Service manual

2.7 Earthing Shielded Cables
Connect the screened control cables to the metal cabinet
of the frequency converter with cable camps at both ends.
Table 2.3 shows earth cabling for optimal results.
Correct earthing Control cables and cables for serial communication must be fitted with cable
clamps at both ends to ensure the best possible electrical connection.
Incorrect earthing Do not use twisted cable ends (pigtails) since they increase screen
impedance at high frequencies.
Earth potential protection When the earth potential between the frequency converter 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 earth loops When using very long control cables, 50/60 Hz earth loops may occur
that can disturb the entire system. This can be resolved by connecting one end of the screen
with a 100 nF capacitor and keeping the lead short.
Serial communication control cables Low frequency noise currents between frequency
converters can be eliminated by connecting one end of the screened cable to frequency
converter terminal 61. This terminal connects to earth through an internal RC link. It is
recommended to use twisted-pair cables to reduce the differential mode interference between
conductors.
Table 2.3 Earthing Screened Cables
Frequency Converter Control
VLT
®
HVAC Basic Drive Service Manual
22 MG90X202 - VLT
®
is a registered Danfoss trademark
22