I live in a house built in the mid 50's. The wiring in the house gives the term 'jack-leg' a new meaning. I thought you might be interested in my latest fiasco.
I was trenching through my back yard a couple of months ago when I hit the underground electrical cable running from my house to my tool shed. I repaired the cable using direct-burial rated splices. I installed a GFCI outlet on the circuit where the line leaves the main brealer box, in case the burried splices begin to fail.
Well lo and behold, the GFCI would trip sporadically, about once a day, sometimes not for several days, sometimes several times a day. I dug up my direct burial splice and disconnected it, ensuring that there was no possible contact between hot and ground.
The problem persisted- the GFCI would trip at seemingly random intervals. Maybe it's a bad GFCI, I thought. I disconnected the line coming out of the GFCI outlet and the problem stoped happening, indicating to me that the GFCI was not the problem here.
So now I have narrowed down the location of the problem to somewhere between the main breaker box and the spot where I cut the cable with the trencher. I started crawling around under the house to see if there was possibly some spot where the insulation on the cable had been cut and was making intermittant contact with ground. I found a strange splice in the cable where someone had tapped into this line to install an additional outlet in the laundry room of the house. I went up into the laundry room to inspect the outlet. Some idiot thought it was a good idea to use the ground wire in the outlet as the neutral!
So what happened was that whenever my wife plugged something into this outlet, current ran from hot to ground, tripping the GFCI. Sometimes my wife used the outlet every day, sometimes not but once a week.
Needless to say I'm inspecting all of the outlets and wiring in the house for other stupid wiring tricks.
I have a theory that the nationwide trend toward DIY home improvement is gradually bringing down the quality of homes in America, and is creating a lot of safety hazards. People who don't know a thing about electricity (or know just enough to be dangerous) are creating situations that could kill someone, even 5 or 10 years down the road. And it's not limited to electrical- people are running their own gas lines and making uninformed structural decisions as well.
It is scary to think that the next house you buy may have been owned by one of the daredevil home improvement hacks that occasionally pop up in this newsgroup.