1.4.6 Motor Cables
See
General Specifications
for correct dimensioning of motor cable cross-section and length. See
EMC Emissions
for relationship between length and EMC emission.
Always comply with national and local regulations on cable cross-section.
NB!
If an unscreened/unarmoured cable is used, some EMC requirements are not com-
plied with, see
EMC test results
in the Design Guide.
If the EMC specifications regarding emission are to be complied with, the motor cable must be
screened/armoured, unless otherwise stated for the RFI filter in question. It is important to keep
the motor cable as short as possible so as to reduce the noise level and leakage currents to a
minimum. The motor cable screen must be connected to the metal cabinet of the frequency con-
verter and to the metal cabinet of the motor. The screen connections are to be made with the
biggest possible surface area (cable clamp). This is enabled by different installation devices in
different frequency converters. Mounting with twisted screen ends (pigtails) is to be avoided, since
these spoil the screening effect at high frequencies. If it is necessary to break the screen to install
a motor isolator or motor relay, the screen must be continued at the lowest possible HF impedance.
1.4.7 Motor Thermal Protection
The electronic thermal relay in UL-approved frequency converters has received the UL-approval
for single motor protection, when parameter 128
Motor thermal protection
has been set for
ETR
Trip
and parameter 105
Motor current, I
M, N
has been programmed to the rated motor current
(see motor nameplate).
1.4.8 Control Cables
Remove the front cover underneath the control panel. Place a jumper between terminals 12 and
27.
Control cables must be screened/armoured. The screen must be connected to the frequency con-
verter chassis by means of a clamp. Normally, the screen must also be connected to the chassis
of the controlling unit (use the instructions for the unit in question). In connection with very long
control cables and analogue signals, in rare cases depending on the installation, 50/60 Hz earth
loops may occur because of noise transmitted from mains supply cables. In this connection, it may
be necessary to break the screen and possibly insert a 100 nF capacitor between the screen and
the chassis.
See section entitled
Earthing of screened/armoured control cables
in the VLT 2800 Design Guide
for the correct termination of control cables.
VLT 2800 Quick Guide
1 Quick Guide
1
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