ABB REU 610, Technical Reference Manual

Page: 118 / 140

RS-485 connection
If the relay is provided with the optional RS-485 communication module, the
cable is connected to terminals X5.5/1-2 and X5.5/4-6. The connection socket
is a 6-pin header-type socket and the terminals are of screw compression type.
The RS-485 communication module follows the TIA/EIA-485 standard and
is intended to be used in a daisy-chain bus wiring scheme with 2-wire, half-
duplex, multi-point communication.
The maximum number of devices (nodes) connected to the bus
where the relay is being used is 32, and the maximum length of
the bus is 1200 meters.
When connecting the relay to the bus, a quality twisted pair shielded cable is
to be used. The conductors of the pair are connected to A and B. If signal
ground is being used for balancing potential differences between devices/
nodes, a quality dual twisted pair shielded cable is to be used. In this case, one
pair is connected to A and B, and one of the conductors of the other pair to
signal ground. When connecting one device to another, A is connected to A
and B to B.
The cable shield is to be connected directly to ground (shield GND) in one
point/device of the bus. Other devices connected to the bus should have the
cable shield connected to ground via a capacitor (shield GND via capacitor).
Signal ground can only be used for balancing potential
differences between devices/nodes if all devices connected to the
bus have isolated RS-485 interfaces.
The RS-485 communication module is provided with jumpers for setting bus
termination and fail-safe biasing. The bus is to be terminated at both ends,
which can be done by using the internal termination resistor on the
communication module. The termination resistor is selected by setting jumper
X5 to the ON position. If the internal termination resistor of 120
Ω
is used,
the impedance of the cable should be the same.
The bus is to be biased at one end to ensure fail-safe operation, which can be
done using the pull-up and pull-down resistors on the communication
module. The pull-up and pull-down resistors are selected by setting jumpers
X3 and X4 to the ON position.
The jumpers have been set to no termination (X5 in the OFF position) and no
biasing (X3 and X4 in the OFF position) as default.
118
REU 610
Voltage Relay
Technical Reference Manual - ANSI Version
1MRS755972