sometimes the most effective method of locating the
trouble. A knowledge of test equipment, an ability to
read drawings or schematics, and an understanding of
electricity are the key factors in locating electrical
Types of Trouble
The same basic types of trouble can occur in the
airfield lighting cable system whether that system is in
series or in multiple; however, the results of these
circuit troubles can cause dramatic differences; for
instance, a short circuit across the terminals of a
distribution transformer supplying a multiple system is
a dangerous overload; and the same short circuit across
the output terminals of a CCR and series transformer is
a no-load condition. An open in the output circuit of a
CCR, on the other hand, creates a dangerous overload.
Burned-out lamps in the secondary of a series circuit
will not damage the transformer, but the secondary
voltage will rise above normal and distort the wave
shape ofthe primary current. When enough lamps bum
out. the primary current may rise high enough to
shorten lamp life and possibly damage the regulator.
These critical factors should tell you why you need to
know the circuit.
In the discussion above, all types of electrical
trouble were mentioned; for example, opens, shorts,
grounds, and improper power.
OPENS.An open circuit is an incomplete
circuit. Somewhere the circuit has a break;
therefore, there is not a complete path for current
flow throughout the circuit. Because there is no
current flow, the circuit cannot operate. In analyzing
circuit trouble, if the lights are not burning, the
motor is not running, and so forth, you need to look
for a break in the circuit. Usually this break will be at
the unit(s) of resistance (burned-out lamp, broken
resistor, motor burned out), but sometimes the break
will happen in the cable. When the cable breaks, this
break is most likely to happen at a splice or
connection. Other cable breaks may be caused by
digging operations being done in the wrong place.
That occurs when base maps are not kept up to date
and when unauthorized digging operations take
place. It is an excellent reason for installing and
maintaining direct burial cable markers.
Improper installation of cables can cause them to
fail. Cables may be damaged by kinking, bruised by
rocks, crushed by wheels, or cut by shovels when
proper care is not exercised during handling and
installation. While the damage at the time it occurs
may not be great enough to take the cable out of
service, it may be the starting point for a cable failure at
a later date. This failure may be either in the form of a
broken cable (open), cross type of short (two cables
touching), or a short to ground (cable in contact with
earth ground). Any of these troubles can render the
circuit inoperative. The indication of the type of
trouble that you have in the circuit and the point in the
circuit where this indication appears should assist you
in locating and repairing the circuit.
With an open circuit, that portion of the lighting
system being supplied by the effected cable will not
operate. A string of lamps that do not light, then, would
indicate an open cable.
SHORTS.If lamps are lit when they are not
supposed to be or if a circuit is affected by another
circuit, you most likely have a cross type of short
between the two circuits. The logical point to start
looking for this trouble is where the two cables cross
orss where they are close to each other.
GROUNDS.When a string of lights bums dim
or when fuses blow on a circuit, you have a short to
ground. The insulation on the supply cable is damaged.
This defect lets current pass directly from the
conductor to the earth and prevents the lamps from
receiving enough power to operate correctly; that is,
some of the resistance of the circuit is being bypassed.
The amount of resistance being bypassed in the circuit
governs the effect of the short to ground. If enough
resistance is removed (bypassed), then the current rises
to a point that is sufficient to blow the fuses and thus
disconnect the circuit.
IMPROPER POWER.Improper power can
result when regulators or distribution transformers are
not connected properly. If the incorrect input voltage is
connected or if the regulator has been purposely
connected for an unusual load requirement, improper
power can be applied to the system and serious damage
Underground Lighting Problems
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