I have an electrical issue at home. I have a power point in the roof. It is a power point and a switch for a light. The heater plugs into the power point. There is also an "extension lead" that runs across the roof that powers the evap cooler. This lead is wired into the power point. For 5 years it all worked fine. Then this year at supers time the control room calls me to tell me there is a mains fail. Wife gets home and half the house is out. The RCD has tripped and will not reset. I get her to call a sparky and the bloke was a dick, he knocked out the power going to the roof as his way of fixing it. When I got home I had a look and couldnt see anything wrong with the wiring or the switches, nothing was burnt out nothing had chewed through the cables etc etc. I got around the problem by running a few leads to other circuits and everything worked fine. Now I don't like leads hanging around everywhere so on the weekend I decided to clean it all up and replace the switch. All good until I plugged the evap cooler in to the "extension lead" it tripped the RCD again. Today I pulled it all apart and ensured that there were no strands of wires touching a neighboring wire. Tested the "extension lead" with a different appliance and it didn't trip. WOOT!!!!! I proceed to snake the "extension lead" across the roof space and plug the cooler in and the RCD tripped again I'm at a loss as to why it's tripping the RCD. Obviously it is leaking to earth but why? To an uneducated person like me it makes no sense. Neither the cooler or the heater were running at the time. It just trips the RCD whenever the cooler is plugged in. Those in the know have any idea why all of a sudden after 5 years the thing decides to trip the RCD?