Sample L
max
Calculation
The example calculation below illustrates the method for determining the maximum allowable wire
length from the NAC1 output to the EOL resistor.
Determine the maximum wire length (L
max
) for three Notification Appliances on NAC channel 1 where,
The manufacturer data sheet for the strobe indicates that the minimum operating-voltage (V
Opmin
)
is 16 VDC.
The manufacturer data sheet for the strobe indicates that the maximum current-draw (I
strobe
) is
209mA DC.
The circuit connection is provided with 18 AWG solid-copper-wire.
The EOL resistor in the circuit is 10K Ohms.
To determine the maximum safe-wire-length (L
max
) of this circuit:
1
Identify the minimum operating-voltage (V
STB-min
) of the strobe from the manufacturer data sheet.
From the manufacturer data sheet:
2
Calculate the total current of the parallel devices in the circuit (I
total
) where,
[ I
total
= I
strobe_1
+ I
strobe_2
+ I
strobe_3
+ (V
Opmin
/ EOLD) ]
= [ ( 0.209 + 0.209 + 0.209 + 16 / 10K ) ] A
= ( 0.627 + 0.0016 ) A
V
STB
-
min
= 16 VDC
I
total
= 0.6286 A
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