24 Vdc Notification Appliance Circuit (Nac) Specifications - General Signal Building BPS6 User Manual

24 Vdc Notification Appliance Circuit (NAC) specifications

No "T" tapping
Note:
permitted.
Typical cable pair resistances
Wire size
12 AWG
14 AWG
16 AWG
18 AWG
16
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The NAC cable must be a minimum 18 gauge. Distance limits
are determined using the maximum allowable circuit resistance
and cable manufacturer's specifications. Restrictions apply when
calculating the wire size for the NACs:
1. Minimum supply voltage available is 18.9 V.
2. Minimum required circuit voltage at any NAC is 17 Vdc.
3. Maximum alarm current required for all NACs.
Using Ohm's law, the NAC current requirement, and a voltage
drop of 1.9 volts (18.9 - 17), the maximum allowable NAC
Resistance per
resistance is determined as follows:
1,000 feet
3.5 Ω
5.2 Ω
R = -------
max
8.0 Ω
13.0 Ω
Using this formula, the maximum permissible circuit resistance
for a loaded (2.5 A) circuit is 0.76 9 as follows:
0.76 Ω = -------
Using the Load vs. Distance table, the maximum allowable length
(D) of any listed wire gauge pair is determined as follows:
R
D = ------- X 1000
R
/1000'PAIR
Using this formula, the maximum length of a loaded (2.5 A) NAC
using a pair of 14 AWG wires is:
146.1' = ------- X 1000
146 feet is the maximum length of a loaded (2.5 A) NAC branch
circuit using a pair of 14 AWG wires.
Quick reference table (load vs. distance NAC circuit (1.9 volt drop))
Load
current
0.1 A
0.25 A
0.50 A
0.75 A
1.0 A
1.5 A
2.0 A
2.5 A
3.0 A
V R = Maximum allowable NAC resistance
drop max
I = Maximum NAC current requirement
max
I V = Maximum allowable voltage drop
max drop
from power supply to NAC
1.9 V
2.5 A
D = Distance in feet
max
R =Maximum allowable wire resistance
max
R = wire resistance per 1000' pair
/1000' PAIR
0.76
5.2
Maximum distance to last appliance, in feet (meters)
12 AWG 14 AWG
5,428 (1656) 3,654 (1114)
2,171 (662) 1,461 (446)
1,086 (331) 731 (223)
714 (218) 487 (148)
543 (165) 365 (111)
360 (110) 243 (74)
271 (83) 183 (56)
217 (66) 146 (44)
180 (55) 122 (37)
16 AWG 18 AWG
2,375 (724) 1,461 (446)
950 (290) 585 (178)
475 (145) 292 (89)
312 (95) 192 (58)
237 (72) 146 (44)
157 (48) 97 (29)
119 (36) 73 (22)
95 (29) 58 (18)
79 (24) 48 (15)
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