7SR210 & 7SR220 Installation Guide
Section 6: Data Comms Connections
6.1
Standard RS485 Connections
The standard RS485 communication port is located on terminal block 2 at the rear of the relay and can be
connected using a suitable RS485 120
Ω
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The RS485 data communications link with a particular relay will be broken if the relay element is withdrawn from
the case, all other relays will still communicate.
A
RS485
Scree
n
B
Te
rm
.
14
16
18
20
RS 485 Twisted pair screened Cable
To
Control
System
To
Control
System
14
16
18
20
RS485 Screened
twisted pair
Rear terminals
14
16
18
14
16
18
RS485 Screened
twisted pair
Rear terminals
Ext Wire loop to
Include line
terminating Res
A
RS485
Scree
n
B
Te
rm
.
14
16
18
20
A
RS485
Scree
n
B
Te
rm
.
14
16
18
20
Figure 6.1-1 RS485 Data Comms Connections Between Relays
6.2
IRIG-B Connections
A BNC plug is provided on the optional additional communication interface modules to connect a co-axial cable
carrying IRIG-B time synchronisation signals. Ensure that the stub length is minimised by connecting the tee-
connector directly to the rear of the relay. A suitable co-axial cable would be type RG 58 50ohms.
©2011 Siemens Protection Devices Limited
Page 15 of 24
