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How to

How to


Products: MP-V, RP-C, RP-V
Functionalities: Hardware
Product version: 2022, 2023, 2024, 7.0
10/29/2024

Wiring the Screw Terminals on an Isolated RS-485 Adapter

You wire the screw terminals on an Isolated RS-485 Adapter to connect a BACnet/IP controller to a BACnet MS/TP (RS-485) network. Always use the recommended wires.

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The Isolated RS-485 Adapter is equipped with an RJ45 port for connection to a BACnet/IP controller RS-485 Com port and a 4-position removable screw terminal block for connection to a BACnet MS/TP (RS-485) network.

 
action_zoom_plus_stroke RJ45 port and screw terminals, Isolated RS-485 Adapter
Figure: RJ45 port and screw terminals, Isolated RS-485 Adapter

The following figure shows an example of how an Isolated RS-485 Adapter is connected to the RS-485 Com B port (RJ45) of an RP-C controller via a Cat 5 (or higher) UTP cable of maximum length 0.3 m (12 in.) and how the BACnet MS/TP network (RS-485) wires from the adapter are connected to the RS-485 Com port screw terminals of an AS-P server.

 
action_zoom_plus_stroke Example with an Isolated RS-485 Adapter used for connection of an RP-C controller to a BACnet MS/TP network and an AS-P server
Figure: Example with an Isolated RS-485 Adapter used for connection of an RP-C controller to a BACnet MS/TP network and an AS-P server
Connection of RJ45 port to BACnet/IP controller RS-485 Com port

A separate connection cable is required to connect the RJ45 port on the RS-485 adapter to the RS-485 Com port (RJ45) on the BACnet/IP controller. The cable is not included and needs to be purchased separately.

Use a Cat 5 (or higher) unshielded, straight-through wired cable with eight conductors (four twisted pairs) and RJ45 connectors. Use a cable with the wire size (cross-sectional area) 22 to 26 AWG (0.34 to 0.14 mm²), a maximum length of 0.3 m (12 inches), and a rating that meets the requirements of the target environment. For example, when devices are installed in a space that handles conditioned air or return air, the cables typically need to be plenum-rated.

Notice

LOSS OF COMMUNICATION

  • Ensure that the length of the cable for connection of the RS-485 adapter to the controller does not exceed 0.3 m (12 inches).

  • Use a Cat 5 or higher unshielded twisted pair cable with eight conductors (four twisted pairs), a cross-sectional area of 22 to 26 AWG (0.34 to 0.14 mm 2 ), and a rating that meets the requirements of the target environment.

Failure to follow these instructions can result in loss of communication.

For more information, see Connecting an Isolated RS-485 Adapter .

For more information, see RJ45 Pinout for the RS-485 Port(s) of the RP-C Controllers .

For more information, see RJ45 Pinout for the RS-485 Port of the MP-V Controller .

Wiring of screw terminals for connection to BACnet MS/TP network

The four screw terminals are wired and connected to a BACnet MS/TP (RS-485) network as described in the following table.

Recommended screw tightening torque: 0.5 Nm (4.5 lbf.in)

Table: Screw Terminals, Isolated RS-485 Adapter

Terminal

Usage

BIAS+

Provides +5 VDC for use to deliver a positive bias to the TX/RX+ data line through an appropriate value resistor. For example, when configuring strong dual end bias such as required by MNB BACnet devices, a 1 kohm resistor would be connected between the BIAS+ and TX/RX+ terminal.

TX/RX+

Data line (+) for connection to the TX/RX+ signal in the BACnet MS/TP twisted pair connecting all devices on the bus.

TX/RX–

Data line (–) for connection to the TX/RX– signal in the BACnet MS/TP twisted pair connecting all devices on the bus.

SHIELD

Provides common (low side) of 5 VDC supply for delivering negative bias to the TX/RX– data signal through an appropriate value resistor. For example, when configuring strong dual end bias such as required by MNB BACnet devices, a 1 kohm resistor would be connected between the SHIELD and TX/RX– terminal. The Isolated RS-485 Adapter removes the need for a separate 5 VDC supply when positioned at the end of the bus.

For more information, see Wiring the Screw Terminals on an Isolated RS-485 Adapter .

For more information, see RS-485 Communications .

To wire the screw terminals on an Isolated RS-485 Adapter

  1. Loosen the screw of the terminal.

  2. Strip approximately 7 mm (0.3 inch) of the insulation from the end of each wire.

  3. Insert the end of the wire fully into its intended terminal. Ensure that no bare wire strands extend from the terminal.

  4. Tighten the screw using a small flat-blade screwdriver. Ensure that the screw is fully tightened. Use the following recommended screw tightening torque: 0.5 Nm (4.5 lbf.in).

  5. Repeat steps 1 to 4 until all screw terminals on the Isolated RS-485 Adapter are correctly wired. For more information, see Isolated RS-485 Adapter Connection and Wiring .

    Follow the recommendations and guidelines for the RS-485 interface configuration in regard to biasing, termination, cable selection, cable length, and cable routing. For more information, see RS-485 Communications .

     
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  6. Use appropriate cable strain relief methods, to help prevent any load applied to the cable from being transferred to conductor terminations.

See Also

  • Isolated RS-485 Adapter Connection and Wiring
  • Connecting an Isolated RS-485 Adapter
  • Installing an RS-485 Adapter
  • Wiring
  • RS-485 Communications