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Do we need additional EMC filter on IT network for ATV61/71...M3X ?

ATV61/71...M3X drives are delivered without EMC filter. These (M3X drives) can only be used on 3-phase 230V supply, which is not a typical pubic network. M3 drives on the contrary can be used also on single phase supply, hence 1x230V is usually part of public network.
It is assumed that non-public network 3-phase 230V is created by a transformer, so it is absolutely up to customer if he creates TN or IT network on 230V volts. From the same point ov view (non-public network) we cannot apply the IEC standards regarding the EMC. To sum up, the EMC requirements for non-public networks are not specified.

Back to your question, the need of EMC filter depends on the requirement. If there are sensitive devices in the same 3x230V network, the filter is needed. EMC filter in general is not only about its connection to the ground. Above all, EMC filter fiters high frequency conductive emissions in each phase (emissions in current) and emissions in line-to-line voltage between each phases.

The problem with additional EMC fitlers is that they are automatically connected to ground by their metal body and so difficult to isolated them from ground. On IT network it is forbidden to  use grounded EMC filters. As mentioned in ATV extract, the only solution with additional EMC filter is to use isolation transformer and to make autonomous TN or TT network for assembly: transformer secondary+EMC filter+ATV+motor. Primary side of transformer with the rest of the devices will be part of IT network.
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