Modbus Cable Information; Opening And Installing The User Interface - Dimplex A8M Installation Manual

Allow sufficient cable length to ensure the connections are not strained when the cover is opened.
Once cables have been routed through the cable glands, close the access cover.
Connect power cable and controller cable as shown in figure 10. Do not strip the cables before pulling
them through the glands in the access panel. Where stranded cable is being used, a ferrule must be fitted
before inserting into the push connections.
The controller (Modbus) cable is then connected from the heat pump to the wiring centre (see wiring
diagrams in Appendices).

4.2.7 Modbus Cable Information

Table 2: Recommended cable specifications/electrical characteristics for Modbus cable
Nominal Characteristic Impedance
Nominal Conductor DC Resistance
Nominal Capacitance Core to Core
*Conversion factor for ft to m = 3.28 ft = 1m
1km of Belden cable would have a resistance of 78.74 Ω/km
1km of Equivalent cable has a resistance of 78.8 Ω/km

4.2.8 Opening and Installing the User Interface

It is recommended to connect the Modbus cable in daisy-chain series (as shown in figure 13) from the
heat pump on to the wiring centre and then on to the UI. The jumpers will be in the correct factory setting
for this wiring configuration by default. If using the recommended configuration, the jumper position does
not need to be changed.
Start
If it is deemed necessary to install the Modbus cable in a different order, please see Appendices.
The cover of the UI must be removed in order to move the jumper. To remove the cover, unscrew the
screw at the bottom of the UI and lift the cover and rotary dial.
Millbrook House, Grange Drive, Hedge End, Southampton, SO30 2DF
Belden Cable 9842
Figure 13: Recommended MODBUS cable configuration
Typical Equivalent Cable
120Ω
24.0Ω/1000ft
78.7401 Ω/km*
12.8pF/ft
41.99pF/m
28
120Ω
78.80 Ω/km*
42pF/m
End
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