Extremely small amount of time is the key to my problem.
Logically, to measure any current, leakage current or normal current, we need a time, small amount of time. Now is to manufacturers to build different devices with different sensibility for different applications. I would like to identify the most sensitive RCB.
The electrical wires length in the house comparing to distance to the Sun is nothing, so I assume the speed of current is instantaneous, in my house. The distance between two RCB is too small to have any delay so the waveform is synchronous, I think.