UFC 3-535-01
17 November 2005
15-10.1.6
An open-circuit may not disable entire circuit.
15-10.2
Disadvantages of parallel lighting circuits are:
15-10.2.1
Intensity of lights decreases with line voltage drop along the circuit. This
could be misinterpreted if noticeable in a pattern of many lights.
15-10.2.2
Two conductors are required along the complete circuit, and larger
conductors may be needed to reduce voltage drop.
15-10.2.3
Lamp filaments are usually longer which may require larger optics and
larger light fixtures.
15-10.2.4
Intensity control, particularly at the lower intensity, is more difficult to
achieve without added equipment cost.
15-10.2.5
A single ground fault on the high voltage feeder will disable the circuits.
15-10.2.6
Ground faults are difficult to locate.
15-10.3
Parallel circuits are used for most area illumination, individual or small
numbers of visual aids, and power distribution. AGL systems typically using parallel
circuits are apron floodlighting, other apron lights, sequence-flashing lights, special
purpose visual aids such as beacons and wind direction indicators, some obstacle
lights, and electrical distribution circuits.
15-11
CURRENT AND VOLTAGE ON SERIES CIRCUITS
The output current for AGL constant current series circuits have become standardized
at either 6.6 amperes or 20 amperes (at highest intensity). The loaded output voltage
from the CCR is limited to 5,000 volts because the cable used for the primary lighting
circuit is rated for 5kV.
15-11.1
The voltage will vary depending on the connected load. Figure 15-4
illustrates the constant current and varying voltage through several examples. As seen
from Figure 15-4, the voltage measured across the outputs of the CCR (at highest
intensity step) is simply the total watts divided by 6.6 A (assuming power factor of 1.0),
or 3,030V for 200 each 100W lamps (such as light fixtures or signs). With 200W lamps,
the voltage is calculated at 6,060V, which exceeds the 5kV cable rating of the primary
circuit. However, if a 20A circuit is used, the voltage calculates to be only 2,000V at the
CCR. Similarly, if 45W lamps are used in the above example, the voltage across the
CCR output terminals is calculated at 1,364V.
15-11.2
The examples above show that the voltage on the primary circuit is
additive and will vary with the load, but the current will remain the same. The secondary
circuit is always 6.6A (highest intensity step), with a 6.6A/6.6A isolation transformer
used with 6.6A primary circuits, and 20A/6.6A isolation transformers used with 20A
primary circuits.
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