ACS Manual —
P/N 15842:
N3
5/4/2022
21
EIA-485 Circuit Connections
Installation, Configuration, and Programming
5.5 EIA-485 Circuit Connections
The accompanying figures provide EIA-485 circuit diagrams for the two different types of annunciators.
5.6 Shielding the EIA-485 Circuit
The EIA-485 circuit must be wired using a twisted-shielded pair cable having a
Characteristic Impedance of 120 ohms, +/- 20%. Do not run cable adjacent to, or in
the same conduit as, 120-volt AC service, noisy electrical circuits that are powering
mechanical bells or horns, audio circuits above 25 Vrms, motor control circuits, or
SCR power circuits.
All enclosures, including the FACP backbox, must be connected
to earth ground! Never use the shield for grounding purposes.
Terminate the EIA-
485 shield at the Fire Alarm Control Panel only.
•
When the EIA-485 shield is in conduit:
Connect it to system reference
(
system common
). The shield can enter the cabinet, but must be insulated from
the cabinet (no electrical contact). Between annunciators, wire-nut multiple
shields together (which can be inside of the respective enclosure, but can not
contact the enclosure).
•
When the EIA-485 shield is not in conduit:
Terminate the shield at the outside of the FACP backbox (
ground
). Do not allow the shield
to enter or even touch the cabinet. Between annunciators, wire-nut multiple shields together
outside
of the respective enclosures (see
5.7 End of Line Resistor for EIA-485 Circuit
For the last device on the EIA-485 circuit, an end-of-line resistor must be installed or enabled (depending on the type of ACS device).
•
For ACM-24AT or ACM-48A, set SW29 to “ENABLE” to install the built-in end-of-line resistor
(see Figure 5.12).
•
For ACM-16AT or ACM-32A, install a 120 ohm End-of-Line Resistor (NOTIFIER Part Number
71244, supplied with the annunciator) must be installed at the last annunciator on the EIA-485
circuit (see Figure 5.10 on page 21).
All other ACS annunciators should be set to “DISABLE” or the ELR removed. Power must be turned
off when connecting the annunciator to avoid damaging the equipment.
NOTE:
See Section 4.3, “EIA-485 Wiring Specifications” for circuit requirements.
TB2 on Last
Annunciator
EIA-485 circuit from
control panel
a
c
s
_
e
ia
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f
In
Out
Out
In
TB2 on First
Annunciator
TB2 on Middle
Annunciators
In
Out
Out
In
In
Out
Out
In
Figure 5.10 EIA-485 Circuit for ACM-16AT and ACM-32A
A
C
M
-2
4
-4
8
-e
ia
.w
m
f
REF
+ ACS
+ ACS
- ACS
- ACS
Ref
Out
Ref In
EGnd
+ ACS
+ ACS
- ACS
- ACS
Ref
Out
Ref In
EGnd
+ ACS
+ ACS
- ACS
- ACS
Ref
Out
Ref In
EGnd
Figure 5.9 EIA-485 Circuit for ACM-24AT and ACM-48A
Note:
See Section 5.7, “End of Line Resistor for EIA-485
Circuit” to set onboard ELR for ACM-24AT/ACM-48A.
EIA-485
Figure 5.11 Terminating the Shield
w
ir
n
o
c
o
n
.w
m
f
Enclosure
Annunciator
Figure 5.12 SW29 on
ACM-24AT or ACM-48A
A
C
M
-S
W
2
9
.w
m
f
