1.4.11 Extra protection
RCD relays/ELCBs, multiple protective earthing or earthing can be used as extra protection, pro-
vided that local safety regulations are complied with.
Three phase VLT frequency converters require an RCD type B. If an RFI filter is mounted in the
drive and either the switch of the RCD or a manually operated switch is used to connect the drive
to the mains voltage, a time delay of minimum 40 ms is required (RCD type B).
If no RFI filter is mounted of a CI contactor is used for mains connection, no time delay is required.
Single phase VLT frequency converters require an RCD type A. There is no particular need for a
time delay whether RFI filters are mounted or not.
See application note MN.90.GX.YY for further information on ELCBs.
1.4.12 EMC-correct electrical installation
General points to be observed to ensure EMC-correct electrical installation.
- Use only screened/armoured motor cables and screened/armoured control cables.
- Connect the screen to earth at both ends.
- Avoid installation with twisted screen ends (pigtails), since this ruins the screening effect
at high frequencies. Use cable clamps instead.
- It is important to ensure good electrical contact from the installation plate through the
installation screws to the metal cabinet of the frequency converter.
- Use starwashers and galvanically conductive installation plates.
- Do not use unscreened/unarmoured motor cables in the installation cabinets.
The illustration below shows EMC-correct electrical installation, in which the frequency converter
has been fitted in an installation cabinet and connected to a PLC.
1 Quick Guide VLT 2800 Quick Guide
14
MG.28.M1.02 - VLT
®
is a registered Danfoss trademark
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