Selecting and connecting the cable:
As far as possible, use symmetrically arranged, shielded connection cables. The cable
shielding, made up of as many strands as possible, must have good electrical conductivity.
Braided shields made of copper or aluminum are very suitable.
● The shield is connected at both ends, at the motor and converter.
● To ensure good discharging of high-frequency currents, provide contacting over a large
surface area:
– as contact established through 360° at the converter
– at the motor, for instance with EMC glands at the cable entries
● If the cable shield is connected as described, then it ensures the specified equipotential
bonding between the motor enclosure and converter. A separate RF equipotential bonding
conductor is then not necessary.
Concentric copper or aluminum shield Steel armor
● If the cable shield is not connected due to special secondary conditions, or not adequately
connected, then the specified equipotential bonding is not provided. In this particular case,
use a separate RF equipotential bonding conductor:
– Between the motor enclosure and protective ground rail of the converter.
– Between motor enclosure and driven machine
– Use braided flat copper straps or high-frequency cables with finely-stranded conductors
for the separate RF equipotential bonding cable. Solid copper cables are not suitable
for high frequency grounding because of the skin effect.
– Ensure that the contacts are established over a large area.
Overall system design
To specifically reduce and prevent damage caused by bearing currents, you must consider
the system as a whole, which comprises the motor, converter, and driven machine. The
following precautions help to reduce bearing currents:
● In the overall system, set up a properly meshed grounding system with low impedance.
● Use the common-mode filter (damping cores) at the converter output. The Siemens sales
representative is responsible for selection and dimensioning.
● Limit the rise in voltage by using output filters. This dampens the harmonic content in the
output voltage.
Electrical connection
6.5 Connecting the auxiliary circuits
SIMOTICS TN Series N-compact 1LA8
Operating Instructions 05/2016 79
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