ABB REU 610 Technical Reference Manual page 111

1MRS755769
Voltage Relay
Technical Reference Manual
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 earth (shield GND) in one point/
device of the bus. Other devices connected to the bus should have the cable shield
connected to earth 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.
REU 610
111