Just a quick note, he didn't invent the RCD. He did design the first working 30-mA RCD though. Older ones had trip currents of up to 3 amps but they were sold in fairly large numbers. My great-grandparents' house in Germany was built in 1955 and has an original 1-amp RCD serving a single three-phase socket right next to the meter, close to the front door. Everything else is straight TN-C with Diazed fuses, except for some 1970s upgrades. I suppose the reasoning behind putting that one socket on an RCD was that it was most likely to power questionable outdoor loads.
