broadcasts signal into an area.  No access to the cable is necessary.  Use
this only when there are no other buried conductors present, or when locating all conductive
buried services in a general area.  Perform the following steps to use the Induction method.
2.2 Place the Transmitter on the ground over the cable to be located. The Transmitter hinge should be
in line with the cable path, as shown above.  Be certain that the Transmitter is directly over the
cable to be located.
2.3 Turn the Transmitter on and choose a frequency of 33 kHz or higher.
2.4 Use the Receiver to test the signal level by placing the Receiver 50 feet away from the Transmitter
on the ground near the cable.  Move the Transmitter back and forth across the path.  Listen for the
strongest signal from the Receiver.  If the Receiver has trouble picking up the cable path, return to
the Transmitter and switch to a higher frequency. If the highest Transmitter frequency will not
give satisfactory Receiver response, then boost the Transmitter output as instructed in the unitÕs
Operating Instructions. 
						

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3. Applying Signal to CATV Cables: Direct-Connect Method
3.1 The direct-connect method requires access to the cable shield.  Disconnect the cable at the
near-end where the Transmitter is connected.  Do not disconnect at the far-end (subscriberÕs
premises) since this supplies a far-end ground.  Perform the following steps to use the
direct-connect method.
3.2 Connect the red lead of the Transmitter to the cable shield and the black lead to the ground
rod.
3.3 Place the ground rod as far away from
the cable path as possible (90 degrees
from the suspected cable path).  Never
ground to water pipe or other services
in the area. The returning signal on
these services may mislead the trace.
3.4 Remove the ground bonding at the
near-end. The far-end should have a
good ground. Turn the Transmitter on
and choose a low frequency signal to
get greater signal distance down the
cable.