Grounding Shielded Cables - Danfoss VLT Series Service Manual

Grounding Shielded Cables

It is recommended that shielded control cables be connected
with cable clamps at both ends to the metal cabnet of the
drive. Figure 1-3 shows ground cabling for optimal results.
Correct grounding
Control cables and cables for serial communication must be
fitted with cable clamps at both ends to ensure the best possible
electrical connection.
Incorrect grounding
Do not use twisted cable ends (pigtails) since these increase
shield impedance at high frequencies.
Ground potential protection
When the ground potential between the drive and the PLC or
other interface device is different, electrical noise may occur that
can disturb the entire system. This can be resolved by fitting an
equalizing cable next to the control cable. Minimum cable cross-
section is 8 AWG.
50/60 Hz ground loops
When using very long control cables, 50/60 Hz ground loops may
occur that can disturb the entire system. This can be resolved by
connecting one end of the shield with a 100 nF capacitor and
keeping the lead short.
Serial communication control cables
Low frequency noise currents between drives can be eliminated
by connecting one end of the shielded cable to drive terminal 61.
This terminal connects to ground through an internal RC link. It is
recommended to use twisted-pair cables to reduce the differential
mode interference between condutors.
Figure 1-3. Grounding Shielded Cables
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