Fire-Lite ACM-32AF Annunciator Modules - Manual (Page 19)

ACM-16ATF/ACM-32AF Manual PN 51480:A0 02/02/01
19
3. Design Considerations
Limits
The standard Fire•Lite EIA-485 circuit can drive up to 32 annunciators or
expanders. The number of annunciators that can engage in two-way
communication is dependent on the number of addresses available with a
given fire alarm control panel. The actual number of annunciator/expander
modules that can be powered in a particular system depends on the current
available from the control panel’s power supply.
Note: Refer to the instruction manual of the particular Fire Alarm Control Panel for
more details.
Wire Runs
Communication between the control panel and the annunciator occurs over
a power-limited 2-wire EIA-485 serial interface. This communication is
supervised by the fire alarm control panel. Each annunciator/expander
module also requires a filtered 24 VDC power connection. This power
circuit is inherently supervised; loss of power registers as a communication
failure at the control panel.
Figure 1 Wire Run Diagram
Wiring Specifications
The EIA-485 circuit cannot be T-Tapped; it must be wired in a continuous
fashion. The maximum wiring distance is 6,000 feet at 16 AWG. The wiring
size must be a 12 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.
Fire Alarm Control Panel
Annunciator
ACS Power
Filtered & Power-limited
A
C
S
f-
w
ir
eru
n.cdr
EIA-485 Circuit
(two-wire)
Power-limited & Supervised