Shield Shiel A-XT - NAC Wiring Length

Calculations B
Shield Fire, Safety and Security Ltd.
Shield A-XT Releasing Fire Control Panel - Installation and Operation Manual SEXTCP-OM
Revision E01.00
80 of 127
NAC Wiring Length
Determine the maximum wire length that can safely operate Notification Appliances under worst case conditions.
To determine the maximum wire length under worst case conditions:
Sample L
max
Calculation
The example calculation below illustrates the method for determining the maximum allowable wire length from the
NAC1output 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 (Vop
min
) 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 (Vop
min
) of Notification Appliances on the NAC channel.
2 Calculate the maximum current of the circuit (I
max
).
3 Identify the wire-resistance-per-foot of the circuit (R
wire
).
4 Calculate the maximum wire length (L
max
) of the circuit.
1
Identify the minimum operating-voltage (Vop
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
+ (Vop
min
/ EOLD) ]
=
[ ( 0.209 + 0.209 + 0.209 + 16 / 10K ) ] A
=
( 0.627 + 0.0016 ) A
V
opmin
= 16 VDC
I
total
= 0.6286 A