We always plugged our old camper into an outlet at the side of the house when not using it. Our new fifth wheel trailer was OK the first couple of days but then started dropping the GFI breaker immediately at plug in. We took it back to the dealer and it wouldn't drop their breaker, worked just fine. We had an electrician replace our GFI at home, everything was great for about two weeks. Now its dropping the breaker again. Very frustrated.

GFCI's are a special interest of mine...
Are you making any other conection to your house? Water? tv antenna?

None that I can think of.

Okay .. GFCI's work by comparing the electric current going through the "Hot" leg of the circuit against the current coming back through the neutral leg of the circuit. If there is an imbalance the circuit opens the contacts inside the GFCI. The only way for an imbalance to exist is for some of the electric current to bypass the neutral leg like...through your body or some other path going to ground.

Since the GFCI trips immediately, your search for the alternate path is made easy. Start unpluging each appliance in your RV and testing to see if the GFCI holds. You'll soon figure which appliance it is. If all of the appliances are unplugged then you've got a wiring issue.

Well I through all the circuit breakers and that didn't help, but I'm desparate enough to go back and unplug all the appliances.

If you opened all the circuit breakers, You've covered all the circuits unless someone wired something around a CB. Disconnect the trailer from the house (safety issue) Then open the circuit breaker panel and the inlet cord box. You should see Three wires feeding the panel from the trailer's inlet. A white(Neutral), a black(Hot) and a green or bare wire(The ground). The white and ground wire should NOT be connected together anywhere. If it is... there's your problem.

Here's a link to an article on Mr Truck's web site... (A shameless plug) that explains the issue further.

http://www.mrtrailer.com/hosspuller.htm

Well, I got it narrowed down to one circuit. Disconnecting that white wire from the bar makes everthing OK. Throwing the breaker doesn't help, only pulling the white wire. That circuit is marked 'kitchen-microwave'. Unplugging the microwave doesn't help. There is a GFI above the sink. I thought one white wire on it was loose but tightening all those wire didn't help. Ended up just taking the GFI all the way out and leaving all wires hanging loose. When the white wire in the box is touched to the bar it still drops the whole RV.

Paddy ... There's not enough description of the trailer wiring in your posts to help you. Have you looked at my article?

It sounds like the white wire is connecting to a grounding bus bar. (not correct) But without looking at the whole system, I can't be sure.

May I suggest you take my article to someone familar with wiring, to correct the problem.