VLT® 2800 Series
■ Grounding of shielded/armoured control cables
In general control cables must be shielded/armoured,
and the shield must be connected to the unit’s metal
cabinet with a cable clamp at each end.
The drawing below shows the correct way to perform
the grounding, and what to do when in doubt.
1. Correct grounding
Control cables and cables for serial
communication must be attached with cable
clamps at both ends to ensure maximum
possible electrical contact.
2. Incorrect grounding
Do not use twisted shield ends that are
plaited together (pigtails), as these increase shield
impedance at higher frequencies.
3. Protection with respect to ground
potential between PLC and VLT
f the ground potential between the VLT
variable frequency drive and the PLC (etc.)
is different, electric noise may occur that will
disturb the whole system. This problem can
be solved by fitting an equalising cable, to be
placed next to the control cable. Minimum cable
cross-section: 6 AWG (16 mm
2
).
4. n the event of a 50/60 Hz ground loop
If very long control cables are used, 50/60 Hz
ground loops can arise, and these can interfere
with the whole system. This problem is resolved
by attaching one end of the shield to the gr
ound
via a 100 nF capacitor (short pin length).
MG.28.A8.22 - VLT is a registered Danfoss trademark
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