neb: Doesn't the RCD do that too, or is it a pure RCD function? I'm also not 100% certain that that's the actual problem, I went as far as I could without pulling apart the distribution panel but it could be something else. The symptoms are that with the RCD off there's no power, with the RCD on and the MCBs on or off, doesn't matter, there's power. The reason why I hadn't noticed it until now is that one of the three MCBs powers nothing I can identify (see "Casa de Cowboy"), the second is for a circuit that never gets turned off because there's a bunch of stuff that may get upset about power losses, and the third is for the kitchen with nothing very obvious that changes state when power is lost.
When its done the cheap way like that, the RCD is only doing RCD stuff, and then the 3 breakers after it (used to be no limit so you would see one RCD or 2 per house for all breakers) do the over current.
The A on the RCD is its maximum, nothing to do with overcurrent.
If you go for combined RCBOs, like you should do, it costs a little more but takes up less space, doesn't need the mess of neutral bars and means that half your stuff doesnt get turned off when the flatmate leaves his window open and a powerstrip on the windowsill.