RM7890A,B/EC7890A,B 7800 SERIES RELAY MODULES
32-00157-03 4
9. The KDM, or Data ControlBus Module™ (for remote
mounting) 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 connections over 100 feet (31
meters).
10. For recommended grounding practices, see Table 2.
11. Be sure loads do not exceed the terminal ratings.
Refer to the label on the RM/EC7890 or to the termi-
nal ratings in Table 3.
Table 1. Recommended Wire Sizes and Part Numbers.
a
The KDM, Data ControlBus™ Module (for remote mounting or communications) or Communication Interface Control-
Bus™ 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 electri-
cal connectors for connections over 100 feet (30.5 meters).
Table 2. Recommended Grounding Practices.
Application Recommended Wire Size Recommended Part Numbers
Line Voltage Terminals
14, 16, or 18 AWG (0.75, 1.5 or 2.5 mm
2
) copper
conductor, 600 volt insulation, moisture-resistant
wire.
TTW60C, THW75C, THHN90C.
Keyboard Display
Module KDM
a
22 AWG (0.34 mm
2
) two-wire twisted pair with
ground, or five-wire.
Belden 8723 shielded cable or
equivalent.
Data ControlBus™
Module
Remote Reset Module
22 AWG (0.34 mm
2
) two-wire twisted pair, insulated
for low voltage.
—
Communications
Interface ControlBus™
Module
22 AWG (0.34 mm
2
) two-wire twisted pair with
ground.
Belden 8723 shielded cable or
equivalent.
13 Vdc full wave rectified
transformer power input
18 AWG (0.75 mm
2
) wire insulated for voltages and
temperatures for given application.
TTW60C, THW75C, THHN90C.
Ground Type Recommended Practice
Earth ground (subbase
and relay module).
1. Use to provide a connection between the subbase and the control panel of the equip-
ment. Earth ground must be capable of conducting enough current to blow the 15A
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 leadwire is required, use 14 AWG copper wire.
3. Make sure that mechanically tightened joints along the ground path are free of non-
conductive coatings and protected against corrosion on mating surfaces.
Signal ground (Keyboard
Display Module, Data
ControlBus Module™
Use the shield of the signal wire to ground the device to the signal ground terminals—3(c)—of
each device. Connect the shield at both ends of the daisy chain to earth ground.
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