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If a 30mA ELCB on the input trips, there's something wrong with the drive (or wiring). Good idea to use it. Don't know where you're located, but it could be mandatory anyway.

I checked in more detailed data sheet on Micromaster 430 meanwhile and found the following: ELCB (RCD) can be used with Micromaster. It must be B type, the trip limit of the RCD should be 300 mA (I understood it as minimum trip limit), supply neutral must be grounded, only one inverter per RCD, output cables must be less than 50m (screened) or 100m (unscreened). RCD must be suitable for briefly suppressing power pulse current paks (I understood it as not to tripp instantly), so I suppose it must be S type. It is, also, recomended to to protect the frequency inverter by fuse separately.

My bad ! I didn't look at the spec & consider the application. I (wrongly) assumed that this was for a domestic set-up. Anything with 300mA earth leakage in a domestic environment would be a no-no.

The point to note, however, is:

The regulations of the individual country (e.g. VDE regulations in Germany) and the regional power suppliers must be observed!

(taken from the datasheet).

If in the UK, then a 30mA residual current device would be mandatory for any outdoor circuit, under Part P of the Building Regulations, and under British Standard 7671.

So there is no technical problem whatsoever.

The problem the OP would be left with is a system that doesn't work. The datasheet for the controller states that a 300mA trip is needed to avoid false tripping.

I based my schenatic diagram on example diagram made by people from Oase and they put everything on RCD except frequency controller driven pump. So we have all consumers protected by RCD (including low voltage lighting, 12V), and one pump which is not. The problem is that in Siemens operating instructions it is not clearly explained what realy happens if we use RCD in combination with Micromaster. For instace: 1. Type B ELCB is to be used, and then a possibility of brifly suppressing power pulse current peaks is asked for. Why B type? To protect Micromaster as fast acting device? If we use fast fuses in combination with ELCB or RCD C type or S type (time lag) we shall have short circuit protection for static elements of micromaster and current pulses withstanding. 2. The trip limit of of RCD is to be 300mA. Why? Is there a problem with harmonics that frequency controller generates? Maybe it can be solved with input filter which is standard accessory? I think that we deserve a clearly defined solution from a producer, if he recognized a problem in his product usage. Using RCD in fountain installation is common practice in Serbia, but I must admit i do not know if there is regulation that stipulates its use in this case.