UFC 3-535-01
17 November 2005
15-14
CIRCUIT CONFIGURATION
There are three circuit configurations that are normally used to power runway and
taxiway systems:
15-14.1
Single Circuit per Lighting System
This is the standard FAA configuration, with a single circuit for each of the different
lighting systems (for example, one circuit for the runway edge lights, one for the
touchdown zone lights, or one for the runway centerline lights). It is the most
economical configuration. In some cases, however, this approach may create very high
voltages on the primary series circuit, which can reduce the life and reliability of the
system and increase the potential hazards for maintenance personnel. In addition, in
the event of a fault in the circuit, the entire circuit is out of service. Also, the trouble-
shooting of line faults can be a lengthy, time consuming process because of the length
of the circuit.
15-14.2
Multiple Circuits per Lighting System - Split Circuits
Advantages include easier troubleshooting and reduction in circuit voltages. A
disadvantage with this configuration is the higher cost compared with a single circuit,
particularly if the available space in the vault or the duct system is limited. The designer
should also consider the possible consequences of a partial system failure. For
example, where two circuits power a runway edge lighting system, the failure of one
circuit leaves the other circuit to light only half the runway, indicating a much shorter
available runway to the pilot. It may be necessary to install an interlock between the
regulators so that both circuits will shut down if either circuit fails.
15-14.3
Multiple Circuits per Lighting System - Interleaved Circuits
This is the type of circuit configuration specified by ICAO. Although this is the most
expensive configuration, requiring more cable, it has the advantage of preserving the
full pattern of the airfield lighting system for the pilots in the event of one circuit failure,
hence provides a measure of additional operational safety. Further, it has the
advantages noted for the split circuit configuration.
15-15
PARALLEL CIRCUITS
Parallel (or multiple) circuits have circuit elements connected across the conductors to
which input voltage is applied. In theory, the same voltage is applied to each light,
although voltage drop occurs along the conductor, which can be significant for longer
circuits. The reduced voltage can reduce the intensity of lights at the far end of a circuit.
If intensity control is required for this type lighting circuit, tapped transformers of
inductive-voltage regulators are used, which increases the cost and reduces efficiency
of the circuit.
15-16
PHOTOMETRIC CHARACTERISTICS OF LIGHT FIXTURES
15-16.1
Airfield lighting provides visible light to pilots for guidance during landing
and taxiing operations. The guidance provided is a function of configuration of the lights,
light color, and strength and "shape" of the light output (photometric performance). The
strength is the brightness or intensity of the light output, measured in candelas. The
required shape of the light "beam" from a light fixture is typically represented by an
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