14
RS485 / RS232
The RS485 cabling must be overall shielded 3-conductor Belden 8735 or similar. Terminate the
shield at one unit only using the cable clamp provided.
For details on connecting NEXUS integrated burner controllers, PPC5000 fuel/air ratio controllers
and a PC onto the communications bus, refer to bulletin NEX-1501 (ComFire combustion analysis
tool) or NEX-SO (boiler sequencing).
Controlled Shutdown Triac and Safety Shutdown Relay
The controlled shutdown triac should be wired into the ”stat" circuit to switch the burner on/off as
the temperature/pressure reaches the limit condition.
The safety shutdown relay
must
be wired to ensure that the burner is immediately switched off if the
relay opens, to prevent any hazardous condition occurring. See recommended interface wiring for
details of how this is accomplished via connection to burner controllers.
PURGE and IGN Outputs
The PURGE (PC7) terminal will be connected to the COM (PC5) terminal when the 5000 is at purge
position.
The IGN (PC6) terminal will be connected to the COM (PC5) terminal when the 5000 is at the igni-
tion position.
See Appendix for details of how these terminals should be interfaced to burner controllers.
HI/LO Input
This input is active during start-up only.
When this terminal is connected to mains potential, the 5000 will move to purge position. When this
terminal is not connected to mains potential, the unit will move to ignition position.
See Interface to Burner Control Units section on page 11 for details of how these terminals should be
interfaced to burner controllers.
Alarm Relay
This is provided to add an external siren or
lamp for indication of a unit fault or flue
gas alarm limit.
The alarm relay must not
be used to shutdown the burner. This
function is provided by the safety shut-
down relay.
RS485 COMMS
BUS
To PC /
modem (via
converter) or
Nexus /
PPC5000
+
GND
-
CL
AMP
Rx
Tx
GND
CLAMP
RS232 to
local PC
or modem
+
GND
-
CL
AMP
Rx
Tx
GND
CLAMP
+
GND
-
CL
AMP
Rx
Tx
GND
CLAMP
CLOSED IN ALARM PB12
OPEN IN ALARM PB13
COMMON PB14
LIVE SUPPLY
Siren or
Lamp
NEUTRAL
