UFC 3-260-11FA
25 May 2005
3-10.5
Series Circuits. Most visual NAVAID light systems are installed in
constant current series circuits, circuits in which light elements are connected in series
with the same current flowing to each light element. The circuit is one continuous loop
starting and ending at the power source. Runway and taxiway lighting systems and
steady burning approach light systems are on constant current series circuits, which
provide more uniform intensity and better brightness control of the lights. Runway and
approach lights are installed with five steps of brightness, while taxiway lights, medium
intensity runway lights, flashing lights, and Medium Intensity Approach Lighting Systems
with Runway Alignment Indicator Lights (MALSR) are installed with three brightness
steps. Because of the number of fixtures in runway and taxiway light systems, it is
common for multiple circuits to serve a runway and its taxiways. Switching is required to
simultaneously operate all circuits on an individual runway or an individual taxiway
system.
3-10.5.1
Runway Circuit Lights. Lights that are connected to a runway circuit or
circuits for simultaneous switching include:
Edge lights
Threshold lights
Runway end lights
Runway distance markers and arresting gear markers
Mandatory signs
Runway exit signs
3-10.5.2
Taxiway Circuit Lights. Lights that are connected to a taxiway circuit
include:
Edge, centerline and runway exit lights
Taxiway hold lights/stop bar, and runway guard lights
Information signs
Location signs
3-10.5.3
isolation transformers at each light or group of lights to reduce the high voltage of the
series circuit to the low voltage for light operation and to provide a constant current to
the light at 6.6 amperes (at high step brightness). The isolation transformer also acts as
a bypass to prevent an open condition (caused by a lamp failure) on the primary circuit
that would cause the entire series circuit to shut down.
3-10.6
Circuits Other Than Series Circuits. Beacon, wind cones, obstruction
lights, MALSR, floodlights, sequence flashers, REIL, and electronic NAVAIDS are
powered by constant voltage circuits. Devices with lower power requirements are
served by 120V circuits. Devices with larger power requirements (or where long
distances result in excessive voltage drop) use 480V or higher.
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