9
4
Wiring Requirements
RS-485 Communication Bus
•
Maximum Length = 4000 feet
• Cable
Specifi cation = 24 AWG / A,B (twisted pair)
and GND Shielded, with characteristic Impedance =
120
ohm
•
Maximum Load = 32 units (32 nodes)
NOTE:
Cable must be terminated with 120 ohm impedance
matching resistor on each end.
Note that when the System Supply / System Return
Temperature and/or the Tank Temperature are provided by
the BAS, they need to be refreshed every few seconds. This is
required in order to prevent unwanted fl uctuations in these
temperatures. If these values are not provided every few
seconds (timeout is programmable), the boiler will revert to
its own internal control. If neither of these temperatures is
provided by the BAS, but any of the other control signals are
being provided, the BAS will still need to refresh these inputs
at least every 4 minutes.
Physical Wiring
Figure 4-1
_Terminal Strip Connections
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
AL
AR
M
CON
TA
CT
S
RUN T
IM
E
CON
TA
CT
S
TA
NK
TH
ER
M
OS
TA
T
ENA
BL
E
LO
UV
ER
PROVI
NG
LO
UVER
REL
AY
AU
X
SWI
TCH
1
AU
X
SWI
TCH
2
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
CA
SCA
DE
SY
ST
EM
PUM
P
IN
BM
S
IN
OU
TD
OO
R
SENS
O
R
SENS
O
R
SENS
O
R
SENS
O
R
TA
NK
SYST
EM
SUPPL
Y
SYS
TEM
RET
URN
BO
IL
ER PUMP
OU
T
OU
T
RA
TE
MO
DB
US
SHI
EL
D
SHI
EL
D
B
A
-
+
+
-
-
-
+
+
SHI
EL
D
SHI
EL
D
B
A
B
U
IL
DI
NG
MA
NA
GEME
N
T
SY
STEM
TA
N
K
THER
M
O
STA
T
EN
ABLIN
G
D
E
VIC
E
LOU
V
ER
PR
OVI
N
G
SW
ITCH
LOU
V
ER
RE
L
A
Y
AU
X
SW
ITCH
1
AU
X
SW
ITCH
2
F
R
OM
PR
EVIO
U
S BOILER
TO
N
E
X
T
B
O
IL
E
R
A
B
B
A
SH
IELD
SH
IELD
0-
10V I
N
PUT
SY
STEM
PU
M
P
O
U
TD
OO
R
SEN
S
O
R
T
A
NK
S
E
NS
OR
SY
STEM
SU
PPLY
SEN
S
OR
SYS
T
E
M RE
T
U
RN S
E
NS
OR
0-
10V OUTPUT
BOILER
PU
M
P
MO
DBUS
CO
MM
UNI
C
AT
IO
N B
U
S
SH
IELD
A
B
B
A
SH
IELD
ModBus Instructions