[happytrails]

Originally Posted by ktmracer

not quite the correct info on a GFI. A GFI detector detects an imbalance in CURRENT between the hot and neutral not a voltage difference. Newer GFI's also will detect a neutral to ground short downstream of the GFI. By NEC code, ground and neutral must only be bonded together at the main entrance panel. Power cord length should not affect the GFI unless the cord is not well insulated and there is leakage current somewhere. The best approach to determining the fault IMHO is a as follows.

1) turn off the main breaker in the trailer and connect to the power source. If the source GFI trips it means there is a leakage path between the power source and the panel in the trailer or a ground/neutral short. If it doesn't trip then:
a) turn off ALL the breakers in the trailer panel and then turn on the main breaker. If it trips, then the fault is in the main panel, likely a loose hot or neutral or a neutral tied to a ground somewhere. If it doesn't trip then
b) turn on the other breakers one at a time till the GFI trips. That indicates the circuit that has a leakage current.

A few common faults are
1) the fridge AC heater element having a leakage path to ground as it begins to fail.
2) A hot water heater element with a leakage path to ground as it begins to fail
3) Not as common, but motors that develop a leakage current, such as the
AC compressor or fan
4) Outside outlets that have moisture in them. This is one of the most common faults.

the reason it probably doesn't trip at a campground etc. is that most campgrounds don't have a GFI on the 30A or 50A circuit, neither do most generators.

I wouldn't be a bit suprised if your problem is either a ground/neutral bond (short) somewhere in the main trailer panel.

I agree with this.

I do want to add that I have seen a couple other posts about replacing the GFI and that would be my first thing I would try, however, don't just replace the GFI with a 20Amp GFI unless the one you have now is a 20Amp GFI. You should be able to tell what you should put in by looking at the breaker that feeds the GFI and/or it will be stamped on the GFI. If it is a 15Amp breaker then put in a 15Amp GFI. DO NOT REPLACE the 15Amp breaker with a 20Amp breaker or you may just start a fire. You most likely won't start a fire by putting in a 20Amp GFI in place of a 15Amp, but it is just bad practice and can be confusing to the next guy.

Someone mentioned hospital grade GFI or non-Home Depot. I agree but I think you can find a good durable GFI at Home Depot. If you look at the outlets section in HD or Lowes you will notice that some outlets are $0.50 or so and some are $4. By looking at them you won't notice much difference. Pick them up and really get a look and feel of them. This is one case where you really do get what you pay for. See if they actually have someone in the electrical department who knows about electrical stuff. Hard to find, but sometimes they actually do have knowledgable people in the right departments. My electronics professor in college retired and went to work for Lowes, they put him in plumbing. go figure!