56 XLS140 Installation Manual Form Number 95-7673-3 P/N 51927:C  12/06/2005 
Installation Wiring a Signaling Line Circuit (SLC)
3.15  Wiring a Signaling Line Circuit (SLC)
 Overview
Communication between the control panel and intelligent and addressable initiating, monitor, and 
control devices takes place through a Signaling Line Circuit (SLC). You can wire an SLC to meet 
the requirements of NFPA Style 4, Style 6, or Style 7 circuits. This manual provides requirements 
and performance details specific to this control panel; for installation information and general 
information, refer to the SLC Wiring Manual. 
 Wiring
Maximum wiring distance of an SLC using 12 AWG (3.31 mm
2
) wire is 12,500 feet (3810 meters) 
total twisted-pair for Style 4, Style 6 and Style 7 circuits.
 Capacity
The XLS140 provides one (1) SLC, with a total capacity of 318 intelligent/addressable devices:
• 01-159 intelligent detectors
• 01-159 monitor and control modules
An optional expander board provides one (1) additional SLC, with the same capacity.
 Installation
This control panel supports one or two SLC loops; a second SLC loop is obtained by installing an 
LEM-320 module. SLC loop #1 connects to TB16 on the control panel; SLC loop #2 connects to 
TB1 on the LEM-320. For details on designing, installing and configuring SLC loops, see the SLC 
Wiring Manual.
 B+  A+   B-   A- B+  A+   B-   A-
T-Tapping is not allowed 
on a four-wire SLC.
SLC B (output loop)
SLC A (loop return)
SLC B SLC A
Style 4 SLC Loops Style 6 SLC Loops
TB1
B+  A+   B-   A-
SLC1
 B+  A+   B-   A-
TB16
SLC Loop #2 Connections
on Loop Expander Module
SLC Loop #1 Connections 
on FACP’s main circuit board
Use either 
SLC Loop #1 
or SLC Loop #2 
nfs640-slcloops.cdr, nfs640-slc-tb.cdr, LEM320-slc-tb.cdr
Figure 3.30  SLC Loop Connections and Wiring