The two previous posters have given you some good advice about grounds - both DC and RF. But to answer your question, tripping a GFCI somewhere else in the house, that is NOT in use, should not be dangerous.

A GFCI measures current between neutral and ground in a 3 wire outlet and if there are more than a few milliamps flowing in the neutral/ground circuit, the device assumes a hot-to-cabinet short in the connected appliance and "trips" or shuts the outlet down. What is likely happening in your case is that you're getting RF into the GFCI and causing a few millamps to flow in the sensing circuit. It senses danger and trips.

I have a friend who once could be heard coming from the clock on his kitchen stove. He also had a flourescent tube lying on his operating table that would light and pulse in step with his voice. Of course, the DX couldn't hear him since most of his power was staying in the house even though he had a backyard dipole.

I hope the grounding advice will help you but with the antenna inside, I dunno. You're going to tend to brute-force overload everything around you. It took some work to clean up my friend's installation and make the RF go where it was supposed to.

Allan - N4NLQ

Perhaps there is a section of plastic pipe somewhere unseen, and you are grounding through only the water in that section of pipe. Try using a different ground and see whether this makes a difference.

I don't think it's a ground issue as much as it's simply RF energy. With my 5W HT I can trip GFCI outlets at close range, or prompt my Garmin Nuvi to shut down.

Move the Buddipole outside, or stop transmitting at 100W inside.

Tom, avoid attaching "ground" wires to cold water pipes. Your cold water pipe that goes to the hot water heater, is it a high or low-impedance? Is the cold water pipe connected to other pipes in other apartments? What if the telephone company has grounded its equipment to the same pipe? Cable TV? In all probability, you have created more problems for yourself than if you had left the station totally “ungrounded”. Actually, in the “ungrounded” situation there may be some capacitive coupling to the AC power line, which may act like a phantom ground. This is why a brute force filter is sometimes needed to clear up TVI. Keep in mind the whole idea of grounding the station for RF is to have the equipment at a low-impedance and therefore a low-voltage position. A workable compromise is to tie the station equipment to a central point through short pieces of braid. Quarter-wavelength radials are cut for each band to be used and attached to the central point in the station. This is referred to as a 'counterpoise'. If you have a transmatch (antenna tuner) this should be the central point. The ARRL handbook provides invaluable information about appropriate grounding and I recommend this.

Best Regards Larry