Honeywell 7800 Series Installation Instructions Manual page 5

chain configuration string require a 120 ohm (1/4 watt
minimum) resistor termination across terminals 1 and 2 of
the electrical connectors, for connections over 100 feet
(31 meters).
5. See Table 2 for recommended grounding practices.
6. Use recommended wire routing of leadwires:
a. Do not run high voltage ignition transformer
wires in the same conduit with the flame
detector, Data ControlBus Module™, or Remote
Reset Module wiring.
b. Do not route flame detector, Data ControlBus
Module™, or Remote Reset Module leadwires in
conduit with line voltage circuits.
c. Enclose flame detector leadwires without armor
cable in metal cable or conduit.
7. Follow directions in flame detector, Data ControlBus
Module™, or Remote Reset Module
Instructions.KDM: Because the KDM is powered
from a low voltage, energy limited source, mount it
outside of a control panel if it can be protected from
mechanical damage.
Ground Type
Earth Ground (Subbase and relay
module)
Signal Ground (KDM, Data
ControlBus Module™).
Table 2. Recommended Grounding Practices.
1. Use to provide a connection between the subbase and the control panel of
the equipment. Earth ground must be capable of conducting enough current
to blow the 15A fast blow, type SC or equivalent, fuse (or breaker) in the event
of an internal short circuit.
2. Use wide straps or brackets to provide minimum length, maximum surface
area ground conductors. If a lead wire must be used, use 14 AWG copper
wire.
3. Make sure that mechanically-tightened joints along the ground path are free
of nonconductive coatings and protected against corrosion on mating
surfaces.
Use the shield of the signal wire to ground the device to the signal ground terminal
3(c) of each device. Connect the shield at both ends of the daisy chain to earth
ground.
5
RM7838B, RM7838C 7800 SERIES RELAY MODULES
NOTE: Use a separate 13 Vdc power supply any time
more than two Data ControlBus Modules™ or
KDM are used or are placed more than 100 feet
(31 meters) from the relay module.
8. Use maximum wire lengths:
a. RM7838B,C leadwires—300 feet (91 meters) to
terminal inputs (Control, Preignition Interlock,
Running/Lockout Interlock, High Purge Switch
and Low Fire Switch).
b. Flame Detector leadwires—limited by the flame
signal strength.
c. Remote Reset leadwires—1000 feet (305 meters)
to a Remote Reset push button.
d. Data ControlBus Module™—depends on the
number of system modules connected, the noise
conditions and the cable used. The maximum
length of all Data ControlBus Module™
interconnecting wire is 4000 feet (1219 meters).
9. Make sure loads do not exceed the terminal ratings.
Refer to the label on the RM7838B,C or to the ratings
in Table 4.
Recommended Practice
32-00211—01