Wiring the eia-485 terminal blocks, Wiring specifications, Eia-485 shield in conduit – Fire-Lite ACM-8RF Control Relay Module User Manual
Page 13: Wiring the eia-485 terminal blocks 2. installation, Motor control circuits, or scr power circuits

Wiring the EIA-485 Terminal Blocks
2. Installation
ACM-8RF PN 50362:C 03/21/01
13
Wiring the EIA-485 Terminal Blocks
Communications between the Fire Alarm Control Panel and the ACM-8RF is
accomplished over a two-wire EIA-485 serial communications bus which must
be power-limited. Communications between the host FACP and ACM-8RFs
is supervised by the fire alarm control panel.
Wiring Specifications
• The EIA-485 circuit cannot be T-tapped; it must be wired in a
continuous fashion from the control panel to the ACM-8RFs.
• The maximum wiring distance between the panel and ACM-8RFs is
6,000 feet.
• The wiring must be a 18 AWG to 14 AWG twisted shielded pair cable
having a characteristic impedance of 120 ohms, +/- 20%.
• Limit the total wire resistance to 100 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 V
RMS
, motor control circuits, or SCR
power circuits.
Note: Never use the EIA-485 shield for grounding purposes. Terminate the EIA-485
shield at the Fire Alarm Control Panel only.
Table 2 Wire Specifications
EIA-485 Shield in Conduit
When the EIA-485 wiring is in conduit, connect the shield to system common.
The shield can enter the cabinet, but must be insulated from the cabinet (no
electrical contact). Between ACM-8RFs, wire-nut multiple shields together
(which can be inside of the respective ACM-8RF enclosure but ensure that the
shield does not contact earth ground).
Figure 5 Terminating the Shield in Conduit
Standard Annealed Copper Wire
Wire Size
A.W.G
Diameter
in Mils
Cross Section
Ohms per 1000 feet
Pounds per
1000 feet
Circ. Mils
Sq. Inch
@ 77°F.
@ 149°F.
14
64
4110
0.00323
2.85
2.97
12.4
16
51
2580
0.00203
4.09
4.73
7.82
18
40
1620
0.00128
6.51
7.51
4.92
1 IN (+ )
4 IN (– )
T B 2
3 O U T (– )
2 O U T (+ )
A
C
M8
R
F
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