Tripping a GFI power source?

[branson4020]

OK, one more try here. I think we almost have it. When this is all done, everyone who reads this will be an electrician and they'll owe you a beer .

Suppose you have 20 amps flowing through the hot side of the GFCI. As long as there is 20A flowing through the neutral return everything is good. We know that the neutral and ground are connected together somewhere behind the GFI so all that current eventually flows to ground. Now, suppose you connect neutral to ground somewhere in front of the GFCI, maybe at the coach end of the power cord. Now, 20 amps still flows in through the hot side, but, on the return path, the current splits at the point where neutral and ground are connected togeter. Only 10A flows back through the neutral, the other 10A goes through the ground wire, which as you pointed out goes around the GFI. The GFI sees 20A in but only 10A out.

 

[hoefler]

Use your scenario but with a 2 prong plug. There is no ground for the bleed over.

 

[Willym]

Use your scenario but with a 2 prong plug. There is no ground for the bleed over.

The GFI will trip if there is a path from hot to ground, say through a person touching a live part, and some current going to ground through that person. The GFI will trip and protect the person even on a two prong plug circuit. As Bob states, GFI's work by checking the current difference a between live and neutral sides of the circuit. They trip if that difference exceeds a certain value and it just requires milliamps.
On the circuit in question here, there is a ground conductor which is providing the leakage path to ground and tripping the GFI.

 

[Jimmy]

Could be increased moisture inside your wall or ceiling, maybe a leak or increased condensation??

 

[Bram]

Love the conversations. We always learn from other peoples expertise/opinions.

After branson4020 mentioned other plugs on the circuit I thought "the switch." With some further investigation with my meter, I found intermittent continuity between the common and ground on the the wire from the switch to the fan. By wiggling the wire I could get the continuity to come and go. So... I'm going with my original diagnosis of a stapled wire in the wall and leaving the ground disconnected in the electrical panel. Thanks for all the inputs.

Bram