UTC Fire and Security interlogix AL-1255 Installation Manual page 15

7
System bus connections
Connect DGP devices to the system bus to provide extra zones and remote arming stations (RAS) to the
Alliance system control panel. Remote devices can be up to 5,000 ft. (1.5 km) from an Alliance system control
panel. DGP and RAS devices must be connected via a 2-pair twisted, shielded data cable from the system bus
connection. We recommend you use Beldon 8723. Connect the shield of the data cable to earth at the Alliance
system control panel and leave it disconnected at any other end. Where the distance between the arming station
and the nearest device is more than 328 ft. (100 m), use a separate power supply to power the arming station.
To power the arming station do not connect the (+) from the system bus, connect the (+) of the local power
supply to the (+) on the arming station and connect the (0 V) from the power supply and (0 V) from the system
bus to the arming station (-) terminal.
Note: The first and last devices on the system bus must be terminated. All other devices on the system bus must not be
terminated.
Figure 6 shows the system bus connection.
Figure 6. System bus connection
System bus
12 V connection
D- D+ 0V
D- D+ 0V+12
D- D+ 0V+12
DGP RAS Control panel