3.3.9 Grounding of Screened/armoured
Control Cables
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.
shows the correct way to perform the
grounding, and what to do when in doubt.
Correct grounding
Control cables and cables for serial communication must
be attached with cable clamps at both ends to ensure
maximum possible electrical contact.
Incorrect grounding
Do not use twisted screen ends that are plaited together
(pigtails), as these increase screen impedance at higher
frequencies.
Protection about ground potential between PLC and VLT
If the ground potential between the frequency converter
and the PLC (etc.) is different, electric noise may occur that
disturbs the whole system. This problem can be solved by
fitting an equalising cable next to the control cable.
Minimum cable cross-section: 16 mm
2
.
If 50/60 Hz ground loop occurs
If 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 screen to
the ground via a 100 nF capacitor (short pin length).
Illustration 3.19 Grounding Examples
Installation
Design Guide
MG27E402
Danfoss A/S © Rev. May/2014 All rights reserved.
43
3
3
