RS-485 Data Highway, Connections and MFU Setup
Publication PUB091-003-00_0119
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4.3 Cable Types
The network must be connected using a suitable cable. Two conductors plus a shield and drain wire
are required as a minimum, though Rotork recommends the use of a 3 wire cable to ensure the
common mode voltage between all the actuators and the PLC is kept within the RS-485 specified
limits.
Amongst the cable manufacturers Belden have the PVC jacketed 3105A single pair 2 core cable,
which meets the minimum requirement. Belden 3106A has an extra core and therefore has sufficient
conductors to include a common wire between all the nodes on the network and meets the Rotork
recommendation. Information on Belden cable may be found on the Belden web site
(www.belden.com) or at http://bwcecom.belden.com/, where a search on RS-485 will reveal technical
papers and cable information.
Belden Part No.
Total Number of
Conductors
AWG
(stranding)
dia. Inches
Nom. DCR
Insulation material
Nominal
O.D.
Nom
Impedance
(ohms)
Nominal
Capacitan
ce
3105A
Paired
- EIA Industrial
RS-485 PLTC/CM
2
22 AWG
(7 x 30)
48.2 ohm/km
Overall PVC jacket
Datalene insulated
twisted pair
7.26 mm
120
11.0 pF/ft.
3106A
Composite - EIA
Industrial RS-485
PLTC/CM
3
22 AWG
(7 x 30)
48.2 ohm/km
Overall PVC jacket
Datalene insulated
twisted pair
7.67 mm
120
11.0 pF/ft.
Fig 13: Typical RS-485 cable
The terminals to which the wires connect in the each actuator type will be different and the actuator
wiring diagram must be consulted to establish the connections.
Data Pair
Screen
Belden 3105A
Belden 3106A
Common
Data Pair
Screen