VLT
®
2800 Series
■
Earthing of screened/armoured control cables
In general control cables must be screened/armoured,
and the screen 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 earthing, and what to do when in doubt.
1.
Correct earthing
Control cables and cables for serial
communication must be attached with cable
clamps at both ends to ensure maximum
possible electrical contact.
2.
Incorrect earthing
Do not use twisted screen ends that
are plaited together (pigtails), as these increase
screen impedance at higher frequencies.
3.
Protection with respect to earth
potential between PLC and VLT
If the earth potential between the VLT
frequency converter 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: 16 mm
2
.
4.
In the event of a 50/60 Hz earth loop
If very long control cables are used, 50/60 Hz
earth loops can arise, and these can interfere
with the whole system. This problem is resolved
by attaching one end of the screen to the earth
via a 100 nF capacitor (short pin length).
MG.28.E9.02 - VLT is a registered Danfoss trademark
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