Control cables must be screened/armoured. Use a clamp
from the accessory bag to connect the screen to the
frequency converter decoupling plate for control cables.
130B
T340.10
Illustration 3.25
Generally speaking, control cables must be braided
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 indicates how correct earthing is
carried out and what to do if in doubt.
a. Correct earthing
Control cables and cables for serial communication must
be fitted with cable clamps at both ends to ensure the
best possible electrical contact.
b. Wrong earthing
Do not use twisted cable ends (pigtails). They increase the
screen impedance at high frequencies.
c. Protection with respect to earth potential between
PLC(Program Logic Controller) 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 entire system. Solve this problem by fitting an
equalising cable, next to the control cable. Minimum cable
cross-section: 16 mm
2
.
d. For 50/60 Hz earth loops
If very long control cables are used, 50/60 Hz earth loops
may occur. Solve this problem by connecting one end of
the screen to earth via a 100 nF capacitor (keeping leads
short).
e. Cables for serial communication
Eliminate low-frequency noise currents between two
frequency converters by connecting one end of the screen
to terminal 61. This terminal is connected to earth via an
internal RC link. Use twisted-pair cables to reduce the
differential mode interference between the conductors.
PE
FC
PE
130BA051.11
PE
PE
FC
PE
PE
FC
100nF
PE
FC
69
FC
PE
PE
PE
68
61
68
69
FC
PE
a
b
c
d
e
PLC etc.
PLC etc.
PLC etc.
PLC etc.
Equalizing cable
Min. 16mm
2
Illustration 3.26
How to Install
Operating Instructions VLT
®
CDS302 and CDS303
MG34M302 - VLT
®
is a registered Danfoss trademark/Commercial Compressor
25
3
3
