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How to

How to


Products: MP-V, RP-C, RP-V
Functionalities: Hardware
Product version: 2022, 2023, 2024, 7.0
11/1/2024

Wiring the Screw Terminals on a Non-isolated RS-485 Adapter

You wire the screw terminals on a Non-isolated RS-485 Adapter to connect an RP or MP controller to a BACnet MS/TP (RS-485) network or Modbus RTU (RS-485) subnetwork. Always use the recommended wires.

Notice

LOSS OF COMMUNICATION

Ensure that the total length of the RS-485 bus, from the controller to the end of the bus, does not exceed the recommended maximum cable length. For more information, see RS-485 Communications .

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

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The Non-isolated RS-485 Adapter is equipped with an RJ45 port for connection to an RP or MP controller RS-485 Com port and a 4-position removable screw terminal block for connection to a BACnet MS/TP (RS-485) network or Modbus RTU (RS-485) subnetwork.

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

Connection to a BACnet MS/TP network

The following figure shows an example of how a Non-isolated RS-485 Adapter is connected to one of the RS-485 Com ports (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.

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

 
action_zoom_plus_stroke Example with a Non-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 a Non-isolated RS-485 Adapter used for connection of an RP-C controller to a BACnet MS/TP network and an AS-P server

 
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The BACnet MS/TP (RS-485) network should provide a 120 ohm termination resistor across the data pair (+ to -) at each end of the bus, that is, one 120 ohm termination resistor at the head end of the bus and a second 120 ohm termination resistor at the far end of the bus. Follow the recommendations and guidelines for the RS-485 interface configuration and guidance on when bias is required on the network (bias is not required for AS-P and AS-B servers, nor for RP and MP controller models with “-M” in the product name). For more information, see RS-485 Communications .

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 a Non-isolated RS-485 Adapter .

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

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(s) of the RP-V Controllers .

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, Non-isolated RS-485 Adapter

Terminal

Usage

NOT USED

Not connected.

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

Convenience terminal to interconnect two shield drain wires (incoming and outgoing). There is no electrical connection in the device. The shield should be connected to ground at only one location and that is recommended to be at the automation server. The shield should not be connected directly to the RET terminal on the automation server. The transient energy on the drain wire should be conducted to ground and not through the automation server.

For more information, see Wiring the Screw Terminals on a Non-isolated RS-485 Adapter .

For more information, see RS-485 Communications .

Connection to a Modbus RTU subnetwork

The following figure shows an example of how a Non-isolated RS-485 Adapter is connected to one of the RS-485 Com ports (RJ45) of an RP-C controller via a Cat 5 (or higher) UTP cable and how the Modbus RTU network twisted pair wires from the adapter are connected to the screw terminals of a Modbus device. In this example, the Modbus device is a thermostat from the SpaceLogic Thermostat TC907 Series. Additional Modbus devices may be daisy-chained from the thermostat.

Note:

The twisted pair cable used for TX/RX+ and TX/RX- data wires extends in one direction from the adapter to each device in a daisy chain bus configuration without cable stubs.

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

 
action_zoom_plus_stroke Example with a Non-isolated RS-485 Adapter used for connection of an RP-C controller to a Modbus RTU subnetwork and Modbus device(s)
Figure: Example with a Non-isolated RS-485 Adapter used for connection of an RP-C controller to a Modbus RTU subnetwork and Modbus device(s)

 
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The Modbus (RS-485) network should provide a 120 ohm termination resistor across the data pair (+ to -) at each end of the bus, that is, one 120 ohm termination resistor at the head end of the bus and a second 120 ohm termination resistor at the far end of the bus. Follow the recommendations and guidelines for the RS-485 interface configuration and guidance on when bias is required on the network (bias is required when any Modbus devices on the bus are not of the Failsafe type). For more information, see RS-485 Communications .

 
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The twisted pair shielded cable should only have the shield connected to ground at one location and that is the RP or MP controller. At each device, such as thermostat TC907, the shield drain wire from the incoming cable should be spliced to the shield drain wire of the outgoing cable and isolated from ground at each splice.

Connection of RJ45 port to RP or MP 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 RP or MP 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), 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

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.

Notice

LOSS OF COMMUNICATION

Ensure that the total length of the RS-485 bus, from the controller to the end of the bus, does not exceed the recommended maximum cable length. For more information, see RS-485 Communications .

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

For more information, see Connecting a Non-isolated RS-485 Adapter .

For more information, see Communication Port Wiring .

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

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(s) of the RP-V Controllers .

Wiring of screw terminals for connection to Modbus subnetwork

The four screw terminals are wired and connected to a Modbus RTU (RS-485) subnetwork as described in the following table.

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

Table: Screw Terminals, Non-isolated RS-485 Adapter

Terminal

Usage

NOT USED

Not connected.

TX/RX+

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

TX/RX–

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

SHIELD

Convenience terminal to interconnect two shield drain wires (incoming and outgoing). There is no electrical connection in the device. The shield should be connected to ground at only one location and that is recommended to be at the hosting RP or MP controller. The shield should be connected through to the next segment at each device without additional connections to ground. The shield should not be connected directly to the SHIELD terminal on the adapter. The transient energy on the drain wire should be conducted to ground and not through the adapter and on to the controller.

For more information, see Wiring the Screw Terminals on a Non-isolated RS-485 Adapter .

For more information, see RS-485 Communications .

To wire the screw terminals on a Non-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 Non-isolated RS-485 Adapter are correctly wired. For more information, see Non-isolated RS-485 Adapter Connection and Wiring .

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

    Note:

    The following figure shows the BACnet MS/TP daisy-chain example. For Modbus, the cable typically extends in one direction from the adapter.

     
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  6. Ensure that the total length of the RS-485 bus, from the RP or MP controller to the RS-485 device at the end of the bus, does not exceed the recommended maximum cable length. For more information, see RS-485 Communications .

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

See Also

  • Non-isolated RS-485 Adapter Connection and Wiring
  • Connecting a Non-isolated RS-485 Adapter
  • Installing an RS-485 Adapter
  • Wiring
  • RS-485 Communications