Section 5: Data Comms Connections; Rs485 Connection; Figure 5.1-1 Rs485 Data Comms Connections Between Relays - Siemens 7SR224 Manual

Section 5: Data Comms Connections

5.1

RS485 Connection

The RS485 communication port is located on the rear of the relay and can be connected using a suitable RS485
120Ω screened twisted pair cable.
The RS485 electrical connection can be used in a single or multi-drop configuration. The RS485 master must
support and use the Auto Device Enable (ADE) feature.
The last device in the connection must be terminated correctly in accordance with the master driving the
connection. A terminating resistor is fitted in each relay, when required this is connected in circuit using an
external wire loop between terminals 18 and 20 of the power supply module.
Up to 64 relays can be connected to the RS485 bus.
The RS485 data comms link will be broken if the relay element is withdrawn from the case.
The relay is available with an additional RS485 port as an ordering option. The terminal arrangement for this port
are shown in Section 3: of this document. Connections shown below are duplicated on these ports to provide a
separate, parallel, interface.
To
Control
System
Rear terminals
RS 485 Twisted pair screened Cable
To
Control
System
RS485

Figure 5.1-1 RS485 Data Comms Connections Between Relays

©2010 Siemens Protection Devices Limited
14
16
18
RS485 Screened
twisted pair
RS485
7SR224 Argus Installation
14
16
18
RS485 Screened
Rear terminals
twisted pair
RS485
Ext Wire loop to
Include line
terminating Res
14
16
18
20
Chapter 5 Page 12 of 16