Don and Pete,

GFIs are Ground Fault Interupters. GFCIs are receptacles with GFI protection built in to them. Either one senses current flow on the grounding wire which is the U or 3rd prong on the receptacle and the bare of green wire in the panel board, or juction box. Any uneven current flow on the black wire (or the brass terminal), vs. the white wire (or the silver terminal), will also trip the circuit breaker.

Lots of campers have little wiring problems that really won't allow a GFI or GFCI to work properly. Between dust, spider webs, moisture, and poor wiring methods, etc., the GFIs and GFCIs trip sporadically for no apparent reason. But there is a reason--somewhere! Having GFI circuit breakers could/would protect the whole trailer.

I use GFI type devices only where they are absolutely necessary. They won't fit in the Airstream's outlet boxes for the 1st reason and there is a polarity detection light on my camper that will light if the live wire and the neutral are reversed in a campground outlet.

There is a little item on the market that checks for polarity too. It costs about $10(?) and can be plugged into any outlet to check the polarity (black/white reversal).

Rich Walbridge