Technical data

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 commu-
nication 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 plai-
ted 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 fre-
quency converter and the PLC (etc.) is differ-
ent, 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 re-
solved by attaching one end of the screen to
the earth via a 100 nF capacitor (short pin
length).
VLT
®
2800 Series
46 MG.27.E3.02 - VLT
®
is a registered Danfoss trademark