UFC 3-535-01
17 November 2005
often have low efficiency that imposes higher than expected loads on the regulator. The
proper sizing of the regulator requires careful consideration of the types of loads on the
circuit and the true impact of those loads on the regulator.
15-6.2
As described in paragraph 15-6.1, the REIL can impose significant loads
on the CCR powering the circuits to which they may be connected. It is preferable, if the
budget permits, to have separate circuits with 240/120 volt service to power the REILs,
thereby eliminating any adverse impacts on series lighting circuits.
15-6.3
Sample calculations and comparison with test data, as well as guidance
for setting taps, are shown in Figure 15-4. A table format for calculating airfield lighting
series circuit loads is shown in Table 15-4. Carefully consider the notes in Table 15-4.
when determining load values.
15-7
CABLE
The primary series circuit utilizes FAA L-824 Type C cable, which is XLP (cross-linked
polyethylene) insulated 5kV, single conductor, stranded. L-823 connectors are used for
connections. For 6.6 ampere primary series AGL circuits, a #8 AWG conductor is
normally used. A #6 AWG conductor is used with 20 ampere circuits. For the secondary
side lighting loads, a two-conductor #10, 600V insulation is normally used.
15-7.1
The cable is installed in conduit, although it may be direct buried (L-824
cable is rated for direct burial). It is important that insulation is intact and that proper
connections are made. Deteriorated or damaged cable can result in current leakage and
may present a high voltage hazard to maintenance personnel. While installation in
conduit may cost more, this method usually provides longer circuit life, and makes
troubleshooting and replacement of cable segments easier.
15-7.2
The types of faults associated with series circuit cable are open circuit
conditions and shorts-to-ground. An open circuit condition will turn off all the lights. A
single short-to-ground will not impact the lighting, but multiple shorts-to-ground can
cause dimming of lights or outages for portions of the circuit or for the entire circuit.
15-8
TRANSFORMERS
The isolation transformer provides: electrical isolation between the high voltage series
circuit and the low voltage secondary feeding the lighting load (such as a fixture or
sign), constant current output for a constant current input at the correct ratio, and an
effective short circuit in the event of an open condition in the light fixture, for example
with lamp filament failure.
15-8.1
With the isolation transformer, only low voltage is brought to the light
fixture (via the secondary circuit), and failure of the light does not cause an open
condition on the primary circuit that would result in other lights and other connected
loads to be shut off.
15-8.2
Isolation transformers for AGL are covered by FAA Specification L-830
(for 60 Hz) and FAA Specification L-831 (for 50 Hz), and are typically 6.6 amperes on
the secondary side, with either 6.6 amperes or 20 amperes on the primary side for
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