750-166 1-11
CB780/CB784
WIRING
1. a. For proper subbase wiring, refer to Fig. 7.
b. For proper remote wiring of the Keyboard Dis-
play Module, refer to Fig. 8, 9 or 10 or to the
Specifications for the Keyboard Display Module,
Communication Interface Base Unit or Control
Bus.
2. Disconnect the power supply from the main discon-
nect before beginning installation to prevent electrical
shock and equipment damage. More than one disconnect
may be involved.
3. All wiring must comply with all applicable electrical
codes, ordinances and regulations. Wiring, where required,
must comply with NEC, Class 1 (Line Voltage) wiring.
4. Recommended wire size and type:
a. All Line Voltage terminals use no. 14 or 16 cop-
per conductor (90°C or higher) 600 volt insula-
tion wire (wire size must be coordinated with fuse
protection). For high temperature installations,
use wire selected for a temperature rating above
the maximum operating temperature. All leadwires
should be moisture resistant.
b. Keyboard Display Module—For communica-
tions purposes, use an unshielded 22 AWG 2-wire
twisted cable and one wire for ground if the
leadwire run and noise conditions permit; how-
ever, some installations may need up to five wires,
three for communications and two for remote reset
(in either a single cable or separate cables for com-
munications or remote reset) or use Belden 8771
shielded cable or equivalent. The Keyboard Dis-
play Module, Control Bus (for remote mounting or
communications) or Communication Interface
ControlBus Module must be wired in a daisy chain
configuration, (1(a)-1(a), 2(b)-2(b), 3(c)-3(c)). The
order of interconnection of all the devices listed
above is not important. Be aware that modules on
the closest and farthest end of the daisy chain
configuration string require a 120 ohm (1/4 watt
minimum) resistor termination across terminals
1 and 2 of the electrical connectors, for connec-
tions over 100 feet, see Fig. 8, 9 and 10.
c. Control Bus—For communications purposes,
use an unshielded 22 AWG 2-wire twisted cable
if the leadwire run and noise conditions permit;
however, some installations may need up to five
wires, three for communications and two for re-
mote reset (in either a single cable or separate
cables) or use a Belden 8771 shielded cable or
equivalent. The Keyboard Display Module, Con-
trol Bus (for remote mounting or communications)
or Communication Interface ControlBus Module
must be wired in a daisy chain configuration,
(1(a)-1(a), 2(b)-2(b), 3(c)-3(c)). The order of inter-
connection of all the devices listed above is not
important. Be aware that modules on the closest
and farthest end of the daisy chain configuration
string require a 120 ohm (1/4 watt minimum) resis-
tor termination across terminals 1 and 2 of electri-
cal connectors, for connections over 100 feet, see
Fig. 8, 9 and 10.
d. Remote Reset*—Use no. 22 AWG or greater
twisted pair wire, insulated for low voltage; see
Fig. 8, 9 and 10.
e. Communication Interface ControlBus Module—
For communications purposes, use an unshielded
22 AWG 2-wire twisted cable if the leadwire run
and noise conditions permit or use a Belden 8771
shielded cable or equivalent. The Keyboard
Display Module, Control Bus (for remote mount-
ing or communications) or Communication Inter-
face ControlBus Module must be wired in a daisy
chain configuration, (1(a)-1(a), 2(b)-2(b), 3(c)-3(c)).
The order of interconnection of all the devices
listed above is not important. Be aware that
modules on the closest and farthest end of the
daisy chain configuration string require a 120
ohm (1/4 watt minimum) resistor termination
across terminals 1 and 2 of the electrical connec-
tors, for connections over 100 feet, see Fig. 8, 9
and 10.
f. Use the recommended wire size for the 13 Vdc
full wave rectified transformer power input of
no. 18 AWG wire insulated for voltages and tem-
peratures encountered in the application. Sug-
gested wire types include TTW(60C), THW(75C)
and THHN(90C).
5. Recommended grounding practices:
a. The earth ground provides for a connection be-
tween the subbase and the control panel of the equip-
ment. The earth ground wire must be capable of
conducting the current to blow the 20A fuse (or
breaker) in event of an internal short circuit. The
CB780/CB784 needs a low impedance ground
connection to the equipment frame which, in
turn, needs a low impedance connection to earth
ground. For a ground path to be low impedance
at RF frequencies, the connection must be made
with minimum length conductors that have a
maximum surface area. Wide straps or brackets
are preferred rather than leadwires. Be careful to
ensure that mechanically tightened joints along
the ground path, such as pipe or conduit threads
or surfaces held together with fasteners, are free
of nonconductive coatings and are protected
against corrosion on mating surfaces.
b. Keyboard Display Module,
Control Bus, or
Comm
unication Interface ControlBus Module—
Wiring
*Note: Remote Reset must be mounted within sight
of the boiler control panel.
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