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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
between structures of a faulty cable must be re-
the point indicated by the terminal measurement.
placed. If a structure does not contain a cable splice
When the portion of the cable suspected to be at
it may be augmented by a resonance or radar termi-
fault is raised, it is generally necessary to apply a
__
nal method.
tracer method to verify the fault location. The im-
b. Direct burial. Fault-locating for direct-burial
pulse method is ideally suited to this application, as
installations must pinpoint the fault, so that the
the noise of the discharge is usually quite evident
repairs can be made at the point of failure. Such
when the faulted section leaves the water.
faults generally can be best located with impulse
(2) Cable sheath leaks. Emergency mainte-
equipment such as the TDR method. Faults can also
nance of submarine cables frequently involves re-
be located by patrolling the cable and listening for
pair of a leak in the cable sheath. When a leak is
the noise of an impulse discharge at the fault. On
evident, it should be located as soon as possible; the
longer cables it may be preferable to use some other
cable raised; and the damaged section removed to
means, such as a terminal measurement, to obtain
prevent migration of moisture into the cable. Re-
an approximate fault location. In the absence of
pairs should be made in accordance with standard
audible noise, test holes must be dug so that detec-
splice procedures for submarine cables covered in
tor tests can be made using a tracer method.
section VI.
c. Submarine cable. The approximate location of
a submarine cable fault must be determined by ter-
minal measurements.
method such as any terminal method, except the
(1) Locating the fault. Verification of location
Murray bridge loop, or use the impulse tracer
can be made by pulling the cable out of the water at
method.
Section VI - CABLE REPAIR
5-19. Underground cable repairs.
open up the duct line at the fault point. If the cable
can be repaired without a splice, the duct line can
Underground cable is usually either direct burial or
be reclosed. It may be necessary to build one or
installed in ducts. While repair methods described
more new structures at the point to house any new
below are basically the same for any underground
cable which needs to be spliced into the existing
cable, there are some differences depending on the
cable to replace the faulted section. The method to
installation condition.
be used is largely a matter of judgment based on all
a. Direct burial. While there may be splice boxes,
the factors known at the time.
normally there is no structure to consider, and a
hole will have to be dug to make the repair. This
5-20. Submarine cable repairs.
may be a test hole used to pinpoint the fault loca-
When the approximate location of the fault has been
tion. Such access may have to be enlarged, if the
determined, the cable should be lifted to the surface
repair involves an appreciable length of cable. The
major problem in repairing direct-burial cable may
for examination and repairs. The cable may be lo-
be to provide a dry environment while making the
cated with a grapple hook and lifted with a barge-
repair. A temporary shelter may be required.
type crane. If the cable is difficult to locate, the
services of a diver may be required to determine the
b. Duct line. If the faulted cable length is in a
duct line between structures, there are several re-
location and to attach a line for lifting the cable.
pair methods. Usually, only one circuit is installed
After the cable has been hoisted to the surface, it
in a duct line in order to avoid cable capacity derat-
should be cut at the location of the fault to deter-
ing.
mine if (and how much) water has entered the
(1) Spare duct. If there is a spare duct avail-
cable. The most expedient method of determining
able, the simplest solution may be to pull a new
the distance the water has entered the cable is to
length of cable into this duct and connect it at both
cut the cable 25 to 50 feet (8 to 15 meters) on either
ends to the good ends of the faulted cable. Then pull
side of the fault. This distance depends somewhat
out the faulted cable, if possible, to provide a spare
on the time that the cable has remained in the
duct. At the very least, tag at both ends to indicate
water after the fault occurred and the type of cable
that this cable has been abandoned in place and is
insulation. At the point where the cable has been
faulty.
cut, a sample of insulation should be tested for
(2) No spare duct. The cable should be pulled
moisture as covered in section VII. If there is evi-
and a new cable installed. If this is impossible be-
dence of moisture at the first cut, then a second
cause of duct damage, a new duct must be installed.
section should be removed and another test made.
Alternately, it may be faster and more economical to
This operation should be continued until the point
5-10
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