Earthing/Grounding Of Screened/Armoured Control Cables - Danfoss VLT 8000 AQUA series Operating Instructions Manual

Earthing/Grounding of screened/armoured
control cables
Generally speaking, control cables must be screened/
armoured and the screen must be connected
by means of a cable clamp at both ends to
the metal cabinet of the unit.
The drawing below indicates how correct
earthing/grounding is carried out.
64
®
VLT 8000 AQUA
Correct earthing/grounding
Control cables and cables for serial communication
must be fitted with cable clamps at both ends to
ensure the best possible electrical contact.
Wrong earthing/grounding
Do not use twisted cable ends (pigtails), since these
increase the screen impedance at high frequencies.
Protection with respect to earth potential
between PLC and frequency converter
If the earth potential between the 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 equalizing
cable, to be placed next to the control cable.
Minimum cable cross-section: 8 AWG.
For 50/60 Hz earth loops
If very long control cables are used, 50/60 Hz
earth loopsmay occur that will disturb the whole
system. This problem can be solved by connecting
one end of the screen to via an earth 100nF
capacitor (keeping leads short).
Cables for serial communication
Low-frequency noise currents between two frequency
converter can be eliminated by connecting one end of
the screen to terminal 61. This terminal is connected
to earth via an internal RC link. It is recommended
to use twisted-pair cables to reduce the differential
mode interference between the conductors.
MG.83.A2.02 - VLT is a registered Danfoss trademark