NORD Drivesystems BU0050 - Manual (Page 25)

1.4 USS - Bus structure
BU 0050 GB-3111 Subject to technical amendments 25
1.4.4.2 Cable runs / Shielding (EMC)
If EMC measures are not in place, high-frequency interference which is principally brought about by switch
procedures or lightning often causes electronic components in the Bus participants to become faulty and error-
free operation can no longer be ensured.
Proper shielding of the bus cable reduces the electrical interference which can arise in an industrial
environment. Best shielding characteristics can be achieved with the following measures

Connect the Bus participants with the shortest amount of cable possible.

The shielding of the Bus cable must be applied completely and to a wide area on both sides. *

Avoid using spur lines to connect field devices to the Bus.

Avoid extending the Bus lines using plug connectors.
Bus lines should be laid with a minimum spacing of 20cm to other lines which carry a voltage higher than 60V.
This applies to lines laid inside and outside of control cabinets.
*)Note: If earthing potential values are different, transient currents may flow through shielding which
is connected on both sides. This may be a danger to electronic components. Differences in
potential must be reduced using adequate potential equalisation.
1.4.4.3 Bus termination
The bus lines be terminated at both ends.
For this, a resistance of 120

must be connected between the data signal lines RS485 + and RS485 - on the
first and last participant.
With some modules, the termination resistor can be switched in with DIP switches. As delivered, the bus
termination resistor is not activated.
If the bus termination resistor is not integrated into the module, it must be installed in the module or the
connector housing.