Design Considerations
PN 15842:K 7/23/2002 21
• 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.
• If annunciators are to be mounted in a separate cabinet or powered by a
remote power supply, see Figure 3-2 Using Multiple Power Supplies
With the EIA-485 Circuit. For information on boosting the EIA-485
circuit signal or adding additional devices (not addresses), see the RPT-
485W/RPT-485WF Installation Manual.
All power must be turned off when connecting the annunciator.
3.4 Receive/Transmit and Receive Only Configuration
Receive/Transmit Annunciators
Annunciators that are configured to serve as full function annunciators can both
receive status information as well as transmit commands to the control panel.
This allows the annunciator to remotely execute functions of the control panel in
addition to displaying the status of the system.
Receive Only Annunciators
For redundant annunciation of system points, annunciators can be configured as
“Receive Only” annunciators. Receive Only annunciators must be set to the
same address as the annunciators they duplicate. Receive Only annunciators
intercept information being transmitted to a “Receive/Transmit” annunciator for
duplication at an intermediate display location. When configured for Receive
Only operation, they cannot be used to send information to the system, and as a
result are not supervised by the control panel. They cannot perform remote
functions such as Acknowledge, Signal Silence, or System Reset. Control
switches on Receive Only annunciators can be used only for local functions,
such as lamp test. Wiring to Receive Only annunciators may be supervised by
installing the modules “upstream” of fully supervised, Receive/Transmit
annunciators along the EIA-485 line (see Figure 3-1).
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