Electrical Installation Of Motor Cables - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide

Electrical Installation of Motor Cables

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NB!:
If an unscreened cable is used, some EMC requirements are not complied with.
The motor cable must be screened in order to comply with the EMC specifications regarding
emission, unless otherwise stated for the RFI filter. Keep the motor cable as short as
possible to reduce the noise level and leakage currents to a minimum.
Connect the motor cable screen to the metal cabinet of the frequency converter and to the metal cabinet
of the motor. Make the screen connections with the biggest possible surface (cable clamp). This is
done by using different installation devices in the various frequency converters.
Screening of cables
Avoid installation with twisted screen ends (pigtails). They spoil the screening effect at higher frequencies.
If it is necessary to break the screen to install a motor isolator or motor contactor, the screen
must be continued at the lowest possible HF impedance.
Cable length and cross-section
The frequency converter has been tested with a given length of cable and a given cross-section of
that cable. If the cross-section is increased, the cable capacitance - and thus the leakage current
- increases, and the cable length must be reduced correspondingly.
Switching frequency
When frequency converters are used together with LC filters to reduce the acoustic noise from a motor,
the switching frequency must be set according to the LC filter instruction in Par. 14-01.
Aluminium conductors
Aluminium conductors are not recommended. Terminals can accept aluminium conductors but
the conductor surface has to be clean and the oxidation must be removed and sealed by neutral
acid free Vaseline grease before the conductor is connected.
Furthermore, the terminal screw must be retightened after two days due to the softness of the aluminium. It
is crucial to keep the connection a gas tight joint, otherwise the aluminium surface will oxidize again.
How to Install
MG.33.B4.02 - VLT is a registered Danfoss trademark
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