Danfoss VLT 4000 ME Manual page 24

■ Grounding of shielded/armored control cables
Generally speaking, control cables must be shielded/
armored and the shield must be connected by
means of a cable clamp at both ends to the
metal cabinet of the unit.
The drawing below indicates how correct
grounding is carried out.
36
VLT® 4000 VT
Correct grounding
Control cables and cables for serial communication
must be fitted with cable clamps at both ends to
ensure the best possible electrical contact.
Wrong grounding
Do not use twisted cable ends (pigtails), since these
increase the shield impedance at high frequencies.
Protection with respect to ground potential
between PLC and VLT
If the ground potential between the VLT AFD and the
PLC (etc.) is different, electric noise may occur that will
disturb the whole system. This problem can be solved
by fitting an equalizing cable, to be placed next to the
control cable. Minimum cable cross-section: 8 AWG.
For 50/60 Hz ground loops
If very long control cables are used, 50/60 Hz
ground loops may occur that will disturb the
whole system. This problem can be solved by
connecting one end of the shield to via a ground
100nF capacitor (keeping leads short).
Cables for serial communication
Low-frequency noise currents between two VLT AFD
can be eliminated by connecting one end of the
shield to terminal 61. This terminal is connected to
ground via an internal RC link. It is recommended
to use twisted-pair cables to reduce the differential
mode interference between the conductors.
MG.40.A4.22 - VLT is a registered Danfoss trademark