2.8 Grounding Shielded Cables
It is recommended that shielded control cables be connected with cable clamps at both ends to
the metal cabinet of the adjustable frequency drive. Table 2-3 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 connec-
tion.
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 adjustable
frequency 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 con-
necting one end of the shield with a 100 nF capacitor and keeping the lead short.
Serial communication control cables
Low frequency noise currents between
adjustable frequency drives can be eliminated by connecting one end of the shiel-
ded cable to adjustable frequency 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 conductors.
Table 2.3: Grounding Shielded Cables
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives
2 Operator Interface and Adjustable Frequen-
cy Drive Control
MG.90.L1.22 - VLT
®
is a registered Danfoss trademark
2-19
2
Summary of Contents for VLT HVAC FC 100
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