one sheath, the insulation within the sheath may
deteriorate so that a cross type of short occurs. This
contact almost always creates enough heat and
pressure to rupture the sheath and put the conductors in
contact with ground.
Moisture is one of the most common causes of an
underground system breakdown. Impurities in the
water help set up corrosion cells, break down
neoprene, and rot rubber. Only a trace of moisture,
when superheated by the electrical power of the circuit
and converted to steam, can cause an explosion that
will rip the cable to shreds. Groundwater contains
enough minerals to provide an excellent conductor to
all other parts of the system. Some underground cables
are bonded together. The usual way to find out that an
underground power cable has a problem is to check
when the circuit opens.
In ducted systems, the maximum runs between
manholes are 500 feet. The normal method of repair is
to replace the cable. In direct burial cable systems, the
cable runs may be quite long, and it would be
impractical to replace the entire run. In this case, cable
fault locators are used to locate the fault. Before
starting to work, make sure that all power is off on the
circuits in the trench before you start digging or
repairing the cable.
This chapter does not discuss detailed circuit
troubleshooting because each system is different.
When you troubleshoot complex problems that
involve airfield lighting, you should refer to the
following publications: Definitive Designs for Naval
Shore Facilities, NAVFAC P-272; General
Requirements for Shorebased Airfield Marking and
Lighting, NAVAIR 51-5OAAA-2; and Lighting and
Marking Systems for Expeditionary Airfields.
NAVAIR 51-4OABA-7. Problems, such as improper
power connections, component connections, safety
grounding, cable splices, cable terminations, and cable
installations, are discussed in detail in these