Underground Lighting Problems

As stated earlier in this chapter, the care and craftsmanship of the original installation will, to a large extent, determine the life of the system. Still, no system lasts forever. Even the best installation and the most conscientious inspection and maintenance program cannot prevent the aging and gradual breakdown of a system. In almost all cases when an underground cable breaks down, it goes to ground. Where more than one conductor is enclosed in 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 helps set up corrosion cells, breaks down neoprene, and rots 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 600 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;

this must be done before you start digging or repairing the cable.

This chapter will not discuss circuit troubleshooting in more detail, because each system is different. When you are in charge of installation or maintenance of an airfield, reference material, such as the components' manuals, should be acquired. If unattainable, NAVFAC P-272,

Definitive Designs for Naval Shore Facilities; DM 23.1, Navigational and Traffic Aids; NAVAIR 51-50AAA-2, Visual Landing Aids Design Standards; and NAVAIR 51-40ABA-7, Lighting and Marking Systems for Expeditionary Airfields are recommended as References. Problems, such as improper power connections, component connections, safety grounding, cable splices, cable terminations, and cable installations, are discussed in detail in these publications.