Today I performed some tests and
I obtained what I want without modifying anything in the house. I modified only my portable RCD power strip. When I plug into my security power strip a faulty device (residual current fault) - then my power strip goes off instantaneously and isolate the faulty circuit from the rest of the house, but the main RCD 30mA it's still on! The portable RCD 10mA trips faster than general. Repeated many times - works like a charm. That's what I wanted
Next step is to integrate all in one multi protection RCBO - leakage, short, overload protection, or, add short circuit (phase-neutral) protection to existing circuit. Ultra fast fuse, resetable fuse ... how to deal with shorts ?