Grounding of shielded/armored control cables
In general, control cables must be shielded/armored,
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 commu-
nication must be attached with cable clamps
at both ends to ensure the maximum possible
electrical contact.
2.
Incorrect grounding
Do not use twisted shield ends that are plai-
ted together (pigtails), as these increase
shield impedance at higher frequencies.
3.
Protection with respect to ground poten-
tial between the PLC and VLT
If the ground potential between the VLT ad-
justable 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 equalizing cable next
to the control cable. Minimum cable cross-
section: 0.025 in
2
[16 mm
2
].
4.
In 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 inter-
fere with the whole system. This problem is
resolved by attaching one end of the shield to
the ground via a 100 nF capacitor (short pin
length).
VLT
®
2800 Series
MG.27.A2.22 - VLT
®
is a registered Danfoss trademark 13
Installation
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