Chapter 2
– Electromagnetically compatible installation of drives and drive systems
2-7
Installing the motor cable
If you use an EMC line filter or would like to observe certain limits of line-conducted interference,
the motor cable which you use must be shielded.
The shield is to be grounded on both sides,
over a large area.
For this purpose, turn the shield through 180°, for instance, and make large-area
contact (360°) with the metal PG screw connections. The illustration on the following page shows
you the electromagnetically compatible motor wiring.
Use only copper mesh cable (CY) with 85% coverage. Foil shields often have a higher
coupling impedance than mesh shields and are therefore unsuitable
.
Some motors have terminal boxes and PG screw connections of plastic. In these cases, the
shield should be connected on the motor side to the motor housing, with as large an area as
possible, by means of a cable clamp.
Some motors have a rubber gasket between terminal box and motor housing. Very often, the
terminal boxes, and particularly the threads for the metal PG screw connections, are painted.
Make sure there is always a good metallic connection between the shielding of the motor
cable, the metal PG screw connection, the terminal box and the motor housing, and carefully
remove this paint if necessary.
The shielding should not be interrupted at any point in the cable. If the use of reactors,
contactors, terminals or safety switches in the motor output is necessary, i.e., if the shield
must be interrupted, then the unshielded section should be kept as small as possible. It is
better to install the reactor, contactor, terminal or safety switch in a metal housing with as
much HF damping as possible. The shield connection to the metal housing should again be
made with the smallest possible HF impedance, as already described.
Should no shielded motor cable be available, lay the unshielded cable in a metal tube having the
best possible shielding effect, for example. The metal tube should have good HF contact with the
frequency inverter and the motor housing, e.g., by means of copper gauze tape.
Safety grounding
always takes precedence over HF grounding.
If, for example, a braking chopper / rheostat is to
be connected to the DC intermediate circuit, then this connecting line, too, must be shielded. The
shield is to be connected on both sides, with a large area (e.g. to the protective ground terminal of
the rheostat).
Installing control and signal lines
To ensure reliable operation of the frequency inverter, analog and digital control lines (angular
momentum pulser connection, all analog inputs, the serial interfaces, etc.) should be laid shielded.
You should allow the effective shielding surface to remain as large as possible, i.e., do not move
the shield further away than absolutely necessary. The shield has to be applied on both sides on
PE. As a matter of principle, the shielding of these lines should not be interrupted.
