Littelfuse SCR490D Series, Obstruction Lamp Alarm Relay, Output Form SDPT, 120VAC

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Regular price $449.35
Rated voltage
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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.


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.


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
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 mm2 ) 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)