© 2016 Littelfuse Protection Relays & Controls
Flashers and Tower Lighting Controls
Tower and Obstruction Lighting Controls
www.littelfuse.com/scr490d
Rev: 1-A-062316
Wiring Diagram
SCR490D
Obstruction Lamp Alarm Relay
Description
The SCR490D is used to provide remote monitoring of steady
burning incandescent marker and obstruction lighting. Four
onboard switches allow operator programming for lighting
systems with two through nine lamps on a single AC circuit. The
SCR490D uses a toroidal sensor and electronic circuitry to sense
the failure of one or more lamps.
Operation
When a lamp fails, the SCR490D senses a decrease in current
flow. Then, after a fixed time delay, it transfers to its alarm mode.
In alarm mode, the LED indicator, the output relay (SPDT
isolated contacts), and a non-isolated solid-state output are
energized. Replacement of the failed lamps resets the alarm
outputs and the LED indicator. To prevent false alarm signals,
power must be applied to the SCR490D at the same time that
lamps are energized.
Features & Benefits
FEATURES BENEFITS
Toroidal current sensing
Reliable low cost monitoring of incandescent
marker and obstruction lighting through built-in
CT which also provides isolation from the
lighting circuit
Monitors 2 - 9 lamps
Senses failed obstruction lamps on a single
AC circuit
Isolated, 10A, SPDT alarm
output plus one 1A,
solid-state line voltage
alarm output
Provide alarm indication and can also be used for
remote monitoring of the lighting system
Fixed trip delay (6s) Prevents nuisance alarms
Specifications
Operation
Number of Lamps 2 - 9 (selectable)
Lamp Wattage 116W, incandescent lamps
Rated Lamp Voltage 120 or 130VAC (selectable)
Monitored Voltage 120VAC ±3%
Trip Delay ≅ 6s fixed
Voltage 120VAC
AC Line Frequency 50/60Hz
Tolerance
120VAC - 20% - 10%
Line Voltage Output
(Solid State Rated) ≤ 125W to operate a spare lamp or alarm
Isolated Alarm Output 10A @ 120VAC or 30VDC resistive;
1/4 hp @ 125VAC; 1/2 hp @ 250VAC
Mounting Surface mount with two #6 (M3.5 x 0.6) screws
Dimensions H 88.9 mm (3.5”); W 63.5 mm (2.5”);
D 44.5 mm (1.75”)
Termination Screws with captive clamps for up to 14 AWG
(2.45 mm
2
) wire
Circuitry Encapsulated
Operating/Storage
Temperature -55° to 65°C / -55° to 85°C
Humidity 95% relative, non-condensing
Weight ≅ 6.8 oz (193 g)
V = Voltage
OL = Obstruction Lamps
T = Toroid
SS = Selector Switch
AXL = Auxiliary
Load/Alarm
Relay contacts
are isolated.
