I am adding an exhaust fan to my bathroom and wiring it into an existing receptacle which is at the end of a circuit (only one cable in). I took out the old receptacle and metal box, replaced it with a double size blue plastic box(with no ground terminal) and a GFCI receptacle, and wired a single pole switch, inside the new box, between the GFCI receptacle and the fan, thus protecting the fan as required when installed over a tub. I wired according to the diagram I got from a home wiring book:

BW(Black Wire)from power to GFCI line black, GFCI load black to switch upper terminal, and switch lower terminal to BW of fan.

WW from power wire nutted with WW from GFCI line white and WW from fan.

GW from power wire nutted with GW from GFCI ground, GW from fan, and GW which was connected to the original metal box (but led to some place out side up into the wall)*note that no GW is connected to the switch, as my wiring book does not show one*

When I apply power to the circuit via the breaker box, the GFCI receptacle provides power to anything plugged in, and tests appropriately via the test button. However, whenever I turn the switch to the fan on, I throw the breaker in the GFCI receptacle. When I use a circuit tester (one of those 3-light plug instruments) in the GFCI receptacle as wired above, and push the test button on the circuit tester, this too throws the breaker in the GFCI receptacle.

Am I being dense for not grounding the switch, as it has a grounding terminal, or am I looking a bigger problem, maybe that the ground wire leading up into the wall really doesn't have a proper ground connection:confused:

Thanks to the person who grins to themselves, shakes their head, and points out the error of my ways.

This is what is connected wrong.

You need to separate these whites so that the LINE white needs to connect to the LINE on the GFI, and the LOAD white must connect to the LOAD on the GFI.

The ground wire should have a pigtail to the green on the switch, but not having it is not causing your tripping problem.

Thanks for the quick response! Let me see if I understand you before I go and try this. I believe you are saying that the white wire from the incoming power should go to the line of the GFCI, and the load white on the GFCI should be connected to the white wire from the fan. Is this right?

That is correct. The line and load neutrals need to be separated, as being connected is causing the GFI to trip.