18
LCD-160 P/N 51850:A 09/26/2003
Wiring
The RDP Bus
6.2 The RDP Bus
Wire Runs
Communication between the control panel and any RDP device, such as the LCD-160, occurs over
an RDP interface. This communication is supervised by the fire alarm control panel and the
LCD-160.
The RDP bus can drive up to 32 RDP devices. The FACP must be at one end of the bus and an end-
of-line resistor must be enabled on the last RDP device on the circuit. The actual number of RDP
devices that can be powered in a particular system depends on the system’s available power. Refer
to the system’s power documentation for more details.
Each LCD-160 on the bus requires a non-resettable 24 VDC power connection. This power circuit
is inherently supervised and a loss of power registers as a communication failure at the control
panel. The LCD-160 can be powered by a regulated remote power supply listed for fire-protective
signalling use. If the 24VDC comes from a nonpower-limited source, the wiring must remain
separate from the power-limited RDP bus.
RDP Bus Wiring Specifications
Wire the RDP bus as shown in “Connecting the RDP Bus” on page 19. These requirements must be
followed:
• There is a maximum of 4000 feet at 12 AWG to 18 AWG between the panel and the last
device on the RDP bus (subject to your system’s power restrictions).
• The wiring size must be a 12 AWG to 18 AWG twisted pair cable having a characteristic
impedance of 120 ohms, +/- 20%.
• Limit the total wire resistance to 100 ohms on the RDP bus, and 10 ohms on the RDP device
power circuit. Unloaded resistance between RDP conductors must be greater than 1 Kohm.
A remote power supply is required if total power wiring resistance exceeds 10 ohms.
• 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, SCR power circuits, or nonpower-limited circuits.
• If RDP devices are to be mounted in separate cabinets or powered by a remote power
supplies, see Figure 12, “Using Multiple Power Supplies With the RDP Bus” on page 22.
LCD-160
Fire Alarm
Control Panel
LCD-160 Power
(12 to 18 AWG)
non-resettable
Two-wire RDP Bus
(Maximum of 4000 feet)
power-limited and supervised
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WARNING:
Turn off all power when connecting the LCD-160.