Siemens SINAMICS S120 Combi Equipment Manual page 238

Encoder system connection
10.1 Sensor Module Cabinet-Mounted SMC20
Note
Diminished level of interference immunity due to equalizing currents via the electronics
ground
Make sure there is no electrical connection between the encoder system housing and the
signal lines and the sensor system electronics.
If this is not carefully observed, under certain circumstances the system will not be able to
reach the required interference immunity level (there is then a danger of equalization
currents flowing through the electronics ground).
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SINAMICS S120 Combi
Manual, (GH9), 07/2016, 6SL3097-4AV00-0BP5