Table 3-1: Typical Wire Resistance Chart - Fire-Lite AFM-16ATX User Manual

Design Considerations
Limits
Up to 32 annunciators may be installed on an EIA-485 circuit. The actual number of
annunciator modules may be larger depending on the number of expander modules
employed.
Wire Runs
Communication between the Control Panel and the annunciator is accomplished over a
power-limited two-wire EIA-485 serial interface. This communication, including the
wiring, is supervised by the fire alarm control panel. Power for the annunciators is
provided via a separate power-limited power loop from the control panel which is
inherently supervised (loss of power also results in a communication failure at the control
panel).
Fire Alarm Control Panel
Wiring Specifications
The EIA-485 circuit cannot be T-Tapped; it must be wired in a continuous fashion from
the control panel to the annunciator. The maximum wiring distance between the
panel and the last annunciator is 6,000 feet @ 16 AWG.
The wiring size must be a 14 AWG to 18 AWG twisted
shielded pair cable having a Characteristic Impedance of
120 ohms, +/- 20%. Limit the total wire resistance to 100 ohms on the EIA-
485 circuit, and 10 ohms on the annunciator power circuit. Do not run cable adjacent to,
or in the same conduit as, 120 volts AC service, noisy electrical circuits that are powering
mechanical bells or horns, audio circuits above 25 volts (RMS), motor control circuits, or
SCR power circuits. Twisted-shielded wiring should be used for EIA-485 circuits that are
not contained entirely in conduit.
Wire Size Diameter in
A.W.G. Mils
14 64
16 51
18 40

Table 3-1: Typical Wire Resistance Chart

8
Section Three:
Annunciator Power
Two-wire EIA-485 Circuit
(Maximum of 6,000 feet)
STANDARD ANNEALED COPPER WIRE
Cross Section
Circ. Mils Sq. Inch
4110 0.00323
2580 0.00203
1620 0.00128
15390 Rev D 8/2/96 P/N 15390:D
(14 to 18 AWG )
Ohms per 1000 ft.
@ 77 F. @ 149 F.
2.58
4.09
6.51
Annunciator
Pounds per
1000 ft.
2.97 12.4
4.73 7.82
7.51 4.92