Emc Recommendations - Danfoss VLT 380-500 V Design Manual

EMC and Harmonics

9.5 EMC Recommendations

The following is a guideline to good engineering practice when installing frequency converters. Follow these guidelines in
compliance with EN/IEC 61800-3 First environment. If the installation is in EN/IEC 61800-3 Second environment, industrial
networks, or in an installation with its own transformer, deviation from these guidelines is allowed but not recommended.
Good engineering practice to ensure EMC-correct electrical installation:
•
Use only braided shielded/armored motor cables and braided shielded control cables. The shield provides a
minimum coverage of 80%. The shield material must be metal, not limited to but typically copper, aluminum, steel,
or lead. There are no special requirements for the mains cable.
•
Installations using rigid metal conduits are not required to use shielded cable, but the motor cable must be
installed in conduit separate from the control and mains cables. Full connection of the conduit from the frequency
converter to the motor is required. The EMC performance of flexible conduits varies a lot and information from the
manufacturer must be obtained.
•
Connect the shield conduit to ground at both ends for motor cables and for control cables. Sometimes, it is not
possible to connect the shield in both ends. If so, connect the shield at the frequency converter. See also
chapter 9.5.2 Grounding of Shielded Control Cables.
•
Avoid terminating the shield with twisted ends (pigtails). It increases the high frequency impedance of the shield,
which reduces its effectiveness at high frequencies. Use low impedance cable clamps or EMC cable glands instead.
•
Avoid using unshielded motor or control cables inside cabinets housing the frequency converter, whenever
possible.
Leave the shield as close to the connectors as possible.
Illustration 9.7 shows an example of an EMC-correct electrical installation of an IP20 frequency converter. The frequency
converter is fitted in an installation cabinet with an output contactor and connected to a PLC, which is installed in a
separate cabinet. Other ways of doing the installation could have just as good an EMC performance, provided the guidelines
to engineering practice are followed.
If the installation is not carried out according to the guideline, and if unshielded cables and control wires are used, some
emission requirements are not in compliance, although the immunity requirements are fulfilled.
MG37N102
Design Guide
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