If I had to take a stab at it I would say its a bad power supply.With the RCD working like a GFCI according to the description from Wikipedia that Dirk Broer was so kind to post. The most likely place to have something leak to ground would be a short in a power supply.It could possibly be a Motherboard or graphics card, but this is unlikely with the newer 80 plus certified power supplies and all the over current protection built in. I do not see that happening in a fan, but maybe because of the fan failure causing something to overheat then fail. I also had a power supply fail not to long ago kicking a well loaded 20 amp circuit offline. In the ideal crunching world the internet would be on a separate circuit with battery backup to keep the work flowing to machines on other circuits. Best of luck with the repairs and may you luck our and have your failure covered under warranty