Siemens SINAMICS G130 Engineering Manual page 310

SINAMICS S150
Engineering Information
Note:
The recommendations for the North American market in AWG or MCM must be taken from the appropriate NEC
(National Electrical Code)/CEC (Canadian Electrical Code) standards.
• Switchgear systems and motors are usually grounded via a separate local ground connection. In the case of a
ground fault with this configuration, the ground fault current is divided and flows through the ground connections in
parallel. With this grounding system, no impermissible contact voltages can occur, despite the PE conductor cross-
sections used in the above table.
Based on experience with different grounding configurations, however, we recommend that the ground wire from
the motor should be routed directly back to the converter. For EMC reasons and to prevent bearing currents,
symmetrical, three-wire, three-phase cables should be used in this case rather than four-wire cables. The ground
connection (PE) must be routed separately or must be arranged symmetrically in the motor cable. The symmetry of
the PE conductor is achieved using a conductor surrounding all phase conductors or using a cable with a
symmetrical arrangement of the three phase conductors and three ground conductors. For further information,
please refer to the sections "Bearing currents caused by steep voltage edges on the motor" and "Line filters" of the
chapter "Fundamental Principles and System Description".
• Through their controllers, the converters limit the load current (motor and ground fault currents) to an rms value
corresponding to the rated current. We therefore recommend the use of a PE conductor cross-section analogous to
the phase conductor cross-section for grounding the converter cabinet.
SINAMICS Engineering Manual – May 2008
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