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 earthingControl cables and cables
for serial communication must be attached
with cable clamps at both ends to ensure
maximum possible electrical contact.
2.
Incorrect earthingDo 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 VLTIf 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 loopIf 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.27.E2.02 - VLT is a registered Danfoss trademark
45
In
s
ta
lla
ti
on
