A couple of days to go before Christmas, when today the main RCD tripped all the electric circuits. Isn't it strange how these things always seem to manifest themselves at the time of year when it's virtually impossible to get a tradesman as they're all on holiday. Anyway, I was going around the house unplugging things one at a time, to try and locate the offending appliance. Eventually had everything unplugged and the RCD was still tripping out. Obviously not a direct short as it was taking 20 to 30 seconds for it to trip. So I was racking my brains, to try and find the solution to stave off a cold dark Christmas. I suddenly had a brainwave - the outside security lights! There are 2 x 500w lights c/w sensors at the rear of the house, plus it's a cold wet day, so a chance that moisture could be causing a slight current drain. More than likely it could also be one of the quartz strip bulbs which have a habit of fusing when they fail causing a short. So with the security lights isolated, I reset the RCD, and waited anxiously. Eureka! everything is still working. So my sense of impending doom has been replaced by one of illation. Merry Christmas, everyone.