UFC 3-535-01
17 November 2005
Figure 15-5. Current and Voltage Illustration
6
Jumper
6.6A primary
3
4
5
3'
4'
6.6A on
HOMERUN
Secondary
100W lamp
(to first fixture)
1
2
CCR
EXAMPLES OF VOLTAGE CALCULATIONS
ASSUMPTIONS
200 lights on 6.6A primary series circuit
Each light 100W (fixture or sign, etc)
Power factor of 1.0 for all components.
200ea x 100W
1.
Measured across homeruns at CCR, 1 & 2
voltage =
= 3,030V
6.6A
If only 100 lights, then voltage is 1,515V
or secondary 3' & 4'
4
3 &
2.
Measured across isolation transformer primary
100W
Voltage =
= 15.15V
6.6A
200W = 30.3V
With 200W light, voltage on secondary =
6.6A
200ea x 200W = 6,060V
With 200W lamps, voltage at CCR =
6.6A
200ea x 200W
= 2,000V
3.
With 200W lamps and a 20A primary, voltage at CCR =
20A
If jumper across at light fixtures 5 & 6
4.
, the voltage at CCR is based on load remaining on circuit.
85ea x 200W
5.
If 85 each 200W lights remain on 6.6A circuit:
Voltage =
= 2,576V
6.6A
Note that:
(1) Current is constant regardless of load, while voltage varies and is additive, depending on load.
(2) The low voltage secondary side is isolated from the high voltage primary side by the isolation transformer.
15-12
SELECTION OF 6.6 VERSUS 20 AMPERES SYSTEM
As noted above, the most common constant current regulator outputs used to power the
primary series circuits for runway, taxiway, and approach light systems at airfields and
heliports are 6.6 amperes (6.6A) and 20 amperes (20A). A 6.6A circuit may operate on
three or five different intensity levels. A 20A circuits typically operates only as a five
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