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2.4
Alarm Input Wiring
All alarm inputs require twisted pair wires. An end-of-line (EOL) resistor terminator is required for each
supervised alarm input. Both supervised and unsupervised alarm inputs can support single or multiple
contacts per loop. Connect normally closed (NC) contacts in series and normally open (NO) contacts in
parallel.
2.5
RS-485 Communication Wiring
Proper wiring for RS-485 communication interfaces is critical for successful system turn-up and operation.
The following guidelines apply for all RS-485 wiring.
1.
Use low capacitance shielded cable with 2 twisted pairs, characteristic impedance 120 ohms (Belden
9842 or equivalent) for the main RS-485 run.
2.
Keep the main run maximum end-to-end distance below 4000 feet.
3.
Use daisy chain configuration, NOT star configuration, to connect devices.
4.
Use shielded 24 AWG cable with 2 twisted pair (Belden 9502 or equivalent.) for down leads (drops or
stubs).
5.
Keep down leads as short as possible (no longer than 10 feet).
TO PREVIOUS UNIT
OR TERMINATOR
6.
Terminate cables at both ends with RS-485 terminators (hardware has on-board terminators for RS-485
termination).
7.
Always use the signal ground (SG) connection. Carefully insulate the SG wire for a reliable installation.
Use 24 GA plastic sleeving over the SG wire when terminating the cable to the 5-position insulation
displacement mating connector.
Each RS-485 communication line can have any number of DEPENDENT devices, but must have only one
MASTER device. The transmit lines of the MASTER device are connected to the receive lines of the
RS-485 CABLE, 100 Ohm IMPEDANCE
BELDEN 9842 OR EQUIVALENT
Reader Interface Module
Hardware Installation Guide
TO NEXT UNIT
OR TERMINATOR
KEEP DOWN LEAD SHORT
(10 FEET MAX.)
37
revision 7 —
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