56
MG.30.A7.02 - VLT
®
is a registered Danfoss trademark
EMC installation
Motor cable
In order to comply with the EMC specifi-
cations concerning emission and immu-
nity, the motor cable must be screened
unless otherwise stated for the mains filter
in question. It is important to keep the
motor cable as short as possible so as to
reduce the interference level and the
leakage currents to a minimum.
The motor cable screen should be con-
nected to the metal cabinet of the fre-
quency converter and to the metal casing
of the motor. Screen connections should
be made using as large a surface as
possible. (See the instructions for installa-
tion, pp. 57-59, item D). The motor cable
screen should basically not be broken and
not be earthed in the process. If it be-
comes necessary to break the screen to
install a motor isolator or motor relays, the
screen should be continued at the lowest
possible HF impedance.
Using filters 175H7083 and 175H7084, the
VLT
®
3002-3008 complies with EN55011-
1A using an unscreened motor cable. In
addition to reducing the mains interfer-
ence, the filters also reduce the interfer-
ence radiating from the unscreened motor
cable. As far as the motor cable is con-
cerned, only interference above 30MHz is
reduced (see EN55011-1A).
Control cables
Control cables should be screened. The
screen should be connected using a
clamp to the VLT
®
frequency converter
base (see the instructions for installation,
pp. 57-59, item C). Normally, the screen
should also be connected to the base of
the controlling appliance (follow the
instructions for use of the appliance in
question).
In connection with very long control cables
and analogue signals, 50 Hz ripple loops
may occur in rare cases, depending on the
installation. This is because of interference
coupling from the mains supply cables. In
this connection it can be necessary to
break the screen or possible insert a 100 nF
condenser between screen and base.
Cable for serial
communication
The cable for serial communication should
be screened.
The screen should be installed using a
clamp on the VLT
®
frequency converter
(see the instructions for installation, pp. 57-
59, item B).
With regard to cable specifications and
instructions for installation in general,
reference is made to the PROFIBUS
product manual.
trolling appliance. They can be avoided by
making a tight fit with the cabinet base
rear plate, thereby ensuring that any
equalising currents will run via the base
rear plates and their joints, not via the
cable screens.
Efforts should be made to avoid possible
equalising currents that may occur when
the control cable screen is connected to
the base (earthed) at both ends. Equalising
currents occur because of voltage differ-
ences between the VLT
®
frequency
converter base and the base of the con-
Equalising currents
Brake cables
If a brake module is used, the cable to the
brake resistor must be screened. In the
case of VLT 3002 - VLT 3008, connect the
screen to the conductive rear plate, on
which the VLT frequency converter has
been mounted. If VLT 3011 - VLT 3052 are
used, mount the screen by means of a
special union. In the case of VLT 3060 -
VLT 3250, where the brake module is a
separate module in its own casing, it is
possible to use special unions or to
terminate the screen in the conventional
way. All sizes of unit require the screen to
be connected to the brake resistor
casing.
