NORD Drivesystems BU0750 - Manual (Page 19)

2 Assembly and installation
BU 0750 GB-3311 Subject to technical amendments 19
2.7 Wiring guidelines
The frequency inverter has been developed for use in an industrial environment. In this environment, high
levels of electromagnetic interference can influence the frequency inverter. In general, correct installation
ensures safe and problem-free operation. To meet the limiting values of the EMC directives, the following
instructions should be complied with.
1) Ensure that all equipment in the control cabinet or field is securely earthed using short earthing cables
which have large cross-sections and are connected to a common earthing point or earthing rail. It is
especially important that every control device connected to the frequency inverters (e.g. an
automation device) is connected, using a short cable with large cross-section, to the same earthing
point as the inverter itself. Flat conductors (e.g. metal clamps are preferable, as they have a lower
impedance at high frequencies.
2) The PE lead of the motor controlled by the frequency inverter must be connected as directly as
possible to the earth connection of the cooling element, together with the PE of the corresponding
frequency inverter mains supply. The presence of a central earthing bar in the control cabinet and the
grouping together of all bonding conductors to this bar normally ensures safe operation. (See also
Chapter 8.3/8.4 EMC guidelines)
3) Where possible, shielded cables should be used for control circuits. The shielding at the cable end
should be carefully sealed and it must be ensured that the wires are not laid over longer distances
without shielding.
The shields of analog setpoint cables should only be earthed on one side on the frequency inverter.
4) The control cables should be installed as far as possible from power cables, using separate cable
ducts, etc. Where cables cross, an angle of 90° should be ensured as far as possible.
5) Ensure that the contactors in the cabinet are interference protected, either by RC circuits in the case
of AC contactors or by free-wheeling diodes for DC contactors, for which interference suppressors
must be connected to the contactor coils. Varistors for over-voltage limitation are also effective.
This interference suppression is particularly important when the contactors are controlled by the relay
in the frequency inverter.
6) Shielded or protected cables should be used for load connections (motor cable) and the
shielding/protection should be earthed at both ends, if possible directly to the frequency inverter
PE/EMC terminal.
In addition, EMC-compliant wiring must be ensured. (see also Section 8.3/8.4 EMC). If required, an
optional integrated motor filter is available.
7) Select the lowest possible switching frequency. This will reduce the intensity of the electromagnetic
interference produced by the frequency inverter.
The safety regulations must be complied with under all circumstances when
installing the frequency inverter!
NOTE
The control cables, line cables and motor cables must be laid separately. Under no circumstances
may they be laid in the same protective conduit or cable duct.
The test equipment for high voltage insulation must not be used for cable which are connected to
the frequency inverter.